Genetic variation in populations

Question 1

What is the ultimate source of genetic variation?

Answer 1

Mutation

Mutation introduces new genetic variants into populations.

Question 2

Why is sickle cell disease more prevalent in African Americans compared to northern Europeans?

Answer 2

Genetic variation in populations

Environmental factors and natural selection contribute to these differences.

Question 3

What role does probability play in genetics?

Answer 3

Helps understand gene transmission and genetic variation

It also aids in risk assessment in medical genetics.

Question 4

Define probability in the context of genetics.

Answer 4

Proportion of times a specific outcome occurs

Probabilities range from 0 to 1.

Question 5

What is the probability of transmitting one member of a chromosome pair during meiosis?

Answer 5

1/2

The probabilities of all possible events must add to 1.

Question 6

What does the multiplication rule of probability state?

Answer 6

Probability of independent events occurring together is the product of their probabilities

Example: Probability of obtaining heads on two coin tosses is 1/2 × 1/2 = 1/4.

Question 7

What is the addition rule of probability?

Answer 7

Probability of either one outcome or another is the sum of their probabilities

Example: Probability of getting two heads or two tails in two tosses.

Question 8

How do you calculate genotype frequency?

Answer 8

Divide each genotype count by the total number of subjects

Example: Frequency of MM = 64/200 = 0.32.

Question 9

What is the gene frequency for an allele?

Answer 9

Number of that allele divided by the total number of alleles at the locus

Example: Frequency of M = 248/400 = 0.62.

Question 10

What does the Hardy-Weinberg principle describe?

Answer 10

Predictable relationship between gene frequencies and genotype frequencies under random mating

It is used to estimate gene and genotype frequencies.

Question 11

What is the expected frequency of homozygous recessive individuals (aa) in the Hardy-Weinberg principle?

Answer 11

q²

The frequency of affected homozygotes can be calculated from disease prevalence.

Question 12

What is natural selection?

Answer 12

Process that increases frequency of beneficial alleles and decreases frequency of harmful alleles

It acts differently based on environmental contexts.

Question 13

How does natural selection relate to sickle cell disease?

Answer 13

Heterozygotes have a survival advantage in malaria-prone environments

This leads to higher frequencies of the sickle cell allele in those populations.

Question 14

What is genetic drift?

Answer 14

Random fluctuations in allele frequencies due to chance events

It can lead to significant changes in small populations.

Question 15

What is the formula to calculate the frequency of heterozygotes?

Answer 15

2pq

This formula is derived from the Hardy-Weinberg principle.

Question 16

Fill in the blank: The sum of genotype frequencies must equal _______.

Answer 16

1

This is a fundamental principle in population genetics.

Question 17

True or False: Probabilities of independent events affect each other.

Answer 17

False

Each event is independent of previous outcomes.

Question 18

What is the effect of the environment on genetic variation?

Answer 18

Can confer selective advantages or disadvantages

Example: Lactase persistence in populations that consume dairy.

Question 19

What is the relationship between mutation and natural selection?

Answer 19

Natural selection edits genetic variation introduced by mutation

Favorable mutations increase in frequency, while harmful ones decrease.

Question 20

What happens to allele frequencies in different environments?

Answer 20

Natural selection can increase frequencies of advantageous alleles

Example: Adaptation to high-altitude environments in certain populations.

Question 21

What is genetic drift?

Answer 21

A random evolutionary process that produces larger changes in gene frequencies in smaller populations.

Genetic drift can lead to significant changes in allele frequencies due to chance events, especially in small populations.

Question 22

How does sample size affect genetic drift?

Answer 22

Smaller populations experience greater random fluctuations in gene frequencies compared to larger populations.

In larger samples, deviations from expected ratios are less pronounced.

Question 23

What is the founder effect?

Answer 23

A phenomenon where small founder populations experience large changes in gene frequency due to their small size.

This is a specific case of genetic drift.

Question 24

Give an example of a genetic disease with increased frequency in a small population.

Answer 24

Ellis–van Creveld syndrome.

This syndrome is observed with higher frequency among the Old Order Amish population.

Question 25

What role does gene flow play in populations?

Answer 25

Gene flow occurs when populations exchange migrants who mate with one another, making populations genetically more similar over time. ## Footnote This process can affect the frequency of certain alleles in a population.

Question 26

Why is sickle cell disease less common in African Americans than in many African populations?

Answer 26

Due to gene flow between African Americans and European Americans. ## Footnote This gene flow has also influenced the frequency of cystic fibrosis in the African American population.

Question 27

What is mutation–selection balance?

Answer 27

The predictable relationship between the effects of mutation and selection on gene frequencies. ## Footnote It helps explain why recessive disease-causing alleles generally have higher frequencies than dominant ones.

Question 28

What is the Hardy–Weinberg principle?

Answer 28

A principle that shows most copies of harmful recessive alleles are found in heterozygotes, protecting them from natural selection. ## Footnote This results in higher gene frequencies for recessive alleles compared to dominant alleles.

Question 29

What is the selection coefficient, s, for an allele that reduces offspring by 30%?

Answer 29

s = 0.30. ## Footnote This coefficient is used to estimate gene frequencies in populations.

Question 30

What is the expected frequency of a lethal dominant disease allele?

Answer 30

p = μ. ## Footnote Here, p is the gene frequency, and μ is the mutation rate.

Question 31

What does the 1000 Genomes Project aim to achieve?

Answer 31

To assess DNA sequence variation in large collections of people from many populations. ## Footnote It has sequenced genomes from over 2500 individuals to create an inventory of worldwide genetic variation.

Question 32

What significant historical event does the sequencing data from the 1000 Genomes Project support?

Answer 32

The model that anatomically modern humans arose first in Africa before migrating to other continents. ## Footnote This migration occurred approximately 50,000 years ago.

Question 33

How does natural selection affect the frequency of disease-causing variants?

Answer 33

Natural selection tends to reduce the frequencies of disease-causing variants. ## Footnote This is why rare variants are more likely to be pathogenic.

Question 34

What is the significance of the Simons Genome Diversity Project (SGDP)?

Answer 34

It provides extensive sampling of diversity in many human populations, showing major bottlenecks in non-African populations. ## Footnote The SGDP sampled 300 people from 142 populations.

Question 35

What is the genome aggregation database (gnomAD)?

Answer 35

A database containing exome sequences from more than 120,000 people and whole-genome sequences from over 15,000 people. ## Footnote It is used to assess the frequency of potential disease-causing variants.

Question 36

True or False: Genetic drift can lead to increased frequencies of some genetic diseases in small populations.

Answer 36

True. ## Footnote Small populations can have elevated frequencies of certain alleles due to genetic drift.

Question 37

Fill in the blank: The gene frequency of a recessive allele, q, that is lethal in homozygotes is predicted to be _______.

Answer 37

higher than that of a dominant lethal allele. ## Footnote This is due to the protective effect of heterozygosity.