Chapter 12

Which of the following describes crossing over?

*occurs between homologous chromosomes *increases genetic variation across gametes

The process of meiosis is responsible for creating much of the genetic variation seen in sexually reproducing organisms. Which events in the process of meiosis generate this genetic variability?

*the arms of adjacent chromatids cross over and switch places with each other in prophase 1 *a homologous pair lines up along the metaphase plate independently of the other pairs

An organism has 16 chromosomes in its diploid somatic cells. How many chromosomes are in its gametes?

8

Identify each cell below as either haploid or diploid

Haploid *bacterium *egg cell *sperm Diploid *nerve cell *skin cell apple tree cell

Identify the characteristics of homologous chromosomes and sister chromatids

Homologous chromosomes *may have different alleles *have different parental origins *may exchange genetic material Sister chromatids *identical copies *linked by a centromere *result of a chromosome duplication

What happens during prohpase 1 of meiosis?

Homologous chromosomes form and crossing over occurs between them

Classify each description as a characteristic of nondisjunction in meiosis 1 or nondisjunction in meiosis 2

Meiosis 1 *a tetrad fails to separate properly *affects all of the resulting daughter cells Meiosis 2 *sister chromatids do not separate at the centromere *affects only 2 of the 4 resulting daughter cells

Cell division can occur by either of two distinct processes, mitosis or meiosis. However, each process has a unique function. Determine whether each phrase describes mitosis, meiosis, or both. Place each phrase in the correct category.

Mitosis *results in genetically identical cells *used for asexual reproduction Both mitosis and meiosis *duplication of chromosomes occurs before cell division Meiosis *forms sex cells such as eggs and sperm *contributes to genetic diversity through crossing over

Zygote, gamete, and fertilization are key terms associated with sexual reproduction. Identify the definitions and examples of these three key terms.

Zygote *cell resulting from the fusion of gametes *a fertilized egg cell Gamete *cell produced by meiosis *sperm cell Fertilization *a process fusing the nuclei of two gametes

What is the difference between asexual reproduction and sexual reproduction?

asexual reproduction produces genetically identical offspring, whereas sexual reproduction produces offspring that are genetically different from each other and their parents

How does random fertilization increase genetic variability?

millions of sperm, each with a unique genetic identity, are available to fertilize each egg

Both mitosis and meiosis begin with a single diploid cell, but their end products are different. What are the end results of mitosis and meiosis?

mitosis *two identical cells diploid cells meiosis *four different cells *haploid cells

What happens during metaphase 2 of meiosis?

sister chromatids are distributed in a single layer across the center of the cell

What happens during anaphase 2 of meiosis?

sister chromatids separate from each other and migrate to opposite ends of the cell

Meiosis is a critical process for many living organisms. If an organism became unable to complete meiosis, what effect would it have on the organism?

the organism would no longer produce sex cells

Some stains of yeast are haploid. How do these stains undergo meiosis?

two haploid yeast fuse to form a diploid state that can undergo meiosis