ucsdgensexetal0 - Sex and other Complications Sex...

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Sex and other Complications Sex Determination The determination of a person’s sex is determined by The presence of a particular pattern of sex chromosomes The proper expression of these chromosomes during development Female contributes an X chromosome Male contributes either X or Y If XX, genetic female; if XY genetic male Expression of the SRY gene on the Y chromosome during development is necessary for full male phenotypic development Comparison of sex chromosomes There are genes on the X chromosome that are not present in the Y chromosome (sex-linked traits) Traits distributed unequally Y chromosome lacks genes that are on the X chromosome Male has no counter to disease because of Y Sex linkage Gene is located on the sex chromosome Because of its size, most sex-linked genes are on the X chromosome Females usually need two copies of the recessive allele to be affected Since males have one X and one Y gene; They only need one copy of the X- linked gene to be affected. There is a higher incidence of X-linked diseases in males Mothers contribute the X gene to their sons (Fathers contribute the Y). Females therefore tend to be carriers for the trait (have 1 recessive X-linked allele Females carry two copies of the X chromosome and may be homozygous or heterozygous for a given trait Males carry only one X chromosome and are hemizygous for all genes on the X chromosome A male receives his Y chromosome from his father and his X from his mother
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Analyzing Modes of Inheritance Examine the effects of allelic gene interactions (one locus) on observed phenotype The phenotype of the heterozygote reveals dominance pattern The pattern depends upon at what level the phenotype is examined Remember, dominance is determined by what phenotype is observed in the heterozygote Dominance (Mendelian) One allele dominates other: Example: Y produces yellow seed color;y produces green seed color Genotype YY Yy yy Phenotype Yellow Yellow green Y (Yellow) dominates in the heterozygote (Yy) condition.Simple dominance. Incomplete Dominance Phenotype of the heterozygote is intermediate to the two homozygotes P produces purple flowers;p produces white flowers Genotype PP Pp pp Phenotype Purple violet White Heterozygote (Pp) phenotype (violet) is intermediate between the other two Cystic Fibrosis Is an Example of an Autosomal Recessive Trait Disabling and fatal disorder Affects sweat glands and glands that produce mucus and digestive enzymes Cystic Fibrosis Transmembrane CFTR regulates flow of chloride ions across the plasma membrane Reduces fluid in glandular secretionsConductance Regulator (CFTR) Phenotype of the heterozygote is intermediate to the two homozygotes C functional CFTR protein;c no CFTR protein Genotype CC Cc cc Phenotype
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ucsdgensexetal0 - Sex and other Complications Sex...

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