Q: If a gene has three alleles in a population, how many different genotypes are possible for this gene?

$$\frac{3 \times (3+1)}{2} = 6$$

Question 1

Which of the following best describes Mendel’s law of segregation?

Accepted Answer

Two alleles for a heritable character separate during gamete formation and end up in different gametes.

Question 2

A pea plant with genotype $$Pp is $$self-pollinated. What is the expected phenotypic ratio of purple to white flowers in the offspring?

Accepted Answer

$$3:1$$

Question 3

In a testcross, a plant with the dominant phenotype is crossed with a homozygous recessive plant. If any offspring display the recessive phenotype, what is the genotype of the mystery parent?

Accepted Answer

Heterozygous

Question 4

Which of the following is an example of incomplete dominance?

Accepted Answer

A cross between red and white flowers produces pink flowers.

Question 5

A man with blood type AB ($$I^A I^B) $$and a woman with blood type O ($$ii) $$have children. What are the possible blood types of their children?

Accepted Answer

A and B

Question 6

Which genetic phenomenon explains why cystic fibrosis can cause symptoms in multiple organ systems?

Accepted Answer

Pleiotropy

Question 7

In Labrador retrievers, coat color is determined by two genes. One gene determines pigment color (B = black, b = brown), and another gene determines whether pigment is deposited (E = pigment, e = no pigment). What is the expected phenotypic ratio in the offspring of two dihybrid ($$BbEe) $$dogs?

Accepted Answer

$$9:3:4$$

Question 8

Which of the following best describes polygenic inheritance?

Accepted Answer

A single phenotypic character is affected by two or more genes.

Question 9

A woman who is a carrier for albinism ($$Aa) $$and a man who is also a carrier ($$Aa) $$have a child. What is the probability that their child will have albinism?

Accepted Answer

$$1/4$$

Question 10

Which of the following statements about dominant inherited disorders is correct?

Accepted Answer

Dominant inherited disorders can be passed on even if only one parent has the allele.

Question 11

If a plant with genotype $$YyRr ($$yellow, round seeds) is crossed with another $$YyRr$$ plant, what is the expected phenotypic ratio for the offspring, assuming independent assortment?

Accepted Answer

$$9:3:3:1$$

Question 12

Which of the following is true regarding codominance?

Accepted Answer

Both alleles in the heterozygote are fully expressed.

Question 13

A geneticist observes that two genes are inherited together more often than not. What is the most likely explanation?

Accepted Answer

The genes are located near each other on the same chromosome.

Question 14

Which of the following crosses would produce only heterozygous offspring?

Accepted Answer

$$PP 	imes pp$$

Question 15

A disease is caused by a recessive allele. Two parents are both carriers. What is the probability that their first two children will both be unaffected?

Accepted Answer

$$3/4 	imes 3/4 = 9/16$$

Question 16

Which of the following best explains why Huntington’s disease persists in human populations?

Accepted Answer

Symptoms appear after reproductive age.

Question 17

Which of the following is an example of a character with quantitative variation?

Accepted Answer

Height in humans

Question 18

If a gene has three alleles in a population, how many different genotypes are possible for this gene?

Accepted Answer

$$\frac{3 	imes (3+1)}{2} = 6$$

Question 19

Which of the following best describes the relationship between genotype and phenotype?

Accepted Answer

Genotype is the genetic makeup, phenotype is the observable characteristics.

Question 20

A plant with genotype $$Pp is $$crossed with a plant with genotype $$pp. $$What is the probability that an offspring will have purple flowers?

Accepted Answer

$$1/2$$

Mendel and the Gene Idea: Foundations of Classical Genetics

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