Download 9-2 Genetic Crosses

11-2 Genetic Crosses
1. Genotype and Phenotype
A. Genotype: the genetic make-up of an
organism. The alleles that the organism inherits
from the parents.
1.. Example – BB, Bb, bb, TT, Tt, tt
B. Phenotype: the physical appearance of an
organism as a result of its genotype.
C. Homozygous: when both alleles of a pair
are alike.
1. example – BB or bb
D. Heterozygous: when both alleles of a pair
are different.
1. example – Bb
E. Probability: the likelihood that a specific
event will occur.
Probability
Punnett
Squares - are
used
to see the
probability of
different traits
inherited
by the offspring
2. Different Punnett Square
crosses
• A. Homozygous Dom – Homozygous Dom =
– 100% Homozygous Dominate
B. Homozygous Dom.- Homozygous Rec. =
100 % Heterozygous Dominate.
C. Heterozygous – Homozygous Dom. =
50 % - 50%
D. Heterozygous – Heterozygous =
25% Homo. Dom. , 50% Hetero. Dom., 25%
homozygous rec.
2.
Monohybrid
crosses
A. Involves only
one pair of
contrasting traits.
E. Testcrosses:
an
individual with
unknown
genotype
is crossed with a
homozygous
recessive
individual.
•Chapter 11
•Section 11:3
F.
Incomplete dominance: occurs
when two or more alleles influence
the phenotype resulting in an
intermediate between the two traits,
or a 3rd trait.
Incomplete dominance
Complete dominance
H. Codominance: occurs when both alleles
for a gene are expressed in a heterozygous
offspring.
1. No trait is dominant and there is no
blending of traits. Both traits are shown
equally.
Co-dominance – Blood types
3. Dihybrid Crosses
A. Involves two pairs of contrasting
traits
Constructing a Di-Hybrid cross
• 1. Dominant – Dominant
• 2. Dominant – Recessive
• 3. Recessive – Dominant
• 4. Recessive – Recessive