1/31/12- continued cell genetics and Mendelian traitso females – can be homozygous OR heterozygous for traits on the X chromosomeo Males – Are Hemizygous for any trait on the X chromosome (because they only have one) Pleitropy - One genetic locus affects seemingly unrelated traitso Example: PKUo Lack of an enzyme to break down phenylalanine Phenylalanine creates tyrosine Tyrosine creates a thyroid hormone and without it, severe mental retardation occurs Tyrosine is also a precursor to melanino Mendelian Traits Traits of simple inheritance Governed by one specific locus Discreet traits- ABO blood groupo On chromosome #9 you have one of six genotypes AA AB AO BB BO OOo And one of 4 phenotypes A B O ABo This determines what kind of antogens form around RBCso O has no antogenso O is recessive to A and Bo A and B are co-dominant- 2 individuals are type Ao Child is type Oo Both parents must be heterozygous - AOoo o A o O o A o AA o AO o O o AO o OOo- The differences?o AB can take any bloodo O can donate to anyo Homozygote type B with a type O?o o B o B o O o BO o BO o O o BO o BO o 0% chance of type of child Modes of Mendelian Inheritance- Autosomal Dominant – found on autosomes- Autosomal Recessive – found on autosomes- Sex-linked traits – Found on either X or Y chromosomeso Autosomal dominant – AA/Aa The allele responsible for the trait is dominant Only need one allele to express the trait Affect males and females equally Tend to see them in every generationo Autosomal recessive – only homozygous recessive have trait (bb) The allele responsible for the trait is recessive Must have 2 recessive alleles to express the trait Tendency to skip generations- Because of this, 2 unaffected people can have affected childreno Sex-linked traits Mostly X linked Y only has the SRY gene and gene for hairy ears X linked traits- Hemophiliao 1 in 10,000 males have ito 1 in 100,000,000 females have it- One sex is normally affected more- In England, the queen (XX chromosomes) was unaffectedo Married Xy that was unaffectedo Son had it Mother XHXh Father XHy Results in a 25% chance of son getting ito o X H o X h o X H o X H X H o X H X h o Y o X H Y o X h Y Pedigrees - Circles = Females- Squares= Males- Shaded in = affected individuals I can’t draw the pedigrees on typed notes, so you’re on your own
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