Chapter 15.2 Sex-linked genes exhibit unique patterns of inheritance Flashcards
How is sex of mammals determined
The sex of a mammalian offspring depends on whether the sperm cell contains an X chromosome or a Y.
. In mammalian testes and ovaries , the 2 sex chromosomes segregate during meiosis and each gamete gets one. Each egg contains an x chromosome. In contrast, sperm fall int 2 categories: Half the sperm cells a male produces contain an X chromosome and half contain a Y chromosome
SEX LINKED GENES
A gene located on either sex chromosome : Y-linked gene and X- Linked gene
X linked traits
. Fathers pass X-linked alleles to all of their daughters but to none of their sons
. Mothers can pass Xl-inked alleles to both sons and daughters
.If X-linked trait is due to a recessive allele, a female will express the phenotype only if she is homozygous for that allele
. A male receiving the recessive allele from his mother will express the trait ( far moer males than females have x-linked recessive disorders ( e.g color blindness, hemophilia)
HEMIZYGOUS
alleles on y chromosomes
.
X - Inactivation
Females have 2 x chromosomes in each cell , However one x is randomly turned off
BARR BODY
The inactive X in each cell of a female condenses into a compact object, which lies along the inside of the nuclear envelope
When are Barr bodies reactivated
In the ovaries, Barr body chromosomes are reactivated in the cells that give rise to eggs, so every female gamete has an active X.
Mosaic
having 2 type of cells active and in active at random. ( all mitosis descendants of that inactive x gene cell will also have this inactivation.