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Wednesday
4-14-2010
Unit 8 Notes:
Mendelian
Genetics
(1) Gregor Mendel
Scientist & Monk
 Studied Pea Plants
 Determined how
traits are inherited
 Determined how
traits are expressed

(2) Cross-Breeding
Combining sperm + egg
 Mixing Traits


Monohybrid Cross:
 Cross-Breed
2 organisms
 Observe only 1 trait

Dihybrid Cross:
 Cross-Breed
2 organisms
 Observe 2 traits
(3) Mendel’s Generations
P Generation = Parents
 F1 Generation = First Offspring
 F2 Generation = Offspring from F1 Breeding

(4) Types of Alleles

Dominant Allele:
 Big
Letter
 Always expressed over
the recessive trait.

Recessive Allele:
 Little
Letter
 Only expressed when
you have 2.
(5) Genotype vs. Phenotype

Genotype = Genetic Details of an organism

Phenotype =
Physical Expression
of the genotype
(6) Types of Genotypes

Homozygous:
2
Dominant Alleles
OR
 2 Recessive Alleles

Heterozygous:
1
Dominant + 1 Recessive Allele
(7) Example #1:
A)
Cross-Breed two homozygous pea plants.
One plant is tall, and one plant is short.
B)
What are the offspring genotypes?
C)
What are the offspring phenotypes?
(8) Example #2:
A)
Cross-Breed two heterozygous pea plants.
Both plants are tall.
B)
What are the offspring genotypes?
C)
What are the offspring phenotypes?
(9) Example #3:
A)
Cross two pea plants. One is homozygous
recessive and has wrinkly seeds. One is
heterozygous and has round seeds.
B)
What is the probability that they will produce
round-seed offspring?
C)
What is the probability that they will produce
wrinkly-seed offspring?
(10) Example #4:
A)
Cross-Breed two rabbits. One is
homozygous and black. One is
heterozygous and black.
B)
What are the genotypic ratios?
C)
What are the phenotypic ratios?
(11) Example #5:
In rabbits, B is an allele for black coat and b is
an allele for brown coat. Write the
genotypes for a rabbit that is homozygous
for black coat, and another rabbit that is
heterozygous for black coat.
(12) Example #6:
In pea plants, the allele for yellow seeds is
dominant to the allele for green seeds.
Predict the genotypic ratio of offspring
produced by crossing two parents
heterozygous for this trait. Draw a Punnett
Square to illustrate your prediction.
(13) Example #7:
In sheep, the allele for white wool (A) is
dominant over the allele for black wool (a).
If a sheep is white, how could you
determine if it is homozygous or
heterozygous for white-wool?
(14) Example #8:
In dogs, the allele for short hair is dominant
over the allele for long hair. Two shorthaired dogs are the parents of a litter of
eight puppies. 6 puppies have short hair,
and 2 have long hair. What are the
genotypes of the parents?
(15) Example #9:
In guinea pigs, the allele for a rough coat ® is
dominant over the allele for a smooth coat
(r). A heterozygous guinea pig (Rr) and a
homozygous recessive guinea pig (rr) have
a total of nine offspring. What is the
chance that their offspring will have
smooth coats? Explain how it could be
possible to have 9 offspring, all of which
have smooth coats.
(16) Example #10:
Suppose Mendel crossed two pea plants and
got both tall and short offspring. What
could have been the genotypes of the two
original plants? What genotype could not
have been present?