Genes - Lecture 18 - Sex determination and sex linked inheritance Flashcards
What is the size difference between the X and Y specific region?
X is larger and has over 1000 genes
Y has 80
What is the PARS?
Shared between the X and Y
Around 20 genes in humans
Needed for XY pairing in male meiosis
What is the arrangement of X and Y in mammals?
Females are homogametic
Males are heterogametic
What is the SRY?
Sex determining region on the Y
The one gene required to be defined as male
What were the 2 findings of experiments involving the SRY?
Translocation of SRY to the X chromosome is found in rare XX males
Mutation of SRY gene can give XY females
Transgenic mice expressing SRY will give rise to males
How does the SRY work?
It is a transcription factor that recognises specific DNA sequences found in promotors of genes
The binding of SRY at promotors activates gene expression
This means the effects SRY confers are conveyed by its target genes
What is the genetic system of sex in birds?
Use the ZW system
Males are ZZ
Females are ZW
What is a gyandromorph?
When an organism is a sexual mosaic
Cells on the right side of the body have the female set and on the left side they have the male set
This sets up cell autonomous sex identity which mammals don’t have
How come mammals and birds have different sex chromosomes
They evolved from different autosomes
What did Thomas Hunt Morgan study in relation to sex linked inheritance?
A spontaneous mutant fly with white eyes
It didn’t give the expected phenotypic ratios
What was Thomas Hunt Morgan’s hypothesis?
That the white mutation is on the X chromosome
Which chromosome is more involved in sex linked inheritance?
X chromosome
What are the features of X linked traits in humans?
Nearly all recessive
Most in males
Around 500 known X linked diseases
What is X chromosome inactivation?
One of the X chromosomes in each female cell becomes inactivated
They become highly condense and don’t express genes
What is the process of X chromosome inactivation in early development?
Inactivation starts early on in development randomly, and then it stays for all the next mitotic cell divisions
This means female mammals are mosaics, 50% of cells express only paternal X and 50% only maternal
