Today: More Meiosis plus Asexual vs. Sexual Reproduction Discussions start(ed) this week.

For life to exist, the information (genes) must be passed on. {Mitosis: producing more cells} {Meiosis: producing gametes} Fig 12.3

Each pair of chromosomes is comprised of a paternal and maternal chromosome

extremely low genetic diversity greater genetic diversity vs. Asexual Reproduction Sexual Reproduction How does sexual reproduction generate genetic diversity? Fig 12.13

Crossing- over Meiosis I Meiosis II 4 Haploid cells, each unique Meiosis: In humans, crossing-over and independent assortment lead to over 1 trillion possible unique gametes. (1,000,000,000,000) (Ind. Assort.) Fig 12.2

Fig 12.4

4 haploid cells

Fig 12.5

Sexual reproduction creates genetic diversity by combining DNA from 2 individuals, but also by creating genetically unique gametes. {Producing more cells} {Producing gametes} Fig 12.3

Different organisms have different patterns of haploid and diploid stages

Asexual Reproduction genetically identical to parent (this tree can reproduce both sexually and asexually)

Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity or Replace damage DNA

Fig 30.9 Plant Evolution: different plants have different ploidy for the different parts of their life cycle.

Haploid dominant (algae) Fig Diploid dominant (fern)

Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity or Replace damage DNA

How important is genetic diversity?

Fig Collected snails from different ponds and determined M/F ratio as well as rates of parasitism

Fig On average sexually reproducing snails were more common in areas with many parasites

Does a stressful environment lead to sexual reproduction?

extremely low genetic diversity greater genetic diversity vs. Asexual Reproduction Sexual Reproduction Fig Is genetic diversity critical for survival in “stressful” environments?

Fig 27.8 Environmental changes usually occur slowly

extremely low genetic diversity greater genetic diversity vs. Asexual Reproduction Sexual Reproduction Fig Is genetic diversity critical for survival in “stressful” environments?

Sexual reproduction creates genetic diversity by combining DNA from 2 individuals, but also by creating genetically unique gametes. {Producing more cells} {Producing gametes} Fig 12.3