Genetics Review

A student is investigating patterns of inheritance by crossing two pea plants. She creates the Punnett square shown below. Which explanation of the inheritance of shape in pea plants is supported by the Punnett square?

• The alleles for shape show a pattern of codominance.
• The alleles for shape show a pattern of incomplete dominance.
• The allele for round shape (R) is dominant to the allele for wrinkled shape (r).
• The allele for wrinkled shape (r) is dominant to the allele for round shape (R).

Tay-Sachs disease is a rare inherited disorder that progressively destroys nerve cells in the brain and spinal cord. The allele for Tay-Sachs is recessive and written as “t”. If two people who are heterozygous for Tay-Sachs have four children, how many of the offspring will most likely inherit and develop Tay-Sachs disease?

• none, because none of the children will be homozygous dominant
• one, because one of the children will be homozygous recessive
• three, because three of the children will inherit a dominant allele
• all, because all of the children will inherit one recessive allele

If two people who are heterozygous for Tay-Sachs have four children, how many of their offspring will most likely carry an allele for Tay-Sachs?

• 1
• 2
• 3
• 4

There are three different alleles for blood-type: A, B, and O. A and B are dominant over O. If a person has A and B genes, he or she has blood-type AB. This is referred to as a codominant pattern of heredity. Jane's mother and father have type B blood. When Jane's blood was tested, she found she had a blood-type of O. What does this suggest of Jane's parents?

• Both have a recessive gene for type O blood.
• Both are homozygous for type B blood.
• One of them has a recessive gene for type O blood.
• One of them is homozygous for type B blood.

Due to random chromosome segregation, the gametes of parent pea plants possess the alleles shown in the Punnett square below, where T is a dominant allele for tallness, and t is a recessive allele for shortness. What is the probability that the offspring plant will be short?

• 0%
• 25%
• 50%
• 100%

In cats, fur color is controlled by a single pair of alleles. The alleles for orange fur and for black fur are only located on the X chromosome. Tortoiseshell cats have one allele for orange fur and one for black fur. Which statement concerning fur color in cats is true

• Only male cats can be tortoiseshell.
• Males need two alleles to have orange fur.
• Males need two alleles to have black fur.
• Only female cats can be tortoiseshell.

Fruit flies can have red eyes or white eyes. If a heterozygous red-eyed fly and a homozygous white-eyed fly produced 50% red-eyed offspring and 50% white-eyed offspring, which of the following is true of the traits?

• Having red eyes and having white eyes are both recessive traits.
• Having red eyes is a recessive trait, while having white eyes is dominant.
• Having red eyes and having white eyes are both dominant traits.
• Having red eyes is a dominant trait, while having white eyes is recessive.

A black male guinea pig mates with a white female guinea pig, and the female gives birth to four offspring. Three of the offspring are black, and one is white. Which of the following best explains how one offspring was born with white fur?

• The allele for black fur is dominant.
• The father carried one allele for white fur.
• The allele for white fur is recessive.
• The mother carried one allele for black fur.

In summer squash, the gene for white-colored fruit is dominant over the gene for yellow-colored fruit. If homozygous yellow-fruited plants are crossed with heterozygous white-fruited plants, what is the expected distribution of fruit color produced in the offspring?

• 100% yellow
• 100% white
• 50% yellow, 50% white
• 25% yellow, 75% white

In the dihybrid cross for pea plants shown below, R is dominant for round peas, r is recessive for wrinkled peas, Y is dominant for yellow peas, and y is recessive for green peas. Which statement could be accurately made about the offspring of this cross?

• There is a 100% chance of having round, green peas.
• There is no chance of having any wrinkled, green peas.
• There is a 50% chance of having round, yellow peas.
• There is no chance of having any round, yellow peas.