Part 1: Genetics
Problem- Human Blood Types
Mendel is the father of modern genetics, but there are some
genetic characteristics that cannot be explained by simple Mendelian genetics.
Such is the case with the human blood types in which there are 3 alleles for
the same gene, A B, and o. A parent can pass allele A, B, or o to the offspring
based on the parent’s genotype.
From these 3 alleles, there are 4 blood types (phenotypes):
A, B, AB, and O, and there are six
genotypes: AA, Ao, BB, Bo, AB, or oo. This is an example of codominance in
which both A and B alleles are codominant to each other.
Blood types can be used in forensics to determine if blood
is from the victim or criminal. Blood types can be used to determine parental
source in situation where the father is unknown; however, blood types can only
eliminate certain blood types. DNA fingerprinting is a better method that is
used often in criminal and parental determination cases.
Punnett squares such as the one shown above are used to
determine the probabilities (percentages) for genotypes of offspring given
specific genotypes for the parents.
A) In the example
above, the Punnett Square represents a cross (mating) between a male (on the
left side) with blood type AB, and a female, (top of square), with blood type
A, genotype Ao.
Answer the following for the cross represented above.
1) What are the possible blood types for the offspring?
2) What are the ratios or percentages for each possible
blood type from this cross?
3) What blood type is not possible from this cross?
B) Fill out two Punnett squares for a cross between a male
with blood type B and a female with blood type AB. (Note that we do not know if
the father is genotype BB or Bo from the information given. Thus there are two
solutions to the possible cross.)
Set up two Punnett squares and answer the following
questions about them.
1) What are the
possible blood types for the cross between the type B (BB or Bo?) male and AB
female?
2) What are the
percentages (%) or probabilities for each blood type in the offspring?
3) What blood
type(s) would not be possible in a cross between these two parents?
Hint: There are two answers for questions 1 & 2 above
and only one for 3.
Turn in the Punnett Squares and your answers to the
questions.
Part 2 : Cell
division, mutations and genetic variability.
Eukaryotic cells can divide by mitosis or meiosis. In humans, mitosis produces new cells for
growth and repair. And, meiosis produces
sex cells (gametes), called sperm and eggs. Changes or mutations in genes in
sex cells can be inherited by human offspring.
Genetic variation in a population of organisms is good; however,
sometimes mutations can be harmful or cause genetic disorders.
Briefly, answer the following questions:
How do meiosis and
sexual reproduction (fertilization) produce offspring that differ genetically
from the parents?
Describe one example of a human disorder that is inherited
and also describe the specific inheritance pattern. For this example, pick disorders that result
from mutations in DNA or chromosome number rather than examples such as a genetic
tendency for a disorder such as cancer.
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