Person is affected if all X chromosomes carry allele.

i.e. X^aX^a & X^aY

X^oB - black

X^oO - orange/yellow

X^oBX^oO - calico

*calico is the presense of black and areas on the coat.

Drosophila eye colour as an example of X-linked traits

red eyes female x white eyed males

F1 ?

F2 ?

F1: all red eyed

F2: all females have red eyes

1/2 males have red eyes

1/2 males have white eyes

X^rX^r  X^rX^w  X^rY  X^wY

ABO blood and Nail-Patella Syndrome(rare autosomal dominant condition)

ABO <- 20 map units -> N/n

classic haemophilia and reg-green colourblindness are closely linked on the

X chromosome

H/h <- 10 map units -> CB/cb

W¹W^{1 = white}

W¹W^{2 = pink} 

W²W^{2 = red}  

F¹F¹ = normal plumage

F¹F² = frizzled      

F²F² = naked         

C⁺C⁺ = sorrel/chestnut

C⁺C^cr = palomino        

C^crC^cr = cremello         

expressed in heterozygous and homozyogous dominant

i.e. Huntington Disease

expressed only in homozygous recessive offspring

i.e. individual homozygous for Tay Sachs allele is unlikely to live past age 3

Two individual genes can individually produce the same phenotype.

If individual is homozygous reccessive for only one gene wild type phenotype is observed.

Many different genes can be associated with the lack of pigment associated with albinism

i.e. SS (extensive white)

W- (all white) 

cc (albino)    

Gene C which controls coat colour is epistatic to all other coat colour genes when homozygous recessive.

i.e. AaBBcc = albino

Both males and females have a gene but only one sex expresses the trait.

i.e. milk production, development of secondary sex characteristics

autosomal recessive trait

in dogs

aa females are normal

aa males have undescended testes

follows dominant pattern in males and recessive pattern in females

 (B² = baldness allele)

B¹B¹ - males: normal; females normal   

B¹B² - males: affected; females normal 

B²B² - males: affected; females affected

Paracentric

(inversion does not include centromere)

Pericentric

(inversion does include centromere)