Genetics: Persistence of Rare Alleles

Questions and Answers

Why do rare recessive alleles, such as those causing albinism, persist in a population?

Many individuals are carriers who do not express the trait. (correct)

Only individuals affected by the trait can pass the allele.

They are favored by natural selection over dominant alleles.

They provide a survival advantage in harsh environments.

What does the term 'genetic load' refer to?

The sum of beneficial genes in a population.

The difference between the best observed genotype and the average in a population. (correct)

The total number of genes carried by individuals in a population.

The frequency of recessive traits within a population.

If a population has 10 genes surveyed with 4 polymorphic and 6 monomorphic, what is the proportion of polymorphism (P)?

1.0

0.4 (correct)

0.7

0.6

Which statement best describes mutation-selection balance?

A perpetual equilibrium exists between the wild type and deleterious alleles. Signup and view all the answers

Which of the following best explains why individuals might carry deleterious genes but remain unaffected?

They are heterozygous carriers for these genes. Signup and view all the answers

What is indicated by low genetic load in a population?

Higher likelihood of survival and reproduction. Signup and view all the answers

How does the presence of polymorphic genes impact a population's genetic diversity?

Polymorphic genes enhance genetic diversity. Signup and view all the answers

What is average heterozygosity (H0) a measure of in a population?

Frequency of heterozygous individuals among the population. Signup and view all the answers

Why is it difficult for genetic variation to be eliminated from a population?

Many alleles remain hidden as recessive. Signup and view all the answers

What is the proportion of polymorphism (P) calculated if there are 4 polymorphic genes out of a total of 10 loci?

0.4 Signup and view all the answers

Which of the following formulas correctly calculates the average number of alleles per locus (A)?

A = total alleles / total loci Signup and view all the answers

Using the provided heterozygosity proportions, what is the average heterozygosity (H0) if the proportions are 0.02, 0.03, 0.05, and 0.08?

0.045 Signup and view all the answers

Calculate the average number of alleles per locus (A) if there are the following alleles at six loci: 2, 4, 1, 3, 1, and 3.

2.33 Signup and view all the answers

What is the result for P if 8 out of 12 loci are polymorphic in a population?

0.66 Signup and view all the answers

What defines genetic drift in finite populations?

Random fluctuations in allele frequencies due to sampling effects. Signup and view all the answers

What is the primary consequence of a bottleneck effect on genetic diversity?

Decreased genetic diversity due to random selection. Signup and view all the answers

What is the calculated FST value if Ht is 0.50 and Hs is 0.41?

0.18 Signup and view all the answers

If the average allele frequency (P) across three populations is 0.47, what would be the average frequency of the alternative allele (q)?

0.53 Signup and view all the answers

What does a high value of Fst indicate about a population's gene flow?

Low gene flow and increased fixation in populations Signup and view all the answers

What effect does genetic drift from a frequency of 0.5 to 1 have on a population's gene pool?

Loss of genetic diversity and fixation of alleles Signup and view all the answers

In terms of Hardy-Weinberg equilibrium, what is the carrier frequency of a population where sickle cell anemia has a frequency of 0.16?

0.48 Signup and view all the answers

What is the main goal of conservation genetics?

To manage genetic diversity to minimize extinction risk Signup and view all the answers

How does non-random mating, such as inbreeding, affect a population?

Reduces genetic diversity Signup and view all the answers

What is the effect of migration on allelic diversity within a population?

It increases allelic diversity and gene flow Signup and view all the answers

What is inbreeding depression and what is its primary impact on populations?

It reduces survival and reproduction rates Signup and view all the answers

How does genetic load affect a population?

It increases accumulated deleterious mutations Signup and view all the answers

What role do molecular markers play in wildlife forensics?

They assist in identifying non-human biological samples Signup and view all the answers

What outcome results from population fragmentation for gene flow?

Reduction of gene flow and genetic isolation Signup and view all the answers

Study Notes

Persistence of Rare Alleles

Rare recessive alleles like albinism persist in populations due to high carrier rates, where many individuals carry the gene without expressing the trait.
Only one in 20,000 individuals express albinism, requiring homozygosity (a/a) for the allele.
One in 70 individuals are carriers of the albinism allele, contributing to the concept of "genetic load."

Genetic Load Definitions

Definition 1: Genetic load reflects the difference between the most fit genotype and the average genotype observed in a population, indicating overall population health.
Definition 2: It refers to the total number of deleterious alleles that exist in a population's genome, primarily in a hidden state in heterozygous individuals.

Mutation-Selection Balance

Deleterious alleles can persist in populations despite selection pressures favoring normal/wild alleles.
Selection acts to balance allele frequencies, stabilizing at a certain level between wild (A1) and deleterious (A2) alleles.

Proportion of Polymorphism (P)

In a survey of 10 genes, 4 are polymorphic; thus, P = 4/10 = 0.4 (40% of genes are polymorphic).

Allelic Diversity (A) Calculation

For the African lion population across six loci, calculate A as A = (2+4+1+3+1+3)/6 = 2.33 (average of 2.33 alleles per locus).

Average Heterozygosity (H0) Calculation

Given heterozygous proportions (0.02, 0.03, 0.05, 0.08), H0 = (0.02 + 0.03 + 0.05 + 0.08)/4 = 0.045 (average heterozygosity is 4.5%).

Genetic Diversity in Seahorses

For 12 loci measurement, P = 8/12, A = 21/12, H0 = 2.63/12 = 0.22 (22% of loci are heterozygous).

Genetic Drift and Bottleneck Effect

Genetic Drift: Random fluctuations in allele frequencies due to sampling effects, more pronounced in small populations.
Bottleneck Effect: A severe reduction in population size leads to a decrease in genetic diversity due to genetic drift, caused by events like natural disasters or human activities.

FST Calculation for Subpopulations

With allele frequencies A = 0.2, 0.5, and 0.7 across three subpopulations:
- Expected heterozygosity within subpopulations Hs = 0.41.
- Total heterozygosity Ht = 0.50.
- FST = (Ht - Hs)/Ht = 0.18, indicating moderate gene flow between subpopulations.

Impact of Population Events on Gene Pool

Genetic Drift (0.5 to 1): Potential fixation of an allele with loss of genetic variability.
Genetic Drift (1 to 0.5): Reduction in gene flow.
Migration: Increases genetic diversity via new alleles introduced to populations.
Mutation: Can increase genetic load while reducing overall fitness.
Non-Random Mating (Inbreeding): Leads to decreased heterozygosity and reduced fitness in the population.

Sickle Cell Anemia Frequencies

Frequency of sickle cell anemia (homozygous HbSHbS) is 0.16, giving q = 0.4 for HbS allele.
Frequency of normal condition (homozygous HbAHbA) leads to an HbA allele frequency of p = 0.6.
Carrier state frequency (HbAHbS) calculated as AS = 2pq = 0.48 (48% carriers).

Conservation Genetics Overview

Focuses on using genetic methods to preserve biodiversity and manage species for environmental adaptability.
Genetic factors impacting extinction risk include inbreeding depression, genetic drift, and the importance of maintaining genetic diversity.
Techniques used in conservation genetics involve DNA analysis, alloenzymes, microsatellites, and DNA fingerprinting.

Key Issues in Conservation Genetics

Importance of genetic diversity for species adaptability and survival.
Inbreeding depression leads to reduced reproduction and survival rates.
Population fragmentation can hinder gene flow, with implications for evolutionary potential.
Taxonomic uncertainties must be resolved for effective conservation efforts.
Defining management units is crucial for prioritizing conservation efforts and maintaining distinct subpopulations.

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Description

This quiz explores why rare recessive alleles, such as those causing albinism, do not vanish from populations despite their potential harm. It examines the role of carriers in maintaining genetic variation and the complexities of inheritance patterns.