bio 111 chapter 13 hw1

A test cross can be used to do all of the following except

identify the chromosome on which a gene is located.

Genetic maps are based on recombination frequencies. However, because some multiple crossovers produce parental rather than recombinant gametes, as the physical distance between two loci increases, the maximum recombination frequency levels off at 50%. But suppose you discovered a species where the location of each crossover event occurs at random but there is only one crossover per chromosome and no multiple crossovers occur. In this case, as the physical distance between two loci increases, you would expect the recombination frequency to

increase until it reaches 100%

A human female with only one X chromosome is said to have a condition called

Turner syndrome.

In sickle cell anemia, the defective hemoglobin differs from the normal hemoglobin by

a single amino acid substitution.

In humans, if non-disjunction led to an individual with a genotype of XO, that person would

be female because each cell lacks a Y chromosome.

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.

In Drosophila, the sex of an individual is determined by

the number of X chromosomes

Indicate whether each of the following statements about sex chromosomes in mammals is true or false. false= 1235

01. Dosage compensation involves inactivation of the Y chromosome in males in order to equalize gene expression between the sexes. false 02. 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 03. In a female, the same X chromosome is inactivated in all cells. false 04. 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 05. In males, the inactivated and highly condensed Y chromosome is visible as an intensely staining Barr body attached to the nuclear membrane. false 06. Calico cats are heterozygous for alleles on the X chromosome that produce either black fur or orange fur. true 07. 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 08. Only females can be calico cats. true

Indicate whether each of the following statements about sex determination is true or false. false= 124689

01. In honeybees, haploid individuals develop into females and diploid individuals develop into males. false 02. The form of sex determination found in humans is universal among vertebrates. false 03. Among fish and some species of reptiles, environmental factors can affect gene expression and thus alter the sex of adult individuals. true 04. 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 05. In both humans and Drosophila, XX individuals are female and XY individuals are male. true 06. In both humans and Drosophila, XXY individuals are male. false 07. Some insects have no Y chromosome; females are XX and males are XO (where the O indicates the absence of a chromosome). true 08. In humans, movement of part of the X chromosome to the Y chromosome can cause otherwise XX individuals to develop as males. false 09. In humans, mutations in the SRY gene can cause XX individuals to develop as males. false 10. The number and structure of sex chromosomes vary in different species. true

Indicate whether each of the following statements about genetic recombination is true or false. f=4 5 6 7 8 11 12

01. 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 02. Crossing over involves the physical exchange of genetic material between homologous chromosomes during Prophase I of meiosis. true 03. 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, etc.) occur, then the chromosomes will carry the original parental combination of alleles. true 04. As the physical distance separating two gene loci increases, the probability that crossing over will occur between them decreases. false 05. 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 06. 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 07. Recombination frequency equals the number of recombinant progeny divided by the number of parental progeny. false 08. The distance between two linked gene loci can be determined by crossing doubly heterozygous individuals with individuals who are homozygous for both dominant alleles and then counting progeny to determine the percent recombination. false 09. When constructing genetic maps, each 1% of recombination is equal to a distance of 1 map unit or 1 cM. true 10. As the distance between two gene loci increases, the frequency of multiple crossovers between the two loci also increases. true 11. In order for two gene loci to assort independently, they must be located on different chromosomes. false

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 percentage of the F1 flies are expected to be heterozygous at both gene loci? ( Enter the number only without the percent sign. For example, enter 100% as 100 and enter 12.5% as 12.5 )

100

In humans, individuals with trisomy of the ______ chromosome are most likely to survive until adulthood.

21st

In humans, hemophilia is caused by a recessive allele on the X chromosome. Therefore, if a female with hemophilia marries a normal male, the probability that their first child will be a girl with hemophilia is zero. This assumes normal dosage compensation where the X that is inactivated in females varies randomly from cell to cell. But suppose the normal mechanism of dosage compensation is altered so that the X that is inactivated in any given female is random but the same X is inactivated in every cell of her body. In this case, what is the probability that their first child would be a girl with hemophilia? ( Express the probability as a percent. Enter the number only without the percent sign. For example, enter 100% as 100 and enter 12.5% as 12.5 )

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

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 marries a blue-eyed man who is not colorblind, the probability that their first child will be a brown-eyed, colorblind male is 1 in

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 marries 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 males 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 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 are 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.

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.

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 wing scales and decide to cross it with a wild type female that has gray wing scales. Half of the F1 progeny have black wing scales but all of these F1 progeny with black wing scales are males. Based on these results, a valid hypothesis would be

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

You are studying the genetics of a species where males are ZZ (the 2 sex chromosomes are homologous) and females are ZW (the 2 sex chromosomes are not homologous.) Dosage compensation in this species could be achieved if

Females double the expression of genes on the Z chromosome in each cell

In some species, sex determination is influenced by environmental temperature during development. If you wanted to determine the temperature at which one would obtain a 1:1 sex ratio in a particular species of turtle, which of the following experiments would best address this question?

Grow the turtles in five different incubators at temperatures of 22ºC, 24ºC, 26ºC, 28ºC, and 30ºC.

______________ is a human hereditary disease that is caused by a dominant allele but does not show up in affected individuals until they are in middle age.

Huntington's disease

Huntington's disease is caused by a single dominant allele. It is a lethal disease, yet it persists in the human population. Which of the following statements best describes why?

Huntington's disease presents symptoms in mid-life, after most people have already had offspring.

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

The geneticist who discovered the white eye mutation in Drosophila and helped establish that genes are carried on chromosomes was

Morgan.

The number of allele pairs that assort independently in an organism is generally much higher than the number of chromosome pairs. This phenomenon is due to

crossing over.

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

it is usually inherited entirely from the mother

A genetic _____ indicates the distances between gene loci measured in terms oIn Drosophila, the sex of an individual is determined by f the frequency of recombination.

map

Occasionally, chromosomes fail to separate during meiosis, leading to daughter cells that have an abnormal number of chromosomes. This phenomenon is called

nondisjunction.

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.

Sickle cell anemia is caused by a defect in the

oxygen-carrying pigment hemoglobin.

The classic experiments performed by Creighton and McClintock in Maize

provided evidence for the physical exchange of genetic material between homologues.

Traits that are controlled by genes located on the X chromosome are said to be ________________.

sex-linked

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.