MEIOSIS AND SEXUAL LIFE CYCLES CHAPTER 13

REPRODUCTION Asexual reproduction – single parent passes on all of its genes to its offspring Sexual reproduction – two parents give rise to offspring that have a combination of genes inherited from two parents

Figure 13.1 The asexual reproduction of a hydra

VOCABULARY Karyotype – picture of an organisms chromosomes Homologous chromosomes – pair of similar chromosomes Haploid – single chromosome set (n=23 for humans) Diploid – two sets of chromosomes (2n=46 for humans)

HUMAN FEMALE

HUMAN MALE

Zygote – fertilized egg Fertilization or syngamy – fusion of sperm and egg Somatic cell – body cells Gametes – sex cells Sex chromosomes – determine gender Autosomes – all other chromosomes Sister chromatids – copies of same chromosome

Figure 13.x1 SEM of sea urchin sperm fertilizing egg

LIFE CYCLE Sequence of stages in the reproductive history of an organism Alternation of generations – includes both diploid and haploid multicellular stages Sporophyte – multicellular diploid stage that makes haploid cells called spores

Gametophyte – a multicellular haploid stage made by spores that divide mitotically

Figure 13.4 The human life cycle

Figure 13.5 Three sexual life cycles differing in the timing of meiosis and fertilization

MEIOSIS A process that halves the chromosome number Mitosis vs. Meiosis Genetic recombination

Figure 13.6 Overview of meiosis

Figure 13.7 Meiosis I

Figure 13.7 Meiosis II

Figure 13.8 Mitosis vs. Meiosis

Figure 13.9 Different possible sex cells

MORE GENETIC POSSIBILITIES Synapsis – pairing of homologous chromosomes in prophase I Chiasmata or crossing over – when homologous portions of two nonsister chromatids trade place

Figure Crossing over during meiosis