Bio 108 Master Biology 9 - Chapter 15

Humans are diploid and have 46 chromosomes (or two sets). How many sets of chromosomes are found in each human gamete?

1

You are investigating the inheritance of two rare conditions (A and B) in an extended family of thoroughbred racehorses. You have constructed the following pedigree for these conditions. Identify the inheritance mode of each condition by using the labels to complete the table. Labels can be used once, more than once, or not at all.

Condition A: autosomal recessive Condition B: X-linked recessive

In one of Morgan's experiments, he crossed his newly discovered white-eyed male with a red-eyed female. (Note that all of the females at that time were homozygous for red eyes because the allele for white eyes had not yet propagated through Morgan's flies.) All of the F1 flies produced by this cross (both males and females) had red eyes. Next, Morgan crossed the red-eyed F1 males with the red-eyed F1 females to produce an F2 generation. The Punnett square below shows Morgan's cross of the F1 males with the F1 females. Drag the labels to their appropriate locations to complete the Punnett square for Morgan's F1 x F1 cross.

a) w+ b) w c) w+w+ d) w+Y e)w+w f) wY

What is nondisjunction?

an error in cell division that causes homologous chromosomes or sister chromatids move to the same side of the dividing cell.

What results if a fragment of a chromosome breaks off and then reattaches to the original chromosome at the same place but in the reverse direction?

an inversion

What name is given to the most common phenotype in a natural population?

wild type

Now, suppose that the three tomato genes from Part A did not assort independently, but instead were linked to one another on the same chromosome. Would you expect the phenotypic ratio in the offspring to change? If so, how? Which statement best predicts the results of the cross MmDdPp x mmddpp assuming that all three genes are linked?

All eight possible phenotypes could occur, but a greater proportion of the offspring would have the parental phenotypes.

Mutant tetraploid plants __________.

are unable to interbreed with a diploid plant

__________ is the process by which haploid gametes from a diploid zygote.

fertilization

How are human mitochondria inherited?

from the mother only

Most polyploid plants arise as a result of __________.

hybridization

The pedigree from Part B is shown below. Female III-4 is pregnant via male III-5. The owner of this breeding pair wants to know the probabilities of several possible outcomes for their offspring (IV-3). 1. What is the probability that IV-3 will have condition A? 2. What is the probability that IV-3 will have condition B? 3. What is the probability that IV-3 will have both conditions? 4. What is the probability that IV-3 will have neither condition? 5. What is the probability that IV-3 will have at least of of the two conditions?

1. 1/36 2. 1/8 3. 1/288 4. 245/288 5. 43/288

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.

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 ration of 9 to 3 to 3 to 1.

When can nondisjunction occur? Choose the best answer.

All three answers are correct. (in meiosis, when homologous chromosomes fail to separate. in meiosis, when sister chromatids fail to separate. In mitosis, when sister chromatids fail to separate.)

A white-eyed female Drosophila is crossed with a red-eyed male Drosophila. Which statement below correctly describes the results?

None of the females will have white eyes.

Suppose that you perform the cross discussed in Part B: MmDdPp x mmddpp. You plant 1000 tomato seeds resulting from the cross, and get the following results: PhenotypeGenotypeNumber of individualssolid, normal, smoothMmDdPp420solid, normal, peachMmDdpp21solid, dwarf, smoothMmddPp2solid, dwarf, peachMmddpp52mottled, normal, smooth mmDdPp62mottled, normal, peachmmDdpp4mottled, dwarf, smoothmmddPp23mottled, dwarf, peachmmddpp416 Use the data to complete the linkage map below.

a) 12cM b) 5cM c) d d) p

The pedigree from Part A is shown below. Fill in the most likely genotypes of the indicated individuals in the pedigree. Note that a dominant allele followed by an underscore (_) indicates that either the dominant or the recessive allele may be present at the second position. Drag one label (for condition A, autosomal recessive) to each target in Group 1. Drag one label (for condition B, X-linked recessive) to each target in Group 2. Labels can be used once, more than once, or not at all.

a) AA b) XBXb c) A_ d) XBY e) A_ f) XBY g) AA h) XBXB i) A_ j) XBX- k) A_ l) XBY

Individual IV-3 is born as a male affected with condition B but not condition A. His parents are bred again, and an ultrasound shows that the fetus is another male. The relevant portion of the pedigree is shown below.Use this new information to determine the parents' genotypes (indicated by red arrows). Then calculate the probabilities that the second male offspring will have each condition.

a) A_ b) XBXb c) A_ d) XBY 1. What is the probability that IV-4 will have condition A? 1/36 2. What is the probability that IV-4 will have condition B? 1/2

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?

a) metaphase I b) anaphase I c) telophase II d) two chromosome arrangements equally probable at metaphase plate e) homologous chromosomes separate f) sister chromatids have separated g) chromosomes in haploid gametes combine in diploid zygote h) Y may sort with R or r, y may sort with R or r i) four types of gametes produced: YR, Yr, yR, and yr j) four phenotypes produced in F2 generation in 9:3:3:1 ratio

When Gregor Mendel conducted his genetic experiments with pea plants, he observed that a trait's inheritance pattern was the same regardless of whether the trait was inherited from the maternal or paternal parent. Mendel made these observations by carrying out reciprocal crosses: For example, he first crossed a female plant homozygous for yellow seeds with a male plant homozygous for green seeds, and then crossed a female plant homozygous for green seeds with a male plant homozygous for yellow seeds. Unlike Mendel, however, Morgan obtained very different results when he carried out reciprocal crosses involving eye color in his fruit flies. The diagram below shows Morgan's reciprocal cross: He first crossed a homozygous red-eyed female with a white-eyed male, and then crossed a homozygous white-eyed female with a red-eyed male. Drag the labels to their appropriate locations to complete the Punnett squares for Morgan's reciprocal cross.

a) wY b) Y c) w+ d) w+Y e) w+Y f) Y g) w h) wY

Which of the following results in a situation in which the chromosome number is either 2n+1 or 2n-1 ?

aneuploidy

The diagram below shows two normal chromosomes in a cell. Letters represent major segments of the chromosomes. (AB)(CDEFGH) (I)(JKLMN) The following table illustrates some structural mutations that involve one or both of these chromosomes. Identify the type of mutation that has led to each result shown.

1. (AB)(CDEFH) deletion 2. (I)(JNKLMN) duplication 3. (AB)(CLMN) (I)(JKDEFGH) translocation 4. (AEDC)(BFGH) inversion 5. (AB)(CDDCEFGH) duplication 6. (AB)(CDEKLMNFGH) (I)(J) translocation 7. (I)(JMLKN) inversion

A particular diploid plant has 48 chromosomes, or two sets. A mutation occurs and gametes with 48 chromosomes are produced. If self-fertilization occurs, the zygote will have __________ set(s) of chromosomes.

4

Suppose a diploid cell with three pairs of homologous chromosomes (2n=6) enters meiosis. How many chromosomes will the resulting gametes have in each of the following cases?

1. Meiosis occurs normally (no disjunction) 3 only 2.Nondisjunction of one chromosome pair in meiosis I 2 or 4 3. Nondisjunction of all three chromosome pairs in meiosis I (assume all chromosomes go to the same pole) 4. Nondisjunction of one chromosome in one daughter cell in meiosis II 2, 3, or 4 5. Nondisjunction of all three chromosomes in one daughter cell in meiosis II (assume all chromosomes go to the same pole) 0, 3, or 6

A wild-type tomato plant (Plant 1) is homozygous dominant for three traits: solid leaves (MM), normal height (DD), and smooth skin (PP). Another tomato plant (Plant 2) is homozygous recessive for the same three traits: mottled leaves (mm), dwarf height (dd), and peach skin (pp). In a cross between these two plants (MMDDPP x mmddpp), all offspring in the F1 generation are wild type and heterozygous for all three traits (MmDdPp). Now suppose you perform a testcross on one of the F1 plants (MmDdPp x mmddpp). The F2 generation can include plants with these eight possible phenotypes: solid normal smooth:solid normal peach:solid dwarf smooth:slide dwarf peach:mottled normal peach:mottled dwarf smooth:mottled dwarf peach

1:1:1:1:1:1:1:1

Humans are diploid have 46 chromosomes. How many chromosomes are found inch human gamete?

23

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 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: 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.

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

Down syndrome is caused by trisomy 21, the presence of three copies of chromosome 21. The extra copy usually results from nondisjunction during meiosis. In some cases, however, the extra copy results from a translocation of most of chromosome 21 onto chromosome 14. A person who has had such a translocation in his or her gamete-producing cells is a carrier of familial Down syndrome. The carrier is normal because he or she still has two copies of all the essential genes on chromosome 21, despite the translocation. However, the same may not be true for the carrier's offspring.The diagram shows the six possible gametes that a carrier of familial Down syndrome could produce. Suppose that a carrier of familial Down syndrome mated with a person with a normal karyotype. Which gamete from the carrier parent could fuse with a gamete from the normal parent to produce a trisomy-21 zygote?

gamete from carrier of familial Down syndrome: 14(green)21(yellow) 21(yellow) trisomy-21 zygote 14(green) 14(green)21(yellow) 21(yellow) 21(yellow)

What can we observe in order to visualize Mendel's Law of Segregation?

homologous chromosomes separating during meiosis I

Which of these terms applies to an organism with extra sets of chromosomes?

polyploid

Consider the following family history: -Bob has a genetic condition that affects his skin. -Bob's wife, Eleanor, has normal skin. No on in Eleanor's family has ever had the skin condition. -Bob and Eleanor have a large family. Of their eleven children, all six of their sons have normal skin, but all five of their daughters have the same skin condition as Bob. Based on Bob and Eleanor's family history, what inheritance pattern does the skin condition most likely follow?

x-linked dominant