Genetics: Chapter 4 HW

The platypus is a sexually reproducing mammal in which the sexes are separate. Unlike other mammals, the male has five X and five Y chromosomes. The female has 10 X chromosomes. Select the term that describes the organization of the sexual organs in the platypus.

dioecious

In Caenorhabditis elegans, the level of expression of genes on both X chromosomes of females is reduced by half. What phenomenon is this an example of?

dosage compensation

An X‑linked recessive gene causes red-green color blindness in humans. Suppose John and Cathy have normal color vision. After 10 years of marriage to John, Cathy has given birth to a color‑blind daughter and a color-blind son. John filed for divorce, claiming that he is not the father of at least one of the children. Which statement describes John's paternity claim?

he cannot be the father to Cathy's daughter

Use the Punnet Squares interactive, Level 3 to conduct a cross between a man with normal vision and a woman with the gene for color blindness. A man with normal vision, XB Y, and a woman who is a carrier for color blindness, XB Xb, mate. - How many genotypes result in female offspring with normal vision? - What percentage of male offspring will be color-blind? - If the mother were color-blind, what percentage of male offspring would be color-blind?

- 2 - 50% - 100%

A black female cat is mated with an orange male cat. They produce two tortoiseshell females, two black males, one orange female, and one tortoiseshell male, for a total of six kittens. Orange and black fur color are encoded by different alleles of the same X‑linked fur color gene. Based on the phenotypes of the parents, what sex chromosomes do the orange female and the tortie male offspring have? Select the most likely explanations for the sex chromosome types.

- The orange female has only one X chromosome, and the tortoiseshell male is XXY - The male tortoiseshell received a black X chromosome from his mother and an orange X from his father - When only one X chromosome is present in the female, it does not become inactivated

Match each phenotype description to its corresponding sex chromosome genotype in humans.

- XO with SRY on an autosome: phenotypically male but karyotype indicates presence of only X chromosome - XY with SRY deleted: phenotypically female but karyotype indicates presence of both sex chromosomes - XXX: phenotypically female with some abnormalities and over expression of X chromosome genes - XXY: phenotypically male with sterility and hypogonadism -XYY: phenotypically male with an increase in average stature

Use the karyotype interactive to answer the question. Identify the chromosomal disorders affecting the patients in the Abnormal Karyograms tab of the karyotype interactive. Place each patient according to whether his or her disorder occurs exclusively in biological males, exclusively in biological females, or in both sexes.

- affects both sexes: patient 768 (Turner X Syndrome) patient 251 (Down syndrome) - affects only biological females: patient 367 (Turner syndrome) - Affects only biological males: patient 892 (Klinefelter syndrome)

Select the definition of a Barr body. The first cloned cat, CarbonCopy (CC), was tabby, while the cat she was cloned from, Rainbow, was calico. The surrogate mother was a tabby. Select the explanation that best explains why CC would never have been identical in pattern to Rainbow.

- an inactive X chromosome - the pattern of X-chromosome inactivation is established randomly in cell lineage

Suppose researchers identified two Drosophila melanogaster mutant phenotypes. One phenotype is called thistle and the other is called coffee. In order to determine the mode of inheritance of the mutant allele responsible for each phenotype, males that have both mutant phenotypes are mated with wild‑type (wt) females to produce F1 progeny. Then, the F1 progeny are mated together and the F2 progeny are scored. - What is the mode of inheritance for the genes controlling thistle and coffee? - What is the genotype of the original male parent?

- autosomal dominant for thistle and X-linked recessive for coffee - homozygous mutant at one locus and hemizygous mutant at the other locus

A hobbyist cat breeder purchases a true‑breeding male cat with a black coat and a true‑breeding female cat with an orange coat. When the two cats are crossed, all male kittens have an orange coat, whereas all female kittens have a tortoiseshell coat pattern as shown in the image. The hobbyist then purchases a true‑breeding male cat with an orange coat and a true‑breeding female cat with a black coat to perform the reciprocal cross. In this cross, all male kittens have black coats, whereas all female kittens have a tortoiseshell coat pattern. - Based on this information, what coat colors do you expect in the male progeny of a tortoiseshell female and an orange male? - Based on this information, what coat colors do you expect in the female progeny of a tortoiseshell female and an orange male?

- black and orange - orange and tortoiseshell

A man, Joe, has classic hemophilia, an X‑linked recessive disease. Classify each person depending on whether or not Joe could have inherited the hemophilia gene from him or her.

- could have inherited: maternal grandmother, maternal grand father - could not have inherited: paternal grandmother, paternal grand father

In certain salamanders, the sex of a genetic female can be altered, changing her into a functional male; these salamanders are called sex‑reversed males. When a sex‑reversed male is mated with a normal female, approximately 2/3 of the offspring are female, and 1/3 are male. - Given this observation, which of the statements is most likely to be true for these salamanders? - How do you explain the results of this cross?

- females are the heterogametic sex - both parents were ZW, and WW offspring did not survive

In butterflies, sex is determined by the ZW sex‑determination system. Female butterflies are heterogametic and have both a Z sex chromosome and a W sex chromosome for sex determination. In contrast, male butterflies are homogametic and have two Z sex chromosomes. Select all of the relatives from which a female butterfly could have inherited her Z sex chromosome.

- paternal grandmother - father

The orange coat color allele in cats is located on the X chromosome and is one of two genes responsible for tortoiseshell coat color, as shown in the image. Two true‑breeding orange cats are crossed and researchers examine the X chromosomes in the female progeny throughout various stages of their development. Determine the number of orange alleles that have not been silenced at the indicated developmental stages.

- primary oocyte: 2 - single-cell female embryo: 2 - adult female somatic cell: 1

Hemophilia is called "the royal disease" because many European royal families had members with the condition. Hemophilia is a recessive, X‑linked disorder. Queen Victoria was unaffected by hemophilia, but was a carrier of the hemophilia gene (XHXh). Suppose Queen Victoria's husband, Prince Albert, was affected with hemophilia (XhY). - What is the percent probability that a son of Queen Victoria and Prince Albert would be unaffected by hemophilia? - What is the percent probability that a daughter or son of Queen Victoria and Prince Albert would be affected by hemophilia? - What is the percent probability Queen Victoria and Prince Albert would have two affected females?

- probability of unaffected son: 50% - probability of affected child: 50% - probability of two affected females: 6.25%

Classify whether each gene regularly exists in a hemizygous state.

- regularly hemizygous: a color-blindness gene on the X chromosome in a normal human male; a transgenic gene inserted into only one chromosome of a mouse - not regularly hemizygous: a color-blindness gene on an X chromosome in a normal human female; a gene on chromosome 21 in an individual with Down syndrome

Color blindness is a sex‑linked recessive trait. A female is color blind in one eye, but not both. Select the explanation for this condition. Is it possible for a male to have different color‑blindness phenotypes in each eye?

- silencing of different X chromosomes - yes, in an XXY male where each eye has alternate X inactivation

Which statements describe Y‑linked traits?

- the trait is passed down to a son by his father - the phenotype is solely expressed in males

Suppose a novel disease has been studied in several families and is known to be caused by a mutation in one gene. The given table shows families where the disease is present. The four rightmost columns record the number of offspring in each family. - Select the most likely mode of inheritance of the disease. - Select the description that best matches the female parent in family 6. - Select the description that best matches the male parent in family 3.

- x-linked dominant - has one disease allele - has no disease alleles

Red-green color blindness is an X‑linked recessive trait in humans. Polydactyly (extra fingers and toes) is an autosomal dominant trait. Martha has normal fingers and toes and normal color vision. Her mother is normal in all respects, but her father is color blind and polydactylous. Bill is color blind and polydactylous. His mother has normal color vision and normal fingers and toes. When answering the given question, consider that the answers include the proportions of only some of the possible phenotypes; other phenotypes are also expected to occur but are not included. If Bill and Martha marry, what proportions of children with specific phenotypes would they be expected to produce?

1/8 color-blind girls with polydactyly, 1/8 boys with normal vision and normal fingers

A normal female Drosophila produces abnormal eggs that contain a complete diploid set of her chromosomes. She mates with a normal male Drosophila that produces normal sperm. What will the sex ratio of the progeny from this cross be?

50% female, 50% intersex

In some reptilian species, temperature determines the sex of an embryo. The graph below shows the effect of temperature on the percentage of male reptilian embryos, where Tp is the pivotal temperature. Select the statement that describes the influence of temperature on the percentage of male or female offspring as shown by the graph.

At high temperature, nearly 100% of offspring will be male

Identical, or monozygotic, twins develop from a single egg fertilized by a single sperm. Monozygotic twins are genetically identical because they originate from a single zygote that split into two. Caroline Loat and her colleagues examined nine measures of social, behavioral, and cognitive ability in 1000 pairs of both male and female identical twins. Their study found that pairs of male twins tended to be more alike in their prosocial behavior, peer problems, and verbal ability scores than pairs of female twins. Which statement explains this observation?

Females are mosaic for the expression of heterozygous X-linked loci, because females undergo random X-inactivation

A hobbyist cat breeder purchases a true‑breeding male cat with a black coat and a true‑breeding female cat with an orange coat. When the two cats are crossed, all male kittens have an orange coat, whereas all female kittens have a tortoiseshell coat pattern as shown in the image. The hobbyist then purchases a true‑breeding male cat with an orange coat and a true‑breeding female cat with a black coat to perform the reciprocal cross. In this cross, all male kittens have black coats, whereas all female kittens have a tortoiseshell coat pattern. Based on this information, what is the mode of inheritance of the orange coat color in cats?

X-linked codominant

Anhidrotic ectodermal dysplasia is an X‑linked recessive disorder in humans characterized by small teeth, no sweat glands, and sparse body hair. The trait is usually seen in men, but women who are heterozygous carriers of the trait often have irregular patches of skin with few or no sweat glands (see the illustration). Irregular patches of skin lacking sweat glands in heterozygous female carriers of anhidrotic ectodermal dysplasia are caused by:

inactivation of the X chromosome with the wild-type allele in the cells of the sweat gland lacking patches

Anhidrotic ectodermal dysplasia is an X‑linked recessive disorder in humans characterized by small teeth, no sweat glands, and sparse body hair. The trait is usually seen in men, but women who are heterozygous carriers of the trait often have irregular patches of skin with few or no sweat glands (see the illustration). Why does the distribution of the patches of skin lacking sweat glands differ among the females depicted in the illustration, even between the identical twins?

it is due to random inactivation of different X chromosomes in different cells

Sponges can produce sperm and eggs in a single organism. Which term describes the sex system of the organism?

monoecious

The Talmud, an ancient book of Jewish civil and religious laws, states that if a woman bears two sons who die of bleeding after circumcision (removal of the foreskin from the penis), any additional sons that she has should not be circumcised. The bleeding is most likely due to the X‑linked disorder hemophilia. Furthermore, the Talmud states that the sons of her sisters must not be circumcised, whereas the sons of her brothers should be. Is this religious law consistent with sound genetic principles?

yes, the woman is a carrier and half of her sons will be affected. Her sisters may also be carriers, but her brothers' sons will get their X chromosome from their mothers, who are unlikely to be carriers of the allele.