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.

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. 0b. 1/16c. 1/8d. 1/3

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.

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

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

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.

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.

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.