12. Meiosis

Which of the following processes occurs when homologous chromosomes cross over in meiosis I?

a) Two sister chromatids get tangled, resulting in one re-sequencing its DNA.

b) Two sister chromatids exchange identical pieces of DNA.

c) Maternal alleles are "corrected" to be like paternal alleles and vice versa.

d) Corresponding segments of non-sister chromatids from homologous chromosomes are exchanged.

2448

Crossing over involves each of the following EXCEPT:

a) The transfer of DNA between two non-sister chromatids.

b) The transfer of DNA between two sister chromatids.

c) The formation of a synaptonemal complex.

d) The alignment of homologous chromosomes.

e) All of the above are involved in crossing over.

How many genetically unique gametes can be created in an organism with 4 chromosomes?

a) 256.

b) 23.

c) 16.

d) 1 million.

e) 4.

During which of the following processes does independent assortment of chromosomes occur?

a) In meiosis I only.

b) In meiosis II only.

c) In mitosis and meiosis I.

d) In mitosis and meiosis II.

e) In meiosis I and meiosis II.

2530

Independent assortment of chromosomes is a result of which of the following processes?

a) The random way each pair of homologous chromosomes lines up at the metaphase plate.

b) The random combinations of eggs and sperm during fertilization.

c) The random distribution of the sister chromatids into the two daughter cells.

d) The diverse combination of alleles that may be found within any given chromosome.

4538

Non-disjunction means that chromosomes:

a) Do not cross over during synapsis.

b) Do not replicate during interphase.

c) Have serious mutations.

d) Do not separate correctly from one another during anaphase.

During meiosis, if nondisjunction occurs during anaphase II (shown below in cell #3) what are the possible gametes that can be produced from cell #3?

a) A only.

b) B only.

c) C only.

d) A & C.

e) B & C.

f) A & B.

g) All three.

________ cells have an extra or missing chromosomes after meiosis due to nondisjunction during Meiosis I.

a) Somatic cells.

b) Gametes.

c) Diploid Cells.

d) Aneuploid Cells.

e) Haploid Cells.

f) Sperm Cells.

1028

Which of the following answers is neither involved with crossing over nor an outcome of crossing over?

933

Crossing over occurs during __________.

622

Regions of chromosomes where nonsister chromatids cross over are called __________.

447

Which of the following contributes to genetic variation in sexually reproducing species?

The diploid number of chromosomes in a certain animal is 8 (2n = 8). How do the four pairs of homologous chromosomes align and separate during meiosis?

1626

The major contribution of sex to evolution is that __________.

796

In a diploid set of chromosomes, one member of each pair of homologous chromosomes is derived from the father (paternal), and the other comes from the mother (maternal). If 2n = 6, what is the probability that a particular gamete will contain only paternal chromosomes?

1005

Ignoring crossover events, how many kinds of gametes can be produced by an organism with a diploid number of 8?

547

What is an outcome of genetic recombination? a. the synapsing of homologs during prophase of meiosis I b. the new combination of maternal and paternal chromosome segments that results when homologs cross over c. the new combinations of chromosome segments that result when self-fertilization occurs d. the combination of a haploid phase and a diploid phase in a life cycle

338

A wild-type fruit fly (heterozygous for gray body color and normal wings) is mated with a black fly with vestigial wings. The offspring have the following phenotypic distribution: wild-type, 778; black vestigial, 785; black normal, 158; gray vestigial, 162. What is the recombination frequency between these genes for body color and wing size? Is this consistent with the results of the experiment in Figure 15.9?

2028

A planet is inhabited by creatures that reproduce with the same hereditary patterns seen in humans. Three phenotypic characters are height (T=tall, t=dwart), head appendages (A=antennae, a=no antennae), and nose morphology (S=upturned snout, s=downturned snout). Since the creatures are not 'intelligent,' Earth scientists are able to do some controlled breeding experiments using various heterozygotes in testcrosses. For tall heterozygotes with antennae, the offspring are tall antennae, 46; dwarf antennae, 7; dwarf no antennae, 42; tall no antennae, 5. For heterozygotes with antennae and an upturned snout, the offspring are antennae upturned snout, 47; antennae downturned snout, 2; no antennae downturned snout, 48; no antennae upturned snout, 3. Calculate the recombination frequencies for both experiments.

1133

Nondisjunction that leads to problems in offspring can occur in: a. mitosis b. meiosis I only c. meiosis I and II d. mitosis, meiosis I, and meiosis II

503

Using the information from problem 4, scientists do a further testcross using a heterozygote for height and nose morphology. The offspring are tall upturned snout, 40; dwarf upturned snout, 9; dwarf downturned snout, 42; tall downturned snout, 9. Calculate the recombination frequency from these data, and then use your answer from problem 4 to determine the correct order of the three linked genes.

814

A fruit fly somatic cell contains 8 chromosomes. This means that ___________ different combinations of chromosomes are possible in its gametes. a. 8 b. 16 c. 32 d. 64

1188

A wild-type fruit fly (heterozygous for gray body color and red eyes) is mated with a black fruit fly with purple eyes. The offspring are wild-type, 721; black purple, 751; gray purple, 49; black red, 45. What is the recombination frequency between these genes for body color and eye color? Using information from problem 3, what fruit flies (genotypes and phenotypes) would you mate to determine the order of the body color, wing size, and eye color genes on the chromosome?

1744

What is the physical basis for the independent assortment of alleles into offspring? a. There are chromosome divisions during gamete production; b. Homologous chromosome pairs are separated during gamete production; c. Sperm and eggs are produced by different sexes; d. Each gene codes for more than one protein; e. The instruction manual for producing a human is incomplete.

410

Assume that genes A and B are on the same chromosome and are 50 map units apart. An animal heterozygous at both loci is crossed with one that is homozygous recessive at both loci. What percentage of the offspring will show recombinant phenotypes resulting from crossovers? Without knowing these genes are on the same chromosome, how would you interpret the results of this cross?

977

Two genes of a flower, one controlling blue (B) versus white (b) petals and the other controlling round (R) versus oval (r) stamens, are linked and are 10 map units apart. You cross a homozygous blue oval plant with a homozygous white round plant. The resulting F1 progeny are crossed with homozygous white oval plants, and 1,000 offspring plants are obtained. How many plants of each of the four phenotypes do you expect?

1048

You design Drosophila crosses to provide recombination data for gene a, which is located on the chromosome shown in Figure 15.12. Gene a has recombination frequencies of 14% with the vestigial wing locus and 26% with the brown eye locus. Approximately where is a located along the chromosome?

493

Meiosis results in independent assortment of maternal and paternal chromosomes. If 2n=6 for a given organism, and there is no crossing over, what is the chance that a gamete produced by this diploid organism will receive only paternal chromosomes? a. 0 b. 1/16 c. 1/8 d. 1/3

520

Why are individuals with an extra chromosome 21, which causes Down syndrome, more numerous than individuals with an extra chromosome 3 or chromosome 16? a. There are probably more genes on chromosome 21 than on the others. b. Chromosome 21 is a sex chromosome and chromosomes 3 and 16 are not. c. Down syndrome is not more common, just more serious. d. Extra copies of the other chromosomes are probably fatal.

855

Select True or False for each statement. T/F Linked genes are always inherited together. T/F Genetic map distances measure the number of nucleotides between a pair of genes. T/F The farther apart genes are on a chromosome, the more likely there is to be a crossover between these genes during meiosis. T/F Crossing over occurs between genes on different homologs of a homologous chromosome pair.

494

Briefly describe how three different processes that occur during a sexual life cycle increase the genetic diversity of offspring.

393

Sketch a cell with three pairs of chromosomes undergoing meiosis, and show how nondisjunction can result in the production of gametes with extra or missing chromosomes.

690

Suppose you read in the newspaper that a genetic engineering laboratory has developed a procedure for fusing two gametes from the same person (two eggs or two sperm) to form a zygote. The article mentions that an early step in the procedure prevents crossing over from occurring during the formation of the gametes in the donor's body. The researchers are in the process of determining the genetic makeup of one of their new zygotes. Which of the following predictions do you think they would make? Justify your choice, and explain why you rejected each of the other choices. a. The zygote would have 46 chromosomes, all of which came from the gamete donor (its one parent), so the zygote would be genetically identical to the gamete donor. b. The zygote could be genetically identical to the gamete donor, but it is much more likely that it would have an unpredictable mixture of chromosomes from the gamete donor's parents. c. The zygote would not be genetically identical to the gamete donor, but it would be genetically identical to one of the donor's parents. d. The zygote would not be genetically identical to the gamete donor, but it would be genetically identical to one of the donor's grandparents.

317

What you think of as 'a banana' is a Cavendish, one variety of the species Musa acuminate. It is a triploid organism (3n) with three sets of chromosomes in every somatic cell. The Cavendish cannot be naturally bred; it can only be reproduced by cloning. Explain how its triploid state accounts for its inability to form normal gametes. Discuss how the lack of sexual reproduction might make the species particularly vulnerable to a new pest.

460