Topic 3 Genetics Flashcards
1
Q
What is sexual reproduction?
A
- When genetic information from two organisms combine to produce offspring, which are genetically identical
- At fertilisation, both gametes fuse to produce a fertilised egg, which is a zygote
- The zygote then undergoes cell division and develops into an embryo that inherits chromosomes from both parents
2
Q
What are gametes?
A
- Sex cells (sperm cells, egg cells)
- Haploid so they have half the number of chromosomes
3
Q
What is meiosis?
A
- Form of cell division involved in the formation of gametes
- Chromosome number is halved
- Involves two divisions
4
Q
What must occur prior to meiosis?
A
Interphase - When DNA is spread out into long strings and then increases subcellular structures. Now, it duplicates a copy of DNA and forms an X-shaped chromosome.
5
Q
What happens during the first division meiosis?
A
- Chromosome pairs line up along the centre of the cell
- The pair of chromosomes are pulled apart
- Chromosome number is halved with both parents’ chromosomes mixed
- This also creates genetic variation
6
Q
What happens during the second division of meiosis?
A
- Chromosomes line up along the cell equator
- The chromatids are pulled apart
- Four unique haploid gametes are produced
- They are genetically different
7
Q
Why is meiosis important for sexual reproduction?
A
- It increases genetic variation
- It ensures that the resultant zygote is diploid
8
Q
What is the advantage of sexual reproduction?
A
- Genetic variation and different characteristics if the environment changes, some individuals will survive
- Overtime, natural selection, and evolution will take place to be more adapated
9
Q
Describe the disadvantages of sexual reproduction.
A
- Takes time and energy, e.g. male bowerbirds build structures out of twigs and then dance to impress
- Two parents are needed, and it is a huge problem if individuals are isolated, e.g. polar bears live alone and walk up to 100 miles to find a mate
10
Q
What is asexual reproduction?
A
- Type of reproduction
- Involves mitosis
- Produces genetically identical offspring known as daughter cells
11
Q
Describe the advantages of asexual reproduction.
A
- Only one parent is required
- Lots of offspring can be produced in a short period of time, enabling the rapid colonisation of an area, e.g., bacteria such as E.coli divide every half an hour
- Requires less energy
12
Q
What is the disadvantage of asexual reproduction?
A
- No genetic variation (except from spontaneous mutations), reducing the probability of a species being able to adapt to environmental change
- E.g. Black signora is a disease that affects banana plants, which reproduce asexually, so if this disease had an outbreak, all bananas would be affected
13
Q
What is DNA?
A
DNA is the molecule that carries the genetic instructions for the development and functioning of all living organisms.
14
Q
What are the monomers of DNA?
A
Nucleotides.
15
Q
What are DNA nucleotides made up of?
A
- A sugar
- Phosphate group
- One of four ‘bases’: A, T, C, or G
16
Q
State the full names of the four bases found in nucleotides.
A
- Adenine
- Thymine
- Cytosine
- Guanine
- Uracil instead of Thymine in transcription
17
Q
Describe how nucleotides interact to form a molecule of DNA.
A
- Nucleotides join together to form a single strand. A sugar bonds with a phosphate to create a backbone.
- Two strands of nucleotides coil around each other to form a double helix and are held together by weak hydrogen bonds between the bases.
- The bases pair up in a specific way, known as complementary base pairing:
Adenine (A) pairs with Thymine (T)
Cytosine (C) pairs with Guanine (G)
18
Q
Define genome.
A
All of an organisms DNA. (Including non-coding regions)
19
Q
What is a chromosome?
A
A long, cooled up molecule of DNA. They are found in the nucleas of eukaryotic cells.
20
Q
Define gene.
A
A section of DNA on a chromosome that codes for a particular protein.
21
Q
Describe the method used to extract DNA from fruit.
A
- Place a piece of fruit in a beaker and crush it, e.g., strawberries
- Add detergent to break down the cell membranes and salts to make the DNA stick together
- Filter the mixture and collect the liquid in a test tube
- Add ice-cold alcohol to the filtered mixture
- DNA precipitates forming a stringy white solid
- Use a glass rod to collect the DNA sample
22
Q
Why is ice-cold alcohol added rather than water?
A
DNA is insoluble in cold alcohol, encouraging its precipitation.
23
Q
Explain how a gene codes for a protein.
A
- Each gene contains a different sequence of bases
- Amino acids are coded by a sequence of base triplets read by the cell
- E.g. TCG is a different amino acid to TGG
- The amino acids are then joined together following the order of the bases in the gene.
- This chain of amino acids is a particular protein
24
Q
Why is the ‘folding’ of amino acids important in proteins such as enzymes?
A
The folding of amino acids determines the shape of the active site which must be highly specific to the shape of its substrate.
25
What is protein synthesis?
The formation of a protein from a gene in a cell.
26
What are the two stages of protein synthesis?
1. Transcription
2. Translation
27
What does transcription involve?
The formation of mRNA from a DNA template.
28
Outline transcription.
1. RNA polymerase binds to a non-coding DNA section in front of the gene.
2. DNA unzips, and RNA polymerase moves along the coding strand.
3. mRNA is built using the DNA template-bases pair up to br complementary to the gene.
4. Finished mRNA exits the nucleus and goes to ribosomes to make proteins.
29
Describe the difference between mRNA and DNA.
- mRNA is single-stranded, whereas DNA is double-stranded
- mRNA uses Uracil instead of Thymine
30
Why is mRNA used in translation rather than DNA?
DNA is too large to leave the nucleus, so it can not reach the ribosomes in the cytoplasm.
31
What does translation involve?
A ribosome joins amino acids in a specific order dictated by mRNA to form a protein.
32
Outline translation.
1. mRNA binds to a ribosome, which reads it in codons (base triplets), each coding for an amino acid.
2. tRNA molecules carry amino acids to the ribosome.
3. Each tRNA has an anticodon that is complimentary the mRNA codon, ensuring the correct amino acid is added.
4. The ribosome links the amino acids together, forming a protein (polypeptide).
33
How is a tRNA molecule adapted to its function?
Each tRNA molecule has an anticodon which is specific to the codon of the amino acid that it carries.
34
What is a mutation?
A random change in the base sequence of DNA that can be inherited results in genetic variants, which is a different version of the gene.
35
Describe the effect of a gene mutation in coding DNA.
- If a mutation changes the amino acid sequence, the final protein structure and function may change
- The activities of an enzyme may increase, decrease, or stop and can change the characteristics (phenotype) of an organism
36
What is non-coding DNA?
DNA, which does not code for a protein but is still involved in protein synthesis.
37
Describe the effect of a gene mutation in non-coding DNA.
- A mutation may affect the ability of RNA polymerase to bind to non-coding DNA
- This may affect protein production and the resulting phenotype of the organism
38
Outline how the work of Mendel helped scientists develop their understanding of genetics.
- Mendel studied the inheritance of different phenotypes of pea plants
- He established a correlation between parent and offspring phenotypes
- He noted that inheritance was determined by ‘hereditary units’ passed on to descendants
- Using gene crosses, he devised the terms ‘dominant’ and ‘recessive’
39
Why was Mendel’s work initially overlooked?
Scientist’s didn’t understand Mendel’s work as there was no knowledge of genes, DNA, or chromosomes at the time.
40
What are alleles?
Different versions of the same gene represented by letters.
41
Define genotype.
The combination of alleles an organism has.
42
Define phenotype.
Characteristics determined by your alleles.
43
Define homozygous.
Having two identical alleles of a gene, e.g., FF or ff.
44
Define heterozygous.
Having two different alleles of a gene, e.g., Ff.
45
What is a dominant allele?
Describes an allele that is always expressed represented with a capital letter, e.g., F.
46
What is a recessive allele?
An allele that is only expressed in the absence of a dominant allele represented with a small letter, e.g., f.
47
What is monohybrid inheritance?
The inheritance of a single characteristic.
48
What are sex chromosomes?
A pair of chromosomes that determine sex:
- Males have an X and a Y chromosome XY
- Females have two X chromosomes XX
49
How is offspring with a XX or XY chromosomes decided?
Sex determination is dependent on whether the sperm carries an X or a Y.
50
What is a sex-linked characteristic?
If an allele that codes for it is located on a sex chromosome (X or Y).
51
Why are the majority of genes found on the X chromosome rather than the Y chromosome?
The X chromosome is bigger than the Y chromosome so more genes are carried on it.
52
Why are men more likely to show the phenotype for a recessive sex-linked trait than women?
- Many genes are found on the X chromosome that have no counterpart on the Y chromosome
- Women (XX) have two alleles for each sex-linked gene, whereas men (XY) often only have one allele
- Only one recessive allele is required to produce the recessive phenotype in males
53
Give an example of a characteristic that is determined by more than one allele.
Blood group is determined by three alleles: I^A, I^B, I^O.
^ = To the power of
54
Name the four different blood groups.
A, B, AB, O
55
What are codominant alleles?.
When an individual has two codominant alleles, one isn't dominant over the other one.
56
Describe codominance in blood group.
- I^A and I^B are codominant
- I^A I^B gives the blood group AB
57
What are the characteristics of each allele in blood groups.
1. I^O is recessive, common in Britain
2. I^A is codominant to I^B
3. I^B is codominant to I^A
58
What are the two causes of variation within a species?
- Genetics
- Environment
59
What is genetic variation?
Different alleles to produce different phenotypes.
60
What creates genetic variation in a species?
- Mutations
- Sexual reproduction
61
What is a mutation?
Changes to the base sequence of DNA resulting in genetic variants.
62
What happens when a mutation occurs within a gene?
- They result in a different allele and don't have a big effect on the phenotype.
- Most mutations don't even have any effect, so they are called neutral.
- New alleles combining can cause new phenotypes.
63
What is an example of a small effect from mutations?
Small mutations have a small effect on a phenotype, e.g., a mutation might give a hamster long hair instead of short hair.
64
What is environmental variation?
- Variations in phenotype that are acquired during the lifespan of an organism
- Due to environmental factors, e.g., diet, lifestyle, climate, exposure to light, etc.
65
What is the Human Genome Project?
- Scientific research project involving thousands of scientists across the globe, which successfully mapped the entire human genome
- Scientists now aim to identify the function of every gene in the human genome
- Started in 1990 and ended in 2003 with 20,500 genes found and 1800 genes related to disease
66
What are drawbacks associated with the discoveries of the Human Genome Project?
- Knowledge of predisposition to a disease can be stressful
- Societal pressure influencing the decision to have children
- Discrimination by employers, life insurance, etc.
67
Where are the gametes found in flowing plants?
Male gametes are fihnd in the pollen and female gametes are found in the ovaries at the bottom of the stigma.
68
A monomer is..?
A small, basic molecular unit that can join together with other similar units to form a larger molecule called a polymer. E.g. glucose, amino acids, nucleotides.
69
A polymer is..?
A large, complex molecule made up of many repeating smaller units called monomers. E.g. starch, proteins, DNA.
70
How do cells reproduce asexually?
They divide by mitosis.
71
How do organisms produce sexually?
By meiosis to produce genetically different haploid gametes.
72
How are proteins made if the DNA is too large to leave the nucleas?
Using a molecule called mRNA, which is a polymer of nucleotides like DNA but is shorter and only a single stand complementary to DNA, which uses Uracil instead of Thymine.
73
What does the RNA polymerase enzyme do?
It is involved in joining together RNA nucleotides to make mRNA.
74
What is an example of a genetic variant that changes characteristics.
XDH is an enzyme that if normal fruit flies will have a red eye pigment. If fruit flies have no XDH activity, they have brown eyes since they can produce it.
75
What are Mendel's hereditary units?
Genes - A section of DNA on a chromosome that codes for a particular protein.
They work the same in animals like plants.
76
What happened after Mendel's death?
People realised how significant his work was and the mechanism of inheritance could be fully explained.
77
Who was Mendel?
- Gregory Mendel was an Austrian monk who trained in maths and natural history
- On his garden in the mid-19th century, he noted how characteristics in plants are passed on
- His research was published in 1866 of how characteristics of pea plants were inherited
78
What did Mendal do with pea plants?
- He crossed two pea plants, one tall, one dwarf and the offspring were all tall pea plants
- He bred two of these tall offspring and a ratio of 3:1 of tall:dwarf was produced
- He mentioned T was dominant for tall plants over the t for dwarf plants
79
What was another characteristic Mendel researched other than height?
He found a purple flower colour was dominant over a white colour.
80
What is a family pedigree?
They show monohydrid inheritance of a family tree of a genetic disorder.
81
What is an example of a sex-linked disorder?
Colorblindness is caused by a faulty allele on the X chromosome (X). Since the Y chromosome lacks this allele (Y), males (XY) only need one faulty X to be affected, while females (XX) need two. This makes colorblindness more common in males.
82
What is haemophilia?
Another sex-linked disorder like colourblindness and is where blood doesn't clot properly.
83
What is an example of a big effect from mutations?
Rarely, a single mutation can drastically affect phenotype. For example, in cystic fibrosis, a mutation disrupts a protein that regulates salt and water in cells, causing thick mucus in the lungs and digestive system, leading to breathing and digestion problems.
84
What are the two examples of environmental variation?
- If a plant grows on in a sunny area, it will grow green, whereas if a plant grows in darkness, it will grow tall and yellow.
- A plant and animals maximum height can also depend on how much food it gets
85
What can the Human Genome Project do to predict and prevent diseases?
The Human Genome Project helps identify genetic diseases like cancer or heart disease by analyzing gene interactions. This allows for personalised diet and lifestyle advice to reduce risks, as well as regular monitoring for early detection and treatment in susceptible individuals.
86
What can the Human Genome Project do to test and treat inherited disorders?
The Human Genome Project helps identify faulty alleles linked to inherited disorders (e.g., cystic fibrosis), enabling faster genetic testing. Once disease-causing alleles are found, targeted treatments can be developed, and potential cures may be pursued in the future.
87
What can the Human Genome Project do to help make new and better medicines?
It allows scientists to:
1) Develop personalized drugs tailored to specific genetic profiles
2) Predict how well existing medicines like breast cancer treatments will work for each patient
3) Determine optimal drug dosages based on genetics
4) Design more effective treatments with fewer side effects by understanding diseases at the molecular level
