Sex Linkage Flashcards
What can determine the sex of an animal
Sex is determined by environmental conditions such as temperature
Chromosomes are inherited randomly so should the sex of the individual be random too
Therefore the sex of the individuals with sex chromosome should also be random
What is homigametic sex
Both sex chromosomes are the same
So Gametes are the same
Males are homigametic and have two Z chromosomes
What is heterogametic
Sex chromosomes are different so the gametes are different
Females are heterogametic so have one Z chromosome and one W chromosome
Do most mammals have similar xy system of sex chromosomes
Yes it has similar xy system of sex chromosomes except egg laying mammals
How many Gene’s in the human x chromosome
2000 Genes
10% of the total number of genes in our genome
How many Gene’s in the human y chromosome
200 genes
Many of these are also found on the x chromosome
Describe the process of the mammalian xy system
-Xy system is shared by marsupials and placental mammals- must have evolved before these two groups split
Step 1) process was the co option of the chromosome into the sec determination pathway
Step2) gradual loss of recombination between the two chromosomes this allowed the x and y chromosomes to diverge
Step3)Recombination now only occurs in three short regions of the x and y chromosomes called the pseudoautosomal regions
Step4) within these regions the same Gene’s are present are present on both the x and y chromosome- games inteheruted same as the autosomal Gene’s not sex linked Gene’s
Step 5) x chromosome Gene’s female have 2 copies but male have 1 copy- this difference requires special gene regulation
What results in unbalanced genetic pathways in males and females
If expression on all copies of the x chromosomes are equal then females would express twice the amount of RNA and proteins as males for x linked Gene’s
Chromosomes in male and female
Females- XX
males - XY
Males have half the genes of females because they’ve got one x
