Chapter 15 Notes

Chapter 15 Notes - Chapter 15 Chromosomal Basis Chromosome...

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Chapter 15 Chromosomal Basis Chromosome theory of inheritance Chromosome and genes are both present in pairs in diploid cells Homologous chromosomes separate and alleles segregate during the process of meiosis and fertilization restores the paired condition for both chromosomes and genes Thomas Hunt Morgan, an experimental embryologist from Columbia University o Fruit fly experiment o They have only 4 pairs of chromosomes o Wild type- phenotype for a character most commonly observed in natural populations Alternatives would be a mutant phenotype o The fly eye color was linked to the sex of the fly o A correlation between a particular trait and an individual sex provided support for the chromosome theory of inheritance A specific gene is carried on a specific chromosome Genes located on sex chromosomes exhibit unique inheritance Sex linked genes The identity of the sex chromosome in an individual could be inferred by observing the sex of the fly o The behavior of the two members of the pair of sex chromosomes could be correlated with the behavior of the two alleles of the eye color gene In humans Y and X are sex chromosomes o XX for females o XY for Males o We receive one chromosome form each parent o Short segments at either end of the Y chromosome are the regions that are homologous with corresponding regions of the X o Both testis and ovaries Two sex chromosomes segregate during meiosis, and each gamete receives one Sex determination is a matter of chance 50%-50% Single of sec begin to emerge when the embryo is 2 months old SRY- sex determining region of Y Codes for a protein that regulates other genes Sex-linked gene- a gene that is located on the sex chromosomes o Humans mainly to the X chromosome o If a sex-linked trait is due to a recessive allele The female will express the phenotype only if she is homozygote Males have only one locus Homozygous and heterozygous lack meaning for describing their sex-linked genes
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Hemizygous is used in such cases Recessive allele from the mother will express the trait Double douse are less likely o Duchenne Muscular Dystrophy Affects 1-3,500 males Progressive weakening of the muscles and loss of coordination o Hemophilia- Sex-linked recessive disorder defined by the absence of one or more of the
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This note was uploaded on 04/26/2009 for the course BIOL 111 taught by Professor Rizzo during the Spring '07 term at Texas A&M.

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Chapter 15 Notes - Chapter 15 Chromosomal Basis Chromosome...

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