Explain why mitosis does not produce genetic variation and how meiosis leads to the production of tremendous genetic variation. For example, karyotyping extracting chromosomes from a single cell and photographing them to look for abnormalities is performed on metaphase, rather than interphase, cells. List and briefly describe three major cell cycle checkpoints.
For each checkpoint, predict the consequences if the checkpoint fails to work properly. Indicate centromeres with a small circle, and place the alleles A and a on each of the chromatids. Place the alleles A and a on each of the chromatids. The cells illustrated here belong to a species with a diploid chromosome number of four.
Each of the following cells is in which stage of mitosis or meiosis? Chromosomes condense during. Sister chromatids separate during. Chromosomes are randomly partitioned during , contributing to genetic diversity. Crossing over genetic recombination occurs in. List two differences and two similarities between mitosis and meiosis.
The cells of a mature pea plant have 14 chromosomes. In a pea plant ovary, how many chromosomes would the nucleus of a megaspore contain? How many chromosomes does a nucleus in the pea endosperm contain? Which of the following processes is unique to plants? A meiosis B double fertilization C crossing over D haploid gametes E spermatogenesis. How many different combinations in the gametes are possible? The following figure shows a chromosomal separation taking place.
The letters stand for genes; capital and lowercase letters stand for different alleles. The diploid chromosome number in this organism is four. What process is shown? In a flowering plant, the male part of the flower the stamen produces haploid microspores that divide by to eventually produce sperm.
A mitosis B meiosis C gametogenesis D spermatogenesis E fertilization. In a typical flowering plant, a pollen grain that lands on a stigma grows a pollen tube to deliver how many? Fusion of a sperm with an egg produces a n cell called a. A 1; 1; zygote B 2; 1; megasporocyte C 2; 2; zygote D 1; 2; microsporocyte E 1; 2; megasporocyte To provide food for the developing embryo, a tissue called endosperm is produced through double fertilization.
Endosperm has a ploidy of: A 1n. What might be the result if the breakdown of the shugoshin protein were premature? A The cohesion protein would hold the chromosome arms together longer. B The separation of homologous chromosomes would occur prematurely.
C The separation of sister chromatids would occur prematurely. D Spindle fibers would not form. E Sister chromatids would never separate. As in humans, sex chromosomes determine sex: XX in females and XY in males.
What is the total number of telomeres in a rat cell in G2? What is the total number of chromosomes present in the cell during metaphase I of meiosis? What is the total number of chromosomes in a polar body cell from a rat? A geneticist observes 10 pairs of homologous chromosomes at metaphase I of meiosis in a newly discovered species of flowering plant.
How many chromosomes should be found in a microsporocyte? Assume that cells that are about to undergo meiosis are treated with a chemical that blocks crossing over but does not affect the cells in any other way, and four viable cells are produced by the two divisions of meiosis. What will be the consequence of such a treatment? A The four products of meiosis will be genetically identical.
B The four products of meiosis will all be genetically unique. C All the chromosomes of two of the products of meiosis will have chromosomes that are paternal in origin but the other two products will have chromosomes that are of both paternal and maternal origins. D All the chromosomes of two of the products of meiosis will have chromosomes that are maternal in origin but the other two products will have chromosomes that are of both paternal and maternal origins.
E Two of the products will be genetically identical but genetically different from the other two products, which will also be genetically identical. Assume the second meiotic division is normal. How many chromosomes would be expected in the four cellular products of this meiotic event? A All four cells would have four chromosomes. B All four cells would have three chromosomes. C Two cells would have three chromosomes and two cells would have five chromosomes.
D Two cells would have six chromosome and two cells would have 10 chromosomes. E One cell would have three chromosomes, one cell would have five chromosomes, and two cells would have four chromosomes. Humans have 23 pairs of chromosomes.
The location and presence of a centromere are determined by the attachment of the spindle fibers to the chromosome, which occurs at the centromere in the above diagram. Only the cell in stage a clearly has homologous pairs of chromosomes. So the diploid chromosome number for cells of this species of plant is six. Give the names of each stage of mitosis or meiosis shown. Solution: Cell 1 is undergoing anaphase of meiosis I, as indicated by the separation of the homologous pairs of chromosomes.
Cell 2 in the diagram contains six chromosomes, the diploid chromosome number for this species. Also in this cell, sister chromatids have separated, resulting in a doubling of the chromosome number within the cell from six to Based on the number of chromosomes, the separation of sister chromatids in this cell must be occurring during anaphase of mitosis. In cell 3 again, sister chromatids are being separated, but the number of chromosomes present in the cell is only six.
This indicates that no homologs are present within the cell, so in this cell the separation of sister chromatids is occurring in anaphase II of meiosis. Give the number of chromosomes and number of DNA molecules per cell present at each stage.
Solution: Cell 1, which is in anaphase I of meiosis contains six chromosomes and 12 DNA molecules or sister chromatids. Cell 2 has 12 chromosomes and 12 DNA molecules in anaphase of mitosis.
The amount of DNA per cell of a particular species is measured in cells found at various stages of meiosis, and the following amounts are obtained: Amount of DNA per cell in pictograms pg 3. Match the amounts of DNA above with the corresponding stages of meosis a through f.
You may use more than one stage for each amount of DNA. Stage of meiosis a. G1 Solution: 7. Prophase I Solution: The homologous chromosomes are still located within a single cell, and there are two sister chromatids per chromosome. G2 Solution: Following telophase II and cytokinesis Solution: 3. By the completion of cytokinesis associated with meiosis II, both homologous pairs of chromosomes and sister chromatids have been separated into different daughter cells.
Therefore, each daughter cell will contain only one-half the amount of DNA of the original cell in G1. Anaphase I Solution: Metaphase II Solution: 7. In metaphase II of meiosis, the amount of DNA in each cell is the same as G1 because each chromosome still consists of two DNA molecules two sister chromatids per chromosome. The amount of DNA in the cell will be doubled after the completion of S phase in the cell cycle and prior to cytokinesis in either mitosis or meiosis I.
How would each of the following events affect the outcome of mitosis or meiosis? Mitotic cohesin fails to form early in mitosis. Solution: Cohesin is necessary to hold the sister chromatids together until anaphase of mitosis. If cohesin fails to form early in mitosis, the sister chromatids could separate prior to.
The result would be improper segregation of chromosomes to daughter cells. Shugoshin is absent during meiosis. Solution: Shugoshin protects cohesin proteins from degradation at the centromere during meiosis I. Cohesin at the arms of the homologous chromosomes is not protected by shugoshin and is broken in anaphase I, allowing for the two homologs to separate. If shugosin is absent during meiosis, then the cohesin at the centromere may be broken, allowing for the separation of sister chromatids along with the homologs during anaphase I, leading to improper segregation of chromosomes to daughter cells.
Shugoshin does not break down after anaphase I of meiosis. Solution: If shugoshin is not broken down, then the cohesins at the centromere will remain protected from degradation. The intact cohesins will prevent the sister chromatids from separating during anaphase II of meiosis, resulting in an improper separation of sister chromatids and daughter cells with too many or too few chromosomes.
Separase is defective. Solution: Homologous chromosomes and sister chromatids would not separate in meiosis and mitosis, resulting in some cells that have too few chromosomes and some cells that have too many chromosomes. A cell in prophase II of meiosis contains 12 chromosomes. How many chromosomes would be present in a cell from the same organism if it were in prophase of mitosis?
Prophase I of meiosis? Solution: A cell in prophase II of meiosis will contain the haploid number of chromosomes. For this organism, 12 chromosomes represent the haploid chromosome number of a cell, or one complete set of chromosomes. A cell from the same organism that is undergoing prophase of mitosis would contain a diploid number of chromosomes, or two complete sets of chromosomes, which means that homologous pairs of chromosomes are present.
So a cell in this stage should contain 24 chromosomes. Homologous pairs of chromosomes have not been separated by prophase I of meiosis. During this stage, a cell of this organism will contain 24 chromosomes. A cell has eight chromosomes in G1 of interphase. Draw a picture of this cell with its chromosomes at the following stages. Indicate how many DNA molecules are present at each stage. Solution: a. Metaphase of mitosis. The fruit fly Drosophila melanogaster has four pairs of chromosomes, whereas the house fly Musca domestica has six pairs of chromosomes.
In which species would you expect to see more genetic variation among the progeny of a cross? Explain your answer. Solution: The progeny of an organism whose cells contain more homologous pairs of chromosomes should be expected to exhibit more variation.
The number of different combinations of chromosomes that are possible in the gametes is 2n, where n is equal to the number of homologous pairs of chromosomes. Allele M is located on the long arm of chromosome Ia, and allele m is located at the same position on chromosome Ib. Allele P is located on the short arm of chromosome Ia, and allele p is located at the same position on chromosome Ib. Allele R is located on chromosome IIa and allele r is located at the same position on chromosome IIb.
Draw these chromosomes, identifying genes M, m, P, p, R, and r, as they might appear in metaphase I of meiosis. Assume that there is no crossing over. Solution: M M. A horse has 64 chromosomes and a donkey has 62 chromosomes. A cross between a female horse and a male donkey produces a mule, which is usually sterile.
How many chromosomes does a mule have? Can you think of any reasons for the fact that most mules are sterile? Solution: The haploid egg produced by the female horse contains 32 chromosomes. The haploid sperm produced by the male donkey contains 31 chromosomes. The union of the horse and donkey gametes will produce a zygote containing 63 chromosomes.
From the zygote, the adult mule will develop and will contain cells with a chromosome number of During the production of gametes by meiosis when pairing and separation of homologous chromosomes occurs, the odd chromosome will be unable to pair up. If improper synapsis or no synapsis occurs during prophase I, this will result in faulty segregation of chromosomes to the daughter cells produced at the conclusion of meiosis I.
This leads to gametes that have abnormal numbers of chromosomes. When these abnormal gametes unite, the resulting zygote has an abnormal number of chromosomes and will be nonviable. How many chromosomes and DNA molecules will be present in the following types of horse cells? Solution: Cell type a. Spermatogonium 64 64 Assuming the spermatogonium is in G1 prior to the production of sister chromatids in S phase, the chromosome number will be the diploid number of chromosomes.
First polar body 32 64 The first polar body is the product of meiosis I, so it will be haploid; but the sister chromatids have not separated, so each chromosome will consist of two sister chromatids. Primary oocyte 64 The primary oocyte has stopped in prophase I of meiosis. So the homologs have not yet separated, and each chromosome consists of two sister chromatids. Secondary spermatocyte 32 64 The secondary spermatocyte is a product of meiosis I and has yet to enter meiosis II.
So the secondary spermatocyte will be haploid because the homologous pairs were separated in meiosis I; but each chromosome is still composed of two sister chromatids. Indicate whether each of the following cells is haploid or diploid.
Haploid or Diploid? A primary oocyte divides to give rise to a secondary oocyte and a first polar body. The secondary oocyte then divides to give rise to an ovum and a second polar body. Is the genetic information found in the first polar body identical with that found in the secondary oocyte? Solution: No, the information is not identical with that found in the secondary oocyte. The first polar body and the secondary oocyte are the result of meiosis I.
In meiosis I, homologous chromosomes segregate and thus both the first polar body and secondary oocyte will contain only one member of each original chromosome pair, and these will have different alleles of some of the genes.
Also the recombination that took place in prophase I will have generated new and different arrangements of genetic material for each member of the pair. Is the genetic information found in the second polar body identical with that in the ovum? Solution: No, the information is not identical.
The second polar body and the ovum will contain the same members of the homologous pairs of chromosomes that were separated during meiosis I and produced by the separation of sister chromatids during anaphase II. However, the sister chromatids are no longer identical. The sister chromatids have undergone recombination during prophase I and thus contain genetic information that is not identical to the other sister chromatids.
Can you think of a reason why failure of chromosome division might be more common in female gametogenesis than male gametogenesis? Solution: Male gametogenesis, or spermatogenesis in human males, occurs regularly.
Once the spermatogonium begins meiosis, the process quickly goes to completion, resulting in the formation of four spermatids that can mature into sperm cells.
Female gametogenesis, or oogenesis in human females, is more complicated. Each oogonium enters meiosis I but stops at prophase I, generating a primary oocyte. This primary oocyte remains frozen in prophase I until ovulation begins and continues through meiosis I. Only if the egg is fertilized will meiosis II be completed. Because the primary oocyte is present at birth, the completion of meiosis I by a primary oocyte may not occur for many years 35 to 40 years or more.
The length of time could lead to degradation or damaging of the meiotic machinery such as the meiotic spindle fibers or cohesin complex. The damaged meiotic machinery could result in an improper separation of homologous pairs or of sister chromatids during the meiotic process.
The spermatogenesis process does not have this time delay, which may protect the process from age-induced damage to the meiotic machinery. On average, what proportion of the genome in the following pairs of humans would be exactly the same if no crossing over took place? For the purposes of this question only, we will ignore the special case of the X and Y sex chromosomes and assume that all genes are located on nonsex chromosomes.
Father and child Solution: The father will donate one-half of his chromosomes to his child. Therefore, the father and child will have one-half of their genomes that are similar. Mother and child. Solution: The mother will donate one-half of her chromosomes to her child. Therefore, the mother and child will have one-half of their genomes that are similar.
Two full siblings offspring that have the same two biological parents Solution: The parents can contribute only one-half of their genome to each offspring. So it is likely that the siblings share one-fourth of their genes from one parent. Half siblings offspring that have only one biological parent in common Solution: Half siblings share only one-fourth of their genomes with each other because they have only one parent in common. Some of these questions, marked by a data analysis icon, draw on examples from published, and cited, research articles.
This comprehensive and robust online teaching and learning platform incorporates online homework with the e-Book, all instructor and student resources, and powerful gradebook functionality. Students benefit from just-in-time hints and feedback specific to their misconceptions to develop their problem-solving skills, while instructors benefit from automatically graded homework and robust gradebook diagnostics.
NEW Active learning components One of my main goals for this new edition is to provide better resources for active learning.
In this edition, I have added Think-Pair-Share questions, which require students to work, and learn, in groups. These questions not only focus on the genetics topics covered in the chapter, but also tie them to genetics in medicine, agriculture, and other aspects of human society.
An online instructor guide provides resources for instructors leading the in-class discussion. Chapter Opening Think-Pair-Share Questions get students to discuss the chapter opening story itself and to connect it with what they know about genetics. End-of-Chapter Think-Pair-Share Questions provide more challenging problem solving for students to work on in groups and encourage them to discuss the bigger-picture aspects of the material they learned in the chapter. They also allow students to connect the material they have learned to broader genetics topics.
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