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If two pea plants having red (dominant) coloured flowers with unknown genotypes are crossed, 75% of the flowers are red and 25% are white. The genotypic constitution of the parents having red coloured flowers will be
  • a)
    Both heterozygous
  • b)
    One homozygous and other heterozygous
  • c)
    Both homozygous
  • d)
    Both hemizygous
Correct answer is option 'A'. Can you explain this answer?
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Explanation:
This is a classic example of Mendelian inheritance.

Given: two pea plants having red (dominant) coloured flowers with unknown genotypes are crossed, and 75% of the flowers are red and 25% are white.

Let's assume that the dominant allele for red flowers is R and the recessive allele for white flowers is r.

Possible genotypes of the parents:

- Homozygous dominant (RR): All offspring will have red flowers.
- Heterozygous (Rr): 50% of the offspring will have red flowers, and 50% will have white flowers.
- Hemizygous: This term is used for organisms that have only one copy of a gene (e.g., male humans have one X chromosome, so they are hemizygous for X-linked genes). This term does not apply to pea plants, which have two copies of each gene.

Now, let's use the given information to find out the genotypes of the parents.

Offspring ratio: 75% red : 25% white

This ratio can be explained by the following Punnett square:

| | R | R |
|---|---|---|
| R | RR| RR|
| R | RR| RR|
|---|---|---|
| r | Rr| Rr|
| r | Rr| Rr|

- RR: 4/4 = 100% red
- Rr: 4/4 = 100% red
- rr: 0/4 = 0% red

As we can see, all offspring have at least one dominant R allele, which means both parents must have at least one R allele.

Possible genotypes of the parents based on the offspring ratios:

- Homozygous dominant (RR) x heterozygous (Rr): 100% Rr offspring, which does not match the observed ratio.
- Heterozygous (Rr) x heterozygous (Rr): 25% rr offspring, which matches the observed ratio.
- Homozygous recessive (rr) x heterozygous (Rr): All offspring would be Rr and have red flowers, which does not match the observed ratio.

Therefore, the most likely genotypes of the parents are both heterozygous (Rr).
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If two pea plants having red (dominant) coloured flowers with unknown genotypes are crossed, 75% of the flowers are red and 25% are white. The genotypic constitution of the parents having red coloured flowers will bea)Both heterozygousb)One homozygous and other heterozygousc)Both homozygousd)Both hemizygousCorrect answer is option 'A'. Can you explain this answer?
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