Download Genetics Probability - Elyria Catholic High School

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• Describe the laws of independent
assortment and of segregation
Genetics Probability
Genotype and Phenotype
• Genotype is the Genetic Makeup of an
organism (2 alleles, one from each parent)
• Phenotype is its physical appearance (the
trait that is expressed)
– Humans can change their physical
appearance but they still have the same
phenotype
• Homozygous- when both alleles are the
same
– Homozygous dominant (AA)
– OR Homozygous Recessive (aa)
• Heterozygous- when there are one of each
allele
– (Dominant is always expressed in the
phenotype)
• Probability can be expressed in a fraction
or a percentage
• Results are more likely to be accurate with
more trials or offspring
Monohybrid Crosses
• Cross between two individuals that
involves the genotype of the parents to
predict the genotype of the offspring.
• Punnett Squares are used to determine
the offspring probability.
• We are going to study the
gene that determines
whether or not a rat is
born with hair.
• H- is the allele that
determines hairy rats
• h- is the allele that
determines bald rats
• HH= hairy rats
• Hh= hairy rats
• Hh= bald rats
• We are going to cross
two homozygous
dominant rats
H
H
H
H
• Punnet square says all or their babies will
be hairy and have the same genotype =
homozygous dominant
Two
Homozygous
recessive rats
h
h
h
h
• Yess!!! All their babies will be bald!!
Heteroygous +
Heterozygous
• Both rat
parents are
hairy, however
their genotype
carries the
recessive allele
• 3:1 Ratio
• Hairy:Bald
H
h
H
HH
Hh
h
Hh
hh
Homozygous
recessive with
heterozygous
50 % are
hairy
And 50% are
hairless
H
h
h
Hh
hh
h
hH
hh
• You do the last one yourself!
• The Curve Ball!
Incomplete Dominance
• Mendel’s Peas showed Complete
Dominance
• This is almost always the case!
• Incomplete Dominance is when two or
more alleles influence the phenotype,
resulting in an intermediate phenotype
• One allele for a flower that is red and one
allele for a flower to be white
• When they are in their homozygous state
they will express the expected phenotype
• In the heterozygous state the flower will be
pink !
Codominance
• Both alleles are completely expressed in
the phenotype in the heterozygous state
• Horses have an allele for white and brown
coats. Sometimes both are expressed.
Dihybrid Cross
• Homozygous Dominant Parent for Yellow
and Round Pea crosses with a
homozygous recessive Parent for green
and wrinkled pea.
• Make a key, Draw a dihybrid cross and
find the ratio.
• All the offspring will be round and yellow
• AND!!!.... Heterozygous for both traits.
• Good work !