Sex Linkage and Incomplete Dominance (Leaving Cert Biology): Flashcards
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Sex linkage definition
Sex linkage definition
When a gene on a sex chromosome controls a characteristic
Larger sex chromosome
Larger sex chromosome
X chromosome
Why males express X-linked recessive traits more
Why males express X-linked recessive traits more
Only one X; no masking allele on Y
Two examples of X-linked traits in humans
Two examples of X-linked traits in humans
Colour blindness and haemophilia
% of males with colour blindness
% of males with colour blindness
About 8%
What is haemophilia?
What is haemophilia?
Bleeding disorder; lack of clotting proteins
Male child's haemophilia chance (carrier mother, normal father)
Male child's haemophilia chance (carrier mother, normal father)
50%
Males as carriers of X-linked traits
Males as carriers of X-linked traits
Cannot be carriers
Incomplete dominance definition
Incomplete dominance definition
Both alleles expressed; intermediate phenotype
Cattle coat: red x white offspring colour
Cattle coat: red x white offspring colour
Roan (mixture of red and white)
Genotype for roan cattle coat
Genotype for roan cattle coat
(heterozygous)
Snapdragon: red x white flower colour
Snapdragon: red x white flower colour
Pink
F2 phenotypic ratio in incomplete dominance
F2 phenotypic ratio in incomplete dominance
1:2:1