Genetics: Allele and Genotype Frequencies

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Questions and Answers

What is the definition of a population in the context of breeding?

A collection of individuals that may not interbreed.

A group of organisms of the same species that are genetically identical.

A group of organisms that can only breed with close relatives.

A group of sexually mature individuals occupying a specific space and time. (correct)

What term refers to the total alleles of all genes in a population at one time?

Allelic frequency

Genotype frequency

Gene pool (correct)

Homozygous condition

How many total alleles are present in a population of 10,000 individuals?

20,000 (correct)

10,000

30,000

5,000

What are the possible genotype combinations for a gene with a dominant (F) and recessive (f) allele?

FF, Ff, ff Signup and view all the answers

In terms of allelic frequency, what does it mean when the total number of alleles is considered to be 1.0?

It represents the proportion of one specific allele in the population. Signup and view all the answers

What distinguishes the heterozygous genotype in individuals?

One allele is dominant and the other is recessive. Signup and view all the answers

Which of the following accurately describes allelic frequency?

The proportion of a specific allele compared to the total alleles. Signup and view all the answers

What is meant by heterozygote superiority or heterozygote advantage?

Heterozygous individuals are favored in areas with malaria. Signup and view all the answers

Which type of selection favors average individuals and eliminates extremes?

Stabilising selection Signup and view all the answers

In which scenario is directional selection most likely to occur?

When there is a shift in the optimum value needed for survival Signup and view all the answers

What is a key factor contributing to the frequency of alleles in a population?

The environmental resistances and selection pressures Signup and view all the answers

What happens to individuals with the homozygous state for HbS in malaria regions?

They are often selected against due to health disadvantages. Signup and view all the answers

When environmental temperatures are consistently around a specific norm, how does stabilising selection affect a population?

It leads to a reduction of extreme phenotypes in the population. Signup and view all the answers

What role do environmental factors play in the selection pressures experienced by a population?

They inform the optimal characteristics needed for survival. Signup and view all the answers

How is the gene pool of a population defined?

The total of all alleles of all genes in the population. Signup and view all the answers

Which statement accurately reflects the concept of disruptive selection?

It favors individuals at the extremes of a trait spectrum. Signup and view all the answers

What is the condition for allele frequencies to remain constant in a population according to the Hardy-Weinberg principle?

There is random mating and no selection occurs. Signup and view all the answers

If the frequency of the recessive allele a is approximately 0.0063, what is the frequency of the dominant allele A?

0.9937 Signup and view all the answers

Which equation represents the relationship between genotype frequencies in a population according to the Hardy-Weinberg principle?

p^2 + 2pq + q^2 = 1.0 Signup and view all the answers

In a population where one person in 25,000 displays a recessive characteristic, what is the frequency of the homozygous recessive genotype aa?

0.00004 Signup and view all the answers

What is a characteristic of individuals who are homozygous for haemoglobin-S (HbS HbS)?

They have sickle cell anaemia and are significantly disadvantaged. Signup and view all the answers

What does the Hardy-Weinberg principle help researchers understand in populations?

The frequencies of alleles and genotypes over generations. Signup and view all the answers

Which of the following statements about sickle cell anaemia is correct?

Heterozygous individuals generally do not exhibit severe symptoms. Signup and view all the answers

What is the probability of obtaining a homozygous dominant genotype (AA) if the frequency of allele A is 0.9937?

0.9874 Signup and view all the answers

What effect do environmental factors have on the frequency of alleles in a population?

They do not affect the probability of a mutant allele occurring. Signup and view all the answers

Study Notes

Allele and Genotype Frequencies

Sexually mature individuals within a population can potentially breed with any other.
An organism's alleles can combine with any others in the population.
A population is a group of the same species that occupies a specific area at a specific time and can interbreed.
The gene pool is all the alleles from all genes in a population at a given time.
Allelic frequency is the number of times an allele appears in a gene pool.
One gene can have multiple alleles; for example, in cystic fibrosis, F is the dominant allele for normal mucus, and f is the recessive allele for thicker mucus.
Each individual has two alleles per gene on homologous chromosomes, thus only one pair counts towards the gene pool.
Possible combinations of alleles for cystic fibrosis are FF, ff, or Ff (which can be written as fF).
The total number of alleles in a population is always 1.0.
Hardy-Weinberg principle describes allele frequencies remaining constant in subsequent generations under specific conditions.

Hardy-Weinberg Principle

For allele frequencies to remain static, five conditions must be met:
- No mutations
- No allele flow in or out of population (isolated population)
- Equal passing of all alleles to the next generation (no selection)
- Large population size
- Random mating within the population
Equation: p + q = 1.0 (where p = frequency of allele A, and q = frequency of allele a).
This leads to p² + 2pq + q² = 1.0 (the Hardy-Weinberg equation).

Recessive Allele Example

If a recessive allele causes a characteristic that occurs in 1 out of 25,000 people, the frequency of that recessive genotype (aa) is 1/25,000 (0.00004).
q² = 0.00004
q = ~0.0063 (approximately)
p = 1.0 - q, so p = ~ 0.9937.
Heterozygotes (Aa) frequency is 2pq = ~ 0.0125 (or ~125 in 10,000).

Environmental Effects on Allele Frequencies

Environmental changes affect the survival and thus, frequency of an allele.
Environmental pressures, such as competition for resources, and changes in climate, predation, and disease determine which alleles are passed.
Environmental factors don't create new alleles, rather they affect the frequency of existing ones.
Some environmental factors can affect the overall mutation rate of the gene pool.

Sickle Cell Anemia

Sickle cell anemia is caused by a single base substitution in DNA causing abnormal haemoglobin.
The HbA allele (normal haemoglobin) and HbS allele (sickled haemoglobin) are codominant.
HbS protects against malaria.
- HbSHbS genotype: severe sickle cell anemia (disadvantageous).
- HbAHbA genotype: normal hemoglobin (susceptible to malaria in malaria-prone areas, disadvantageous in such areas).
- HbAHbS genotype: sickle cell trait (with protection against malaria that outweighs tiredness in malaria-prone regions).

Selection Pressures and Types of Selection

Selection pressures are environmental forces that limit a species' population (predation, competition for resources, climate changes, disease).
Three kinds of selection:
- Stabilizing selection: Favors average phenotypes, reducing the extremes.
- Directional selection: Favors one extreme, leads to changing average phenotypes as the environment changes (e.g., temperature change causing a shift in fur length).
- Disruptive selection: Favors both extremes, potentially splitting a population into distinct groups.

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Description

Explore the concepts of allele and genotype frequencies in populations. This quiz delves into the gene pool, allelic frequencies, and the implications of the Hardy-Weinberg principle. Test your knowledge on how alleles interact within a given population.