MEIOSIS AND SEXUAL LIFE CYCLESCHAPTER 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 13.8 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 13.10 Crossing over during meiosis