Sex Determination and Dosage Compensation

Question 1

What is Dosage Complensation?

Answer 1

-a way of equalizing gene expression in the face of different gene dosage
-humans need 2 genes
-humans are very susceptible to this
-causes genetic complications
-meiosis/mitosis can mess up and cause problem

Question 2

What is sex determination and sex-linked determination?

Answer 2

-several different mechanisms of sex determination
-the X and Y chromosomes paired during meiosis even though they’re not homologous (the genes located on each are different)
-the X and Y chromosomes are homologous only at pseudo autosomal regions regions which are essential for X-Y chromosome pairing in meiosis in the male primary pseudo autosomal region (X)
secondary pseudo autosomal region (Y)
-tips on the short arms of the X chromosome interact and cause homozygotes

Question 3

What are the chromosomal sex determination systems for sex chromosomes and non-sex chromosomes (autosomes)?

Answer 3

• XX-XO system:
• XX female have twice as many as males
  -XO-male
  grasshoppers
  -XX-XY system:
• XX female
  -XY male
  -XO female
  -XXY male double X gene seen in grasshoppers
  -mammals does the opposite has one X Gene for females

Question 4

What is X-inactivation?

Answer 4

-interphase nucleus: female cell
-yellow: fluorescent probe that recognizes the X chromosome
-probe stairs X chromosome yellow inactive
-X one is active one is inactive -condensed mass in nucleus of female cells in cats not male
-proposed that the mass was the X chromosome
-one X-chromosome is inactivated in each cell- the process is random it is equally likely that the maternal or paternal X chromosome will be inactivated

Question 5

What is Leon hypothesis and x-inactivation?

Answer 5

• Mary Lyon proposed the random inactivation of one female X chromosome considered Mosaic for chromosomes
  -if a cell contains more than two X chromosomes all but one of them are inactive
  -XO females have no barr bodies xxy males (have ability to inactivate one X) have one barr body XXX females have two barr bodies
  Therefore, females are functionally hemizygous for linked genes at the cellular level approximately 50% cells will express one allele (A) and 50% cells will express the other allele (a)
  -hormones are still fine because it travels throughout body

Question 6

What happens if there are genes on the X-chromosome?

Answer 6

genetics-Calico Cats female xx
-orange gene is on the X-chromosome
O= orange o=black cells inactivated dominant orange alles to show black

Question 7

What is genetic mosaics?

Answer 7

indicates an allele that is present but not contributing to the phenotype