Biology School Worksheet (Page 3 of 6) in pdf

Biology School Worksheet Page 3

The F2 progeny, however, demonstrate Mendelian genetics. When the F1 roan individuals mate, the F2 progeny have

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a phenotypic ratio of 1 red:2 roan:1 white.

This mode of inheritance is called incomplete dominance.

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The phenotypic outcomes for cow color and incomplete dominance in general can be explained biochemically.

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One allele of the gene codes for an enzyme that functions in the production of the red color. The other allele codes

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for the gene to make white color. If both alleles are present, both are expressed, resulting in a cow that has some

red and some white.

Mendel's laws are not compromised here, he just happened to find in peas examples of complete dominance only.

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•Not all alleles are dominant and recessive.

•Some alleles are equally strong and _______________ are ______________ by the other.

•Alleles which are equally strong are said to be "________________".

Codominance

•When _______________ alleles are present, they are _______________ expressed in the phenotype.

•The hybrid is a _______________ of both alleles.

•When expressing codominant alleles, both alleles are represented by different _______________ letters.

Complete the Punnet square for a cross between a black chicken (BB) and a white chicken (ww). Give the phenotype of the offspring?

-Black

-white

-checkered

What is the phenotype if the offspring?___________

What is the name of the inheritance pattern in which both alleles are expressed equally?

Blood Types and Codominance

In humans, there are four blood types (phenotypes): A, B, AB, and O

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Blood type is controlled by three alleles. A, B, O

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O is recessive, two O alleles must be present for the person to have type O blood

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A and B are codominant. If a person receives an A allele and a B allele, their blood type is type AB

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Crosses involving blood type often use an I to denote the alleles - see chart.

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Biology School Worksheet Page 3