Fulmer, 2009 BIO
GENETIC CROSSES
Differentiate: Genotype
Phenotype
Homozygous
Heterozygous
Explain why a phenotype might not always indicate a genotype.
Probability:
Probability = Number of times an event is EXPECTED to happen
Number of times an event COULD happen
Mendel’s experiments:
Dominant trait occurred 6,022
Recessive trait occurred 2,001
What is the probability that the dominant trait will occur?
Expressed as a percentage:
Expressed as a ratio:
What is the probability that the recessive trait will occur?
Expressed as a percentage:
Expressed as a ratio:
Fulmer, 2009 BIO
PREDICTING RESULT OF MONOHYBRID CROSSES
Monohybrid cross is . . .
HOMOZYGOUS X HOMOZYGOUS
Trait: Flower Color
Dominant- PP purple
Recessive- pp white
Phenotype:
Genotype:
HOMOZYGOUS X HETEROZYGOUS
Trait: Coat Color
Dominant- BB black
Recessive- bb brown
Phenotype:
Genotype:
HETEROZYGOUS X HETEROZYGOUS
Trait: Plant Height
Dominant- TT tall
Recessive- tt
short
Phenotype:
Genotype:
Fulmer, 2009 BIO
TESTCROSS
Can determine the genotype of any individual whose phenotype expresses
the dominant trait, but is unknown if individual is actually homozygous or
heterozygous for a trait.
Trait: Pod shape
Dominant: II -Inflated
Recessive: ii -Constricted
Phenotype:
Genotype:
INCOMPLETE DOMINANCE
-Occurs when the phenotype of a heterozygote is intermediate between the
phenotypes determined by the dominant and recessive traits.
Trait: Flower Color
Dominant: RR -Red
Recessive: rr -White
Phenotype:
Genotype:
CODOMINANCE
-Occurs when both alleles for a gene are expressed in a heterozygous
offspring.
Trait: Blood Types
Fulmer, 2009 BIO
DIHYBRID CROSSES
-Cross in which two characteristics are tracked. Thus four alleles from each
parent can combine.
HOMOZYGOUS X HOMOZYGOUS
Trait: Seed texture
Seed color
Dominant: RR – Round
Recessive: rr- Wrinkled
Dominant: YY – Yellow
Recessive: yy – Green
Phenotype:
Genotype:
Fulmer, 2009 BIO
HETEROZYGOUS X HETEROZYGOUS
Trait: Seed texture
Seed color
Dominant: RR – Round
Recessive: rr- Wrinkled
Dominant: YY – Yellow
Recessive: yy – Green
Phenotype:
Genotype: