Were the babies switched? – The Genetics of Blood Types i
Two couples had babies on the same day in the
same hospital. Denise and Earnest had a girl,
Tonja. Danielle and Michael had twins, a boy,
Michael, Jr., and a girl, Michelle.
Danielle was convinced that there had been a
mix-up and she had the wrong baby girl. Tonja and Michael Jr. looked more like twins since they
both had darker skin, while Michelle had lighter skin. Danielle insisted that both families have blood
type tests to check whether there had been a mix-up.
The Genetics of Blood Types
Each person has one of the blood types shown in this chart. Your blood type is determined by
whether your red blood cells have type A and/or type B carbohydrate molecules on the surface.
A Person With: Has:
Type A carbohydrate molecules
Type A blood
on his or her red blood cells
Type B carbohydrate molecules
Type B blood
on his or her red blood cells
Both type A and type B carbohydrate molecules
Type AB blood
on his or her red blood cells
Neither type A nor type B carbohydrate molecules
Type O blood
on his or her red blood cells
These four different blood types result from different alleles of a single gene in the DNA.
These alleles give the directions for making different versions of a protein enzyme that
puts different types of carbohydrate molecules on the surface of red blood cells.
Allel Gives the directions for making a version of the enzyme that:
e
IA puts type A carbohydrate molecules on the surface of red blood cells
IB puts type B carbohydrate molecules on the surface of red blood cells
is inactive; doesn't put either type of carbohydrate molecule
i on the surface of red blood cells
1. Each person has two copies of this gene, one inherited from his/her mother and the other
inherited from his/her father. Complete the following table to relate genotypes to blood types.
Genotyp This person's cells make: Blood Type
e
the version of the enzyme that puts type A carbohydrate molecules on the
IA IA surface of red blood cells.
A
the inactive protein that doesn’t put either type A or type B carbohydrate
ii molecules on the surface of red blood cells.
O
both the version of the enzyme that puts type A carbohydrate molecules on
IA i the surface of red blood cells and the inactive protein
A
2. In a person with the IA i genotype, which allele is dominant, IA or i? Explain your reasoning.;’
Type IA is dominant because a person heterozygous for A (I A i) will still have “A” antigues.
1
, 2
Two couples had babies on the same day in the
same hospital. Denise and Earnest had a girl,
Tonja. Danielle and Michael had twins, a boy,
Michael, Jr., and a girl, Michelle.
Danielle was convinced that there had been a
mix-up and she had the wrong baby girl. Tonja and Michael Jr. looked more like twins since they
both had darker skin, while Michelle had lighter skin. Danielle insisted that both families have blood
type tests to check whether there had been a mix-up.
The Genetics of Blood Types
Each person has one of the blood types shown in this chart. Your blood type is determined by
whether your red blood cells have type A and/or type B carbohydrate molecules on the surface.
A Person With: Has:
Type A carbohydrate molecules
Type A blood
on his or her red blood cells
Type B carbohydrate molecules
Type B blood
on his or her red blood cells
Both type A and type B carbohydrate molecules
Type AB blood
on his or her red blood cells
Neither type A nor type B carbohydrate molecules
Type O blood
on his or her red blood cells
These four different blood types result from different alleles of a single gene in the DNA.
These alleles give the directions for making different versions of a protein enzyme that
puts different types of carbohydrate molecules on the surface of red blood cells.
Allel Gives the directions for making a version of the enzyme that:
e
IA puts type A carbohydrate molecules on the surface of red blood cells
IB puts type B carbohydrate molecules on the surface of red blood cells
is inactive; doesn't put either type of carbohydrate molecule
i on the surface of red blood cells
1. Each person has two copies of this gene, one inherited from his/her mother and the other
inherited from his/her father. Complete the following table to relate genotypes to blood types.
Genotyp This person's cells make: Blood Type
e
the version of the enzyme that puts type A carbohydrate molecules on the
IA IA surface of red blood cells.
A
the inactive protein that doesn’t put either type A or type B carbohydrate
ii molecules on the surface of red blood cells.
O
both the version of the enzyme that puts type A carbohydrate molecules on
IA i the surface of red blood cells and the inactive protein
A
2. In a person with the IA i genotype, which allele is dominant, IA or i? Explain your reasoning.;’
Type IA is dominant because a person heterozygous for A (I A i) will still have “A” antigues.
1
, 2
