Chapter 13 Meiosis and Sexual Life Cycles

Asexual reproduction: Single individual is sole parent, passes copies of all its genes to its offspring (exact copies, or clones, of the parent) 13.2

Sexual reproduction: Two parents give rise to offspring that have unique combinations of genes inherited from the two parents (offspring varies genetically from their siblings and their parents). Offspring resembles their parents more than they do less closely related individuals of the same species 13.1

13.3. Human karyotype. A display of condensed chromosomes displayed in pairs Genetics: The study of heredity and hereditary variation

13.4. Chromosomes in a cell with a diploid number of 6 (2n=6) or 3 homologous pair. Each of the 6 chromosomes consist of 2 sister chromatids, joined at the centromere. locus

Fig Human life cycle Fertilization and meiosis must alternate in all sexual life cycles

13.6. Three types of sexual life cycles. Note alternation of meiosis and fertilization

Concept 13.3: Meiosis reduces the number of chromosome sets from diploid to haploid Like mitosis, meiosis is preceded by the replication of chromosomes Meiosis takes place in two sets of cell divisions, called meiosis I and meiosis II The two cell divisions result in four daughter cells, rather than the two daughter cells in mitosis Each daughter cell has only half as many chromosomes as the parent cell

Meiosis takes place in two sets of cell divisions, called meiosis I and meiosis II Overview of meiosis. How meiosis reduces the number of chromosomes. The two cell divisions result in four daughter cells, rather than the two daughter cells in mitosis. Each daughter cell has only half as many chromosomes as the parent cell.

13.8a. The meiotic division of an animal cell. SynapsisCrossing overInterkinesis

13.8b. The meiotic division of an animal cell.

13.9. Comparison of meiosis and mitosis. Differences between mitosis and meiosis II?

13.9. Comparison of meiosis and mitosis.

Independent assortment of homologous chromosomes in meiosis.

The results of crossing over during meiosis.

The results of crossing over during meiosis.

The results of crossing over during meiosis.

The results of crossing over during meiosis.

The results of crossing over during meiosis.

Example question A cell has a diploid chromosome number of 2n = 4. We will designate these four as chromosomes A, B, C, and D. If meiosis occurred WITH the formation of homologous pairs AC and BD, and the chromosomes were then distributed randomly between the resulting cells, how many gametes could be formed? A) 6 (AB, AC, AD, BC, BD, and CD) B) 3 (AB, BC, and CD) C) 4 (AB, AD, BC, and CD) D) 2 (AB and CD) E) 5 (AB, AC, AD, BC, and CD)

Meiotic non-disjunction Aneuploidy

Alteration of chromosome structure

Chapter 13 Review (see p ) Offspring acquire genes from parents by inheriting chromosomes Fertilization and meiosis alternate in sexual life cycles Meiosis reduces the number of chromosome sets from diploid to haploid Genetic variation produced in sexual life cycles contributes to evolution.