8.1: sex linkage Flashcards
Hemizygous meaning?
Hemizygous: having only one member of a chromosome pair. E.g. males only have one X chromosome.
Why are X-linked disorders more common in alleles?
Males are hemizygous for the X chromosome so while females need to inherit two of the recessive alleles to display a condition, males only need one… if they inherit the allele (will be from mother) they WILL display it.
What’s SRY?
SRY stands for Sex Determining Region of Y chromosome.
- This is the portion of the Y chromosome responsible for producing “maleness”
What’s a Barr Body and why do they form?
A barr body is a condensed, deactivated form of the X chromosome present in female somatic cells.
Females inherit two X chromosomes but since they only need one, the other becomes inactive in the early embryo through lyonisation. This inactive chromosome is then condensed into a chromosome form called a Barr Body where genes aren’t expressed due to methylation. This only occurs in somatic cells.
This X inactivation occurs RANDOMLY so it varies cell to cell which of the X chromosomes are inactivated so females are a mosaic of cell types delineated by which X is active.
–> Some of your cells have the paternal X inactivated, others have the maternal X inactivated.
What are holandric genes?
Holandric genes are Y-linked genes.
- Mostly part of SRY
- Some autosomal genes only expressed in one sex
(Somatic: describes non-sex CELLS)
(Autosomal: describes non-sex CHROMOSOMES)
