Meiosis Part 2

The End result…

Let’s Compare

Why aren't these siblings identical?

Origins of Genetic Variation, I Independent assortment:Independent assortment: homologous pair of chromosomes position and orient randomly (metaphase I)homologous pair of chromosomes position and orient randomly (metaphase I) nonidentical sister chromatids during meiosis II nonidentical sister chromatids during meiosis II Combinations possible: 2 n ; with n the haploid number of the organismCombinations possible: 2 n ; with n the haploid number of the organism

Origins of Genetic Variation, II Crossing overCrossing over prophase I:prophase I: the reciprocal exchange of genetic material between nonsister chromatids during synapsis of meiosis I (recombinant chromosomes) the reciprocal exchange of genetic material between nonsister chromatids during synapsis of meiosis I (recombinant chromosomes)

Crossing-Over A source of Genetic Variation Chromosomes line up during first division of MeiosisChromosomes line up during first division of Meiosis Homologous chromosomes can cross overHomologous chromosomes can cross over

The new chromosomes are no longer exactly like the parent chromosomes.. they are a combination.

Origins of Genetic Variation – III Random Fertilization Random fertilization:Random fertilization: 1 sperm (1 of 8 million possible chromosome combinations) 1 sperm (1 of 8 million possible chromosome combinations) x 1 ovum (1 of 8 million different possibilities) x 1 ovum (1 of 8 million different possibilities) = 64 trillion diploid combinations!

No wonder no two are the same!

7.2 Sexual and Asexual Reproduction

Reproduction The process of producing offspringThe process of producing offspring Can be sexual or asexualCan be sexual or asexual

Asexual Reproduction One parent passes all its genetic information to each of its offspringOne parent passes all its genetic information to each of its offspring No fusion of haploid gametesNo fusion of haploid gametes Produces many organisms in little timeProduces many organisms in little time “Clone”“Clone”

Basic cell division Hydra Red sea star

Evolution of Sexual Reproduction Some protists and prokaryotes can reproduce “sexually” in times of environmental stressSome protists and prokaryotes can reproduce “sexually” in times of environmental stress May allow them to repair their DNAMay allow them to repair their DNA

Bacterium passing DNA molecule to anotherBacterium passing DNA molecule to another

Sexual Life Cycles Life Cycle The entire span on the life of an organism from one generation to the next

Eukaryotes alternate between haploid and diploid stages during their life cycles

Diploid life cycle Humans Adults are diploid Only gametes produced by meiosis are haploid

There are many variations of cell cycles sporophyte gametophyte