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BIOL 103 (103)
Chapter 49

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BIOL 103
Virginia K Walker

BOAG CH. 49 (pg. 1106-1109): SEXUAL REPRODUCTION ASEXUAL REPRODUCTION -occurs when offspring are produced from a single parents, w/o fusion of gametes from 2 parents -offspring are clones of the parent -prevalent in species that live in very stable environments w/ little selection pressure for genetic diversity in a pop'n Advantages: 1. an animal can reproduce even if it's isolated from others of its own species (non- moving or rarely encounters another) 2. can reproduce rapidly (no hassle of finding, attracting, and mating w/ opposite sex) 3. all asexual individuals can produce offspring (w/ sexual reproduction, 2 parents are needed) -efficient way of producing a lot of offspring done by: budding: a portion of the parent organism pinches off to form a new individual -cells from parent undergo mitosis and differentiate into specific types of structures before the new individual breaks away from parents -can have multiple buds forming -each new animal is fully formed but continues to grow -budding throughout an animal's lifetime regeneration: regrowing a complete organism from a small fragment of their body -eg. worms, sea stars -injured limbs are regrown -2 new individuals can be grown if an organism is split -continues through lifetime--> molecular mechanisms responsible for differentiation into a complete animal remain active during entire lifetime --> gene is expressed during early developmental stages, but remains active throughout life Parthenogenesis: development of offspring from an unfertilized egg -eg. some lizards, invertebrates, fish -animals produced this way are usually haploid -some animals can reproduce either sexually or by these means, depending on their situation -eg. Queen bee will store sperm from during mating season: eggs that are fertilized become diploid females, and when sperm runes out, unfertilized eggs become haploid males SEXUAL REPRODUCTION -production of a new individual by the joining of 2 haploid gametes (sperm and ova) -Fertilization: sperm unites w/ ova to create a zygote -as the zygote undergoes cell divisions + develops--> embryo -less straightforward than asexual reproduction and spends much more E -sexual reproduction allows for greater genetic variation through genetic recombination between successive generations -offspring are a combination of parents' genes; not identical to parents -alleles that provide a selective advantage arise independently in members of a pop'n -sexual reproduction provides the opportunity for 2+ beneficial alleles to be inherited by the same offspring, dramatically increasing its chances of success vs if it were to just have either gene by itself -sexual reproduction makes it easier for pop'ns to eliminate harmful alleles Paland and Lynch Provided Evidence that Sexual Reproduction May Promote the Elimination of Harmful Mutations in Populations -costs of sexual reproduction must somehow be outweighed by corresponding benefits -sexual reprod. allows pop'ns to redistribute alleles via crossing over and independent assortment across many generations -offspring are going to have combos of alleles, some good for success and some bad for success -natural selection favours those w/ alleles that provide greater success and ensures that those with less fitness don't live/reproduce to keep their bad genes alive -asexual reproducers can't reassort their genes in this way + more difficult for them to accumulate good genes/eliminate bad genes -->study of water fleas: some pop'ns repro. sexual while others do asexually -studied mitochondrial genes in sexually reprod. and asexually reprod. fleas -both pop'n
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