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In a genetic study, if a trait is controlled by a single gene with two alleles,

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Question: In a genetic study, if a trait is controlled by a single gene with two alleles, where one allele is completely dominant over the other, what is the expected genotypic ratio in the offspring of a monohybrid cross?

Options:

  1. 1:2:1
  2. 3:1
  3. 1:1
  4. 9:3:3:1

Correct Answer: 1:2:1

Solution: 

The expected genotypic ratio from a monohybrid cross is 1:2:1.

In a genetic study, if a trait is controlled by a single gene with two alleles,

Practice Questions

Q1
In a genetic study, if a trait is controlled by a single gene with two alleles, where one allele is completely dominant over the other, what is the expected genotypic ratio in the offspring of a monohybrid cross?
  1. 1:2:1
  2. 3:1
  3. 1:1
  4. 9:3:3:1

Questions & Step-by-Step Solutions

In a genetic study, if a trait is controlled by a single gene with two alleles, where one allele is completely dominant over the other, what is the expected genotypic ratio in the offspring of a monohybrid cross?
  • Step 1: Understand that a monohybrid cross involves one trait controlled by one gene with two alleles.
  • Step 2: Identify the two alleles. Let's say 'A' is the dominant allele and 'a' is the recessive allele.
  • Step 3: Determine the possible genotypes of the parents. They can be homozygous dominant (AA), homozygous recessive (aa), or heterozygous (Aa).
  • Step 4: Perform a cross between two heterozygous parents (Aa x Aa).
  • Step 5: Use a Punnett square to find the possible combinations of alleles in the offspring.
  • Step 6: Fill in the Punnett square: the combinations will be AA, Aa, Aa, and aa.
  • Step 7: Count the genotypes: 1 AA, 2 Aa, and 1 aa.
  • Step 8: Write the genotypic ratio: 1 AA : 2 Aa : 1 aa.
  • Monohybrid Cross – A genetic cross between two individuals that differ in a single trait controlled by one gene with two alleles.
  • Genotypic Ratio – The ratio of different genotypes that result from a genetic cross, specifically in this case, a monohybrid cross.
  • Dominance – The relationship between alleles where one allele masks the expression of another in the phenotype.
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