Science and TechnologySEE 2082, Karnali Province
Study the given table: ♀ R r R RR Rr r Rr rr a) Which filial generation is shown in the table? [1] b) Which combination shows pure characters? [1] c) Write the genotype ratio of this generation. [1]…
Study the given table:
| ♀ | R | r |
|---|---|---|
| R | RR | Rr |
| r | Rr | rr |
a) Which filial generation is shown in the table? [1] b) Which combination shows pure characters? [1] c) Write the genotype ratio of this generation. [1] d) Write the statement of Mendel's law supported by this result. [2]
Answer
a) The filial generation shown in the table is the first filial generation (F₁). This is because the table represents the possible genotypes of offspring produced by crossing two heterozygous parents (Rr × Rr), which is a classic example of a monohybrid cross in the F₂ generation. However, the table itself directly shows the F₂ generation (second filial generation) resulting from self-crossing of F₁ hybrids (Rr × Rr).
b) The combination that shows pure characters (homozygous genotypes) in the table is:
- RR (homozygous dominant)
- rr (homozygous recessive)
These genotypes represent pure-breeding individuals because they carry identical alleles for the trait.
c) The genotype ratio of this generation (F₂) is: 1 RR : 2 Rr : 1 rr
This ratio is derived from the cross between two heterozygous parents (Rr × Rr), where:
- 1/4 of the offspring are RR (homozygous dominant),
- 1/2 of the offspring are Rr (heterozygous),
- 1/4 of the offspring are rr (homozygous recessive).
d) The statement of Mendel’s Law of Segregation supported by this result is as follows:
"During the formation of gametes, the two alleles of a gene segregate (separate) from each other so that each gamete carries only one allele for each gene."
This table demonstrates Mendel’s Law of Segregation because:
- The heterozygous parent (Rr) produces two types of gametes (R and r) in equal proportions (50% each).
- When two heterozygous parents (Rr × Rr) are crossed, the alleles segregate independently during gamete formation, leading to the observed 3:1 phenotypic ratio (if R is dominant over r) and the 1:2:1 genotypic ratio shown in the table.
- The RR and rr genotypes are pure because they carry identical alleles, while Rr is hybrid due to the presence of two different alleles.
This segregation ensures that each offspring receives one allele from each parent, maintaining genetic diversity in the next generation. The table also supports Mendel’s Law of Independent Assortment if multiple traits were considered, but in this case, it primarily illustrates the Law of Segregation for a single gene.
Discussion
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