Sex linked traits and pedigrees

Question 1

The Y chromosome

Answer 1

• Fewer then two dozen genes identified
• One is the master gene for male sex determination (SRY gene)
• SRY present, testes form
  -SRY absent, ovaries form

Question 2

The X chromosome

Answer 2

-Carries more than 2,300 genes
-Genes on X chromosome can be expressed in both males and females

Question 3

Sex linked traits

Answer 3

Traits located on sex chromosomes are called sex-linked traits and are usually on the X chromosome

ONLY FOCUSING ON RECESSIVE X LINKED TRAITS

Question 4

Sex linked traits and males

Answer 4

• A recessive trait located on the X chromosome is more likely to be expressed in males since they need only one copy of the recessive allele while females need two
• Recessive X-linked disorders occur more frequently in males(hemophilia,pattern baldness, colour blindness)

SON CANNOT INHERIT DISEASE FROM HOS FATHER

Question 5

Y linked disorders

Answer 5

Disorders where the allele is located on the Y chromosome and passed on from father to all of his sons

Question 6

Notations

Answer 6

XX for females
XY for males

Dominant allele is capitalized with superscript

Recessive allele is lowercase and written as a superscript

Question 7

Pedigree

Answer 7

family tree of phenotypes

Question 8

Autosomal dominant

Answer 8

• Genotypes are either Aa or AA

-Affected individuals have at least one affected parent

• Therefore 2 unaffected parents can only have unaffected offspring

Question 9

Autosomal recessive

Answer 9

-Genotypes of individuals are homozygous recessive (aa)
-Affected offspring can have unaffected parents