Question 1

A person with polydactyly (a dominant trait) is heterozygous (Aa) and marries a person without polydactyly (aa). What proportion of their children would be expected to have polydactyly?

Accepted Answer

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

Question 2

Which of the following best describes incomplete dominance?

Accepted Answer

The phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes.

Question 3

In the ABO blood group system, which genotype will result in the expression of both A and B antigens on the surface of red blood cells?

Accepted Answer

$$I^A I^B$$

Question 4

A cross between two heterozygous yellow mice ($$Yy 	imes Yy) $$produces offspring in a 2:1 ratio of yellow to non-yellow. What is the most likely explanation for this ratio?

Accepted Answer

Lethal allele in the homozygous state ($$YY)$$

Question 5

Which of the following is an example of pleiotropy?

Accepted Answer

A mutation that affects several aspects of phenotype, such as hair color and embryonic development

Question 6

In Labrador retrievers, the presence of two recessive alleles ($$ee) at $$one locus masks the expression of the black/brown gene at another locus. What genetic phenomenon does this illustrate?

Accepted Answer

Recessive epistasis

Question 7

If two genes are located close together on the same chromosome, which of the following is most likely to occur?

Accepted Answer

They will show linkage and have a low recombination frequency

Question 8

A test cross is performed between a fly heterozygous for two linked genes ($$A^+ B^+ / a b) $$and a fly homozygous recessive ($$a b / a b). $$The offspring numbers are: $$A^+ B^+$$: 390, $$a b$$: 410, $$A^+ b$$: 100, $$a B^+$$: 100. What is the recombination frequency?

Accepted Answer

$$20\%$$

Question 9

Which of the following best describes codominance?

Accepted Answer

The heterozygote expresses both phenotypes of the homozygotes simultaneously.

Question 10

In a population, 50 people have the allele for polydactyly, but only 40 express the trait. What is the penetrance of polydactyly in this population?

Accepted Answer

$$80\%$$

Question 11

Which of the following is true about the Bombay phenotype in humans?

Accepted Answer

Individuals with the Bombay phenotype lack the H antigen and do not express A or B antigens, regardless of their ABO genotype.

Question 12

Which genetic phenomenon explains why a dominant allele can cause a trait (such as hair color) but be recessive for another trait (such as embryonic development)?

Accepted Answer

Pleiotropy

Question 13

In squash, the dominant allele $$W$$ masks the expression of the yellow/green gene. What is the expected F2 phenotypic ratio from a $$WwYy 	imes WwYy$$ cross?

Accepted Answer

$$12:3:1$$

Question 14

Which of the following is NOT a form of dominance described in genetics?

Accepted Answer

Partial penetrance

Question 15

A cross between two hairless Mexican dogs ($$Hh 	imes Hh) $$results in a 2:1 ratio of hairless to hairy offspring. What genotype is lethal in this scenario?

Accepted Answer

$$HH$$

Question 16

Which of the following statements about gene linkage is correct?

Accepted Answer

Linked genes are located on the same chromosome and tend to be inherited together.

Question 17

Which of the following best describes expressivity?

Accepted Answer

The degree to which a character is expressed among individuals with the same genotype.

Question 18

If the recombination frequency between two genes is $$50\%$$, what does this indicate about their physical relationship?

Accepted Answer

They are on different chromosomes or far apart on the same chromosome.

Question 19

Which of the following is an example of complementary gene interaction?

Accepted Answer

Two genes where both must have at least one dominant allele to produce a purple flower.

Question 20

A plant with genotype $$AaBb is $$self-fertilized. If the two genes interact to produce novel phenotypes, what is the expected F2 phenotypic ratio?

Accepted Answer

$$9:6:1$$

Genetics Lecture 4: Extensions of Mendelian Genetics and Chromosome Mapping

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