Chapter 12.4.3 (Exam 3) Sex Determination Flashcards
Genes Are Carried on Chromosomes
What is primary sex determination?
Determines development of the gonads
What is the role of the SRY protein in primary sex determination?
If SRY protein is present, the embryo develops testes
If there is no SRY, the embryo develops ovaries
What is the mechanism that allows the SRY protein the function?
DAX1 → no testis; female
SRY → inhibits DAX1 → testis develops; male
Describe the fruit fly sex determination system.
Fruit flies have an XY sex determination system – different from humans
An XO individual is male
An XXY individual is female
What determines the sex in the fruit fly sex determination system?
Presence of X chromosomes determines sex,
not the presence of a Y chromosome
What is sex-linked inheritance?
Inheritance of a gene carried on a sex chromosome
How was sex linkage for red eye color discovered?
Crossing wild type females (red eyes), with recessive mutant males (white eyes)
All offspring had red eyes
Reciprocal cross:
All female offspring had red eyes
All male offspring had white eyes
What does it mean if an individual is hemizygous?
Gene present as a single copy in a diploid organism
This means the gene is present in only one of the parents
In X-linked recessive traits, which sex is generally affected? Which is the carrier?
Males are affected (only one X chromosome)
Females are carriers (two X chromosomes, one generally dominant)
Can a male with an X-linked recessive mutation pass it to his sons or his daughters?
Males pass X chromosomes to their daughters
What happens when an X-linked recessive mutant phenotype is passed from a male to his daughter?
The phenotype skips a generation and the daughter is a carrier
