Q: Which equation would you use to calculate the percent penetrance of a dominant disease allele in a pedigree?

$$\text{Percent Penetrance} = \frac{\text{observed \# affected}}{\text{observed \# affected} + \text{\# unaffected carriers}} \times 100$$

Question 1

Which of the following best describes incomplete dominance?

Accepted Answer

The heterozygote expresses a phenotype that is intermediate between the two homozygotes.

Question 2

A cross between two snapdragons, one with genotype $$A1A1 ($$red) and one with genotype $$A2A2 ($$white), produces all pink offspring. What is the expected phenotypic ratio in the F2 generation when two pink snapdragons are crossed?

Accepted Answer

1 red : 2 pink : 1 white

Question 3

Which equation would you use to calculate the percent penetrance of a dominant disease allele in a pedigree?

Accepted Answer

$$	ext{Percent Penetrance} = \frac{	ext{observed \# affected}}{	ext{observed \# affected} + 	ext{\# unaffected carriers}} 	imes 100$$

Question 4

A geneticist observes a 2.33:1 phenotypic ratio in the offspring of a cross. Which statistical test should be used to determine if this deviates significantly from the expected Mendelian ratio?

Accepted Answer

Chi-square goodness of fit test

Question 5

Which of the following is an example of codominance?

Accepted Answer

A person with genotype $$MN$$ has both M and N antigens on their red blood cells.

Question 6

In a family with an autosomal dominant disease, some individuals with the disease allele do not show any symptoms. This is an example of:

Accepted Answer

Incomplete penetrance

Question 7

Which of the following best describes variable expressivity?

Accepted Answer

Individuals with the same genotype show different degrees of the same phenotype.

Question 8

A cross between two heterozygous snapdragons ($$An1An2) $$produces 100 offspring: 24 red, 52 pink, and 24 white. What is the chi-square value for this data compared to the expected 1:2:1 ratio?

Accepted Answer

$$\$$chi^2$$ = \sum \frac{(O-E)^2$}{E}$$, where O and E are observed and expected counts for each phenotype

Question 9

Which of the following is a null allele?

Accepted Answer

An allele that produces no functional product

Question 10

A child is born with polydactyly (extra fingers or toes), but the number of extra digits varies among affected family members. What genetic concept does this illustrate?

Accepted Answer

Variable expressivity

Question 11

Which of the following best explains why a heterozygote for the ANS gene in snapdragons has pink flowers?

Accepted Answer

The wild-type allele is haploinsufficient, so one functional copy does not produce enough pigment for red flowers.

Question 12

Which of the following is NOT a possible explanation for variation in phenotype among individuals with the same genotype?

Accepted Answer

Complete penetrance

Question 13

A geneticist observes that a trait appears in all individuals with the genotype, but the severity of the trait varies. What is the most likely explanation?

Accepted Answer

Variable expressivity

Question 14

Which of the following statements about the chi-square test is correct?

Accepted Answer

A low chi-square value indicates a high probability that the observed data fits the expected model.

Question 15

Which of the following is an example of an environmental effect on phenotype?

Accepted Answer

A flamingo's feather color changing based on its diet

Question 16

Which of the following best describes a dominant negative allele?

Accepted Answer

An allele whose abnormal product interferes with the function of the normal protein

Question 17

A cross between two heterozygotes for a codominant trait produces which phenotypic ratio in the F2 generation?

Accepted Answer

1:2:1

Question 18

Which of the following is the correct formula for degrees of freedom (df) in a chi-square test with n phenotypic classes?

Accepted Answer

$$df = n - 1$$

Question 19

Which of the following best describes a hypomorphic allele?

Accepted Answer

An allele with reduced function compared to the wild-type

Question 20

A person with the genotype $$MN$$ for the M/N blood group has which phenotype?

Accepted Answer

Both M and N antigens on red blood cells

Dominance and Its Variations in Genetics

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