Dosage Compenstation Flashcards
What is a dose?
An amount or quantity of something
What is a chromosomal dose?
A specific amount of gene expression, in particular, the expression of essential genes
What is an essential gene?
A gene that is required for viability.
Ex: genes that specify enzymes in aerobic respiration
What is haploinsufficiency?
One allele cannot provide enough gene product for normal development and function.
Occurs in a monosomy
What is gene expression?
The production of a product from the information in a gene
What is dose of gene expression?
The quantity of gene products in particular genes
Are essential genes on X or Y chromosomes?
Essential genes are only found on the X chromosome.
So only found in pseudoautosomal and X-linked genes
How many doses of pseudoautosomal genes do males and females have?
Both sexes have two doses of these genes
How many doses of holandric genes do males and females have?
Males have one dose
Females have zero doses
There are no essential holandric genes
How many doses of x-linked genes do males and females have?
Males have one dose
Females have two doses
There are essential X-linked genes
Is the dose of X-linked genes important?
Yes, as they contain essential genes
What is dosage compensation?
A mechanism that equalizes the dose of X-linked genes in males and females. There are two methods: X chromosome hyperactivation and X chromosome inactivation
What is X chromosome hyperactivation?
Genes in the male’s X chromosome are up-regulated so that it is twice the activity of genes in each X of the females. Each sex has the equivalent of two doses of X-linked genes.
This occurs in many insects
So basically, the X chromosome is expressing more
What is X chromosome inactivation?
Gene expression of the female’s chromosome is silenced/ Each sex has the equivalent of one dose of X-linked genes. This occurs in mammals.
Basically, one X chromosome is no longer expressive
What happens to the X chromosome in females? (kinda worded wrong but oh well)
In females, one X chromosome is always inactivated
What happens to one X chromosome during X inactivation?
One X chromosome becomes tightly packed and condensed permanently. Enzymes cannot access this chromosome.
Most genes on the X chromosome are inactivated, but some genes are spared. Which are spared?
Pseudoautosomal genes and some X-linked genes that are involved in the inactivation process
What is the name of the X chromosome after it has been highly condensed?
Barr Body
How do Barr bodies work?
If a cell contains more than one X chromosome, all but one chromosome will be inactivated. Each inactive X chromosome is considered a Barr body.
Which sex chromosome combination cannot have Barr bodies? Why?
XY cannot have Barr bodies. There is only one X chromosome.
When does X inactivation occur?
During the third week of fertilization
Can the inactive X chromosome undergo replication?
Yes, it can replicate normally during interphase and will be segregated into daughter cells during mitosis.
How does inheritance work with an inactive X?
Daughter cells will inherit the parent cell’s inactive X
When those daughter cells replicate, their daughters will also have the same inactive X
All cells descended from the original parent cell will have the same inactive X
What is the frequency of X inactivation?
X inactivation is random, so each chromosome has a 50% chance of being inactivated
What are the alleles for the X-linked gene involved in producing coat colors in cats?
XO = orange fur
XB = black fur
Where is the coat color gene expressed on the cat?
It is expressed in the skin cells that produce hairs
What is the genotype for male cats for the coat color gene?
XO Y
XB Y
What is the genotype for female cats for the coat color gene?
XBXB
XOXO
XOXB
What do female cats that are heterozygous for the coat color gene look like?
They have a tortoiseshell fur pattern
When a female cat has a tortoiseshell coat color, what does each patch represent?
Each patch represents a group of skin cells with the same active X chromosome carrying either the XO allele or the XB allele
What are the alleles for the X linked gene involved in red-green colorblindness?
XG = normal vision
Xg = red green colorblind
What is the frequency of each allele to be active?
