Unit 7 Target 5: Complex Inheritance

1. Situations in which one allele for a gene is not completely dominant over another allele for that gene are called

Multiple alleles.

Incomplete dominance.

Polygenic inheritance.

Multiple genes.

Incomplete dominance refers to a situation where neither allele is completely dominant over the other, resulting in a phenotype that is an intermediate blend of the two alleles. This means that the heterozygous individual expresses a phenotype that is different from both homozygous individuals. In contrast, multiple alleles refer to the presence of more than two alleles for a particular gene, polygenic inheritance involves the contribution of multiple genes to a single trait, and multiple genes refer to the presence of multiple genes in general.

Explanation

Incomplete dominance refers to a situation where neither allele is completely dominant over the other, resulting in a phenotype that is an intermediate blend of the two alleles. This means that the heterozygous individual expresses a phenotype that is different from both homozygous individuals. In contrast, multiple alleles refer to the presence of more than two alleles for a particular gene, polygenic inheritance involves the contribution of multiple genes to a single trait, and multiple genes refer to the presence of multiple genes in general.

2. Jeanine inherited 2 alleles for round eye shape and has round eye shape. Her brother inherited 1 allele for round eye shape and 1 allele for almond eye shape and has almond eye shape. What type of trait is round eye shape?

Co-dominant

Dominant

Recessive

Sex-linked

Round eye shape is a recessive trait. This is indicated by the fact that Jeanine inherited 2 alleles for round eye shape and has round eye shape, while her brother inherited 1 allele for round eye shape and 1 allele for almond eye shape and has almond eye shape. In genetics, a recessive trait is only expressed when an individual has two copies of the recessive allele. Since Jeanine has round eye shape, it means that both of her alleles are for round eye shape, indicating that round eye shape is a recessive trait.

Explanation

Round eye shape is a recessive trait. This is indicated by the fact that Jeanine inherited 2 alleles for round eye shape and has round eye shape, while her brother inherited 1 allele for round eye shape and 1 allele for almond eye shape and has almond eye shape. In genetics, a recessive trait is only expressed when an individual has two copies of the recessive allele. Since Jeanine has round eye shape, it means that both of her alleles are for round eye shape, indicating that round eye shape is a recessive trait.

3. A cross of a red cow (RR) with a white bull (WW) produces all roan offspring (RRWW). This type of inheritance is known as

Incomplete dominance.

Polygenic inheritance.

Codominance.

Multiple alleles.

Codominance is the correct answer because in this type of inheritance, both alleles are expressed equally in the phenotype of the offspring. In the given scenario, the red allele and the white allele are both expressed in the roan offspring, resulting in a mixture of red and white hairs. This is different from incomplete dominance where one allele is dominant over the other, and from polygenic inheritance and multiple alleles where multiple genes or alleles contribute to the phenotype.

Explanation

Codominance is the correct answer because in this type of inheritance, both alleles are expressed equally in the phenotype of the offspring. In the given scenario, the red allele and the white allele are both expressed in the roan offspring, resulting in a mixture of red and white hairs. This is different from incomplete dominance where one allele is dominant over the other, and from polygenic inheritance and multiple alleles where multiple genes or alleles contribute to the phenotype.

4. A cross of a red flower (RR) with a white flower (WW) produces all pink offspring (RRWW). This type of inheritance is known as

Incomplete dominance.

Polygenic inheritance.

Codominance.

Multiple alleles.

In this scenario, when a red flower (RR) is crossed with a white flower (WW), the resulting offspring have a pink color (RRWW). This indicates that neither the red nor the white allele is dominant over the other, resulting in a blending of the two traits. This type of inheritance, where neither allele is dominant and the offspring display an intermediate phenotype, is known as incomplete dominance.

Explanation

In this scenario, when a red flower (RR) is crossed with a white flower (WW), the resulting offspring have a pink color (RRWW). This indicates that neither the red nor the white allele is dominant over the other, resulting in a blending of the two traits. This type of inheritance, where neither allele is dominant and the offspring display an intermediate phenotype, is known as incomplete dominance.

5. In humans, eye color is controlled by

Simple dominance.

Multiple alleles.

Polygenic inheritance.

Incomplete dominance.

Eye color in humans is controlled by multiple alleles. This means that there are more than two possible versions of the gene that determines eye color. Each individual inherits two alleles for eye color, one from each parent. The combination of these alleles determines the specific eye color that an individual will have. This is why there is a wide range of eye colors observed in the human population, including brown, blue, green, and hazel.

Explanation

Eye color in humans is controlled by multiple alleles. This means that there are more than two possible versions of the gene that determines eye color. Each individual inherits two alleles for eye color, one from each parent. The combination of these alleles determines the specific eye color that an individual will have. This is why there is a wide range of eye colors observed in the human population, including brown, blue, green, and hazel.

6. Horses born to 2 palomino (golden-coated) horses have a 25% chance of having a white coat, a 25% chance of having a chestnut (brown) coat, and a 50% chance of having a palomino coat. Which description of inheritance best explains the coat-color trait in these horses?

Palamino coat color is a recessive trait.

Palamino coat color is a dominant trait.

Coat color is an incompletely dominant trait.

Coat color is a sex-linked trait

The given information states that horses born to two palomino horses have a 25% chance of having a white coat, a 25% chance of having a chestnut coat, and a 50% chance of having a palomino coat. This distribution of coat colors suggests that neither the palomino coat color nor the chestnut coat color is completely dominant over the other. Incomplete dominance occurs when neither allele is dominant, and the heterozygous genotype results in an intermediate phenotype. Therefore, the best explanation for the coat-color trait in these horses is that it is an incompletely dominant trait.

Explanation

The given information states that horses born to two palomino horses have a 25% chance of having a white coat, a 25% chance of having a chestnut coat, and a 50% chance of having a palomino coat. This distribution of coat colors suggests that neither the palomino coat color nor the chestnut coat color is completely dominant over the other. Incomplete dominance occurs when neither allele is dominant, and the heterozygous genotype results in an intermediate phenotype. Therefore, the best explanation for the coat-color trait in these horses is that it is an incompletely dominant trait.