Chapter 15: The Chromosomal Basis of Inheritance

Examples of alterations of chromosomal structures include all of the following except __________.

aneuploidy

In X-linked patterns of inheritance, __________.

fathers pass X-linked alleles only to their daughters, and mothers pass X-linked alleles to both their daughters and their sons

__________ is the failure of __________ to separate in meiosis I or the failure of __________ to separate in meiosis II.

Nondisjunction; homologous chromosomes; sister chromatids

In werewolves hypothetically, pointy ears (P) are dominant over round ears (p). The gene is on the X chromosome. (Sex determination in werewolves is the same as for "other" humans.) A certain female werewolf has pointy ears even though her father had round ears. What percentage of her sons will have round ears if she mates with a werewolf with round ears?

50%

Genomic imprinting in mammals appears to primarily affect genes involved in __________.

embryonic development

In a certain fish, fin rays (supporting structures for the fins) can be either bony or soft in adult fish. Sex linkage in a fish is similar to that in humans. What evidence would most strongly support the idea that the ray locus is on the X chromosome?

Matings of soft ray males and bony ray females give different results from the matings of bony ray males and soft ray females.

In Klinefelter syndrome, individuals are phenotypically male, but have reduced sperm production and may have some breast development in adolescence. The cells of Klinefelter individuals have two X chromosomes and one Y (they are XXY instead of XY).

This occurs because of what meiotic error?

Aneuploidy

Queen Victoria was a carrier of a recessive sex-linked allele for hemophilia. Which of the following possibilities could explain the presence of the hemophilia allele in her genotype?

Either her mother was a carrier or her father had hemophilia.

A linkage map __________.

orders genes on a chromosome based on recombination frequencies

Down syndrome is an example of __________, and the child is __________ for chromosome 21.

aneuploidy; trisomic

When crossing over occurs between two linked genes in an F1 dihybrid testcross, the frequency of the parental types will always __________ the frequency of the recombinant types when compared to Mendel's unlinked genes.

be greater than

Gene silencing is called __________.

genomic imprinting

In a cross between wild-type (red-eyed) female flies and mutant white-eyed male flies, the F1 generation should always produce females with __________ eyes and males with __________ eyes.

red; red

The ability to observe meiosis in gamete production supported Mendel's first law of __________, which applies when __________ separate, and supported Mendel's second law of __________, which applies when __________ sort __________.

segregation; homologous pairs; independent assortment; alleles; independently

In humans, a normal male's somatic cells will have __________ set(s) of chromosomes and sex chromosomes designated as __________ and __________, while in bees and ants, a normal male's somatic cells have __________ set(s) of chromosomes, which are __________.

two; X; Y; one; haploid

When an individual has an additional chromosome, that chromosome set is called __________, and the condition is known as __________.

trisomic; aneuploidy

The chromosome theory of inheritance states that __________.

genes occupy specific positions on chromosomes, homologous chromosomes segregate from each other during meiosis, and chromosomes assort independently during meiosis

You perform a testcross using F1 dihybrid flies. If, in the resulting offspring, the percentages of parental and recombinant offspring are about the same, this would indicate that the two genes are __________.

unlinked

Female mammals have two X chromosomes, one from their mother and one from their father. During X inactivation, one X chromosome in each embryonic cell is randomly inactivated; therefore, all of the tissues that arise from that cell have the same inactivated X chromosome. Female mammals are therefore considered to be __________ of the maternal and paternal cells.

a mosaic

Why did Morgan choose Drosophila for his genetics experiments?

A single mating can produce many offspring and Drosophila chromosomes can be easily distinguishable under a light microscope.

Duchenne muscular dystrophy is caused by a sex-linked recessive allele. Its victims are almost invariably boys, who usually die before the age of 20. Why is this disorder almost never seen in girls?

To express an X-linked recessive allele, a female must have two copies of the allele.

Individuals with an extra X chromosome __________.

may have subnormal intelligence or be at risk for learning disabilities

With a microscope, you examine some somatic cells from a woman and notice that each nucleus has two Barr bodies. What can you infer about the sex chromosomes in this individual?

She is XXX.

Compared to peas, fruit flies were thought to have no variations, until the discovery of a __________ fly by __________.

male white-eyed; Morgan

Linked genes __________.

are located near each other on the same chromosome

Wild type refers to __________.

the most common phenotype thought to be found in the natural population

X inactivation occurs when there is/are at least __________ X chromosomes present in an individual, forming a structure called a __________ by a __________ event.

two; Barr body; random

In an X-linked, or sex-linked, trait, it is the contribution of __________ that determines whether a son will display the trait.

the mother

What appears to be the mechanism for genomic imprinting?

DNA methylation that silences particular genes and DNA methylation that activates particular genes

The __________ states that genes have specific positions on chromosomes and that chromosomes undergo both __________ and __________.

chromosomal theory of inheritance; segregation; independent assortment