Question 1

Which of the following processes contributes most directly to the statement: "except for the rare cases of identical twins, it is likely that no two humans who have ever existed on this planet have been genetically identical"?

Accepted Answer

Crossing over during meiosis

Question 2

A genetic counselor is analyzing a pedigree and notices that a trait appears only in males and is passed from father to all sons, but never to daughters. Which mode of inheritance is most likely?

Accepted Answer

Y-linked

Question 3

Which of the following best explains why X-linked recessive traits are more commonly expressed in males than in females?

Accepted Answer

Males have only one X chromosome, so a single recessive allele will be expressed.

Question 4

In a cross between two heterozygotes for a gene showing incomplete dominance, the phenotypic ratio in the offspring is expected to be:

Accepted Answer

$$1:2:1$$

Question 5

Which of the following is an example of codominance in humans?

Accepted Answer

ABO blood group where both A and B alleles are expressed in AB individuals

Question 6

A plant with red flowers (RR) is crossed with a plant with white flowers (rr). All F1 offspring have pink flowers. When two F1 plants are crossed, the F2 generation shows red, pink, and white flowers in a $$1:2:1$$ ratio. What type of inheritance is this?

Accepted Answer

Incomplete dominance

Question 7

Which of the following diagnostic phenotypic ratios in the F2 generation of a dihybrid cross indicates recessive epistasis?

Accepted Answer

$$9:3:4$$

Question 8

A single gene mutation in a metabolic enzyme causes both anemia and neurological symptoms in a patient. This is an example of:

Accepted Answer

Pleiotropy

Question 9

Which of the following best distinguishes between complementary gene action and duplicative gene action?

Accepted Answer

Complementary gene action requires both gene products for the phenotype, while duplicative gene action requires only one of the gene products.

Question 10

In a population, the gene for coat color in rabbits has four alleles: $$C$$, $$c^{ch}$$, $$c^h$$, and $$c. $$The dominance hierarchy is $$C \u003e c$$^{ch}$$ \u003e c^h \u003e c. $$Which of the following genotypes would result in a chinchilla phenotype?

Accepted Answer

$$c^{ch}/c^h$

Question 11

A geneticist is studying a trait in chickens where the comb shape is determined by the interaction of two genes. The F2 generation from a dihybrid cross shows a $$9:7$$ phenotypic ratio. What does this suggest about the genetic control of comb shape?

Accepted Answer

The trait is controlled by two genes showing complementary gene action.

Question 12

Which of the following best describes a polygenic (quantitative) trait?

Accepted Answer

A trait with a continuous distribution of phenotypes due to the additive effects of multiple genes

Question 13

A researcher wants to determine whether the variation in height among a group of plants is due to genetic differences or environmental factors. Which approach would be most appropriate?

Accepted Answer

Grow genetically identical plants in different environments and compare the variation.

Question 14

In a classic dihybrid cross, the expected phenotypic ratio is $$9:3:3:1. $$Which of the following would most likely cause a deviation from this ratio?

Accepted Answer

Epistatic interaction between the two genes

Question 15

Which of the following is an example of a continuous trait that is primarily determined by genetic factors with minimal environmental influence?

Accepted Answer

Kernel color in wheat

Question 16

A family pedigree shows a trait that appears in every generation, affects both males and females equally, and is transmitted from affected parents to about half of their children. Which inheritance pattern is most likely?

Accepted Answer

Autosomal dominant

Question 17

Which of the following best describes dominant epistasis?

Accepted Answer

A dominant allele at one locus masks the expression of alleles at a second locus

Question 18

In a cross between two pure-breeding parents for a discontinuous trait, the F1 generation is uniform, but the F2 generation shows two distinct phenotypes in a $$3:1$$ ratio. What does this suggest about the inheritance of the trait?

Accepted Answer

The trait is controlled by a single gene with complete dominance

Question 19

Which of the following is a key diagnostic pattern in pedigree analysis for X-linked dominant inheritance?

Accepted Answer

Affected fathers pass the trait to all daughters but not sons

Question 20

A geneticist observes a $$12:3:1$$ phenotypic ratio in the F2 generation of a dihybrid cross. What does this ratio most likely indicate?

Accepted Answer

Dominant epistasis

Genetics Study Guide: Transmission, Sex-Linkage, Dominance, Epistasis, and Quantitative Traits

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