Sex-linked - Sex 04/20/03 6:51 PM Sex -Linked Genes Lecture...

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Sex -Linked Genes Lecture Outline Multiple mechanisms exist for assuring "sexual" reproduction Bacteria: males (donors) contain a fertility (F + ) plasmid, a circle of DNA that codes for proteins that enable a copy of the plasmid to be transferred into cells that do not already contain a copy (F - recipients). Fungi: many fungi require different alleles (A vs a) at one or two gene loci in order to cross; generally, either "mating type" can be male (donor) or female (recipient) in transfer of genetic information. Some turtles: the temperature of the eggs may trigger male or female development. Many plants make both female and male gametes; often in the same flower (ex. = peas) but sometimes in organs separated on the same plant (ex. = corn where pollen is produced in the tassel and eggs are made in the ear). A few species have strictly male and female plants (ex. = apricot). In grasshoppers and many bugs, females have an even number of chromosomes and males an odd #. Female grasshoppers have 12" (pairs) of chromosomes while males have 11" and one that remains unpaired in meiosis. When McClung noticed this in 1902, he called the mystery chromosome an X chromosome and the name stuck.
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Sex-linked - Sex 04/20/03 6:51 PM Sex -Linked Genes Lecture...

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