Q: Using the Hardy-Weinberg equation, what is the frequency of heterozygous individuals in the population? ($$p = 0.3$$, $$q = 0.7)$$

$$2pq = 2 \times 0.3 \times 0.7 = 0.42$$

Question 1

In a population of 500 diploid organisms, 245 individuals display the recessive phenotype for a gene with alleles R and r. What is the proportion of the population that is homozygous recessive? Show your calculation.

Accepted Answer

245/500 = 0.49

Question 2

Given the proportion of homozygous recessive individuals in the population is $$q^2 = 0.49$, what is the frequency of the recessive allele (r) in the population? Show your calculation.

Accepted Answer

$$q = \sqrt{0.49} = 0.7$$

Question 3

What is the frequency of the dominant allele (R) in the population, given that $$q = 0.7$$? Show your calculation.

Accepted Answer

$$p = 1 - q = 1 - 0.7 = 0.3$$

Question 4

Using the Hardy-Weinberg equation, what is the frequency of heterozygous individuals in the population? ($$p = 0.3$$, $$q = 0.7)$$

Accepted Answer

$$2pq = 2 	imes 0.3 	imes 0.7 = 0.42$$

Question 5

How many heterozygous individuals are predicted in a population of 500, given $$2pq = 0.42$$?

Accepted Answer

$$0.42 	imes 500 = 210$$

Question 6

In the cross WwZz × wwzz, offspring genotypes are equally distributed among four types. What does this suggest about the linkage between the W and Z loci?

Accepted Answer

There is no evidence of linkage; the loci assort independently.

Question 7

In the cross GgHh × gghh, offspring genotypes are distributed as follows: 80 GgHh, 20 Gghh, 20 gghH, 80 gghh. What does this suggest about the linkage between the G and H loci?

Accepted Answer

There is evidence of linkage; parental genotypes are more frequent than recombinants.

Question 8

Calculate the genetic distance between the G and H loci using the offspring data: 80 GgHh, 20 Gghh, 20 gghH, 80 gghh. Show your calculation.

Accepted Answer

Recombinants = 20 + 20 = 40; Total = 200; Genetic distance = $$(40/200) 	imes 100 = 20 cM$$

Question 9

Why are linkage experiments typically set up with one parent heterozygous for both loci and the other parent homozygous recessive?

Accepted Answer

This allows the phenotypes of offspring to directly reflect the genotypes inherited from the heterozygous parent.

Question 10

If a DNA sequence is 600 bp long and EcoRI cuts at 200 bp from one end, and BamHI produces two fragments of 200 bp and 400 bp, where is the BamHI site located?

Accepted Answer

BamHI is at 400 bp from the same end as EcoRI.

Question 11

How would the gel results change if the starting DNA were circular instead of linear and cut with EcoRI only?

Accepted Answer

A single band would appear, representing the full length of the DNA.

Question 12

If segment A is removed from a promoter and reporter gene activity does not change, what does this suggest about segment A?

Accepted Answer

Segment A does not contain functional elements affecting gene expression.

Question 13

If segment B is removed and reporter gene activity decreases, what does this suggest about segment B?

Accepted Answer

Segment B contains a positive regulatory element.

Question 14

If segment C is removed and reporter gene activity increases, what does this suggest about segment C?

Accepted Answer

Segment C contains a negative regulatory element.

Question 15

Summarize the mapping of functional elements in the promoter region based on the removal experiments.

Accepted Answer

Segment B contains a positive element; segment C contains a negative element; segment A has no effect.

Question 16

What is the probability of the sequence ACGT occurring at a given site in a genome, assuming each nucleotide has a probability of 0.25?

Accepted Answer

$$0.25 	imes 0.25 	imes 0.25 	imes 0.25 = 0.00390625$$

Question 17

Phage λ has a genome size of 48,500 bp. How many times is the sequence ACGT expected to occur?

Accepted Answer

$$48,500 	imes 0.00390625 = 189.45 \approx 189$$

Question 18

How does the length of a specific DNA sequence relate to its probability of occurring at a given site?

Accepted Answer

The probability decreases exponentially with sequence length: $$P = 0.25^n$$ for a sequence of length $$n.$$

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