Genetic Diagrams & Punnet Squares

This lesson covers:

  1. How to draw Punnett squares 
  2. How to use Punnett squares to find the probability of a child having a certain trait

How would you describe the genotype 'AA'?

Homozygous dominant 

Heterozygous 

Homozygous recessive 

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How would you describe the genotype 'Hh'?

Homozygous recessive 

Homozygous dominant 

Heterozygous 

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Punnett square showing genotypes DD and Dd with one empty section.

Which genotype completes the empty section of the Punnett square?

DD

Dd

dd

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How would you describe the genotype 'dd'?

Homozygous recessive 

Homozygous dominant 

Heterozygous 

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Genetic cross diagram showing the probability of heterozygous genotype in offspring.

Looking at the genetic cross diagram above, what is the percentage probability that the offspring will have a heterozygous genotype?

50

%

%

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Punnett square diagram showing genetic cross with dominant allele Q for brown eyes and recessive allele q for green eyes.

In the genetic cross shown, what is the ratio of brown-eyed : green-eyed phenotypes in the offspring?


Q = dominant allele for having brown eyes

q = recessive allele for having green eyes

1:3

2:1

1:1

3:1

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Diagram of a Punnett square showing four cells with alleles T and t.

Use pen and paper to complete the Punnett square above.


Press 'Continue' when you're ready to check your answer.

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Use pen and paper to complete a Punnett square between a homozygous dominant individual GG, and a heterozygous individual Gg. 


Press 'Continue' when you're ready to check your answer.

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In mice, fur length can be short or long. Draw a Punnett square for the cross between a homozygous dominant individual and a homozygous recessive individual. 


H = dominant allele for short hair 

h = recessive allele for long hair


Press 'Continue' when you're ready to check your answer.

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