12. Meiosis

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

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.

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.

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.

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.

1333

Crossing over occurs during __________.

995

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

774

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?

2255

The major contribution of sex to evolution is that __________.

1154

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?

1454

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

922

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

2197

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.

882

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

1046

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.

1460

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

820

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.

1381

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.

645

A mule is the offspring of a horse and a donkey. A donkey sperm contains 31 chromosomes and a horse egg cell contains 32 chromosomes, so the zygote contains a total of 63 chromosomes. The zygote develops normally. The combined set of chromosomes is not a problem in mitosis, and the mule combines some of the best characteristics of horses and donkeys. However, a mule is sterile; meiosis cannot occur normally in its testes (or ovaries). Explain why mitosis is normal in cells containing both horse and donkey chromosomes but the mixed set of chromosomes interferes with meiosis.

2301

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.

905