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Lecture

Bio LEcture 3

5 Pages
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Department
Biology
Course Code
Biology 1001A
Professor
Tom Haffie

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BIO1001 Jash Parikh 2012/11/05 Biology for Sciences I Lecture 16 Notes from Readings: Chapter 7  Relationship between sexual reproduction and genetic variation o Genes do not necessarily assort independently from each other if linked on same chromosome o Some sex-linked genes are localized to the X or Y chromosomes, which are not partitioned equally to females and males o Due to recombination, sections of chromosomes can exchange material thereby forming different linear arrays of nucleotides o As nucleotide sequences constitute genes, recombination can produce different combinations of genes along a chromosome o Millions of different kinds of gametes can be formed by recombination o Different proposals  Sex originated as a way of overcoming DNA damage by using recombinational DNA repair mechanisms  Any genetic variation created is an accidental by-product  The production of genetic variation is the primary reason for he persistence of sex  Removing deleterious mutations  More mutations accumulate with asexual than with sexual reproduction in the water flea  Sex is advantageous to organisms that exist in variable environments and that parasitic elements such as transposons and plasmids initiated or promoted sexual fusion as a mechanism to infect other cells  Sexual crossing in a population allows single individuals to incorporate different beneficial mutations from other members through mating and genetic recombination  Enable relatively rapid combinations of existing mutations  Additional genetic variation allowing a population to persist in a changing environment  Different modes of genetic sex determination o Penis fencing in flatworms  Hermaphrodites-consisting of both male and female parts  Hunt and fight for mates  Some have two penises giving a decided advantage o Temperature-Dependent Mechanisms  Sex of alligators and other reptiles are set during the embryonic development by the temperature at which the egg develops  High temp determines maleness, low temperature determine femaleness o Fish That Change Their Sex as Adults  Tropical reef fish change sex during lifetime in matters of hours  Switching without inhibiting the other sex o Compensatory Mechanisms in Chickens  Males have right and left testes of normal sizes BIO1001 Jash Parikh 2012/11/05  Females have left and right gonads but only the left one functions as an ovary, right being rudimentary  If functional ovary is removed, rudiment can develop into an ovary, testis, ovotestis, with features of both sexes o Fertilized Versus Unfertilized Eggs  Haplodiploidy  Honeybees: male; haploid, female; diploid  Only one female becomes a queen and lays eggs  All other females help raise the queen’s eggs and contribute to her reproductive success  Queen releases a hormone that supresses fertility in the workers  Female lays differently sexed eggs in response to the size of the wheat grain containing the larval host  Large; fertilized female egg, Small; unfertilized male egg  Different Modes of Environmental Sex Determination o Bonellia  Green spoon worm larvae that free swim and settle on sea bottom develop into females with a 10-20 cm long body and meter long proboscis  Larvae that land on proboscis metamorphose into tiny 1mm males that lack digestive organs producing nothing but sperm o Osedax  Tubeworm females lack digestive system but contain endosymbiotic bacteria thought to produce the enzymes responsible for digesting whale bones  Females are surrounded by non-feeding males  Larvae that settle on bone develop into females while larvae that settle on females become dwarf males with development arrested at larval stage o Painted Turtles  High temp incubation of eggs in painted turtle (recall reptile) make females o Social Fish  Loss of socially dominant males from a group is followed by conversion of the dominant female in the group into a male  Females become males when the surrounding fish in the group are relatively small o Parasitoid Wasps  Female parasitoid wasps deposit eggs that will develop into females into large host larvae and eggs developing into makes into small host larvae  Females grow large sizes in larger hosts therefore producing more eggs  Differentiate by size Why Sex?  Copulation? Recombination? Reproduction? Ge
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