BIOL-1100 Lecture Notes - Lecture 17: Genotype Frequency, Allele Frequency, Population Genetics

Hardy-Weinberg Equilibrium Problems

p is the frequency of the dominant allele in the population

q is the frequency of the recessive allele in the population

p2 is the frequency of the homozygous dominant genotype

q2 is the frequency of the homozygous recessive genotype

2pq is the frequency of the heterozygous genotype

p + q = 1

p2 + 2pq + q2 = 1 Find q2 ïƒ q ïƒ p ïƒ p2 ïƒ 2pq

A rare disorder of cystic fibrosis (characterized by abnormal transport ofchloride and sodium across an epithelium, leading to thick, viscous secretions) occurs every 1 in 3,300 births. To express this trait one must be homozygous recessive (ff).

The cystic fibrosis allele is represented by f. The normal allele is F. Suppose both parents have alleles Ff. The possible combinations of alleles in the children are FF, Ff, Ff and ff. The alleles ff will cause the disease. So, although the parents do not have cystic fibrosis, they can produce children with the disease. The parents are called 'carriers' of the disease

What is the frequency of the population that carries the trait? (Ff)

Suppose that red flower color (A/A or A/a) is dominant to white flower color (a/a) in petunias. The common allele (A) encodes the red pigment for petal colour. The rare allele (a) encodes a nonsense mutation in the pigment gene, so no pigment is produced (such that petals are not coloured and appear white). Among the petunias in a greenhouse population, 480 are A/A and 90 are A/a. There are no white-flowered petunias observed. Is this population of petunias in genetic equilibrium? Show all of your steps and calculations clearly (including use of a χ 2 test) and write a brief (2-3 sentence) conclusion about whether this population of petunias is in Hardy–Weinberg equilibrium. Make sure the expected genotype frequencies equal to 1

You have selected a petunia plant from the greenhouse with red flowers and want to determine whether the plant is A/A or A/a.

a) What kind of experiment (what kind of cross) could you perform to determine the genotype of the selected petunia plant? Explain briefly.

b) How will the cross in (a) help you determine the genotype of your red-flowered petunia? That is, explain how will the results from this cross differ if the red-flowered petunia is A/A versus A/a?

c) You end up choosing two red plants that are both of the genotype A/a and you cross them. If the cross produces six plants, what is the probability that four of them will be white and two will be red?

MY ANSWERS SO FAR

Allele frequency of p= 1/2 (2pq)+ p²

P= 1/2 (0.1578) + 0.8421

=0.921

Allele frequency of q = 1/2 (2pq) + q²

⁼ 1/2 (0.1578) + 0.0

= 0.0789

Expected genotype of the population:

AA(p2)= 0.848 aa (q2)= 0.006

(2pq)Aa =0.0105

I'm confused as to why this doesn't total upto 1

Q1. Which of the following statements is true about the disease Kuru?
Kuru is caused by a virus, which is contracted by eating human brain material.
Kuru is caused by a prion (PrP), which is contracted by eating human brain material.
Kuru is caused by a recessive allele for PrP; if a person has two copies, he or she will develop Kuru.
Kuru is caused by a dominant allele for PrP; if a person has two copies, he or she will develop Kuru.
Kuru is caused by having one copy of the dominant allele and one copy of the recessive allele for PrP.

Q2. True or false: One can calculate the frequency of alleles in a population if the genotypes of the members of the population are known.

True False

Q3. The Hardy-Weinberg equation is p2 + 2pq + q2. In this equation, q2 stands for the frequency of ____________ in a population.

The recessive allele O

ne of the homozygous genotypes

The dominant allele

Heterozygous genotype

Q4. Which of the following descriptions best fits the relationship between the terms gene, allele, locus, and chromosome?

Alleles are different forms of a gene, which can be found at a locus on a chromosome.

Genes are made up of chromosomes, which can be found at a locus on an allele.

Chromosomes are different forms of a gene, which can be found at an allele on a locus.

A locus is made up of alleles, which can be found at a gene on a chromosome.

Q5. Mead and his colleagues proposed a hypothesis for the apparent heterozygote advantage for the PrP locus. What did they suggest as the basis for the high presence of both alleles?
History of cannibalism.
Protection from malaria.
Protection against plague.
They did not propose a heterozygotic advantage for the PrP locus.

Q7. A frog population has two alleles for skin color at the following relative frequencies: Allele SC1= 0.8, Allele SC2 = 0.2. Allele SC2 is:
Dominant
Recessive
Co-dominant
Impossible to determine dominance from the information given.

Q8. A bird population has two alleles for feather color at the following relative frequencies: Allele FC1 = 0.5, Allele FC2 = 0.5. Allele FC1 is:
Dominant
Recessive
Co-dominant
Impossible to determine dominance from the information given.

Q9. Use the following information for both questions 9 and 10: You encounter a few populations of millipedes with variation in skin color. Genotype can be inferred from coloration: CC millipedes are black, Cc millipedes are brown, and cc millipedes are yellow. [You can launch a calculator byclicking here.]

If one millipede population has 60 black individuals, 20 brown individuals, and 20 yellow individuals, what is the relative frequency of allele C in that population?

0.5
0.6
0.7
0.8
Impossible to calculate from the information given.

Q10. If another millipede population's allele frequencies are 0.5 for C and 0.5 for c, what is the expected frequency of the cc genotype in the population, if the population is in Hardy-Weinberg equilibrium?
0.125
0.25
0.5
1.0
Impossible to calculate from the information given.