Topic 3/10 Flashcards
1
Q
Gene
A
Heritable factor that consists of a length of DNA and influences a specific characteristic
2
Q
Locus
A
Specific position of a gene on the chomosome
3
Q
Allels
A
- Various specific forms of a gene
- Occupy the same position on one type of chromosome
- They differ from each other by one or a few bases only
4
Q
Give examples of multiple allele genes
A
- Coat colour in mice
- Blood type in human
- Eye colour in fruit flies
5
Q
Outline the formation of new alleles
A
- Mutations that resulted in difference of one or a few bases in the sequence
- Developed by evolution over millions of years
6
Q
Mutations
A
- Random changes in the base sequence
- Usually neutral or harmful
7
Q
Explain the cause of sickle-cell anemia
A
- Mutation of the gene that codes for the alpha-globin polypeptide in hemoglobin (symbol is Hb)
- The sixth codon GAG is changed to GTG due to base subsitution mutation
- New allele is formed (HBS other than the normal HBA)
- The amino acid produced becomes valine instead of glutamic acid
- Causes hemoglobin molecules to stick together in tissues with low oxygen concentration
8
Q
Outline the danger of sickle cell anemia
A
- Sickle cells cause damage to tissues by becoming trapped in blood capillaries, blocking them and reducing blood flow
- When sickle cells return to high oxygen conditions in the lung, the bundles break up and return to normal shape
- Both the hemoglobin and the plama membrane are damaged and the life of a red blood cell is shortened
- The body cannot replace red blood cells quick enough and anemia therefore develops
9
Q
Genome
A
Whole of the genetic information of an organism
10
Q
What does the human genome consist of
A
- 46 moledules that fomr the chromosomes in the nucleus
- DNA molecule in the mitochondrion
11
Q
Human Genome Project
A
- Aims to find the base sequence of the entire human genome
- Comparison of the base sequence gives proof to the evolutionary history of species
12
Q
Compare and contrast the genetic information in prokaryotes and eukaryotes
A
Similarity
- store genetic information in chromosomes
Difference
- prkaryotes have circular DNA molecule; eukaryotes have linear
- prokaryotes DNA is not associated with proteins (naked); eukaryotes DNA is associated with histones
- prokaryotes DNA is single stranded; eukaryotes DNA is double stranded
- prokaryotes have plamid; eukaryotes don’t
13
Q
Define plasmids
A
Small, circular, and naked DNA containing a few genes (ex. antibiotic resistance in bacteria)
- Can be transferred from one cell to another to spread resistence
14
Q
Outline the use of autoradiography to measure the length of DNA molecules
A
- Cells are grown with radioactively labelled nucleotides
- Placed in a dialysis membrance and the DNA is released onto the surface of the membrane
- Thin film of photographic emulsion was applied to the membrane and left in darkness
- Radioactive atoms emit high energy electrons and leave a mark on the film
15
Q
Explain why human chromosome is referred to as 2n
A
- Homologous chromosomes that carry the same sequence of genes but not necessarily the same alleles
- Inherit one chromosome from each parent
16
Q
List the following species in order of genome size (largest to smallest) T2 phage (virus), Escherichia coli (bacteria), Drosophila melanogaster (fruit fly), Homo sapiens (human), Paris japonica (plant)
A
Paris japonica (150,000) Homo sapiens (3000) Drosophila melanogaster (140) Escherichia coli (5) T2 phage (0.18)
17
Q
Explain the correlation between genome size and complexity of organism
A
- Positively correlated but not directly proportional
- Proportion of the DNA that acts as functional genes is very variable and also the amount of gene duplication varies
- Plants may have 3n or 4n
18
Q
Define and give examples of haploid nuclei
A
- Haploid nuclei have one chromosome of each pair
- One full set of the chromosomes that are found in its species (ex. contains 23 chromosomes in human)
- Represented as n
- Ex) gametes or sex cells that fuse together during sexual reproduction, human egg and sperm cells
19
Q
Define and give examples of diploid nuclei
A
- Diploid nuclei have pairs of homologous chromosomes
- Two full sets of the chromosomes (ex. contains 46 chromosomes in human)
- Represented as 2n
- Ex) body cells, nerve cells
20
Q
Outline the advantages of diploid nuclei
A
- Effects of harmful recessive mutations can be avoided if a dominant allele is also present
- Organisms are often more vigorous if they have two different allels of genes instead of just one (hybrid vigours)
- Genetic diversity
21
Q
List the following species in order of diploid chromosome numbers (largest to smallest) Homo sapiens (human), Pan troglodytes (chimpanzee), Canis familiaris (dog), Oryza sativa (rice), Parascaris equorum (horse threadworm)
A
- Canis familiaris (78)
- Pan troglodytes (48)
- Homo sapiens (46)
- Oryza sativa (24)
- Parascaris equorum (4)
22
Q
Explain the use of a karyogram
A
- Shows the chromosomes of an organism in homologous pairs of decreasing length
- Stains are used to make the chromosomes show up during mitosis and a micrograph is taken
- Chromosomes are in homologous pairs, arranged by size (starting with the longest)
23
Q
What can be identified with a karyogram
A
- Down syndrome (with an extra chromosome 21)
- Sex (2 X chromosome for female and X+Y chromosome for male)
24
Q
How many haploid cells does a diploid nucleus produce in meiosis
A
4
25
Outline the advantages of sexual reproduction over asexual reproduction
- Meiosis, fertilization result in genetic variation
26
When does DNA replication occur
- Before meiosis and mitosis
| - does NOT occur between the two stages of meiosis (results in the halving of chromosomes)
27
Explain synapsis in meiosis
- Pairing of homologous chromosomes in the beginning stage of meiosis
- Crossing over occurs
28
Explain crossing over and the advantages of that
- A junction is created where one chromatid in each of the homologous chromosomes breaks and rejoins with the other chromatid
- Occurs during synapsis
- Connection point between sister chromatids is called chiasmata
- Occurs in random positions with random frequency (genetic variation)
- Allows for combinations of genes
29
Explain how the random orientation of the homologous chromosomes add to genetic diversity
- The two homologous chromosomes in a bivalent are attached to different poles.
- The pole to which each chromosome is attached depends on the orientation of the chromosomes
- Equal chance for each chromosome to be ended up in either poles
- Orientatio of one pair does not affect the other pair
30
Name the two procedures used for obtaining cells containing the fetal chromosome for karyotype
- Chroionic villus sampling
| - Amniocentesis
31
Explain amniocentesis
- Passing a needle through the mother's abdomen wall, using ultrasound to guide
- The needle withdraws a sample of the amniotic fluid containing the fetal chromosome
32
Explain chroionic villus sampling
- Sampling tools enters the vagina and obtain cells from the chorion (membrane from which placenta develops)
33
Evaluate amniocentesis and chroionic villus sampling
- Chroionic villus sampling as a higher chance of miscarriage
- It can be done earlier in pregnancy
34
During meiosis, outline what occurs in Prophase I
- Cell has 2n chromosomes (double chromatid)
- Homologous chromosomes pair (synapsis).
- Crossing over occurs.
35
During meiosis, outline what occurs in Metaphase I
- Spindle microtubules move homologous pairs to equator of the cell.
- Orientation of paternal and maternal chromosomes on either side of equator is random and independent of other homologous pairs.
36
During meiosis, outline what occurs in Anaphase I
- Homologous pairs are separated. One chromosome of each pair moves to each pole.
37
During meiosis, outline what occurs in Telophase I
- Chromosomes uncoil. During interphase that follows, no replication occurs.
- Reduction of chromosome number from diploid to haploid completed.
- Cytokinesis occurs.
38
During meiosis, outline what occurs in Prophase II
- Chromosomes, which still consist of two chromatids, condense and become visible
39
During meiosis, outline what occurs in Metaphase II
- Chromosomes line up in the middle and spindle fibres are attached to the centromeres
40
During meiosis, outline what occurs in Anaphase II
- Centromeres separate and chromatids are moved to opposite poles.
41
During meiosis, outline what occurs in Telophase II
- Chromatids reach opposite poles.
- Nuclear envelope forms.
- Cytokinesis occurs.
42
Explain how fusion of gametes from different individuals promote genetic diversity
- The combination of allels is unlikely ever to have existed before
- Each sperm and egg carries differnt genes, gusion of gametes further promote genetic variation, which is essential for evolution
43
Define non-disjunction and give an example
- Non-disjunction is when homologous chromosomes fail to separate at anaphase
- Can happen with any of the pairs of homologous chromosomes
- Result will be a gamete has an extra chromosome or deficient in chromosomes
- Most trisomies in human do not survive
- Ex) Down syndrome has trisomy 21 -- hearing loss, heart and vision disorder, mental and growth retardation
- Ex) Klinefelter's syndrom has XXY sex chromosomes
- Ex) Turner's syndrom has only one sex chromosome X
44
Who discovered patterns in inheritance
Gregor Mendel
45
How did Mendel discovered patterns of inheritance
- Large numbers of pea plants
| - Crossed them with each other, observing the changes in phenotype
46
Explain why human have two different alleles or two copies of the same allele
- Fusion of gametes result in diploid zygotes with two allels of each gene, one from each parent
- The alleles may be different or the same
47
Define dominant allele
- Allele that mask other alleles (expressed in phenotype)
| - Represented by a capital letter
48
Define recessive allele
- Allele that is masked by other alleles (not expressed in phenotype)
- Represented by a lower case letter
49
Explain co-dominant alleles and give an example
- Pairs of alleles where both have an effect when they are present together
- Ex) red-flower and white-flower product pink flower
50
Explain the inheritance pattern for blood type in human
- A and B are dominant allels while O is recessive
| - Type AB is codominance with alleles A and B
51
Explain why blood type O is a universal donor
- O does not have any antigen on its blood cells
- Although blood of a type O person will have antibodies for both antigen A and B, once they are filtered out, the blood cells of O can be donated to all blood types
52
Explain why blood type AB is a universal receiver
- AB has both antigen A and antigen B
- It cannot donate blood to anyone else other than blood type AB (antibodies in other blood type will destroy the blood cells
- A type AB person does not have antibodies and can receive blood from other blood type
53
Explain why some individuals carry the gene for genetic diseases but themselves do not show symptoms of the disease
- Most genetic diseases are caused by a recessive allele of a gene
- If a person has one recessive allele with one dominant allele, the symptoms do not show, but the person could potentially pass on the recessive allele to their offspring
54
Give an example for each of the following types of genetic diseases: recessive, dominant, co-dominant, sex-linked
- Recessive: cystic fibrosis
- Dominant: Huntington's disease
- Co-dominant: sickle cell anemia
- Sex-linked: colour blindness, hemophilia
55
Explain why individuals with hybrid genes for hemoglobin show resistence to malaria
- Copies of sickle cell genes make the blood cells a little sticky and difficult for parasite to enter
- Increase resistence to malaria
- Develop mild anemia
56
Explain the symptoms of cystic fibrosis
- Sweat containing excessive amounts of NaCl
- Digestive juices and mucus are secreted with insufficient NaCl
- Sticky mucus builds up in the lungs, causing infections, digestive ducts are blocked
57
Explain the symptoms of Huntingtom's disease
- Causes degeneratvie changes in the brain
- Changes to behavior, thinking and emotions become severe
- Develop between 30 to 50 years old
58
Explain why the pattern of inheritance is different with sex-linked genes
- Only the X chromosome carry the genes (usually)
| - The punnett square is different
59
Explain why males have a higher chance of inheriting red-green blindness
- Red-green blindness is a recessive gene on the X chromosome
- Males only have one X chromosome, but girls have two (as long as one of them is dominant, females do not develop colour-blindness)
60
Explain the symptoms of hemophilia
- Inability of make Factor VIII, one of the proteins invovled in the clotting of blood
- More prevalent in males
61
Outline the causes of mutation
Radiation
- Increases the mutation rate if it has enough energy to cause chemical changes in DNA
Mutagenic chemicals
- Cause chemical changes in DNA
62
How does mutation cause cancer
- Mutations of the genes that control cell division cause a cell to divide endlessly and develop into a tumour
- Leads to cancer
63
Outline the consequences of radiation after nuclear bombing in Hiroshima and Nagasaki and the nuclear accidents at Chernobyl
- Cancer, mutations, malformation and death and stillbirths were conjectured
- No evidence has been found of mutations caused by the radiation
- Damage the environment
64
Outline the purpose of gel electrophoresis
- Separate proteins or fragments of DNA according to size
- Crime scene fingerprints
- Paternity tests
65
Explain the mechanism of gel electrophoresis
- Samples are placed in wells cast in a gel immersed in a conducting fluid
- Electric field is applied
- DNA carry negative charges so move in the same direction
- Small fragments move faster than large ones
66
Outline the purpose of Polymerase Chain Reaction (PCR)
- Amplify small amounts of DNA in little time
| - Sequence can be selected for copying by using a primer that binds to the start of the desired sequence
67
Outline the stages of DNA profiling
- Sample of DNA is obtained, either from a known individual or from another source such as fossil or crime scene
- Sequences in the DNA that vary considerably between individuals are selected and are copied by PCR
- Copied DNA is split into fragments using restriction endonucleases
- Fragments are separated using gel electrophoresis
- Produces a pattern of bands that is always the same with DNA from the same individual
- Compared to other people
68
Define genetic modification
Transfer of genes from one species to another
69
What makes genetic modification possible
- Universal genetic code (ATCG bases)
| - Technology
70
Give an example of genetic modification and the advantage of it
- Goats have been produced that secrete milk containing spider silk protein (immensely strong)
- GM crops (snapdragons' genes in tomatoes produce purple tomatoes, golden rice)
71
Explain how gene can trasfer to bacteria with plasmids
- Restriction enzyme (endonucleases) cut DNA molecules at specific base sequences
- Cut open plasmids and link together pieces of DNA
- DNA ligase is an enzyme that joins DNA molecules together after desired gene has been inserted into a plasmid
- Recombinant plasmid is placed into the host cell and produce desired protein
72
Explain the benefits of GM crops
- Increased yields
- Reduced pesticide and herbicide
- Require less water
- Increase shelf-life of fruit and vegetable
- Nutritional value can be improved
- Varieties of crops lack allergens or toxin
- Edible vaccine
- Resistant to drought, cold, salinity, diseases
73
Explain the risks of GM crops
- Antibiotic resistance genes could spread to bacteria
- Transferred genes could mutate and cause health risks
- Non-target organisms could be affected by toxins that are intended to control pests
- Herbicide resistant could spread to wild plants and lead to super-weeds
- Reduced biodiversity
- Farmers are not permitted by patent law to save and re-sow GM seed from crops they have grown
74
Define clone
A group of genetically identical organisms
75
Outline an example of a natural method of cloning
- All the bulbs in a garlic are clones
- Strawberry plants grow long horizontal stems with plantlets at the end. These plantlets grow roots and become independent of the parent plant but are geneically identical
- Hydra clones itself by budding
- Female aphids can give birth to offspring from diploid egg cells produced by mmitosis
76
Outline the method to clone animals at the embryo stage
- All cells at an early stage are pluripotent (capable of developing into all types of tissue)
- Breaking up animal embryos artifically and allow each separated parts to develop into individual clones
- Impossible to assess whether a new indidvidual has desirable characteristics -- this method is of little interest
77
Outline the method to clone adult animals
- Adult cells were taken and the genes are made inactive
- Unfertilized eggs were taken from the ovaries and nuclei were removed
- Electric pulse was used to fuse the two cells together
- Embryo were then injected into the uterus
78
Define chiasmata
- These connection points between sister chromatids
79
Outline how crossing over promote genetic variety
- Produces new combinations of alleles on the chromosomes (recombinations)
80
Explain the difference in inheritance pattern in fruitfly, not following Mendelian inheritance
- Association of eye colour and wing type is linked (located on the same chromosome)
- Are not independent of each other
81
Define variations
The differences between individual organisms
82
Give an example of discrete variation in genes
Ex) Blood types in humans (fit distinctly in each of the three categories, no in-between)
83
Give an example of continuous variation in genes
Ex) Heights in humans (no distinct categories like "short" "tall")
- Usually polygenetic characteristics (close to a normal distribution)
84
Give an example of polygenetic trait and how it can be influenced by the environment
Ex) Human heights
- Nutrition can play a role
- Identical twins raised differently show different phenotypes
Ex) Human skin colour
- Sunlight stimulates the production of the black pigment melanin in the skin
85
The calculated value for chi-squared is in the critical region, what does that mean
- Reject the null hypothesis
86
The calculated value for chi-squared is below the critical value, what does that mean
- Null hypothesis is not rejected
87
What is the critical region in chi-squared test
Any value larger than value in the table (determined by degree of freedom)
88
Define gene pool
- Consists of all the genes and their different alleles present in an interbreeding population
89
Define species
- A group of potentially interbreeding populations, with a common gene pool that is reproductively isolated from other species
- Possible to have multiple gene pools to exist for the same species if they are geographically isolated
90
Define evolution
- Cumulative change in the heritable characteristics of a population over time
- Occur due to mutations (introducing new alleles), selection pressures (favouring the reproduction of some varieties over others) and barriers to gene flow emerging between different populations
- Random events can also have a signifcant effect on allele frequency for small population
91
Define selection pressure
- Environmental factors that act selectively on certain phenotypes resulting in natural selection
92
State the three patterns of natural selection
- Directional
- Stabilizing
- Disruptive
93
Outline stabilizing selection and give an exmple
- Selection pressures act to remove extreme varieties
| Ex) average birth weights of humans are favoured over low or high weight
94
Outline disruptive natural selection and give an example
- Selection pressures act to remove intermediate varieties, favouring the extremes
Ex) Asymmetric lower part of the redcrossbills is an adaption to extract seeds from conifer cones (the bill can be crossed to either side)
95
Outline directional selection and give an example
- Population chnages as one extreme of a range of variation is better adapted
Ex) Giraffes with longer necks are favoured over giraffes with shorter necks
96
Define speciation
- Formation of a new species by the splitting of an existing population
- Can occur because of geographic separation (allopatric) or sympatric speciation
97
Outline how geographic separation lead to speciation
- Geographic separation leads to isolation of populations that are subject to different selection pressures
- When the populations recombined, they can be unable to produce viable and fertile offspring
98
Outline how behavioral isolation can lead to speciation
- When closely related individuals differ in their courtship behaviour, they are often only successful in attracting members of their own population
99
Outline how temporal isolation can lead to speciation
- Populations may mate or flower at different seasons or different times of day
- The lapse between the stimulus and flowering/mating lead to speciation
100
Explain gradualism in terms of speciation
- Idea that species slowly change through a series of intermediate forms
- Confornted by gaps in the fossil record (absence of intermediate forms)
101
Explain punctuated equilibrium in terms of speciation
- Long periods of relative stability in a species are "punctuated" by periods of rapid evolution
- Gaps in the fossil record might not be gaps at all
- Events such as geographic isolation and opening of new niches can lead to rapid speciation
- Common in organisms with short generation times
102
Explain speciation by polyploidy using the genus Allium
- The Allium genus includes onions, leeks, garlic, and chives
- Polyploidy events are common within the genus
- Result in a number of reproductively isolated but otherwise similar populations
- Polyploidy may confer an advantage over diploidy
