You Inherited Your Blood Type Blood is the bodily substance most commonly found at the scene of a crime or on a person, clothing, or a weapon potentially

You Inherited Your Blood Type

• Blood is the bodily substance most commonly found at the scene of a crime or on a person, clothing, or a weapon potentially associated with a crime.

• The presence of antigens on cells is genetically determined.

• Every person can inherit two A, B or O blood type antigens – one from the mom & the other from the dad.

You Inherited Your Blood TypeGenotypes or Antigens

Phenotype or Blood Type

AA or AO A

BB or BO B

AB AB

OO O

Antigens A & B are called Codominant.

O (absence of both antigens) is recessive.


• Punnett squares are used to predict the probable genes you inherit from your parents.

• Biology Vocabulary review:

• Homozygous – same alleles (or antigens) = AA or BB or OO

• Heterozygous – different alleles (or antigens) = AO or BO or AB


• What is the probability (or possibility) of blood types if a mother (AA) has a child with a father (AO)?

• Do a punnett square using dry erase boards.

• Show genotypes and phenotypes as well as ratios (fractions & percentages).

• A refresher is next.


A A

A AA AA

O AO AO

GENOTYPE PHENOTYPE

AA – 2/4 (50%) Type A – 4/4 (100%)

AO – 2/4 (50%) Type B – 0/4

BB – 0/4 Type AB – 0/4

BO – 0/4 Type 0 – 0/4

AB – 0/4

OO – 0/4

AA X AO


• Do the following crosses on the dry erase boards provided.

• Pick a partner. Work in collaborative pairs.

• Assessment: Self & Peer Review – check your work & your partner’s work.

• 1. BB x BO





• 2. AA x AB





• 3. AB x AB





• 4. AO x AO


• In the Rh blood system, people are classified as either Rh positive or Rh negative.

• Rh positive have the Rh antigen.• Rh negative do NOT have the Rh antigen.• Rh positive can receive Rh negative blood,

but Rh negative cannot receive Rh positive blood. This can cause serious transfusion reactions.

You Inherited Your Blood Type• What would be the problem if an Rh

positive father has a child with an Rh negative mother? What might happen with future pregnancies?

• Distributed Summarizing: Use Numbered Heads = Choose a partner. The one with the earliest birthday in the year is #1, the later birthday is #2.

• Discuss the possibilities of the problem listed above.


• Blood typing is useful in forensics because it shows that two samples did not have the same origin.

• This information is called “exclusion” & is an important aspect of criminology that has freed many criminal suspects as well as those who were wrongly convicted.


• Blood typing is also used to exclude people in paternity cases.

• Blood typing cannot prove a man IS the father, but may be useful in showing he IS NOT the father. DNA testing would be the next step.

• Blood typing can give information to narrow down a list of possible suspects.


% of people with A, B, AB & O blood types

Type of Blood % people with blood type

A 41

B 10

AB 4

O 45


% of people with Rh + & Rh - blood types

Type of Blood % people with this type

Rh + 85

Rh - 15


• With this information, you can calculate the possibility that a person would have a particular combination of blood types.

• This was done in the O.J. Simpson Case when experts stated “…you would have to go to another galaxy to find a person with the same blood type as O.J. Simpson…”


• “Who Dunnit” Blood Typing Lab

• Lab is due before you leave at end of period.

• Work with lab partners & table mates

• READ THE DIRECTIONS! They are simple to follow.

• Have Fun & Learn!!!!

• Start Blood Spatter Lab Tomorrow!

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You Inherited Your Blood Type Blood is the bodily substance most commonly found at the scene of a crime or on a person, clothing, or a weapon potentially