Biology 2581B Lecture Notes - Lecture 8: Phylogenetic Tree, Genetic Load, Sexual Reproduction

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Very difficult to find older fossil evidence due to gametes. 425 mya: first evidence of sex in animals. Fossilized colymbosathon ecplecticos ( astounding swimmer w/ large penis ) 100 mya: first evidence of sex in land plants. Found pollen tubes growing out of pollen & penetrating flower"s stigma. Sexual reproduction arose after mitochondria developed (~1. 8 bya) Sexual reproduction favoured when environment is variable and changing. Offspring may benefit from new combination of genes. Might be more suited to new environment. Sexual reproduction a result of selection pressure. Asexual reproduction favoured when environment is constant. Parents survived so offspring w/ same genes should survive as well. Heterozygosity helps overcome evolutionary ratchet of high genetic load. Deleterious mutations less severe if organism has 2nd functioning copy of gene. Offspring have 50% their offspring have 25% etc. Reproductive output halved (2 parents: 1 child) Must search for and court a mate (+ chance of not finding one)

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