105. Define

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• Dominant - allele that overrides another allele. Written as a capital letter (A, T, Y, etc)

• Recessive - allele that gets overridden by another allele. Written as a lower case letter (a, t, y, etc).

• Homozygous - two of the same allele (Example: AA, aa)

• ​Heterozygous - two different alleles (Example: Aa, Tt)

• Genotype - allele combination that codes for a particular trait (Example: TT - tall; tt - short; Bb - brown eyes)

• Phenotype - physical characteristics determined by the genotype (Example: tall, short, brown hair, blue eyes)

106. a. Monohybrid Cross

Two heterozygous tall plants are crossed. If tall is dominant over short, what are the expected phenotypic results?

(Show your work!)​

Monohybrid Cross

Phenotypes:

75% TALL  (TT, Tt),  25 % SHORT (tt)

Incomplete Dominance

Sometimes a dominant allele is not completely dominant.

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In that case, there is a mixing between the two traits.

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RR: red flower

WW: white flower

RW: pink flower​

108. Incomplete Dominance

When Red and white flowers are crossed, pink flowers are produced. What is expected when two pink flowers cross?

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RR: red flower

WW: white flower

RW: pink flower​

Codominance

When two different alleles are equally dominant, they BOTH get expressed.

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This happens sometimes in cattle.

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It also happens with bloodtypes.

Codominance

Mr. Jones has blood type I^A i and Mrs. Jones has blood type I^B i.

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What is the probability that they will have a child with blood type ii?

110. Is it possible for a man with type A blood and woman with type B blood to have a child with type O blood?

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I^A i x I^B i​

111. Pedigrees

Square = male

Circle = female

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Shaded = has the trait

Unshaded = does not have the trait​

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Is this pedigree showing a dominant or recessive trait?

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111. Pedigrees

Is this pedigree showing a dominant or recessive trait?

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Remember that recessive traits have a tendency to skip generations. ​

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If the trait does not skip generations, it is probably dominant.​

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Dihybrid Cross

To cross two traits, use the FOIL method:

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First

Outer

Inner

Last

Dihybrid Cross

R: red eyes

r: black eyes

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D: dark fur

d: light fur

Dihybrid Cross

Show a cross between:

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RRdd x RrDD

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Red eyes are dominant to black eyes and dark fur is dominant to light fur.

Sex-linked Traits

• Sex linked traits are carried on the sex chromosomes (X or Y). Males have XY, females have XX.

• Males will more commonly express the phenotype because they only have one X chromosome.

• Females will express the phenotype only if she inherits 2 copies because she has 2 X chromosomes. 

• Females can be carriers if the trait is recessive.

B - normal vision

b - colorblind

Color blindness is a sex-linked recessive trait. A woman with normal color vision is married to a man who is color blind.

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What would be the phenotypic ratio of their offspring?