6. The role of sex in inheritance

Question 1

Sex-influenced traits

Answer 1

• Inherited autosomally, but has a higher penetrance in one sex than the other.
• The allele is dominant in one sex and recessive in the other

Question 2

Sex linked characteristics

Answer 2

Genes located on the sex chromosome

Question 3

Sex limited characteristic

Answer 3

Autosomal genes whose expression is limited to one sex only (require specific hormones for expression)

Question 4

Examples of sex limited traits

Answer 4

Breast, beard

Question 5

Cytoplasmic inheritance

Answer 5

Cytoplasmic genes which are usually inherited entirely from only one parent

Question 6

Y-linked inheritance

Answer 6

• Male to male transmission

- Vertical pedigree (manifestation in every generation)

Question 7

Genetic maternal effect

Answer 7

The genotype of the mother determines the phenotype of the offspring

Question 8

Mechanism of maternal effect

Answer 8

Substances in the cytoplasm of the egg determines the way the cytoplasm decides during early cleavage of the zygote

Question 9

Genomic imprinting

Answer 9

Genes whose expression is affected by the sex of the transmitting parent

Question 10

Example of diseases with XR inheritance (7)

Answer 10

• Hemophilia A
• Duchenne/Becker muscular dystrophy
• X-linked neonatal Adrenoleukodystrophy (ALD)
• OTC deficiency
• Androgen insensitivity syndrome (AIS)
• Kallmann syndrome
• Favism (G6PD def.)

Question 11

Kallmann syndrome inheritance

Answer 11

Can be XR, AD and AR

Question 12

Example of diseases with XD inheritance

Answer 12

• Hypophospatemia = Vit. D resistant rickets
• Fragile X syndrome
• Rett syndrome

Question 13

What causes fragile X syndrome?

Answer 13

Too many CGG repeats -> Hypermethylation causes FMR1 silencing

Question 14

Cause of Rett syndrome

Answer 14

Mutations in the X-linked MECP2