Karyotyping And X Linked Disorders

Question 1

What is sex linked inheritance

Answer 1

Refers to the pattern of inheritance shown by genes on either of sex chromosomes

Question 2

X linked recessive inheritance

Answer 2

Mostly in males

If male has mutant allele on his single X chromosome he is hemizygous

Question 3

What are the genetic risks for x linked inheritance

Answer 3

▪️Male affected will have carrier daughters but non of his sons will be affected
▪️Carrier females may transmit disease to their sons
▪️if carrier female marries normal male each of her sons have a 50% chance of being affected and each daughter has a 50% chance of being a carrier
▪️Duchenne muscle dystrophy

Question 4

X linked dominant inheritance

Answer 4

Uncommon

Manifest in heterozygous female as well as in male who has mutant allele on his single X chromosome

Question 5

What are the genetic risks of x linked dominant inheritance

Answer 5

▪️affected female transmit the trait to both her daughters and sons equally with a 50% chance of being affected regardless of sex
▪️affected male transmits to his daughters but not sons

Question 6

What are examples of x linked dominant inheritance

Answer 6

X linked hypophosphatemia
Vitamin d resistant rickets
Short stature
Bowed long bones

Question 7

Examples of y linked inheritance

Answer 7

Genes involved in spermatogenesis
Leads to infertility as genes are deleted
And passed on to his son

Question 8

What is karyotyping

Answer 8

Process of pairing and ordering all chromosomes of an organism thus providing a genome wide snap shot of an individual’s chromosomes

Question 9

How are karyotypes prepared

Answer 9

From mitotic cells in metaphase as this is when chromosomes are most condensed
Add stains that bind with DNA such as
G(giesma) Q(quinarcine) R(reverse) banding

Question 10

What stains more darkly in G-banding

Answer 10

Hectochromatic as they are AT rich and relatively gene poor

Question 11

What stains lightly in G-banding

Answer 11

Less condensed chromatin which is CG rich and more transcriptionally active

Question 12

How many chromosomes should be analyzed to get an accurate diagnosis

Answer 12

20-25

Question 13

Karyotype formula

Answer 13

\+ for gain eg 47,XX,+8
-for deletion eg 45,XY,-7
T for translocation eg t(8;21)(q22;q22)
Inv for inversion eg inv (16) (p13q22)
Del for deletion eg (5)(q13q31)