Discuss the concepts of homologous chromosomes, diploidy, and haploidy. What characteristics do two homologous chromosomes share?

VISUALIZE Sketch a series of diagrams showing each of the following, making sure to end each series with haploid cells: (a)How a pair of alleles for a single locus segregate in meiosis (b)How the alleles of two unlinked loci assort independently in meiosis (c)How the alleles of two linked loci undergo genetic recombination

VISUALIZE Draw a simple sketch illustrating how nondisjunction in meiosis can lead to Down syndrome.

What is independent assortment? Does independent assortment occur during mitosis or during meiosis?

Human sex chromosomes are XX for females and XY for males. a. With respect to an X-linked gene, how many different types of gametes can a male produce? b. If a female is homozygous for an X-linked allele, how many different types of gametes can she produce with respect to this allele? c. If a female is heterozygous for an X-linked allele, how many different types of gametes can she produce with respect to this allele?

Figure 13.6 Which of the following statements about nondisjunction is true? Nondisjunction only results in gametes with n+1 or n-1 chromosomes. Nondisjunction occurring during meiosis II results in 50 percent normal gametes. Nondisjunction during meiosis I results in 50 percent normal gametes. Nondisjunction always results in four different kinds of gametes.

Can haploid cells divide by mitosis? by meiosis?

Which of the following statements is not true in comparing mitosis and meiosis? a. Twice the number of cells are produced in meiosis as in mitosis. b. Meiosis is involved in the production of gametes, unlike mitosis. c. Crossing over occurs in meiosis I but not in meiosis II or mitosis. d. Meiosis and mitosis both produce cells that are genetically identical. e. In both mitosis and meiosis, the parental cell is diploid.

Assume that a meiotic-nondisjunction event causes trisomy 8 in a newborn. If two of the three copies of chromosome 8 are absolutely identical, at what point during meiosis did the nondisjunction event take place?

Individuals with trisomy 21 are more likely to survive to adulthood than individuals with trisomy 18. Based on what you know about aneuploidies from this module, what can you hypothesize about chromosomes 21 and 18?