Week 13 - meiosis inheritance connection Flashcards Preview

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Sex linkage

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


Red-green colour blindness

- 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


dosage compensation

- 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


nondisjunction of sex chromosomes

- 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


chromosome theory exception

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


Mitochondral genes are maternally inherited

- 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