Mastering Biology Ch. 15a HW

Cinnabar eye color is an X-linked, recessive characteristic in fruit flies. If a female having cinnabar eyes is crossed with a male having wild-type, red eyes, what percent of the F1 males will have cinnabar eyes?

100%

A sexually reproducing animal has two unlinked genes, one for head shape (H) and one for tail length (T). Its genotype is HhTt. Which of the following genotypes for these two genes is possible in a gamete from this organism?

HT

In cats, an X-linked locus is responsible for fur color. There are two known alleles at this locus. One results in black fur color; the other results in orange fur color. A heterozygote animal has patches of orange and black fur (tortoiseshell). Which coat color phenotypes are expected from the cross of a black female and an orange male?

tortoiseshell females; black males

At the time of Mendel's pea plant experiments, no one knew how organisms formed gametes. As Mendel studied the inheritance of two different characters, he wondered how the alleles for the two characters segregated into gametes. Mendel had two hypotheses for how this might work. Under the hypothesis of dependent assortment, the alleles inherited from the parental generation should always be transmitted to the next generation in the same combinations. Under the hypothesis of independent assortment, alleles for different characters should segregate independently of each other, meaning that alleles should be packaged into gametes in all possible combinations, as long as each gamete has one allele for each gene. The figure below shows the experiment that Mendel used to distinguish between these two hypotheses. The results of the experiment confirmed that the alleles for these characters undergo independent assortment. Drag the terms to the appropriate blanks to complete the sentences below. Not all terms will be used.

1. In the P generation, a true-breeding pea plant with genotype YYRR is crossed with a true-breeding plant with genotype yyrr. 2. The resulting offspring--the F1 generation--have genotype YyRr. 3. According to Mendel's law of independent assortment, the alleles for seed color and seed shape are transmitted into gametes in all possible combinations. 4. This means that the F1 generation makes gametes with the following genotypes: YR, Yr, yR, yr. 5. At fertilization, two gametes (egg and sperm) come together. The resulting F2 generation exhibits four different phenotypes in the ratio of 9 to 3 to 3 to 1.

A recessive allele on the X chromosome is responsible for red-green color blindness in humans. A woman with normal vision whose father is color blind has children with a color-blind male. What is the probability that this couple's first son will be color blind?

1/2

Imagine a human disorder that is inherited as a dominant, X-linked trait. How would the frequency of this disorder vary between males and females?

Females would display this disorder with greater frequency than males. Men have only one X chromosome, whereas women have two. Thus, women have twice the chance of inheriting the dominant allele that causes this disorder. Remember that the disorder is caused by a dominant allele, so an individual who inherits a single dominant allele will display the disorder. Read about the inheritance of X-linked genes.

In biology lab, you conduct a breeding experiment to test Mendel's law of independent assortment. You study two characters in a new plant species recently discovered on campus:Flower color, which can be blue (BB) or purple (bb)Petal shape, which can be pointy (PP) or rounded (pp) You use the following procedure. In the parental generation, you breed a plant that you know to be homozygous for blue-pointy flowers (BBPP) with a plant that you know to be homozygous for purple-rounded flowers (bbpp). In the F1 generation, all your plants have blue-pointy flowers (BbPp). You then allow the F1 plants to self-pollinate to produce F2 offspring. In the F2 generation, you obtain 80 plants with the following phenotypes. Note that an underscore "_" in the genotype indicates that the second allele for that gene could be either dominant or recessive: PhenotypeNumber of individualsBlue flower/pointy petal (B_P_)59Blue flower/rounded petal (B_pp)1Purple flower/pointy petal (bbP_)0Purple flower/rounded petal (bbpp)20 To try to explain this unusual data, you come up with two alternate hypotheses in addition to your original hypothesis of independent assortment. Hypothesis 1: The alleles for flower color and petal shape are found on different chromosomes. (This is independent assortment as observed by Mendel with the characters of seed color and shape.) Hypothesis 2: The alleles for flower color and petal shape are found on different chromosomes, but the blue-rounded (B_pp) and purple-pointy (bbP_) phenotypes typically do not survive, for a reason that has yet to be determined. Hypothesis 3: The alleles for flower color and petal shape are found close to each other on the same chromosome. Drag the labels to their appropriate locations in the table below. Labels may be used more than once. (Hint: First, figure out the predicted F1 gametes for each hypothesis; then construct a Punnett square to help you fill in the rest of the table.)

Hypothesis 1: a. no Hypothesis 2: -b. BP, Bp, bP, bp in equal numbers, d. 2 predominant phenotypes, f. 9 blue-pointy:1 purple-rounded, h. no Hypothesis 3: c. mostly BP and bp, e. 2 predominant phenotypes, 3 blue-pointy:1 purple-rounded, i. yes

In the figure below, you can see Mendel's experiment again, this time superimposed on the events of meiosis and fertilization. How does chromosomal inheritance during meiosis explain Mendel's law of independent assortment? Drag the labels to their appropriate locations in the table below. The number at the top of each column corresponds to the same number in the image above. Each column describes what happens at that numbered stage.

Phase of meiosis/fertilization: a. metaphase I, b. anaphase I, c. telophase II Chromosome behavior: d. two chromosome probable at metaphase plate, e. homologous chromosomes separate, f. sister chromatids have separated, g. chromosomes in haploid gametes combine in diploid zygote. Allele assortment for seed color and seed shape: h. Y may sort with R or r; Y may sort with R or r, i. Four types of gametes produced: YR, Yr, yR, yr, j. Four phenotypes produced in F2 generation in 9:3:3:1 ratio

Which of these descriptions of the behavior of chromosomes during meiosis explains Mendel's law of independent assortment?

The arrangement of each pair of homologous chromosomes on the metaphase plate during metaphase I is random with respect to the arrangements of other pairs.

In humans, what determines the sex of offspring, and why?

The male gamete determines sex, because each male gamete can contribute either an X or a Y chromosome. In humans, the male produces both X- and Y-bearing sperm, whereas females only produce X-bearing eggs

Select the correct statement(s) about sex determination in animals.

The mechanism of sex determination varies with different animal species. There are various chromosomal systems for sex determination found in animals.

Which of these descriptions of the behavior of chromosomes during meiosis explains Mendel's law of segregation?

The two alleles for each gene separate as homologous chromosomes move apart during anaphase I.

Red-green color blindness is an X-linked recessive trait in humans. Two people with normal color vision have a son with colorblindness. Given this information, the genotypes of the parents are ________.

XNXn and XNY

Males are more often affected by X-linked traits than are females because ________.

males are hemizygous genes on the X chromosomes

Video Tutor Session Quiz: Sex-Linked Pedigrees

part a: X^H Y^0 part b: it could be X^B X^B or X^B X^b part c: 100% part d: X^B X^b part e: it could be X^B X^B or X^B X^b