AP BIOLOGY

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HEREDITY

CODOMINANCE

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
When a red four o’clock flower and a white flour o’clock flower were crossed, all of the offspring were pink. If two pink flowers from the F1 generation are crossed, then what would be the phenotypic ratio for the F2 generation?
A
0 red:4 pink:0 white
B
1 red:2 pink:1 white
C
1 red:1 white
D
3 red:1 white
Explanation: 

Detailed explanation-1: -So, the correct answer is ‘1RR: 2RW: 1WW’.

Detailed explanation-2: -INCOMPLETE DOMINANCE: In Four O’Clock plants RED FLOWERS (R) are INCOMPLETELY DOMINANT over white (r) flowers. Heterozygous plants show a BLENDED INTERMEDIATE phenotype of PINK flowers.

Detailed explanation-3: -He took two true-breeding flower traits (red color as dominant allele and white color as a recessive allele) of four o’clock flowers and crossed them. The results show an intermediate heterozygote with pink color flowers (none of the alleles get dominant). This situation in inheritance is known as incomplete dominance.

Detailed explanation-4: -A red-flowered four-o’clock (any red-flowered four-o’clock) has the genotype RR; a white-flowered four-o’clock has the genotype rr. So, this cross is RR × rr. The F1 offspring will therefore all be Rr, all pink.

Detailed explanation-5: -Answer and Explanation: Two hybrids would be the flowers that are pink; this also means they are heterozygous with the genotype “Rr". If these two are crossed, there would be a 50% chance of producing offspring with pink flowers with the genotype “Rr".

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