Question 1

In humans, aniridia, a type of blindness, is due to a dominant allele A. Migraine headaches are due to another dominant allele M. If a man who suffers from both conditions (AaMm) marries a woman who suffers from both (AaMm), what are the chances of an offspring expressing both traits?

Accepted Answer

To have both conditions, an offspring must inherit at least one dominant allele (A) for aniridia and one dominant allele (M) for migraines from their parents. Each parent is AaMm, so for each trait (aniridia and migraines), the chance of passing on the dominant allele is 3/4 (AA, Aa, or aA for aniridia and MM, Mm, or mM for migraines). The chance of an offspring inheriting both dominant alleles (and thus expressing both traits) is (3/4) * (3/4) = 9/16.

Question 2

Consider skin color is regulated by three genes: A, B, and C. All recessive alleles would be 0 or white on the color scale. All dominant alleles would be 6 or black on the color scale. What color is a person with AAbbCc genotype?

Accepted Answer

Each dominant allele contributes to the skin color, with AAbbCc having two dominant alleles (one from A and one from C), the color would be medium brown, as it's in the middle of the scale from 0 (white) to 6 (black).

Question 3

In which kind of cross could you expect to find ratios of 1:1:1:1 among the offspring?

Accepted Answer

A two-trait testcross involves crossing an individual heterozygous for two traits with an individual homozygous recessive for those traits, resulting in offspring ratios of 1:1:1:1 for the different possible combinations of traits.

Question 4

If one parent has type B blood and the other has type AB, what type might the child have?

Accepted Answer

A child can inherit either A or B from the AB parent and either B or O from the B parent, resulting in possible blood types A, B, or AB. Type O is not possible.

Question 5

Hydrangeas are flowering plants with large, showy blooms. When the plant is grown in alkaline soil, the flowers are pink. When the plant is grown in acidic soil, the flowers turn blue. This change is phenotype is an example of

Accepted Answer

The change in color of hydrangea flowers based on soil acidity is an example of environmental influence, as it is not determined by genetic factors but rather external factors such as soil pH.

Question 6

You have two true-breeding rose bushes, one with red flowers and one with white flowers. A cross between these two roses yields a rose bush with two-color flowers. Each flower is both red and white. This is an example of

Accepted Answer

In codominance, both alleles are expressed equally in the heterozygous condition. In this case, the red and white alleles are both expressed in the flower, resulting in a two-color flower. Incomplete dominance would result in a blending of red and white, producing a pink flower. Environmental effects, polygenic inheritance, and epistatic interactions do not apply to this scenario.

Question 7

When two or more sets of alleles affect the same trait, it is termed

Accepted Answer

Polygenic inheritance is when multiple sets of alleles contribute to the expression of a single trait. This results in a continuous variation of the trait and is not simply controlled by one or a few genes. Examples of polygenic traits in humans include height and skin color.

Question 8

In four o'clock flowers, R = red, r = white, and Rr = pink. If two hybrids are crossed, what are the chances that an offspring will have pink flowers?

Accepted Answer

When two hybrids are crossed (Rr x Rr), there is a 25% chance of getting an offspring with two copies of the recessive allele (rr), which results in white flowers. There is also a 50% chance of getting an offspring with one copy of R and one copy of r (Rr), which results in pink flowers. Therefore, the chances of getting an offspring with pink flowers are 50%.

Question 9

The inheritance of blood types in humans can be explained by

Accepted Answer

The inheritance of blood types in humans is explained by multiple alleles, as the ABO blood group system is determined by three alleles: IA, IB, and i.

Question 10

In the determination of eye color, the HERC2 gene overrides the instructions of the OCA2 gene. If individuals are homozygous for a recessive allele of HERC2, they will have blue eyes regardless of the genotype associated with OCA2. This is an example of

Accepted Answer

This is an example of epistatic interactions, where one gene overrides the effects of another gene. The HERC2 gene is epistatic to the OCA2 gene in determining eye color.

Question 11

A man with blood type O would not be able to father a child with

Accepted Answer

A man with blood type O can only pass on an O allele to his offspring, as he has two O alleles. If the mother has blood type AB, she has both A and B alleles, and one of them will be passed on to the child. Therefore, it is not possible for a man with blood type O to father a child with blood type AB, as neither A nor B allele will be present in the father's genome to pass on to the child.

Question 12

Given that curly hair (WW) and straight hair (ww) exhibit incomplete dominance, what are the chances that two individuals with wavy hair will have a curly-haired child?

Accepted Answer

In cases of incomplete dominance, the heterozygous phenotype (Ww) is a blend of the two homozygous phenotypes. Wavy hair (Ww) results from one allele for curly hair (W) and one allele for straight hair (w). When two wavy-haired individuals (Ww x Ww) mate, their offspring have a 25% chance of being WW (curly-haired), 50% chance of being Ww (wavy-haired), and 25% chance of being ww (straight-haired), according to the Punnett square.

Question 13

In horses, black coat (B) is dominant over brown coat (b), and being a trotter (T) is dominant over being a pacer (t). A black horse who is a pacer is crossed with a brown horse who is a trotter. The offspring is a brown pacer. What is the genotype of the brown trotter parent?

Accepted Answer

The brown trotter parent must carry the recessive allele for coat color (b) to produce a brown offspring and must have at least one dominant allele for trotting (T). Since the offspring is a pacer (tt), the brown trotter parent must also carry a recessive allele for pacing (t), making the genotype bbTt.

Question 14

You have two true-breeding rose bushes, one with red flowers and one with white flowers. A cross between these two roses yields a bush with pink flowers. The pink flower color is an example of

Accepted Answer

Incomplete dominance occurs when neither allele is completely dominant over the other, resulting in a blended phenotype. In this case, the red and white alleles are incompletely dominant, resulting in the pink phenotype. Codominance would result in both red and white being expressed equally, which is not the case here. Environmental effects, polygenic inheritance, and epistatic interactions do not apply to this scenario.

Question 15

Which of the following produces an intermediate phenotype?

Accepted Answer

Incomplete dominance is when the heterozygous phenotype is an intermediate of the homozygous dominant and homozygous recessive phenotypes. The classic example is the flower color inheritance in snapdragons - red and white flowers can produce pink offspring when crossed.

Question 16

Traits that are controlled by several sets or pairs of alleles, such as skin color and height in humans, are the result of what form of inheritance?

Accepted Answer

Traits that are controlled by several sets or pairs of alleles are the result of polygenic inheritance. Polygenic inheritance occurs when multiple genes code for a particular phenotype, and each gene may have multiple alleles. Skin color and height in humans are both examples of traits that are controlled by many genes and multiple alleles.

Question 17

Mr. X has been accused by Miss Z of fathering her child. The child's blood type is AB and Miss Z's blood type is A. Which blood type(s) would eliminate Mr. X as a possible father of the child?

Accepted Answer

Mr. X must have the A antigen in his blood type in order to be the father of a child with AB blood type. Therefore, blood types A and O would eliminate Mr. X as a possible father.

Question 18

A cross is made between two parents with genotypes AaBB and aabb. If there are 32 offspring, how many of them would be expected to exhibit both dominant characteristics?

Accepted Answer

The dominant characteristics are represented by the alleles A and B. 
The possible gametes for parent 1 (AaBB) are AB and aB.
The possible gametes for parent 2 (aabb) are ab.

The Punnett square for the cross would be:

| A  | a
--|---|--
B | AB | aB
b | Ab | ab

The offspring genotypes and phenotypes would be:

- 25% AaBB (dominant for A and B)
- 25% Aabb (dominant for A)
- 25% aaBB (dominant for B)
- 25% aabb (no dominant characteristics)

Thus, the number of offspring with both dominant characteristics (A and B) would be 25% of 32, which is 8. Therefore, the answer is C.

Question 19

The leaves of a maple tree vary in size depending on the location of the leaves on the tree. Those growing at the outer region of the tree tend to be smaller than those growing closer to the trunk of the tree. This allows leaves that are growing in the shade to have a larger surface area. This is an example of

Accepted Answer

The variation in leaf size in relation to location on the tree indicates a response to environmental factors, specifically the amount of sunlight the leaves receive. This is an example of phenotypic plasticity, where an organism's phenotype can be modified by environmental factors. The other options (B-E) are not relevant to the given scenario.

Question 20

Huntington disease is an autosomal dominant disorder that leads to progressive degeneration of brain cells. There is no effective treatment for the disorder and individuals usually die in their 40s or 50s, 10 to 15 years after the onset of symptoms. Which of these statements about Huntington disease is true?

Accepted Answer

Huntington disease is caused by a mutation in the gene that codes for the protein huntingtin, located on chromosome 4, not chromosome 9. It does not require both parents to carry the trait to be expressed, does not typically skip generations, and although it can appear in the teenage years, it more commonly presents in mid-adult life.

Quiz 23: Patterns of Gene Inheritance

In humans, aniridia, a type of blindness, is due to a dominant allele A. Migraine headaches are due to another dominant allele M. If a man who suffers from both conditions (AaMm) marries a woman who suffers from both (AaMm) , what are the chances of an offspring expressing both traits?