Use genetic diagrams to predict the results of monohybrid crosses involving codominance or sex linkage and calculate phenotypic ratios
Use genetic diagrams to predict the results of monohybrid crosses involving codominance or sex linkage and calculate phenotypic ratios
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To predict the results of monohybrid crosses involving codominance or sex linkage, we can use genetic diagrams such as Punnett squares. Below, I will demonstrate how to set up these diagrams for both scenarios and calculate the corresponding phenotypic ratios.
1. Monohybrid Cross Involving Codominance
Example: Blood Type InheritanceIn the ABO blood group system, the alleles involved are:
- IA: A antigen (dominant)
- IB: B antigen (dominant)
- i: No antigen (recessive)
Cross: A person with blood type A (genotype IAi) is crossed with a person with blood type B (genotype IBi).
Parental Genotypes
- Parent 1: IAi (Blood Type A)
- Parent 2: IBi (Blood Type B)
Gametes
- Parent 1 can produce: IA or i
- Parent 2 can produce: IB or i
Punnett Square Setup
Results
- Offspring Genotypes:
- 1 IAIB (AB)
- 1 IAi (A)
- 1 IBi (B)
- 1 ii (O)
Phenotypic Ratios
- Phenotypes:
- 1 AB : 1 A : 1 B : 1 O
- Ratio: 1:1:1:1
2. Monohybrid Cross Involving Sex Linkage
Example: Red-Green Color BlindnessRed-green color blindness is an X-linked recessive trait. The alleles are:
- X^c: X chromosome with the allele for color blindness (recessive)
- X: Normal X chromosome
Cross: A color-blind male (genotype XcY) is crossed with a carrier female (genotype XcX).
Parental Genotypes
- Parent 1 (Male): XcY (Color Blind)
- Parent 2 (Female): XcX (Carrier)
Gametes
- Parent 1 can produce: Xc or Y
- Parent 2 can produce: Xc or X
Punnett Square Setup
Results
- Offspring Genotypes:
- 2 XcX (Carrier females)
- 1 XcY (Color-blind male)
- 1 XY (Normal vision male)
Phenotypic Ratios
- Phenotypes:
- 2 Carrier females : 1 Color-blind male : 1 Normal vision male
- Ratio: 2:1:1