Chapter 13: Homework

When gene loci are close together on the same chromosome, the number of recombinant progeny is higher than the number of parental progeny, and the genes are said to be linked.

false

The genotype of the female is best represented as _________.

ww

Which of the following can directly cause genetic disease? Check all that apply.

- altering a single base pair in the DNA of an organism - altering multiple base pairs in the DNA of an organism - a mutation that alters a single amino acid within a protein - a mutation that alters several amino acids within a protein - a mutation that changes a gene that codes for a normal protein into a gene that codes for a defective protein or no protein at all - loss of a small section of a chromosome - one or more extra chromosomes - one or more missing chromosomes

Among the female F1 offspring, the predicted proportion with white eyes is _________.

0%

In the fruit fly Drosophila, there is a dominant gene for normal wing shape and its recessive allele for dumpy wings. At another gene locus on the same chromosome, there is a dominant gene for tan body color and its recessive allele for ebony body color. A male that is homozygous for both dominant alleles is crossed with a female that is homozygous for both recessive alleles. What percentage of the F1 flies are expected to be heterozygous at both gene loci? (Enter the number only without the percent sign. For example, 100% as 100 and enter 12.5% at 12.5)

100

Among the male F1 offspring, the predicted proportion with white eyes is _________.

100%

If you assume that these two allele pairs are located on two different pairs of homologous chromosomes, the expected frequency of flies with normal wings and red eyes in the F1 generation is ________.

25%

In the fruit fly Drosophila, the gene "T" for tan body color is dominant to its allele "t" for ebony body color. At another gene locus on the same chromosome the gene "B" for normal bristles is dominant to its allele "b" for short bristles. Two flies are crossed that both have the same genotype: the alleles "T" and "B" are on one chromosome and the alleles "t" and "b" are on the homologous chromosome. If we assume that no crossing over occurs between these two gene loci, what proportion of the offspring are expected to have normal bristles and tan body color?

3/4

In the fruit fly Drosophila, there is a dominant gene for normal wing shape and its recessive allele for dumpy wings. At another gene locus on the same chromosome, there is a dominant gene for tan body color and its recessive allele for ebony body color. A male that is homozygous for both dominant alleles is crossed with a female that is homozygous for both recessive alleles. If we assume that no crossing over occurs between these two gene loci, what proportion of the F2 flies are expected to have normal wings and tan body color?

3/4

In the fruit fly Drosophila, the gene "T" for tan body color is dominant to its allele "t" for ebony body color. At another gene locus on the same chromosome the gene "B" for normal bristles is dominant to its allele "b" for short bristles. Two flies are crossed that both have the same genotype: the alleles "T" and "B" are on one chromosome and the alleles "t" and "b" are on the homologous chromosome. If we assume that no crossing over occurs between these two gene loci, what is the expected phenotypic ratio among the offspring?

3:1

In this experiment, the mating produced 1,000 flies and 470 have normal wings and red eyes. The observed frequency of flies with normal wings and red eyes in the F1 generation is ______.

47%

At an autosomal gene locus in humans, the allele for brown eyes is dominant over the allele for blue eyes. At another gene locus, located on the X chromosome, a recessive allele produces colorblindness while the dominant allele produces normal color vision. A heterozygous brown-eyed woman who is a carrier of colorblindness has children with a blue-eyed man who is not colorblind. The woman becomes pregnant and an ultrasound test shows that the child is a boy. What is the probability that he will be colorblind?

50

Among all F2 offspring, the predicted proportion with white eyes is _______.

50%

If you assume that these two allele pairs are located on the same pair of homologous chromosomes (with both dominant alleles on one homologue and both recessive alleles on the other homologue) and no crossing over occurs between them, the expected frequency of flies with normal wings and red eyes in the F1 generation is _____.

50%

At an autosomal gene locus in humans, the allele for brown eyes is dominant over the allele for blue eyes. At another gene locus, located on the X chromosome, a recessive allele produces colorblindness while the dominant allele produces normal color vision. If a heterozygous brown-eyed woman who is a carrier of colorblindness has children with a blue-eyed man who is not colorblind, the probability that their first child will be a brown-eyed, colorblind male is 1 in

8

In 1910, Morgan did a series of experiments with the fruit fly Drosophila, an organism where females are XX and make are XY. When a mutant male fly with white eyes was crossed with a wild type female with red eyes, none of the F1 progeny had white eyes but 18% of the F2 flies had white eyes. Unexpectedly, all of these white-eyed F2 flies were males. From these results, Morgan concluded that the white eye trait is caused by a recessive allele located on the X chromosome. Instead of fruit flies, suppose Morgan had done his experiments with grasshoppers, where females were XX and males are XO. In this case, if a male with a recessive X-linked trait was crossed with a wild-type female, what would you expect among the F2 progeny?

All the F2 progeny with the recessive trait would be males.

The developmental defects associated with three copies of chromosome 21 are referred to as _____________________.

Down syndrome

Suppose you are carrying out a series of crosses with an insect where the mechanism of sex determination is unknown. You discover a mutant male with black wings and decide to cross it with a wild type female that has gray wings. Half of the F1 progeny have black wings but all of these F1 progeny with black wings are females. Based on these results, a valid hypothesis would be

Females are XX, males are XY and wing scales are caused by a dominant allele on the X chromosome.

Dosage compensation involves inactivation of the Y chromosome in males in order to equalize gene expression between the sexes.

false

If two gene loci are located on the same chromosome, then chromosomes that are recombinant for these two loci will be produced if an odd number of crossovers occur anywhere along the length of the chromosome.

false

The developmental defects associated with two X chromosomes and one Y chromosome are referred to as ________________.

Kleinfelter syndrome

Suppose you are carrying out a series of crosses with an insect where the mechanism of sex determination is unknown. You discover a mutant female with short wings and decide to cross it with a wild type male that has normal wings. None of the F1 progeny have short wings but among the F2 progeny 26% have short wings. However, all of these short-winged F2 progeny are females. Based on these results, a valid hypothesis would be

Males are ZZ, females are ZW, and short wings is caused by a recessive allele on the Z chromosome.

In a female, the same X chromosome is inactivated in all cells.

false

In both humans and Drosophila, XXY individuals are male.

false

In honeybees, haploid individuals develop into females and diploid individuals develop into males.

false

In humans, movement of part of the X chromosome to the Y chromosome can cause otherwise XX individuals to develop as males.

false

In humans, mutations in the SRY gene can cause XX individuals to develop as males.

false

In humans, some of the active genes on the X chromosome, notably the SRY gene, are responsible for the development of male genitalia and secondary sex organs.

false

In males, the inactivated and highly condensed Y chromosome is visible as an intensely staining Barr body attached to the nuclear membrane.

false

The developmental defects associated with a single X chromosome and no Y chromosome are referred to as ___________.

Turner syndrome

The genotype of the male is best represented as ________.

WY

In order for two gene loci to assort independently, they must be located on different chromosomes.

false

Having one or more extra or missing chromosomes is called _____________.

aneuploidy

One of the X chromosomes in each cell of a female is inactivated early in embryonic development, before the embryo's sex is determined.

false

Recombination frequency equals the number of recombinant progeny divided by the number of parental progeny.

false

The genotypes of all or most of the 56 F, flies that have either vestigial wings and red eyes OR normal wings and purple eyes were most likely caused by the process of ________________.

crossing over

The distance between two linked gene loci can be determined by crossing doubly heterozygous individuals who are homozygous for both dominant alleles and then counting progeny to determine the percent recombination.

false

The form of sex determination found in humans is universal among vertebrates.

false

As the physical distance separating two gene loci increases, the probability that crossing over will occur between them decreases.

false

Because multiple crossovers no not always produce recombinant progeny, longer map distances are more accurate than shorter map distances.

false

Which of the following best describes the pattern of inheritance for mitochondrial DNA?

it is usually inherited entirely from the mother

Humans that are missing a single autosome are called _______________.

monosomics

During meiosis, the process of _______________ produces gametes, and therefore offspring, that have extra or missing chromosomes.

nondisjunction

You examine the F1 offspring from this cross and count the following: 470 normal wings with red eyes, 30 vestigial wings with red eyes, 26 normal wings with purple eyes, and 474 vestigial wings with purple eyes. Based on these results, these two gene loci are probably located ________________________________.

on the same chromosome

Traits controlled by organellar DNA do not show Mendelian inheritance because

organellar DNA is not partitioned with the nuclear genome by the process of meiosis

Female gametes with no sex chromosomes are produced when the two X chromosomes fail to ______________ during meiosis.

separate

Genomic imprinting leads to non-Mendelian inheritance because in genomic imprinting

the expression of an allele varies depending on which parent it was inherited from.

Morgan's experiments with red and white eye color in the fruit fly Drosophila provided evidence that alleles are located on chromosomes because

the results of his crosses could be explained if he assumed that the alleles controlling eye color are located on the X chromosome.

Humans that have one extra autosome, in addition to the normal diploid number, are called ____________.

trisomics

Among fish and some species of reptiles, environmental factors can affect gene expression and thus alter the sex of adult individuals.

true

As the distance between two gene loci increases, the frequency of multiple crossovers between the two loci also increases.

true

Calico cats are heterozygous for alleles on the X chromosome that produce either black fur or orange fur.

true

Crossing over involves the physical exchange of genetic material between homologous chromosomes during Prophase I of meiosis.

true

If a female is heterozygous for an X-linked trait, some of her cells will express one allele and some the other, resulting in a genetic mosaic.

true

If an odd number of crossovers (1,3,5,etc...) occurs between two gene loci, it leads to the production of chromosomes that are recombinant for those two loci; if no crossovers or an even number of crossovers (2,4,6,8,etc...) occur, then the chromosomes will carry the original parental combination of alleles.

true

In both humans and Drosophila, XX individuals are female and XY individuals are male.

true

In calico cats, whether the fur in a particular area is black or orange depends on which of the two X chromosomes is inactivated.

true

Only females can be calico cats.

true

Some insects have no Y chromosome; females are XX and males are XO (where the O indicates the absence of a chromosome).

true

The independent assortment of traits that Mendel observed during his dihybrid crosses is due to crossing over and the independent assortment of chromosomes during meiosis.

true

The number and structure of sex chromosomes vary in different species.

true

When constructing genetic maps, each 1% of recombination is equal to a distance of 1 map unit or 1 cM.

true