Sheet 4 Flashcards
What happens if nondisjunction occurs with X or Y chromosomes?
Sexual aneuploidies
Which gene is smaller: X or Y? What does this mean?
Y; that there are genes in the X chromosome that are absent in the Y chromosome
What do we call the sex chromosomes?
Hemizygous genes: Only one allele for a certain gene
What are Psuedoautosomal regions?
Look like autosomal regions where there are 2 versions of the same gene (2 alleles) {Some regions of X are shared on Y}
What can you find on the Y chromosome?
1) SRY (Sex determining Region Y)
2) AZFa
3) AZFb
4) AZFc
What is the SRY region responsible for?
The development of male anatomical features
Explain what causes the case in which the karyotype is: 46, XY, but the primary sexual organs indicate a female (ovaries, not testes).
There’s a deletion in the SRY region.
What are the AZFa, AZFb, and AZFc regions responsible for?
The formation of sperm
If a male presents with infertility (low or zero sperm count = azoospermic), what should you check for?
Mutations in the 3 AZF regions on the Y chromosome.
True or false:
All the genes carried on sex chromosomes are sex-related.
False; not all are sex-related (some genes are not related to a sex trait)
What are some non-sex related genes found on the sex chromosomes?
1) Hemophilia gene
2) DMD (Duchenne Muscular Dystrophy) gene
Where is the hemophilia gene found?
Bottom of the Q arm of the X chromosome
Overall, we have - genes on X chromosome, - genes on Y chromosome.
900-1600; 70-200
What causes chromosomal disorders?
1) Numerical abnormalities (a missing or an extra chromosome)
2) Structural abnormalities (i.e., deletion, duplication, inversion or translocation).
What are some diseases caused by numerical abnormalities?
1) Klinefelter Syndrome (KS)
2) Turner Syndrome
(Both sex chromosome aneuploidies)
What are some diseases caused by structural abnormalities?
1) Cri-du-chat (cry of the cat) Syndrome
2) Certain cancers such as Chronic Myelogenous Leukemia (CML)
What is the karyotype for Klinefelter Syndrome (KS)?
47, XXY (MALES only)
Individuals with KS develop __(female/male) primary sexual organs. Why?
Male; regardless of how many X chromosomes they have, there’s still a Y chromosome and an SRY region.
What are the characteristics of Klinefelter Syndrome?
1) Secondary female characteristics:
Female fat distribution (hips) with breast development (gynecomastia)
2) Underdeveloped primary male sexual organs (testicular atrophy/small testes = absent sperm) = they’re infertile males.
3) Coarse/reduced body hair
4) Taller than average
5) Evidence of mental retardation that may or may not be present
6) Evidence of osteoporosis
What is the karyotype for Turner syndrome?
45, XO (missing X chromosome)
What kind of patients does Turner syndrome produce?
Sterile females
Which syndrome is the ONLY VIABLE monosomy?
Turner syndrome
Why are patients of Turner syndrome ALWAYS female?
Because there’s neither a Y
chromosome nor an SRY region.
What are the characteristics of Turner syndrome?
1) Skin brown spots (nevi)
2) Underdeveloped breasts with a wide distance between the nipples
3) Webbed neck
4) 20 cm shorter than average
5) Rudimentary ovaries and underdeveloped gonads = infertility
6) No menstrual cycle
7) Abnormal elbow position
8) Secondary non-significant features (small fingernails and shortened metacarpals)
