A pure breeding plant with the dominant phenotype of character P and the recessive phenotype of character Q was crossed with another pure breeding plant with the recessive phenotype of character P and the dominant phenotype of Q. The offspring of this cross were crossed with a double homozygous recessive for P and Q and the following results were obtained: 22 were phenotypically dominant for P and recessive for Q 5 were phenotypically dominant for both P and Q 4 were phenotypically recessive for both P and Q 24 were phenotypically recessive for P and dominant for Q Which one of the following types of Inheritance is illustrated by these results?
Correct answer: A. Gene linkage of P and Q
- A. Gene linkage of P and Q
- B. Independent segregation of P and Q
- C. Mendelian dihybrid Inheritance
- D. Multiple alleles
- E. Polygenic Inheritance
Explanation
When a pure breeding phenotypic dominant character P and recessive character Q is crossed with pure breeding recessive character P and dominant character Q, the cross is below:- PPqq X ppQQ will give PpQq. Now when this PpQq is crossed with recessive for both:- PpQq X ppqq will give PpQq ; Ppqq ; ppqq ; ppQq The ratio when there is a dihybrid cross between heterozygous character and homozygous recessive character is 9:3:3:1. However, the above ratio is not consistent with what it should be. This happens when there is a gene linkage between two characters
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About Inheritance
Mendel's laws explain segregation, independent assortment and the prediction of genetic ratios using alleles, genotypes and phenotypes. The chapter also covers linked genes, recombination and crossing over during meiosis, then applies pedigree reasoning to X-linked recessive traits, which show different inheritance patterns in males and females.
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