Question 1

Which of the following statements correctly describes the role of the SRY gene in human sex determination?

Accepted Answer

SRY is located on the Y chromosome and its presence leads to male phenotype, even if multiple X chromosomes are present.

Question 2

A woman with genotype $$X^NX^n ($$where $$X^N is $$normal vision and $$X^n is $$colorblindness) marries a man with genotype $$X^nY. $$What is the probability that their child will be colorblind?

Accepted Answer

$$0.25$$

Question 3

Which of the following best explains dosage compensation in mammals?

Accepted Answer

Females randomly inactivate one X chromosome in each cell, forming Barr bodies.

Question 4

In a pedigree, a rare trait skips generations and affected fathers do not pass the trait to their sons. Which inheritance pattern is most likely?

Accepted Answer

X-linked recessive

Question 5

A person who is homozygous for long earlobes (autosomal dominant trait with 30% penetrance) mates with a person who is homozygous for normal earlobes. What is the probability their child will show the phenotype for long earlobes?

Accepted Answer

$$0.30$$

Question 6

Which of the following is an example of codominance?

Accepted Answer

A person with genotype $$I^A I^B$$ has both A and B antigens on their red blood cells.

Question 7

In Labrador retrievers, coat color is determined by two genes: B (black) and E (pigment deposition). The genotype $$bb$$ produces brown, $$ee$$ produces yellow regardless of B. What is the expected phenotypic ratio in the F2 generation from a dihybrid cross ($$BbEe 	imes BbEe$$)?

Accepted Answer

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

Question 8

A complementation test is performed by crossing two white-flowered pea plants. The offspring all have purple flowers. What does this result indicate?

Accepted Answer

The mutations are in different genes.

Question 9

Which of the following best describes pleiotropy?

Accepted Answer

A single gene affects multiple, seemingly unrelated traits.

Question 10

Which inheritance pattern is observed when a trait is expressed only in one sex, even though the gene is present in both sexes?

Accepted Answer

Sex-limited

Question 11

A Siamese cat has a temperature-sensitive allele for coat color. Which term best describes this type of allele?

Accepted Answer

Conditional allele

Question 12

Which of the following is true about mitochondrial inheritance?

Accepted Answer

Mitochondrial DNA is inherited only from the mother.

Question 13

A man with blood type O ($$ii) $$and a woman with blood type A ($$I^A I^i) $$have a child with blood type B ($$I^B I^i). $$What does this suggest about paternity?

Accepted Answer

The man cannot be the biological father.

Question 14

Which of the following best describes epistasis?

Accepted Answer

One gene masks the effect of another gene at a different locus.

Question 15

Which equation correctly calculates penetrance if 38 out of 42 individuals with a genotype express the expected phenotype?

Accepted Answer

$$\frac{38}{42} 	imes 100\%$$

Question 16

Which of the following is an example of a multifactorial trait?

Accepted Answer

Height

Question 17

Which of the following best describes a phenocopy?

Accepted Answer

A mutant phenotype produced in a genetically wild-type individual due to environmental factors.

Question 18

In fruit flies, males increase the transcription of their single X chromosome by two-fold to match female expression. What is this mechanism called?

Accepted Answer

Dosage compensation

Question 19

Which of the following is true about polygenic traits?

Accepted Answer

They show continuous variation and are influenced by multiple genes.

Question 20

Which of the following is a hallmark of X-linked inheritance in reciprocal crosses?

Accepted Answer

Reciprocal crosses yield different offspring ratios depending on which sex carries the mutant allele.

Extensions and Modifications to Inheritance: Genetics Study Notes

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