Cellular control Flashcards
1
Q
Define gene
A
A length of DNA that codes for one or more polypeptides
2
Q
Define polypeptide
A
A polymer consisting of a chain of amino acid residues joined via peptide bonds
3
Q
Define genome
A
The genome of an organism is the entire DNA sequence of that organism
4
Q
Define protein
A
A large polypeptide that consists of 100 amino acids or more. They can consist of 1 or more polypeptide chains
5
Q
Define transcription
A
The creation of a single stranded mRNA which is a copy of the DNA coding strand
6
Q
Are genes hereditary?
A
Yes
7
Q
Are there any genes in mitochondria?
A
Yes
8
Q
Where are genes situated?
A
On linear chromosomes within the nucleus on a specific locus
9
Q
What do chromosomes consist of?
What is the DNA in a chromosome associated with?
A
Chromosomes consist of one molecule of DNA
The DNA is associated with histone proteins
10
Q
List 5 out of 10 polypeptides that genes code for
A
- Collagen/keratin (structural proteins)
- Haemoglobin
- Immunoglobulins
- Cell surface receptors
- Antigens
- Actin/myosin in muscle cells
- Tubulin proteins in the cytoskeleton
- Channel proteins
- Electron carriers
- Enzymes
11
Q
How are genes involved with the synthesis of all non-protein molecules?
A
Because they code for enzymes which are involved in the control of metabolic pathways that synthesise non-protein molecules.
12
Q
List 4 characteristics of a genetic code
A
- They are triplet codes and consist of three bases that code for an amino acid. There are only 20 amino acids but 64 possible triplet codes.
- Genetic codes are degenerate meaning that all amino acids (except methionine) have more than 1 code
- Some codes are stop codons and indicate the end of the polypeptide chain
- Genetic codes are widespread but no universal. For example the code TCT codes for serine in any organism which is useful for genetic engineering as you can transfer genes between organisms. There are some variations
13
Q
Where are chromosomes found?
A
In the nucleus
14
Q
Where are proteins assembled?
How does the genetic code get from the nucleus to the ribosome?
A
At ribosomes
A copy of the code is made in the form of mRNA which can pass through the nuclear pores in the nuclear envelope.
15
Q
Define genetic code
A
The sequence of nucleotides that forms a gene
16
Q
Define locus
A
A specific place on a DNA molecule
17
Q
What is the first stage of protein synthesis?
Where does it occur?
A
Transcription
In the nucleus
18
Q
What is made from transcription?
What strand is used as a template?
A
mRNA
The template strand of DNA
19
Q
Where are the free DNA and RNA nucleotides found for transcription?
A
DNA: Nucleoplasm
RNA: Nucleolus
20
Q
At the start of transcription, nucleotides are activated, how do you activate a nucleotide?
A
By attaching 2 extra phosphoryll groups
21
Q
What are the 4 RNA nucleotides that are activated for transcription?
A
A, U, G and C
also known as ATP, UTP, GTP and CTP
22
Q
Describe the 5 stages of transcription in detail.
A
- The length of DNA unwinds and unzips and the hydrogen bonds between complementary bases break. The length of DNA dips into the nucleolus
- Free activated RNA nucleotides bind via hydrogen bonds to the exposed complementary bases on the template strand. U and A (A and T on the DNA strand) and C and G. RNA polymerase catalyses this
- This releases the phosphoryll groups which releases energy. This energy is used to bind adjacent nucleotides
- This creates mRNA which is complementary to the template strand and is an exact copy of the coding strand
- The mRNA is released from the DNA and passes out of the nucleus via nuclear pores in the envelope
23
Q
Define translation
A
The assembly of polypeptides at ribosomes
24
Q
What is the second stage of protein synthesis?
A
Translation
25
Amino acids are assembled at ribosomes to form polypeptides, what determines the sequence of amino acids?
The codons which are triplets of nucleotide bases on the mRNA
26
What is a chain of amino acids called?
A polypeptide
27
Where are ribosomes found? 2 places
In the cytoplasm
| Bound to the RER
28
Where are ribosomes assembled?
| What are they assembled from?
In the nucleolus of eukaryote cells
| They are assembled from rRNA and protein
29
What does mRNA stand for?
What about rRNA?
And tRNA?
Messenger RNA
Ribosomal RNA
Transfer RNA
30
Describe the appearance of ribosomes and how that enables their function
They consist of 2 subunits with a groove inbetween them
The groove enables the mRNA to fit into it and slide long the groove. The ribosome can then read the code and assemble the amino acids in the correct order
31
Name 4 reasons why the sequence of amino acids in a protein is essential
1. It forms the primary structure of the protein
2. The primary structure determines the tertiary structure which is the 3D shape held by ionic and hydrogen bonds between the R groups of amino acids
3. The tertiary structure is essential for its function. For example to create the complementary shape for enzymes
4. If the tertiary structure is altered then the protein will no longer function. For example the active site will no longer be complementary or channel proteins won't be the right shape to fit ions through it.
32
True or false
| A tRNA molecule isn't specific for one amino acid
False, it is specific for ONE amino acid
33
Where do amino acids attach to tRNA?
In the cytoplasm
34
Where is tRNA found and where is it assembled?
It's found in the cytoplasm and assembled in the nucleus.
35
Describe the appearance of tRNA molecules
They are lengths of RNA folded into a hairpin shape. There are 3 exposed bases at one end which is where the specific complementary amino acid binds. On the other end there are three unpaired nucleotide bases which are called an anticodon.
36
What is the function of an anticodon on a tRNA molecule?
To temporarily bind with the codon on the mRNA strand so that the amino acids can bind together to form a polypeptide.
37
Describe the 5 stages of translation in detail
1. mRNA binds to a ribosome and 2 codons attach to the small subunit of the ribosome. Methionine is always the first amino acid attached to a tRNA molecule, the tRNA molecule has the anticodon UAC and the tRNA molecule binds via hydrogen bonds to the complementary codon: AUG.
2. A second tRNA with a different amino acid binds to the second codon attached to the small subunit
3. A peptide bond forms between the 2 adjacent amino acids, an enzyme catalyses this
4. The ribosome begins to slide along the mRNA and more and more amino acids bind to each other via peptide bonds. After then amino acids bind together, the tRNA molecule leaves and collects another amino acid.
5. The polypeptide chain grows until it reaches a stop codon which doesn't have a corresponding tRNA molecule.
38
How many stop codons are there?
What are they?
What is the start codon?
3
UAA, UAG, UGA
ATG/ AUG
39
Once a polypeptide has been made, some need to be activated. What activates these proteins?
How does it activate them?
A chemical called cAMP, a nucleotide derivative
| It does this by changing their 3D shape so that they are a better fit to their complementary molecules
40
How is protein synthesis different in prokaryotes?
It's different because DNA isn't found in the nucleus of the cell meaning that translation starts as soon as mRNA is made.
41
Define mutation
A random change in the amount of/arrangement of genetic material in a cell
42
Define chromosome mutations
Random changes to the structure of a chromosome
43
Define DNA mutations
Changes to genes due to changes in nucleotide base sequences
44
Give 3 examples of DNA mutation
| And 4 examples of chromosome mutation (explain each one)
Base deletion, addition or substitution
Deletion (a part of the chromosome is lost), inversion (a section of the chromosome turns 180 degrees), non-disjunction (chromosomes/chromatids fail to separate during meiosis resulting in polyploidy) or translocation (a piece of one chromosome becomes attached to another)
45
Give 2 examples of causes of mutations
DNA replication before nuclear division and mutagens (tar, x rays etc)
46
Why is it unlikely for DNA mutation to occur?
Because the structure of DNA molecules makes them stable which reduces the chances of things corrupting the encoded genetic information
47
Define somatic mutations
Mutations associated with mitosis that aren't passed on to offspring but can lead to cancer
48
Are mutations associated with meiosis and gamete formation hereditary?
Yes, they can be inherited
49
What are the two main classes of DNA mutation? Explain them
| What diseases do they cause?
Point mutation/substitutions, this is when one base pair replaces with another. It can sometimes change the primary structure. Sickle-cell anaemia, tumours
Insertion/deletion mutations, this is when one or more nucleotides are inserted or deleted from a length of DNA, it causes a frameshift meaning all the amino acids change.
Huntington's disease (but it isn't a frameshift) and cystic fibrosis
50
Once triplets of nucleotide bases have been transcribed, what do they become?
Codons
51
Which mutations have a greater effect on the resulting protein: point mutations or insertion/deletion mutations?
Insertion/deletion mutations because they change all of the amino acids after the mutation
52
Name 3 types of point mutations. Also describe the effect they have on the protein.
Missense mutation: One nucleotide base changes meaning only 1 amino acid changes
Nonsense mutation: One nucleotide base changes which changes the codon to a stop codon, prematurely ending the polypeptide
Silent mutation: One nucleotide base changes but it still codes for the same amino acid.
All of the above alter the helix tertiary structure.
53
Why do degenerate codons reduce the chance of DNA mutation?
Because it increases the likelihood of a silent mutation which has no effect on the protein
54
Give 2 examples of diseases caused by DNA mutations
Sickle-cell anaemia and cystic fibrosis
55
How is cystic fibrosis caused?
It is caused by a deletion mutation. A triplet of base pairs is deleted which completely deletes an amino acid
56
How is sickle-cell anaemia caused?
It is caused by a point mutation on codon 6 for beta-polypeptide chains of haemoglobin, this means that valine replaces glutamic acid (amino acids)
57
Describe how a mutation can lead to a tumour
Protooncogenes (growth promoting genes) can be changed via a point mutation to oncogenes which alters the ability of that gene to be switched off. This means the gene is permanently switched on so unregulated cell division occurs (that is the function of oncogenes)
58
How is Huntington's disease cause?
| Name 2 symptoms
Via a stutter mutation, this means that a triple nucleotide repeat is expanded over the threshold number, altering the protein sufficiently. In a Huntington gene, the triple nucleotide repeat has repeat CAG sequences.
Loss of motor control and dementia
59
Define allele
An alternative version of the same gene. It's still at the same locus and codes for the same polypeptide but the polypeptide structure may be different
60
Give two causes for a mutation producing no change.
1. A silent mutation
| 2. A mutation in a non-coding region of the DNA
61
What is a neutral mutation?
A mutation that has no advantage or disadvantage but still changes the structure of the protein.
62
Give 2 examples of a neutral mutation
1. Being able/not able to smell honeysuckle. It has no advantage or disadvantage
2. Being able to roll your tongue. This is hereditary and is a dominant allele.
63
Give an example of a beneficial mutation
Being able to taste PCT because in large quantities, it's poisoness
64
Give an example of 1 beneficial AND harmful mutation (depending on the conditions you are in)
Harmful: People who live in Africa having a mutation for paler skin, causing them to burn and get skin cancer
Beneficial: Melanin (more melanin is present in darker skins) protects the skin from ultraviolet light but that means less vitamin D is synthesised from the sun. When humans migrated to cooler climates, having the mutation for paler skin was advantageous as they could synthesise sufficient vitamin D whereas darker skin people couldn't as the sunlight wasn't intense enough.
65
Why is it bad to have a lack of vitamin D?
It can cause rickets, a narrow pelvis (causing difficulties in childbirth) and an increased risk of cancer and heart disease because vitamin D helps protect us from them
66
Why wouldn't there be evolution without genetic mutations?
Because genetic mutations can provide people with a greater advantage in a certain environment, for example a lack of melanin in a cooler climate. This leads to natural selection because the people with the mutation will out compete those without it.
67
Define operon
A length of DNA made up of structural genes and control sites. The structural genes code for proteins and the control sites consist of the promoter and operator region.
68
Define operator and promoter region
They are in the control sites on an operon, they are genes that don't code for polypeptides.
69
Define repressor protein
A protein that can bind to the operator region, preventing the transcription of the Z and Y genes
70
Define enzyme induction
When bacteria vary the synthesis rates of specific enzymes in response to environmental changes like a type of food being available.
71
Name a bacteria that can perform enzyme enduction.
True or false
There is a great variation in the numbers of different polypeptides.
Escherichia coli
| True
72
Define inducible enzymes
Enzymes that aren't synthesised at a constant rate, they are synthesised at varying rates depending on the ell's circumstances
73
What enzymes are synthesised at a fairly constant rate?
Enzymes involved in basic cellular functions
74
Give an example of when E. coli might synthesise a inducible enzyme
When lactose is present it can be respired instead if glucose. The presence of lactose can activate the synthesis of enzymes involved in the respiration of lactose.
75
What type of sugar is lactose
A disaccharide sugar
76
What happens when E. coli (after being grown without the presence of lactose) is placed in a medium with lactose?
5 things
At first, the lactose isn't metabolised as there are only small amounts of the enzymes needed to respire it.
The enzymes are beta-galactosidase and lactose permease
Beta-galactosidase catalyses the hydrolysis of lactose to glucose and galactose. Lactose permease transports lactose into the cell
After a few minutes of being in the medium, E. coli rapidly increases its synthesis of the two enzymes.
Lactose is the inducer because it triggers the production of the 2 enzymes
77
What type of organism is the lac operon found in?
The section of DNA known as the lac operon is found in a bacterial organism
78
What are the 3 sections of the lac operon and what is their function?
What gene is involved with the lac operon but isn't a part of it?
```
Structural genes: There are 2 structural genes, gene Z and gene Y. Z codes for the enzyme beta-galactosidase and Y codes for lactose permease. The genes, when turned on, are transcribed
Operator region (O): It's a length of DNA found next to the structural genes and it can turn the genes on and off.
Promoter region (P): A length of DNA that RNA polymerase can bind to to begin the transcription of Z and Y.
The regulatory gene
```
79
How does the lac operon work when lactose is absent from the growth medium? 4 stages
1. The regulator gene is expressed (aka transcribed and translated) which synthesises a repressor protein. A repressor protein has 2 binding sites one that binds to the operator region and one that binds to lactose.
2. The repressor protein binds to the operator region which covers part of the promoter region. This means RNA polymerase can't bind to the promoter region where it normally attaches
3. Because it can't bind to the promoter region, it means that the Z and Y genes can't be transcribed into mRNA
4. This means the genes won't be translated and no beta-glacatosidase or lactose permease will be synthesised
80
How does the lac operon work when lactose is present in the growth medium? 4 stages
1. Lactose molecules aka the inducers bind to the other repressor protein's binding site. This changes the shape of the repressor protein so its other binding site is no longer complementary to that of the operator region's binding site. The repressor protein therefore dissociates from the operator region
2. The promoter region is now unblocked so RNA polymerase binds to it, initiating the transcription of the Z and Y genes.
3. The operator repressor inducer system together act as a molecular switch allowing the Z and Y genes to be expressed as beta galactosidase and lactose permease
4. E. coli can then use these enzymes to create a respiratory substrate (glucose) and respire it thus gaining energy from lactose.
81
Define homeobox genes
Genes that control the development of the body plan of an organism. E.g. the polarity or positioning of organs
82
Define body plan
The general structure or layout of an organism
83
What happens if homeobox genes get mutated?
| Name a chemical that can mutate them.
Then changes will our in the body plan
| Thalidomide
84
Define maternal effect genes
Genes that control the embryo's polarity
85
Define segmentation genes
Genes that control the polarity of each segment of an embryo
86
Define homeotic selector genes
Genes that determine the identity of each segment and they direct the development of them. They are master genes found in the control networks of regulatory genes
87
What organism is a drosophila melanogaster?
A fruit fly
88
What happens as soon as a drosophila melanogaster lays its eggs?
A series of mitotic divisions are triggered every 6-10 minutes, this rate of DNA replication is one of the fastest known for eukaryotic organisms
89
What are the 7 stages of drosophila development. Name them in order.
1. A multinucleate syncytium is formed but nonew cell membranes are formed.
2. After the 8th division, the nuclei migrate to the outer part and by the 11th division, the nuclei have formed an outer layer around the yolk filled core.
3. The division rate then slows and nuclear genes switch from replicating to transcribing
4. The plasma membrane invaginates around the nuclei, forming a single outer layer
5. After 2-3 hours, the embryo then divides into segments which correspond to the body plan
6. 3 segments then merge to form the head. There are 3 thoracic segments and 8 abdominal segments
7. The egg hatches and the larvae (after a period of time) undergo metamorphosis, this is where legs, wings and antennae develop.
90
What are the 2 gene families in terms of development?
Genes that regulate the development of the abdomen and thorax
Genes that regulate the development of the head and thorax
91
What is antennapedia?
| How is it caused?
It is when a fruit flies antennae looks more like legs
| It's caused by a mutation of a gene that changes one body part to another
92
What organisms are homeobox genes found in?
Organisms that are segmented
93
How many base pairs makes up a homeobox gene?
| How many amino acids are found in the polypeptide that the homeobox gene synthesises?
180
| 60
94
What type of polypeptide CAN homeobox genes make?
| What is the function of this polypeptide?
Transcription factors
Their function is to bind to genes further upstream on the DNA molecule and initiate transcription. This allows the expression of other genes
95
True or false
| Homeobox genes are only found in animals
False, they are found in plants aswell
96
What is a cluster of homeobox genes called?
A Hox cluster
97
How many Hox clusters do nematodes aka round worms have?
What about drosophila
What about vertebrates?
How many genes are found in each hox cluster in vertebrates?
1
2
4
9-11 genes
98
What order are homeobox genes activated in?
They are activated in the same order as they are expressed, from head to tail.
99
What is retanoic acid a derivative of?
| What is its function?
Vitamin A
It activates the homeobox genes in the order that they are expressed. Just like the axial skeleton and the CNS which are also expressed from head to tail
100
Define morphogen
| Give an example of one
A substance that governs the pattern of tissue development
| Retanoic acid
101
How can cranial deformities be caused?
When there is too much presence of vitamin A during the development of an embryo, this means that there is too much retanoic acid which can interfere with the normal expression of genes
102
Define apoptosis
Programmed cell death that occurs in multicellular organisms
103
Define necrosis
Cell death caused by damage or physical trauma
104
What is the Hayflick constant
The Hayflick constant is when cells undergo about 50 mitotic divisions and once the ave done this, they undergo biochemical events which results in an orderly and tidy cell death aka apoptosis
105
Name 2 differences between necrosis and apoptosis
1. Necrosis releases hydrolytic enzymes which results in puss as leukocytes die
2. Necrosis is untidy and damaging to other cells
106
Define phagocytosis
The endocytosis of large solid molecules into a cell
107
What are the 5 stages of apoptosis?
| How quickly does apoptosis occur?
1. Enzymes break down the cell's cytoskeleton
2. The cytoplasm becomes dense and the organelles are tightly packed
3. The cell surface membrane changes and blebs form
4. Chromatin condenses and the nuclear envelop breaks. DNA also breaks into fragments
5. The cell then breaks into vesicles which are then taken up by phagocytes via phagocytosis so the components can be reused. The cellular debris are disposed of and no other cells or tissues are damaged
This process occurs VERY quickly.
108
How is the process of apoptosis controlled?
| Describe in detail
It's controlled by cell signals from inside or outside the cell.
Cytokines, made by cells from the immune system, hormones, growth factors and nitric oxide are cell signals.
Nitric oxide can induce (help) apoptosis because it makes the inner mitochondrial membrane more permeable to hydrogen ions. This dissipates the proton gradient.
Nitric oxide also causes proteins to be released into the cytosol (the aqueous part of the cytoplasm), the proteins then bind to apoptosis inhibitor proteins, allowing the process to take place.
109
What is the purpose of apoptosis inhibitor proteins?
| What proteins bind to them to allow apoptosis to occur?
To ensure that the cell doesn't undergo apoptosis prematurely
Signal proteins bind to them
110
Why is apoptosis tightly regulated during development?
And do different tissues use different signals to induce it?
What type of cell does undergo apoptosis during development?
To ensure that not too many/too little enzymes are destroyed which could have negative effects
Yes.
Ineffective or harmful T lymphocytes during the development of the immune system
111
Why is apoptosis essential for limbs during development?
Because it causes the digits aka finger and toes to separate from each other. Otherwise you can get syndactyly toes/fingers (ones that are joined together)
112
In children, between the ages of 8 and 14, how many cells each day undergo apoptisis?
How many cells undergo apoptosis each day in adults?
Why is it less in adults?
What should the rate of apoptosis be equal to?
20-30 billion cells
50-70 million cells
Because there is less mitotic divisions as the organism is no longer growing and developing
The rate of apoptosis should equal the rate of cells produced via mitosis
113
What happens when the rates of apoptosis and the rates of cell production aren't balanced?
What process plays a crucial role in ensuring the two rates are balanced?
If the rate of apoptosis is higher than the rate of cell production then it will lead to cell loss or degeneration
If the rate of cell production is higher than the rate of apoptosis then it can lead to the formation of tumours
Cell signalling plays a crucial role
114
Define meiosis
A reduction division where the resulting daughter cells have half the original number of chromosomes as they are haploid cells. These cells are used in sexual reproduction
115
Define zygote
When two gametes fuse
116
Define gametes
Sex cells. Sperm/egg cells
117
Define haploid
A cell with half the usual number of chromosomes
118
Define diploid
A cell with a full set of chromosomes
119
How can asexual reproduction be achieved in eukaryotes and in prokaryotes?
In eukaryotes it's achieved via mitosis
| In prokaryotes it's achieved via binary fission
120
How are the offspring produced via asexual reproduction different to those of sexual reproduction?
They are different because they are genetically identical to their parents and genetic variation only occurs via mutation
121
What happens after 2 gametes fuse?
Once they fuse they form one cell called a zygote and the chromosomes are combined into one nucleus. This is when fertilisation occurs
122
Why do gametes need to be haploid cells?
So that when two gametes fuse, the original number of chromosomes is restored
123
How are haploid cells made, what is the process called?
Meiosis
124
How many divisions occur during meiosis? What is each division called?
How many stages does each division have?
What are the stages called in order of occurrence?
2
Meiosis I and meiosis II
4
Prophase, metaphase, anaphase, telophase
125
What is the phase called before meiosis?
| What happens in this phase?
Interphase
During this phase, DNA replicates. From this, pairs of homologous chromosomes are formed each chromosome consisting of 2 identical sister chromatids joined at the centromere. Before this, the cell contained 2 copies of each chromosome, after this, there a 4 copies of each.
126
Describe the 6 stages of prophase I.
1. The chromatin condenses and supercoils causing the chromosomes to shorten and thicken. They can now be seen under a light microscope
2. The homologous pairs come together to form a bivalent
3. The non sister chromatids wrap around each other and attach at the chiasmata
4. Crossing over then occurs which is when the non sister chromatids swap sections of chromatids with one another
5. The nucleolus disappears and the nuclear envelope disintegrates
6. A spindle forms, it's made of protein microtubules
127
Define homologous chromosomes
Chromosomes that have the same gene at the same loci, one (original) chromosome is paternal and one is maternal.
128
How long does prophase last for?
It depends on the species and whether the gamete being formed is male or female but it can occur over a couple of days or it can occur over a couple of years.
129
Describe the 3 stages of metaphase I.
1. The bivalents line up across the equator of the spindle and attach to the spindle fibres at centromeres. The chiasmata are still present.
2. Random assortment occurs meaning the bivalents are randomly arranged. Each member of the homologous pair is facing opposite poles
3. The chromosomes are now ready to independently segregate as they are facing opposite poles
130
Describe the 3 stages of anaphase I
1. The homologous chromosomes are pulled to opposite poles by the spindle fibres
2. The centromeres don't divide
3. The chiasmata separates and the lengths of chromatids that have been exchanged remain with their newly attached chromatid
131
Describe the 2 phases of telophase I
1. A nuclear envelope forms around each set of chromosomes at each pole and the cells divide via cytokinesis (the cytoplasmic division of a cell to form daughter cells).
2. There is a brief interphase where the chromosome uncoil
132
In what organisms does telophase occur in?
| What happens if telophase doesn't occur in an organism?
It occurs in most animals and doesn't occur in plants
| In plant cells, the cell goes straight to meiosis II from anaphase I.
133
What is the plane of division in meiosis II?
The plane is at a right angle to meiosis I
134
What are the 2 stages of prophase II?
1. The nuclear envelope that has just been formed breaks down again
2. The nucleolus disappears, the chromosomes condense and spindles form.
135
What are the 2 stages of metaphase II?
1. The chromosomes arrange themselves on the equator of the spindle and attach to the spindle fibres at centromeres
2. Random assortment occurs for the chromatids
136
What is the 1 stage of anaphase II?
The centromeres divide (they don't divide in anaphase I) and chromatids are pulled to opposite poles of the cell via spindle fibres. They are randomly segregated.
137
What are the 3 phases of telophase II?
1. The nuclear envelope reforms around each haploid daughter nuclei (aka the chromatids at each pole).
2. In animals, the 2 cells divide to form 4 haploid daughter cells
3. In plants, a tetrad of 4 haploid cells is formed
138
What are the 2 differences between meiosis I and meiosis II?
In meiosis I, chromosomes are pulled apart. In meiosis II chromatids are pulled apart.
In meiosis I, the centromeres don't divide. In meiosis II the centromeres do divide
139
Define maternal chromosomes
The set of chromosomes in an individuals cells that were contributed by the egg
140
Define paternal chromosomes
The set of chromosomes in an individuals cells that were contributed by the sperm
141
Define crossing over
When lengths of DNA are swapped from one chromatid to another
142
What is an advantage of sexual reproduction? Explain
It increases genetic variation because genetic material in cells from two unrelated organisms combine.
143
Why is genetic variation advantageous?
Because it increases the chances of evolution as natural selection will favour the organisms that are best adapted to the ever changing environment.
144
List 4 processes during meiosis that lead to genetic variation.
List 1 reason as to why fertilisation leads to genetic variation
1. In prophase I when crossing over occurs, the alleles are shuffled
2. The random distribution and segregation of chromosomes during meiosis I leads to genetic reassortment
3. The random distribution and segregation of chromatids in meiosis II leads to genetic reassortment
4. Random mutations
1. Because 2 sets of chromosomes from genetically unrelated individuals are randomly combined
145
What is the significance of meiosis?
The significance is to create haploid cells that can fuse with other haploid cells to combine chromosomes/genetics and to therefore increase variation
146
How many cross over events occur on each pair of human chromosomes?
2-3
147
How does crossing over increase genetic variation?
Because it means that alleles are swapped between chromatids which results in new combinations of alleles on that chromatid
148
Why are the chromosomes held together on the spindle?
To ensure that one member of each pair goes to each pole
149
True or false
Each gamete acquires a different mixture of maternal and paternal chromosomes
Explain
True, this is because of the genetic reassortment of chromosomes
150
After crossing over, are sister chromatids still genetically identical?
No they are not
151
How does genetic reassortment increase genetic variation?
It increases genetic variation because it means that a random combination of chromosomes and subsequently chromatids are combined into one haploid daughter cell.
152
How many ovum are released from the ovary at a time?
How many spermatozoa are released?
How many spermatozoa fertilise the secondary oocyte?
Are the spermatozoa ALL genetically different?
Only one ovum (scientifically called a secondary oocyte as it's an immature ovum that hasn't completed its second meiotic division) is released from the ovary at a time
300 million are released
Only 1 can fertilise the oocyte
Yes they are
153
How does fertilisation increase genetic variation?
Because 1 spermatozoa combines with a secondary oocyte to form a zygote out of 300 million spermatozoa. This means that it's randomised and if fertilisation occurred again, a different spermatozoa with different genetic material would combine with the ovum and produce a genetically different zygote
154
What stage of meiosis does DNA mutation occur?
This is a trick question, DNA mutation only occurs during interphase, mitosis or binary fission which isn't part of meiosis
155
How do mutations increase genetic variation?
They increase genetic variation because it can alter a chromosome and subsequently that chromsome would be present in all of the offspring's cells. It would be unlikely for another organism to have the same mutation on the same chromosome.
156
Define codominant
When 2 dominant alleles both contribute towards the phenotype of a heterozygote
157
Define genotype
The genetic makeup of an organism in terms of the alleles it contains
158
Define homozygous
When an organism has 2 identical alleles for a particular gene
159
Define heterozygous
When an organism has 2 different alleles for a particular gene
160
Define autosomes
Chromosomes that aren't concerned with determining sex
161
Where do mutations for cystic fibrosis occur?
On autosomes
162
What does the cystic fibrosis mutation do?
It disrupts the transport of of chloride ions and water across the membranes of cells lining the airways, gut and reproductive tracts. It does this by changing the shape of the transmembrane chloride ion channels.
163
What effect does the cystic fibrosis mutation have?
It means the cilia in the lungs are hydrated properly and they therefore can't shift the mucus. The mucus then dehydrates and accumulates, allowing bacterial infections to occur. Recurrent infections can lead to lung failure
164
What genotypes do carriers of cystic fibrosis have? Explain
| What effects does this have?
They have heterozygous alleles meaning they have 1 normal allele for chloride ion channels and they have 1 abnormal allele for them. The normal alleles are dominant so it would be CFcf.
Effects: They have no symptoms but they still have some abnormal chloride ion channels. This can be passed to the offspring and potentially give them cystic fibrosis
165
What genotypes do people with cystic fibrosis have?
| What about people without it?
People with it: They have homozygous recessive alleles as the mutation is recessive so it would be cfcf
Without it: They will have homozygous dominant alleles: CFCF
166
Define phenotype
The characteristics that are expressed in an organism, they are the result of genotypes
167
Describe the mutation that siamese cats have
They have a mutation in the gene for the enzyme tyrosinase which is involved in melanin production (pigmented skin/fur). As a result of this, the enzyme only works in cooler regions causing the cats to have albinism in the warm areas of their body but dark fur in the cooler areas, e.g. head, tail, feet.
168
Define dominant allele in detail
An allele that is always expressed in the phenotype if it's present even if a different allele from the same gene is present. The phenotype and inheritance is also dominant
169
Define recessive allele in detail
An allele that's only expressed in the phenotype if another identical allele is present for the same gene. No dominant allele can be present. E.g. cystic fibrosis is caused by recessive alleles, making it less common. It's inheritance pattern is also recessive
170
Give 2 examples of codominance
Cattle colour. The allele for red cows is Cr, the allele for white cows is Cw. Both of these alleles can both contribute to a roan cattle colour: CrCw- this is heterozygous.
Blood groups: The allele for blood type A is Ia, the allele for blood type B is Ib and the allele for blood type O is Io. This depends on the type of antigen on the cell surface membrane. Io is recessive and has no antigen so it isn't codominant but Ia and Ib are codominant
171
Define linkage
When 2 or more genes are located on the same chromosome. The linked alleles don't segregate independently during meiosis unless a chiasmata forms between them
172
What happens during cross over in meiosis in terms of linkage
The alleles from one chromatid become linked to the alleles from the other chromatid. This reduces the number of phenotypes resulting from a cross because the linked genes are passed on together, not separately.
173
Define sex linkage
When the gene that codes for a characteristic is found on one of the sex chromosomes. (X or Y) (Males are XY and females are XX)
174
Which chromosome has more genes on it, X or Y chromosomes?
| What is the effect of this?
X has more genes on it and Y has less
This means that recessive genetic diseases are less likely to have an effect on females because they would need a recessive gene on both X chromosomes whereas it would only need to be on one X chromosome for males meaning they are more likely to get it.
175
Define homogametic and heterogametic.
| Which gender in which organisms are homogametic?
Homogametic: XX. Heterogametic: XY.
Mammals: Females are XX
Birds, butterflies and moths: Males are XX
176
If you get a question to do with sex linkage and the expected ratio of the offspring isn't met, what could be the reason for this?
Because the alleles are sex linked, they could have been swapped over during crossing over in meiosis. This means that the genotypes would change in the offspring and therefore the phenotypes wouldn't meet the expected ratio
177
Give 5 examples of sex linked diseases
Red-green colour blindness, haemophilia, Duchenne muscular dystrophy, fragile X syndrome and vitamin D-resistant rickets
178
Why do people have haemophilia?
| What are the effects of this?
Because a recessive allele that is present on the X chromosome codes for the protein, factor VIII. This protein clots the blood after a wound so when the allele is mutated, the altered protein doesn't work. This means that the blood takes longer to clot around the wound, this is haemophilia.
This means that knocks can lead to internal bleeding which could bleed into joints, this is extremely harmful.
179
Why are males more likely to get haemophilia?
Because its present on the X chromosome so they only need one faulty allele to have it as they are hemizygous. Females however need to have two of this allele as it's recessive and they have 2 X chromosomes.
180
If there is a carrier mother XHXh (for haemophilia) and a normal father XHY, what are the expected ratios in the offspring? What about percentages? List the genotypes as well.
```
1:1:1:1
25% will be normal male: XHY
25% normal female: XHXH
25% carrier female: XHXh
25% haemophiliac male: XhY
```
181
Why do people have Duchenne muscular dystrophy?
What are the effects of this?
Are males more likely to get it?
Because the gene that codes for dystrophin on the X chromosome is faulty so it codes for shorter/no dystrophin. Dystrophin is a large protein that's involved in structures needed for muscular contraction so without out it, you get DMD.
The effects of DMD are muscle weakness in early childhood, wheelchair bound by age 10 and death in early 20s due to muscle degeneration.
Yes because it's present on the X chromosome
182
What is a good tip in solving genetic diagrams?
ALWAYS look at the offspring, they give you clues.
183
How do you know whether the question you're answering is about sex linkage?
It's about sex linkage if the letters are X and Y with small letters next to them, indicating the alleles
184
List 6 out of 10 facts about sickle cell anaemia
1. All individuals with the disease have the same mutation
2. An amino acid at position 6 is different on beta-strands of haemoglobin, this results in the disease.
3. Valine is present instead of glutamic acid at position 6
4. When the abnormal haemoglobin is deoxygenated, it becomes crystalline and less globular, deforming the red blood cells and making them inflexible. This means they can't squeeze through capillaries.
5. After many cycles of oxy and deoxygenation, some cells become irreversibly sickled and some are destroyed
6. If enough sickled cell haemoglobin get lodged in capillaries then organs and bones don't recieve enough oxygen and painful crisis occurs
7. Eventually the heart, lungs and kidneys become damaged
8. Normal haemoglobin genotype: HAHA
9. Carrier: HSHA
10. Sufferers: HSHS
185
Why are carriers of sickle cell anaemia symptomless?
Because they are heterozygous meaning they have half normal and half sickled haemoglobin. The presence of the normal haemoglobin prevents the sickling of the whole red blood cell and therefore you are symptomless
186
Is sickle cell anaemia, codominant, sex linked or just normal? Explain
Codominant because both alleles contribute towards the phenotype. This is why you can get carriers. If it wasn't codominant you would either be a sufferer or not, no in between.
187
If red and white shorthorn cattle are interbred, what will the offspring be? Red= CRCR. White= CWCW
All the offspring will be roan: CRCW
188
Define epistasis
The interaction of different gene loci resulting in one gene masking the expression of another
189
What are the expected ratios for dominant epistasis?
What about recessive epistasis?
And complementary fashion?
12: 3:1 or 13:3
9: 3:4
9: 7
190
Genes involved in epistasis can control the expression of one phenotypic characteristic in one of 2 ways. What are the 2 possible ways that the genes can control the phenotype?
The genes can work antagonistically and therefore one masks another
Or the genes can work together in a complementary fashion.
191
In terms of recessive epistasis, when one recessive allele has a homozygous presence which prevents the expression of another allele, which allele is epistatic and which one is hypostatic?
The first allele is epistatic as it is preventing the expression of the second allele
The second allele is hypostatic
192
Is epistasis inherited?
| What does epistasis reduce?
No as it's just the interaction between loci
| It reduces phenotypic variation
193
Describe recessive epistasis
If no dominant allele is present in the first loci, then the second loci is masked. So if the first loci is homozygous recessive then it is epistatic but if it's heterozygous/ homozygous dominant then epistasis doesn't occur.
194
Give an example of recessive epistasis
The inheritance of flower colour in Salvia:
Pure breed pink is: AAbb
Pure breed white is: aaBB.
They were crossed to produce: AaBb which had purple flowers.
These were interbred to produce purple, pink and white flowers with the ratio 9:3:4.
If a was homozygous recessive then the flower would be white no matter what b was.
195
How do you work out the gametes in a genetics question?
You expand double brackets on the parental genotypes.
196
What do you use for the headers in punnet squares?
Use the gametes!!!
197
Finish the sentence, if an organism is a pure breed then it....
is homozygous
198
Describe dominant epistasis
If any dominant alleles are present on the first locus then it masks the expression of the second locus. If the first locus is homozygous recessive then the second locus can be expressed and epistasis doesn't occur
199
Give 2 examples of dominant epistasis. Each one gets a different ratio.
1. Fruit colour in summer squash. The presence of D results in white squash regardless of any other alleles. The presence of dd and E at the second locus results in yellow fruits and ee produces green fruits. DdEe squash are white.
2. Feather colour in chickens. I- = white feathers, iiC- = coloured, iicc= white again. IICC= Pure breed white Leghorn chickens, iicc= Pure breed white Wyandotte chickens. They were crossed to produce IiCc offspring. They were then interbred to produce white and coloured chickens with the ratio 13:3
200
Define progeny
The descendants/ offspring of an organism
201
In dominant epistasis, if two heterozygous squash: DdEe are crossed, then what is the phenotypic ratio of the offspring? D= white. E= yellow ee= green
12 white (D---): 3 yellow (ddE-): 1 green (ddee)
202
Describe complementary fashion
If homozygous recessive alleles are present on EITHER locus then the offspring will have a certain phenotype as the other locus is masked. E.g. white flowers. If a dominant allele is present on BOTH alleles then a different phenotype will be expressed. E.g. purple flowers and no phenotype is masked.
203
Give an example of complementary fashion
White flowered sweet peas with the genotypes: ccRR + CCrr were crossed. All the offspring were purple because a dominant allele was present on each locus. The purple flowers were interbred to produce white and purple flowers with the ratio 9:7.
204
Explain how complementary fashion works in terms of pigments
One dominant gene codes for an intermediate colourless compound and the other dominant gene codes for an enzyme that converts the compound to the final purple pigment.
205
Define agouti coat colour in mice
A coat colour that has alternating bands on each hair, making the fur look grey.
206
Talk about epistasis in terms of mice coat colour
aa is a mutation and produces a black coat. bb cannot produce a pigment, resulting in a white coat. To produce agouti mice, you need a dominant B to produce a black pigment and then a dominant A to then produce an agouti pattern. A dominant allele needs to be present on both loci to get agouti. When agouti mice are crossed you get the ratio: 9:3:4
207
What ratio does a normal dihybrid cross produce?
9:3:3:1
208
Talk about epistasis in terms of chickens and their comb shape
The effects of P/p depends on the presence of the R/r alleles. Pea combed chickens= PPrr. Rose combed chickens= ppRR. Walnut combed chickens= PpRr. Single combed chickens= pprr. When walnut combs are interbred, you get the ratio 9:3:3:1.
209
When should you accept the null hypothesis?
When there is no statistically significant difference between observed and expected numbers and therefore any difference is due to chance. Aka if the final value has a probability below 0.05% accept null
210
In the chi squared formula, what does the O stand for?
| What about the E?
```
O= observed numbers
E= Expected numbers
```
211
When using the chi formula, how do you find out the O and E values?
```
O= Look at the numbers given to you in the question
E= Add up the ratio (in its simplest form) and divide the total of observed numbers by the ratio. This gets you the value of one. Then times this answer by each individual number in the ratio.
```
212
How do you know what your degrees of freedom are?
It is always 1 less than your number of classes.
213
When should we use chi squared? (Biology) 5 things
When the data is categorical/nominal.
When there is a strong biological theory meaning we can work out the expected values
When there is a large sample size
When there are no percentages/ratios but just raw numbers
When there are no zero scores
214
Compare continuous and discontinuous variation. (5 for each)
Continuous:
1. Quantitative differences between phenotypes
2. Wide range of variation/ characteristics
3. No distinct categories
4. Polygenic (many genes are involved)
5. Environment affects it
Discontinuous:
1. Qualitative differences between phenotypes
2. Limited number of traits/ less variation
3. Distinguishable categories with no intermediates
4. Monogenic (a few genes with multiple alleles)
5. Environment doesn't really affect it
215
Give examples of continuous variation.
| What about discontinuous?
Height, mass, length
| Blood group, Squash shape, gender
216
What happens to a population when there is low environmental resistance?
What about when there is high environmental resistance?
The population increases
| The population decreases
217
What does selection pressure determine?
| Give an example
It determines which traits are successful
If it snows, snow is the selection pressure, it will mean that white rabbits have the successful trait and brown rabbits don't so they'll be more likely to get eaten.
218
Does the competitiveness within a population increase or decrease when there is more variation?
The competitiveness increases
219
If more offspring die than survive, what is there a struggle for?
There is a struggle for existance
220
When there is a stable population, what is the competition for?
There is a competition for limited resources like food
221
What is the result of heritable variation?
Gradual evolution
222
Can continuous and discontinuous variation both be the result of more than one gene?
Yes
223
If there is more than one gene involved in discontinuous variation then how do the genes interact?
In an epistatic way where one gene masks the expression of another
224
Give an example of a monogenic discontinuous variation condition
The condition of cystic fibrosis, when a person has two faulty alleles of the CFTR gene preventing chloride ion channels working effectively.
225
List three facts about discontinuous (aka qualitative) variation. All the facts have to do with genes.
1. Different alleles on a single gene locus have a large effect on the phenotype (cystic fibrosis)
2. Different gene loci have large effects on the phenotype (epistasis-pigment colour)
3. Types of discontinuous variation: Epistasis and dominant and recessive patterns of inheritance
226
List four facts about continuous (aka quantitative) variation. All the facts have to do with genes
1. Traits are controlled by two or more genes
2. Each gene provides an additive component whether recessive or dominant (contributes towards the outcome)
3. Different alleles on each locus have small effects on the phenotype
4. Many genes have a combined effect on the phenotype as they are polygenes. But they aren't linked.
227
Give an example of each gene providing an additive component in terms of continuous variation
The alleles: A, B and C are from different genes
Recessive alleles add 1cm to cob's length whereas dominant ones add 2cm. Each gene adds to the length. So AABBCC will produce a cob length of 12cm whereas aabbcc will produce a cob length of 6cm. But the environment can affect this
228
List the environmental factors that can effect continuous variation in terms of cob length.
Water
Light
Minerals
These can limit the expression of the genes
229
What is influenced by the environment more, polygenic traits or monogenic traits?
Polygenic traits
230
Why is genetic variation necessary?
Because if the selection pressure changes then some individuals will have genes that are adapted to that environment so some will survive.
231
What selects the favourable traits/variations within a population?
The environment (natural selection) or humans (artificial selection)
232
Define population
A group of individuals of the same species that can interbreed
233
Is a population static? Explain
No it's dynamic because a population can expand or contract due to changes in birth or death rates or migration.
234
Define gene pool
The total set of genetic information carried by a population at a particular time
235
How can we measure the populations of specific traits (genetic diversity)?
By using the Hardy-Weinberg principle
236
List 4 factors that alters the genetic variation within a population.
1. Mutation
2. Genetic drift
3. Migration
4. Selection
237
Give an example of 2 scientists that helped develop the basic principles of population genetics
Hardy and Weinberg
238
What is the aim of population genetics?
To focus on the genetic structure of populations and measure the changes in allele frequency between generations
239
What 2 things do we need to know in order to measure the frequency of an allele?
1. The mechanism of inheritance
| 2. How many different alleles for that gene are in the population
240
How do you know whether a trait shows codominance? (Population genetics)
If a recessive allele is involved, what problems does it cause?
If the heterozygous phenotype frequency is the same as the heterozygous genotype frequency then the trait shows codominance.
It means that you can't directly determine the frequency of the alleles because some of heterozygotes may express a domnant allele instead of a codominant one
241
How do you work out the frequency of alleles in terms of codominance? There is a population of 100, 36 are MM, 48 are MN and 16 are NN.
You add up the total amount of alleles: 2 X 100 = 200
Then add up the total amount of one allele: 36 X 2= 72 + 48 = 120.
Then divide the total of one allele by the total allele number: 120/200= 0.6.
To work out the other allele frequency you: 1 - 0.6= 0.4.
242
When is the Hardy-Weinberg principle used?
When the traits are either dominant or recessive
243
In order for the Hardy-Weinberg principle to be accurate, what 4 things should be fulfilled?
1. There needs to be a large population
2. The mating needs to be random
3. There should be no selective advantage
4. There should be no mutation, migration or genetic drift.
244
When you get to this question, read the example on page 139!!!
Read it you little bitch.
245
List 5 things that changes a gene pool
1. An interdeme gene flow
2. A small population
3. Assortive mating
4. Natural selection
5. Mutation
246
List 5 things that stabilises a gene pool
1. No interdeme gene flow
2. A large population
3. Random mating
4. No natural selection
5. No mutation
247
What are the three conditions that are required in order for evolution to occur?
1. Genetic variation
2. Selection pressure
3. Hereditary
248
What are the three types of selection pressure?
Disruptive selection, Directional selection, Stabilising selection
249
What is genetic drift?
| Name 2 things that increases it?
Changes in allele frequency
| A small population, artificial selection
250
Define carrying capacity
When a population reaches the maximum size that the environment can sustain meaning the population size stabilises
251
Define environmental resistance and give 7 examples of it
Limiting factors that prevent the growth of a population
| Space, availability of: food, water, minerals, light, predation and infection from pathogens
252
Define abiotic and biotic and give examples of them in terms of environmental resistance
Abiotic: Non-living components of the environment
Biotic: Living components of the environment
Abiotic: Space, Availability of light, minerals, water
Biotic: Pathogens, predators, prey
253
List the series of events that occur if the environmental resistance is too high.
1. The population size will fall
2. There will be less competition so the population will grow again
3. There will be increased intraspecific competition for resources
4. The population will fall again
254
Define intraspecific competition
Competition within a population
255
Define selection pressure
An environmental factor that increases the chance of survival for some members of the population
256
What determines which individuals in a population will survive?
The organisms will favourable, advantageous alleles will survive. They can then pass the favourable alleles to their offspring.
257
Define stabilising selection
| Draw what it would look like on a graph and check answer on page 140
When there is only one most common favourable allele due to selection pressures causing the favourable alleles to be passed on.
New phenotypes are unlikely to confer an advantage
258
Define disruptive selection
| Draw what it would look like on a graph and check answer on page 140
When a selection pressure makes two alleles favourable causing them to be passed on. There are 2 extreme modal values
259
Define directional selection
| Draw what it would look like on a graph and check answer on page 140
When the selection pressure changes causing changes in allele frequency as new alleles will become favourable.
It leads to evolutionary change and is an evolutionary force.
260
List three isolating mechanisms that can separate a large population into subgroups
What happens to each subgroup?
1. Geographic barriers like rivers
2. Seasonal barriers like climate
3. A change in reproductive mechanisms
Eventually they will have different allele frequencies and the different subgroups won't be able to interbreed resulting in a new species. This is called the founder effect
261
Why is genetic drift higher in small populations?
Because 1 change can drastically change allele frequencies as there isn't many organisms in the population to cancel it out.
262
What happens in extreme cases of genetic drift?
An allele can be eliminated which reduces genetic variation and therefore the ability to survive under different selection pressures. It could either cause extinction or founder effect
263
What is a population bottleneck?
Give an example
Give a case study
A large reduction in allele frequency across a population
Volcanic eruptions
A storm reduced a human population to 30 on an island. 5% of them had an eye defect, there is now 2000 inhabitants there from the original 30 and the likelihood of getting the defect is 0.23. This is drastically higher than other populations, the bottleneck completely changed allele frequencies.
264
Define the biological species concept
A concept that defines a species as "a group of similar organisms that can interbreed and produce fertile offspring. It's also reproductively isolated from other groups"
265
Define the phylogenetic species concept
A concept that defines a species as "a group of organisms that have similar morphology, physiology, embryology and behaviour and they also occupy the same environmental niche"
266
Define a monophyletic group
A group that includes an ancestral organism and all of its descendants
267
Define a paraphyletic group
A group that includes the most recent ancestor but not all of its descendants. One or more clades are excluded
268
Define allopatric speciation
Speciation that occurs due to geographical isolation
269
Define sympatric speciation
Speciation that occurs due to changes in the reproductive mechanism
270
Name 2 problems with the biological species concept
1. It's problematic when classifying asexual species
| 2. Some members of the same species look very different to each other and don't look 'similar'.
271
How do they work out the percentage of divergence when comparing haplotypes (a type of chromosome) of different organisms?
You divide the number of substitutions by the number of base pairs analysed and then times this by 100
272
What is a clade?
What is the cladistics approach?
What are cladistics?
A group of organisms with more similar haplotypes in comparison to other groups, it's a taxonomic group comprising of a single organism and all of its descendants
Using molecular systematics/analysis to work out the variance in organisms
The hierarchical classifcation of species based on their evolutionary ancestory
273
What does the cladistics approach assume? (2 things)
1. The classification of living organisms corresponds to their phylogenetic descent
2. All taxa must be monopyletic
274
What is another term for a clade?
A monopyletic group
275
How are cladistics different from taxonomic classification systems? Name 3 out of 5 reasons
1. It focuses on evolution rather than similarities between species
2. It uses objective, quantitative analysis
3. It uses DNA and RNA sequencing
4. It uses computer programmes to generate cladograms representing the tree of life
5. Both extinct and extant species are included and both are on the cladograms
276
Compare cladistics to Linnaean classification systems. 1 similarity and 2 differences.
Similarity: They both reflect on evolutionary relationships
Differences: Linnaean shows monophyletic AND paraphyletic groups as taxa whereas cladistics only shows monophyletic groups.
It excludes kingdoms, phylums and classes as the evolutionary tree is too complex.
277
Define natural selection
It's a mechanism for evolution where those organisms who are best adapted to their environments survive, reproduce and pass on their favourable alleles. Nature is doing the selecting
278
Define artificial selection
When humans select the organisms with useful characteristics and allow them to breed but prevent the other organisms with unfavourable characteristics from breeding. Humans have a significant effect on evolution with these populations
279
What is the similarity between artificial and natural selection?
The genetic processes underlying both types of selection are the same.
280
GB: What is another term for the central dogma of molecular biology?
Transcription and translation
281
GB: How did they know that glucose was metabolised before lactose in E. coli
Because they gave the E. coli a nutrient medium containing both glucose and lactose. From this they found that E.coli had 2 growth phases, 1 from metabolising glucose first and then one from lactose.
282
GB: Give an example of a good type of E. coli and a bad type.
Good: Harmless strains of E. coli that live in our gut
Bad: 1 harmful strain that can cause food poisoning.
283
GB: List 4 scientists that helped discover apoptosis.(They were all from different periods of time)
Carl Vogt, Walter Flemming, John Foxton Ross Kerr and Leonard Hayflick.
284
GB: What did Hayflick discover?
That normal cell only divide a certain number of times but cancerous cells are immortal.
285
GB: Who disovered chromosomes?
Walter Flemming
286
GB: List 4 characteristics that farmers want their cows to have
Docility, meat production, milk production and survival in their environment
287
GB: Give an example of modern artificial selection
Bulls who produce daughters with high milk yields are kept. There sperm is collected and females are given hormones so that they produce many eggs. The eggs are then fertilised in vitro (in glass) and the embryo is placed in a surrogate mother.
288
GB: Define polyploidy and give an example of it
When nuclei can contain more than one diploid set of chromosomes
For example modern wheat is hexaploid (each diploid contains 14 chromosomes) and has 42 chromosomes in each cell. The nuclei and therefore cells need to be larger because of this. Modern wheat contains genomes from various wheat species like wild goat grass. This is within the genus: Triticum
289
GB: List 5 characteristics that farmers want their wheat to have.
Resistance to fungal infections, High protein content, Straw/stem stiffness, Resistance to lodging (stems bending) and increased yield
