Chapter 6 - Matters of Sex
Section 4 - X Inactivation
Section 5 - Parent-of-Origin Effect
X-Inactivation
- Early in female development, the maternal or paternal X chromosome is turned off in each cell. So females exhibit traits from mom in some cells and traits from dad in other cells.
- X inactivation compensates for differences between males in females in the number of gene copies on the X chromosome.
- The XIST gene encodes RNA that inactivates these genes.
- The inactivated X takes up stain and appears as a Barr body. The hypothesis proposed that the Barr body was the inactive X chromosome
- A female may express a sex-linked trait if the mutant allele is on the active X in affected tissues.
X-Inactivation
Examples
X-Inactivation Examples
- Anhidrotic ectodermal dysplasia - skin lack sweat glands in a mosaic pattern
- Women who are carriers of hemophilia have a less than normal blood clot time but this may reduce risk of cardiovascular disease
- Calico cats - black, orange, and white patches because of epistasis that shuts off pigment synthesis
- tortoiseshell cats - black and orange
- X-inactivation can be used to detect Lesch-Nyhan syndrome -Mutation defective HGPRT an enzyme
- Hair can be taken from a suspected carrier at different parts of the head to see of hairs contain HGPRT
Genomic Imprinting
- The disease may be more severe or different depending upon which parent transmitted the gene
Genomic Imprinting
Angelman Syndrome & Prader-Willi Syndrome
Angelman & Prader-Willi
- Small deletion in the same region of chromosome 15
- Prader-Willi Syndrome-is obese, small hands and feet, eats uncontrollably and does not mature sexually, fathers chromosome has a deletion
- Angelman Syndrome – is mental impairment, extended tongue, large jaw and poor muscle coordination and convulsions that make the arms flap. Mothers chromosome has a deletion
Additional Resources
Science in Pajamas
Other Videos
Additional Resources
Science in Pajamas
Sex-Linked Traits
Birds Sex-Linked Dihybrid Cross
Science in Pajamas
Birds Sex-Linked Dihybrid Cross
Other Videos
AK Lectures - Sex Chromosomes and Sex-Linked Traits
FuseSchool - Sex Determination
Amoeba Sisters - Punnett Squares and Sex-Linked Traits
UCD Medicine - X-Linked Recessive
Khan Academy - Example Punnett Square for Sex-Linked Recessive Trait
Catalyst University - X-Chromosome Inactivation, Barr Bodies, and Calico Cats
Bozeman Science - X Inactivation
Dirty Medicine - Prader-Willi vs Angelman Syndrome (Imprinting)
Other Videos
AKL - Sex Chromosomes and Sex-Linked Traits
AS - Punnett Squares and Sex-Linked Traits
UCDM - X-Linked Recessive
KA - Example Punnett Square for Sex-Linked Recessive Trait
KA - Example Punnett Square
CU - X Chromosome Inactivation, Barr Bodies, and Calico Cats
CU - X-Chromosome Inactivation
DM - Prader-Willi vs Angelman Syndrome (Imprinting)
DM - Prader-Willi vs Angelman