Download Other Patterns (Exceptions to Mendel`s Laws)

Other Patterns ~ Exceptions to Mendel’s Laws
 Phenotypic expression can vary based on different types of
gene expression:
 Incomplete Dominance = Hybrids have an intermediate
phenotype
Ex. In Snapdragons and Four-o-clock flowers, red, white, and pink
offspring can be produced. Show a cross between a red flower
and a white flower
What is the probability two pink flowers will produce red or white
offspring?
 Codominance = both alleles in a hybrid affect the phenotype;
both alleles are expressed.
Ex. Roan coat color can be expressed in cows and horses. Show a
cross between a roan cow and a red cow. What is the probability
that the offspring will be red? roan? white?
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Note: blood typing is an example of codominance, as well.
Other Patterns…
 Multiple alleles = more than two alleles can affect the
expression of a single gene.
Ex. In humans, there are 3 alleles that control the
expression of blood types. (IA, IB, i)
Phenotype
A blood type
B blood type
AB blood type
O blood type
Genotype
IAIA, IAi
IBIB, IBi
IA IB
ii
Expression
Dominance
Dominance
Codominance
Dominance
Ex: If a mother has A blood type, a baby has O blood type, and
the father has B blood type. Could he be the dad?
Ex: If mother has AB blood type and her has baby has B blood
type, and the father has A blood type, could he be the dad?
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Polygenic traits = multiple genes controlling one trait.
- Example = pigmentation (skin)
 Nature or Nurture?
phenotype.
Environment has an effect on
This phenotypic range is called norm of reaction
- Examples:
o Lack of nutrients in soil = shorter plant with smaller leaves
o Alcohol in blood moving to developing fetus = fetal alcohol
syndrome
o Cold temperatures = Darker pigments in fur of Siamese
cats where blood circulation decreases.
o Acid content of soil: high acid = blue hydrangea; less
acidic = pink hydrangea
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FAS
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Pedigrees – Can trace one trait through a family over many
generations.
 Can be used to trace different types of expression
Example: Autosomal dominance
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Example: Sex Linked
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