multiple and missing alleles

how is your blood group determined?

which blood group you have is determined by whether you have certain ‘marker molecules’ on the outside of your blood cells

what are the three types of marker molecules?

A, B, and O

what are the three alleles for the ABO system?

Iᴬ, Iᴮ, and Iᴼ

which of the ABO alleles are dominant?

Iᴬ, Iᴮ

which of the ABO alleles are recessive?

Iᴼ

explain why ABO blood groups show codominance

a person with the genotype IᴬIᴮ shows the effect of both alleles and has the blood group AB.

what is codominance?

when both alleles for a gene affect the phenotype

how does the human Y chromosome differ from the X chromosome?

the Y chromosome is missing some of the genes found on the X chromosome

why do men have only one allele for some genes on the X chromosome?

because those genes are missing on the Y chromosome

what happens if a man inherits a disorder-causing allele on the X chromosome?

he will develop the genetic disorder since he has no second X chromosome to provide a healthy allele

why are women less likely to develop X-linked recessive disorders?

they have two X chromosomes, so a healthy allele on one can mask a recessive disorder on the other

what must happen for a woman to develop an X-linked recessive disorder?

she must inherit two recessive disorder alleles, one on each X chromosome

what are sex-linked genetic disorders?

disorders that show a different pattern of inheritance in men and women due to the X and Y chromosome differences