Genetic and phenotypic variation

Question 1

Define an allele.

Answer 1

each of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

Question 2

Define genotype.

Answer 2

The genetic constitution of an individual organism

Question 3

Define phenotype.

Answer 3

The set of observable characteristics of an individual resulting from the interaction of its genotype with the enviroment.

Question 4

Define a gene.

Answer 4

A distinct sequence of nucleotides forming part of a chromosome, its order determines the order of monomers in a polypeptide or nucleic acid molecule which a cell (or virus) may synthesize.

Question 5

What is a gene pool?

Answer 5

All of the different alleles of all of the genes existing in all individuals of a population.

Question 6

what is genetic flow?

Answer 6

The exchange of genes between poplulations through migrations or exchange of gametes.

Question 7

If the amount of gene flow is high enough between two populations, what will happen?

Answer 7

Two populations will share one gene pool instead of two disctinct ones –> two populations have equivalent allele frequencies.

Question 8

What is genetic drift?

Answer 8

Changes in allele frequencies within a population from generation to generation as a result of random (chance) process.

Question 9

Why are small populations more affected by genetic drift?

Answer 9

Which alleles gets passed onto the next generation is random, and small populations are proportionately more influenced by random sampling.

Question 10

What are the effects of genetic drift?

Answer 10

• fixation: allele frequency increases to 100%
• elimination: allele frequency decreases to 0%
• overall, a decrease in genetic variety.

Question 11

What may result in a strong genetic drift?

Answer 11

• Bottleneck effect: when population sharply reduce in size
• Founder effect: when a small group from a population splits off from the main population to found a colony. Those few individuals that split off are called pioneers.

Question 12

How does the bottleneck effect reduce genetic variety?

Answer 12

• sharp reduce in individuals
• allele frequencies likely to be different from the original population just by chance
• likely to be less number of alleles because of small population size
• Result: Less genetic variety and different allele frequencies compared to before

Question 13

How does the founder effect reduce genetic variety in a population?

Answer 13

• Small size of the group of pioneering individuals unlikely to pocess all the alleles in the main population
• allele frequencies in prioneering indivuduals may differ from main population by chance
• result: new population have a decrese in genetic variety –> genetically drifted

Question 14

What is the equation of the Hardy-Weinberg model

Answer 14

p² + 2pq + q² = 1

Question 15

What are the assumptions of the Hardy-Weinberg model?

Answer 15

1. No selection
2. No mutation
3. No migration
4. Large population
5. Random Mating

Question 16

p + q = ?

Answer 16

1

Question 17

What does it mean when the allele genotype frequencies in a population does not match the frequencies calculated using the Hardy-Weinberg model?

Answer 17

One or more assumptions have been violated. E.g Evolution has occured

Question 18

How does population size relate to allele fixation and loss?

Answer 18

Larger population –> smaller chance of losing an allele

Question 19

How does the p:q ratio relate to allele fixation and loss?

Answer 19

More q –> less likely to lose allele.

Example:

A gene of p = 0.5, q = 0.5 is more likely to lose alleles than if it was p = 0.1, q = 0.9

Question 20

For genetic drift, how can you know the fixation probablity of an allele?

Answer 20

The probablity of fixation of an allele is its initial frequency in the population

Example:

allele freqeuncy = 0.01 –> probability of fixaiton = 1%