L2: Laws of Segregation

how many copies of a trait do offspring need to express an X-linked dominant?

-only one

how many copies of a trait do offspring need to express an X-linked recessive?

-females → two

-male → one

how many copies of a trait do offspring need to express an autosomal recessive?

-two

how many copies of a trait do offspring need to express an autosomal dominant?

-one

summary:

autosomal dominant

-generation 2 generation (cannot skip)

-affected offspring has at least one affected parent

-♀ & ⚦ affected equally

-homozygous recessive can not have autosomal dominant offspring

-affected parents (must be heterozy) → normal offsping

summary:

autosomal recessive

-can skip generations (not always)

-parents are homozy recessive

-♀ & ⚦ affected equally

summary: 
X-dominant

-♀ & ⚦ not affected equally

-every affected offspring has (at least) one affected parent

-affected males + normal female → to all female offspring, no male offspring

• X - ♀

• Y - ⚦

summary:

X-recessive

-♀ & ⚦ not affected equally

-can skip generations

-two affected parents

• affected ⚦ + normal homozy ♀ → ♀ offspring carriers

• normal ⚦ + affected ♀ → ♀ offspring carriers, ⚦ affected

why are there fewer Y chromosome-linked disorders?

-fewer genes than X-chromosomes

-Y genes generally related to male sex determination and spermatogenesis, not general body fxs

-Y is non-coding or repetitive

-Y does not undergo recombination

-mutations stop transmission

A female dog who is a carrier for X-linked haemophilia A is crossed to a male dog who does not have haemophilia A.

What is the chance that a female pup from this litter will have the disease haemophilia A? Why? 

How to tell it’s a X-recessive? 

0

-X recessive

-female offspring inherit father’s normal X-chromosome

-female would need both parents to be affected 

-if it were dominant, the female would present with the disease

This pedigree shows a family afflicted with a rare genetic disease. The circles
represent females, squares represent males, and individuals with solid black
symbols show clinical signs of the disease. The genetic mode of inheritance
that is most consistent with this pedigree is:

X-dominant

-affected males have all affected female offspring and no affected male offspring

In cats black coat colour is caused by deposition of melanin in hair, governed
by the Cb allele. A co-dominant Cy allele produces orange hair colour. The
tortoise-shell coat colour is normally seen only in heterozygotes. In a population
of cats in Brisbane, the following phenotypes were seen:

Why are the tortoise-shell cats all female?

-must be an X-linked trait since no males are affected