Monohybrid Crosses (Punnet Squares)

Monohybrid Crosses (Punnet Squares)

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Why is it important for you to know about Punnett squares?

 The answer is that they can be used as predictive tools when considering having children. Let us assume, for instance, that both you and your mate are carriers for a particularly unpleasant genetically inherited disease such as cystic fibrosis . Of course, you are worried about whether your children will be healthy and normal. For this example, let us define "A" as being the dominant normal allele and "a" as the recessive abnormal one that is responsible for cystic fibrosis. As carriers, you and your mate are both heterozygous (Aa). This disease only afflicts those who are homozygous recessive (aa). The Punnett square allows the prediction of having a child with the disease (aa).

Fill in the Blank

The first thing to do for this is to make a key. Remember we are using the letter A. The dominant is normal, recessive is cystic fibrosis

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Fill in the Blank

If both parents are heterozygous for cystic fibrosis, the next step is to write the genotypes of the parents. Write them in the format __x__ Remember we are using the letter A for this trait.

The answer to the last question is here (the program may not have corrected you for incorrect capitalization)

• Aa x Aa

• Use this for the next question

Multiple Choice

What is the next step in completing this problem?

• Fill in the boxes in the punnett square with potential offspring

• Determine the gametes and put them on the outside of the punnett square

• Determine the potential outcome by listing genotypic and phenotypic ratios

Multiple Choice

What is the next step in completing this problem?

• Fill in the boxes in the punnett square with potential offspring

• Determine the gametes and put them on the outside of the punnett square

• Determine the potential outcome by listing genotypic and phenotypic ratios

Multiple Choice

What is the next step in completing this problem?

• Fill in the boxes in the punnett square with potential offspring

• Determine the gametes and put them on the outside of the punnett square

• Determine the potential outcome by listing genotypic and phenotypic ratios

Open Ended

In a particular kind of mouse grey fur is dominant to brown fur. A cross between a heterozygous mouse and a brown mouse would produce what potential offspring?

Fill in the Blank

In a particular kind of mouse grey fur (G) is dominant to brown fur (g). In order to determine the potential offspring for a cross between a heterozygous mouse and a brown mouse list the parent genotypes? __x __

Multiple Select

In a particular kind of mouse grey fur (G) is dominant to brown fur (g). In order to determine the potential offspring for a cross between a heterozygous mouse and a brown mouse list the gametes from the grey mouse and the gametes from the brown mouse . Check all that apply

• Grey mouse produces gametes that have G allele

• Grey mouse produces gametes that have g allele

• Brown mouse produces gametes that have G allele

• Brown mouse produces gametes that have g allele

• Grey mouse produces only the G allele gametes

Multiple Choice

The correct punnett square on the last slide was

• A

• B

• C

• D

Multiple Choice

When Grey fur is dominant to brown fur the Genotypic Ratio for the cross between a heterozygous mouse and a brown mouse is

• GG 1: Gg 2: gg 1

• Grey 3: Brown 1

• GG 0:Gg 2:gg 1

• Grey 2: Brown 2

Multiple Choice

When Grey fur is dominant to brown fur the Phenotypic Ratio for the cross between a heterozygous mouse and a brown mouse is

• GG 1: Gg 2: gg 1

• Grey 3: Brown 1

• GG 0:Gg 2:gg 1

• Grey 2: Brown 2

Multiple Choice

A Phenotypic ratio could also be written as a phenotypic probability such as

• Grey 50%: Brown 50%

• Grey 2: Brown 2

• GG 0%:Gg 50%:gg 50%

• GG 0:Gg 2:gg 2