Unit 6 Genetics

From a single fertilized ovum undergoing a series of rapid cell divisions, a human infant develops. The embryonic cells become specialized for a variety of functions. Which of these statements best describes how different cell types develop?

• Each cell type contains only the active parts of the DNA needed for that cell type.

• Each cell type has only one chromosome containing the DNA needed for that cell type.

• Each cell has an identiacl copy of DNA with enzymes controlling the expression of specific genes, leading to a variety of cell.s

• Eahc cell has multiple copies of DNA that are affected in different ways by the environment to change the function of the cell at regular intervals.

As a fertilized egg divides, the cells differentiate because they...

• contain a lipid bilayer

• can clump together

• metabolize sugars rapidly

• have specific genes activated

The arctic fox inhabits northern areas of North America. The same arctic fox is shown in the drawing at different times of the year. What causes this change in fur color?

• The alleles for fur color change as the arctic fox grows older.

• Gene expression for fur color is regulated by latitude.

• The arctic fox has two traits for fur color that are determined at birth.

• Gene expression for fur color is regulated by temperature.

Human bone, muscle, and nerve cells all contain the same number of chromosomes with the same complement of genes. What enables these cells to perform specialized activities?

• The ability of some cells to remove unnecessary DNA sequences

• The regulation of gene expression within each cell type

• The mutation of genes within each cell type

• The use of different methods of cell division

At birth Himalayan rabbits are usually white over their entire bodies. But when parts of their bodies reach temperatures below 35º C, a pigment that causes these parts to turn black is produced. Which of the following is most likely the cause of this phenomenon?

• Poor blood circulation

• Infection caused by cold temperatures

• Gene expression that is regulated by temperature

• A trait that is both sex-linked and hormone dependent

Albinism is an autosomal recessive condition. Which circle graph shows the genotype probability when an albino female mates with a male that is heterozygous for the albinism trait?

• F

• G

• H

• J

In Holstein cattle the allele for black hair color (B) is dominant over the allele for red hair (b), and the allele for polled (P), or lacking horns, is dominant over the allele for having horns (p). What is the expected phenotypic ration of the offspring of a BbPp x Bb Pp cross is these alleles sort independently?

• 16 black/polled : 0 black/horned : 0 red/polled : 0 red/horned

• 12 black/polled : 0 black/horned : 0 red/polled : 4 red/horned

• 4 black/polled : 4 black/horned: 4 red/polled : 4 red/horned

• 9 black/polled : 3 black/horned : 3 red/polled : 1 red/horned

The four butterflies in the illustrations represent the offspring in the F₁ generation. Which statement is best supported by the phenotypes of these offspring?

• The F₁ generation is composed only of males.

• Two of the offspring in the F₁ generation will not be able to reproduce.

• The F₁ generation is the result of a dihybrid cross.

• Two of the offspring in the F₁ generation will experience a spontaneous mutation.

Chickens can have different types of feathers. Frizzled feathers curl toward a chicken's head. Assume that feather type is determined by a single gene and that the allele for frizzled feathers is dominant over the allele for straight feathers. In a cross between two chickens with straight feathers, what percentage of the offspring can be expected to have frizzled feathers?

• 0%

• 25%

• 50%

• 100%

Facial dimples and free earlobes are both considered dominant human traits. What are the expected phenotypes of the offspring of a female with dimples and free earlobes (DDFf) and a male with no dimples and attached earlobes (ddff)?

• 50% with dimples and free earlobes and 50% with dimples and attached earlobes

• 50% with dimples and free earlobes and 50% with no dimples and attached earlobes

• 75% with dimples and free earlobes and 25% with no dimples and attached earlobes

• 75% with dimples and attached earlobes and 25% with no dimples and free earlobes