Genetics Exam 2 Review - Genetics Exam 2 Review SEX...

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Genetics Exam 2 Review SEX CHROMOSOMES Hemophilia and the European Royalty Queen Victoria was a carrier of sex linked hemophilia The trait got passed into many ruling families by intermarriage Victoria appeared to have a de novo mutation in the F9 gene (hemophilia B) Open square – male nonhemophiliac Open circle – female nonhemophiliac Open square/circle with black dot – heterozygous recessive allele Black square – male hemophiliac This may have had a profound impact on history because Alexis, the son of the Russian Tsar (Nicholas II), was a hemophiliac Rasputin “cured” Alexis’s hemophilia by telling doctors not to bother him & not to give him aspirin o Aspirin has anti-coagulative properties, if he would have taken aspirin he would have bled out and died Hemophilia – biological basis Multiple forms o Two X-linked forms: Hemophilia A – factor VIII deficiency Hemophilia B – factor IX deficiency (aka Christmas disease) o Also have autosomal forms Deficiencies in blood clotting factors, protease activity o Why X-linked? Males are hemizygous for X chromosome, lends itself to recessive allele diseases The Romanovs appeared to have hemophilia B (Christmas disease) DNA from Romanov graves was extracted and the exons of the F8 and F9 genes were amplified Mutation appears to be in the exon boundary, not the F8 or F9 coding regions Introns begin with GT and end with AG (GT-AG Rule) A-to-G mutation occurs upstream of exon 4 in the F9 gene and is predicted to create a new splice acceptor site that could lead to production of a truncated factor IX protein. o If you delete/add nucleotides that are not in a factor of 3, you change the translation o Stop codon half of the protein is missing o Change in sequence changes the protein The Androgen Receptor is on the X Mutations in the androgen receptor can lead to testicular feminization syndrome Androgen male phenotype Androgen receptor is on the X chromosome o Non-functioning androgen receptor may sex-reverse Symptoms: micorpenis, gynecomastia, development of female external genitalia
Traits on the X can be dominant Many mutations have been localized to the X because recessive mutations are evident in males, but there is no reason that X linked mutations have to be recessive o X-linked recessive: can see them in men but not in women Dominant allele activate a protein Human Y chromosome has Few Genes Except for the testis determining factor (SRY for sex determining region of Y) there are few genes on the Y Most are directly involved in male fertility (e.g., mutations cause azoospermia, etc.) DAZ: deleted in azoospermia Hairy ear trait How would Y-linked inheritance be described? o It appears exclusively in males o Always passed from father to son Location of genes is important – genes on the sex chromosomes show a distinct pattern of inheritance o Either X and Y or Z and W Males will be hemizygous in an XY system (females in a WZ) o So recessive trait will be apparent

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