Q: A genetic counselor is working with a couple, both of whom have a sibling with a recessive genetic disease but are themselves unaffected. What is the probability that both are carriers?

$$\frac{2}{3} \times \frac{2}{3} = \frac{4}{9}$$

Question 1

Which of the following best explains why certain CFTR gene mutations can provide a selective advantage in regions affected by cholera outbreaks?

Accepted Answer

CFTR mutations reduce chloride and water loss, decreasing the severity of cholera-induced dehydration.

Question 2

A couple, both carriers for cystic fibrosis (genotype Cc), want to know the probability that their child will be a carrier. What is the probability?

Accepted Answer

$$\frac{1}{2}$$

Question 3

Which Mendelian law explains why alleles for a gene separate so that each gamete receives only one allele?

Accepted Answer

Law of Segregation

Question 4

In a dihybrid cross between two heterozygotes (AaBb x AaBb), what is the expected phenotypic ratio if the genes assort independently?

Accepted Answer

$$9:3:3:1$$

Question 5

Which genetic phenomenon is illustrated when the heterozygote for sickle cell disease (AS) is protected against malaria, but the homozygote (SS) suffers from the disease?

Accepted Answer

Heterozygote advantage

Question 6

If two parents with achondroplasia (Dd) have a child, what is the probability that the child will have a lethal genotype (DD)?

Accepted Answer

$$\frac{1}{4}$$

Question 7

Which of the following best describes incomplete dominance?

Accepted Answer

The heterozygote phenotype is intermediate between the two homozygotes.

Question 8

A man with blood type AB marries a woman with blood type O. What are the possible blood types of their children?

Accepted Answer

A and B only

Question 9

Which rule should be used to calculate the probability of two independent genetic events both occurring?

Accepted Answer

Product rule: multiply the probabilities

Question 10

In Labrador retrievers, coat color is determined by two genes: B (black/brown pigment) and E (pigment deposition). What is the expected phenotypic ratio when two BbEe dogs are crossed?

Accepted Answer

$$9$$ black : $$3$$ brown : $$4$$ yellow

Question 11

Which process during meiosis is primarily responsible for independent assortment of genes located on different chromosomes?

Accepted Answer

Random orientation of homologous chromosomes during Metaphase I

Question 12

A genetic counselor is working with a couple, both of whom have a sibling with a recessive genetic disease but are themselves unaffected. What is the probability that both are carriers?

Accepted Answer

$$\frac{2}{3} 	imes \frac{2}{3} = \frac{4}{9}$$

Question 13

Which of the following is an example of polygenic inheritance?

Accepted Answer

Height

Question 14

Which genetic concept explains why the probability of a child inheriting a genetic disorder is the same for each pregnancy, regardless of previous outcomes?

Accepted Answer

Independent events in probabilistic inheritance

Question 15

If a gene has two alleles, A and a, and both parents are heterozygous (Aa), what is the probability that their child will be homozygous recessive (aa)?

Accepted Answer

$$\frac{1}{4}$$

Question 16

Which of the following best describes codominance?

Accepted Answer

The heterozygote expresses both alleles distinctly in the phenotype.

Question 17

Which mechanism ensures that linked genes on the same chromosome can assort independently?

Accepted Answer

Crossing over during Prophase I of meiosis

Question 18

A cross between a black-feathered chicken (CBCB) and a white-feathered chicken (CWCW) produces offspring with speckled feathers (CBCW). What inheritance pattern does this illustrate?

Accepted Answer

Codominance

Question 19

Which of the following is a classic example of epistasis in mammals?

Accepted Answer

Labrador retriever coat color

Question 20

How many possible combinations of chromosomes can be produced in human gametes due to independent assortment, given $$n = 23$$?

Accepted Answer

$$2^{23} = 8$$,388,608$$

Patterns of Genetic Inheritance: Dominant and Recessive Alleles, Disease, and Evolutionary Benefits

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