Question 1

Which of the following best explains why the shell coiling direction in snails is considered a classic example of a maternal effect gene?

Accepted Answer

The phenotype of the offspring is determined by the genotype of the mother, not the offspring's own genotype.

Question 2

A female snail with genotype Dd (dextral) is crossed with a male snail with genotype dd (sinistral). What will be the phenotype of all F1 offspring, and why?

Accepted Answer

All F1 offspring will be dextral because the mother's genotype provides D gene products to the egg during oogenesis.

Question 3

Which of the following mechanisms is responsible for dosage compensation in placental mammals?

Accepted Answer

Inactivation of one X chromosome in females, forming a Barr body.

Question 4

A heterozygous female for the G-6-PD gene (one fast and one slow allele) has her skin cells cultured and cloned. What would you expect to observe if you analyze the G-6-PD enzyme from individual clones?

Accepted Answer

Each clone will express only one type of enzyme, either fast or slow, due to permanent X-chromosome inactivation.

Question 5

In the context of genomic imprinting, what is the expected phenotype of a mouse with genotype Igf2 / Igf2- if the Igf2- allele is inherited from the father?

Accepted Answer

The mouse will be small because only the paternal allele is expressed and it is nonfunctional.

Question 6

Which of the following best describes the process of X-chromosome inactivation in mammals?

Accepted Answer

It is initiated at the X-inactivation center (Xic), spreads along the chromosome, and is maintained through subsequent cell divisions.

Question 7

A woman with heteroplasmy for a mitochondrial mutation has children with a healthy man. Which of the following best predicts the possible outcomes for her children?

Accepted Answer

Some children may be affected, and others unaffected, depending on the proportion of mutant mitochondria inherited (heteroplasmy).

Question 8

Which of the following is a key difference between maternal effect and maternal inheritance?

Accepted Answer

Maternal effect involves nuclear genes whose products are deposited in the egg, while maternal inheritance involves organelle genes transmitted through the cytoplasm.

Question 9

In the four o'clock plant (Mirabilis jalapa), a variegated female is crossed with a green male. What is the expected distribution of phenotypes among the offspring, and why?

Accepted Answer

Offspring may be green, white, or variegated, depending on the types of chloroplasts present in the egg cytoplasm.

Question 10

Which of the following best explains why some human females with triple X syndrome (XXX) have two Barr bodies in their cells?

Accepted Answer

All but one X chromosome is inactivated, so the number of Barr bodies equals the number of X chromosomes minus one.

Question 11

A deletion in the maternal copy of chromosome 15 in humans can lead to which syndrome, and why?

Accepted Answer

Angelman syndrome, because the maternal copy of the UBE3A gene is deleted and the paternal copy is silenced by imprinting.

Question 12

Which of the following equations correctly represents the relationship between the number of X chromosomes ($$n) $$and the number of Barr bodies ($$B) in a $$human cell?

Accepted Answer

$$B = n - 1$$

Question 13

Which of the following is NOT evidence supporting the endosymbiotic origin of mitochondria and chloroplasts?

Accepted Answer

Both organelles have linear chromosomes similar to eukaryotic chromosomes.

Question 14

A woman with a mitochondrial disease caused by a mutation in the ATPase6 gene undergoes the 'three parent baby' procedure. Which genetic material will her child inherit?

Accepted Answer

Nuclear DNA from the mother and father, and mitochondrial DNA from a healthy donor female.

Question 15

Which of the following best describes heteroplasmy and its significance in mitochondrial diseases?

Accepted Answer

Heteroplasmy is the presence of both normal and mutant mitochondria in a cell, leading to variable disease expression depending on the ratio.

Question 16

Which of the following mechanisms is NOT a way that maternal inheritance of mitochondria is ensured in animals?

Accepted Answer

Doubling the number of paternal mitochondria in the zygote.

Question 17

Which of the following statements about dosage compensation in Drosophila melanogaster is correct?

Accepted Answer

The expression of X-linked genes in males is doubled to match the expression in females.

Question 18

Which of the following best explains why some genes on the inactivated X chromosome are still expressed in female mammals?

Accepted Answer

They are pseudoautosomal genes, present on both X and Y chromosomes, and do not require dosage compensation.

Non-Mendelian Inheritance: Mechanisms and Examples

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