Question 1

Which structural feature of hemoglobin allows it to carry oxygen efficiently in vertebrate red blood cells?

Accepted Answer

Its quaternary structure, composed of four polypeptide chains (two α and two β)

Question 2

A mutation in the β-globin gene causes sickle-cell hemoglobin. Which amino acid substitution is responsible for this phenotype?

Accepted Answer

Glutamic acid replaced by valine at position 6

Question 3

In the cross between red-flowered (CRCR) and white-flowered (CWCW) snapdragons, the F1 generation is pink (CRCW). What type of inheritance is demonstrated?

Accepted Answer

Incomplete dominance

Question 4

In cases of incomplete dominance, what is the relationship between the phenotypic and genotypic ratios in the F2 generation?

Accepted Answer

Phenotypic ratio is identical to genotypic ratio

Question 5

Which blood group genotype results from codominance of two alleles?

Accepted Answer

IAIB

Question 6

A woman is genetically type B for blood but functionally type O due to the Bombay phenotype. What is the molecular cause?

Accepted Answer

She is homozygous for a mutation at the FUT1 locus, preventing H substance formation

Question 7

In mice, coat color is determined by two genes: B (black/brown) and C (color/no color). What is the expected phenotypic ratio in the offspring of BbCc × BbCc?

Accepted Answer

$$9:3:4$$

Question 8

Which scenario best illustrates epistasis?

Accepted Answer

The genotype at one locus masks the expression of another gene's phenotype

Question 9

A pedigree shows a woman with blood type O whose parent is AB. What genetic explanation accounts for her phenotype?

Accepted Answer

She has the Bombay phenotype, lacking H substance

Question 10

A dihybrid cross of AaBb × AaBb produces a modified phenotypic ratio due to gene interaction. What is the expected ratio for a dominant epistatic gene?

Accepted Answer

$$12:3:1$$

Question 11

A loss-of-function mutation in an essential gene is tolerated in the heterozygous state but lethal in the homozygous state. What is this allele called?

Accepted Answer

Recessive lethal allele

Question 12

Huntington disease is caused by a dominant lethal mutation. What molecular feature characterizes this mutation?

Accepted Answer

Expansion of CAG repeats in the HD gene

Question 13

Human skin color is a polygenic trait. If three genes (A, B, C) contribute additively, what is the expected proportion of offspring with the darkest skin from parents AaBbCc × AaBbCc?

Accepted Answer

$$1/64$$

Question 14

Marfan syndrome is an example of pleiotropy. Which statement best describes pleiotropy?

Accepted Answer

One gene affects multiple phenotypic characters

Question 15

A person with a disease-causing genotype does not exhibit the disease phenotype but can transmit the mutation. What is this phenomenon called?

Accepted Answer

Reduced penetrance

Question 16

Neurofibromatosis Type 1 shows a wide range of phenotypic expression among individuals with the same genotype. What term describes this phenomenon?

Accepted Answer

Expressivity

Question 17

A newborn is diagnosed with phenylketonuria (PKU). What dietary intervention can prevent the associated phenotype?

Accepted Answer

A diet low in phenylalanine

Question 18

Dosage compensation in mammals involves which mechanism?

Accepted Answer

Random inactivation of one X chromosome in females, forming a Barr body

Question 19

Which gene is critical for X-inactivation in female mammals?

Accepted Answer

XIST gene

Question 20

Pattern baldness in humans is an example of which type of inheritance?

Accepted Answer

Sex-influenced inheritance

Extensions of Mendelian Genetics: Beyond Simple Dominance

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