Week 13 - meiosis inheritance connection

Genes on X chromosome are called X-linked • males only have one X chromosome, so one copy of a recessive allele will result in recessive phenotype in men • women have two copies of X so can be heterozygous of X-linked recessive trait w/o showing phenotype eg: hemophilia, colour blindness, muscular dystrophy

• colour blindness is an X-linked recessive disorder. - the inability to differentiate certain colour perceptions

• disease that affects single protein in a cascade of proteins involved in formation of blood clots • form of hemophilia cased by x-linkedrecessive allele → heterozygous females are asymptomatic carriers

• in each female cell • all but one X-chromosome is inactivated and is highly condensed into a Barr body • ENSURES AN EQUAL’ expression of genes from the sex chromosomes even though females have two X chromosomes and males have one • females heterozygous for genes on the X chromosome are genetic mosaics

• do not generally experience severe developmental abnormalities • individuals have somewhat abnormal features but often reach maturity in some cases may be fertile • XXX : female • XXY: male → klinefelter syndrome • XO: female →turner syndrome • OY: nonviable zygoes • XYY: makles → jacob syndrome • if dosage compensation occurs in females, why do XO females or XXY males show a phenotype

maternal inheritance: - uniparental inheritance from the mother mitochondria in a zygote are from the egg cell; no mitochondria come from the sperm during fertilisation in plants, the chloroplasts are often inherited from the mother, although this is species dependednt

• a male cant pass on the trait, only female passes the trait on to all her children • mitochondrial genes encode proteins that participate in protein synthesis and energy production • major symptoms: great fatigue