JAMB - Biology (2025 - No. 109)
Use the illustration above to answer the question that follows
What is the genotypic ratio of the F\(_2\) generation?
2 :1 :1
3 : 1
1 : 1
1 : 2: 1
Explanation
The problem states the parents are both heterozygous (Rr). When these individuals are crossed, each parent contributes one allele (R or r) to the offspring.
| R | r | |
| R | RR | Rr |
| r | Rr | rr |
Based on the Punnett Square, we count the frequency of each unique genetic combination:
Homozygous Dominant (
RR): 1 occurrence
Heterozygous (
Rr): 2 occurrences
Homozygous Recessive (
rr): 1 occurrence
In Mendelian genetics, although the prompt labels the result of an Rr X Rr, crosses as the F\(_1\) this specific distribution (RR,Rr, Rr, rr) is standard for the F\(_2\),(the offspring of two F\(_1\)). Regardless of the label, the ratio of these specific results is 1∶2∶1.
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