Download Sex linked trait: A trait that is carried by alleles on the X sex

Sex linked trait: A trait that is carried by alleles on the X sex
chromosome only, NOT the Y.
Examples of sex linked traits:
Colorblindness
Hemophilia
Hypertrichosis
Let’s use colorblindness as an example to show patterns seen in sex linked traits
C = normal vision allele
c= color blind allele
Genotypes
C
X
C
Phenotypes
X =
Normal vision female
C
X XC =
Normal vision female
XC XC =
Color blind female
C
X Y =
Normal vision male
c
X Y =
Color blind male
NOTE: As seen from the example above, Males have a greater probability of expressing a sex linked trait
because they lack the heterozygous condition. Whatever allele they have on their X chromosome is what will
show up in their body. Females have the advantage of being a carrier of the allele without expressing the trait.
Multiple Allele Traits: Traits that are determined by more than two different
alleles. Ex. Blood Types
There are three alleles that determine human blood types: A, B, and O
• The A allele is dominant to the O allele
• The B allele is dominant to the O allele
• A and B are said to be CODOMINANT to each other. This means they
contribute equally to the phenotype.
• O is recessive to both A and B
Genotype
Phenotype
AA
AO
BB
BO
AB
OO
Type A blood
Type A blood
Type B blood
Type B blood
Type AB blood
Type O blood
When two incompatible blood types mix together, the result is called
agglutination. (see pictures below) THIS IS NOT GOOD! LETHAL IN FACT.
Agglutination
Compatible Blood
We also have another surface protein on our cells known as Rh factor (as
first discovered in Rhesus monkeys). If you have this factor, your are said
to be positive for it or, (Rh+). If you do not have it, you are negative for it
or, (Rh-).
Problems can occur if your Rh factors are not compatible. (see fig.below)