QQuestion
What is the role of genetic counselling in the eradication of geneticdisease from the society? Black-smooth hair is produced in F₂ generation resulting from a cross between pure black-rough haired guinea pig (BBRR) and pure white-smooth haired guinea pig (bbrr). Show their possible genotypes and genotypic ratios with the help of a table. [3 + 2]
✓Answer
Genetic counselling detects carrier status in parents for autosomal recessive diseases like thalassemia (heterozygous parents have 25% chance of affected child, 50% carriers). Counsellors advise risks, recommend prenatal testing or avoiding marriage between carriers, preventing birth of homozygous affected children. This reduces disease incidence across generations, eradicating it from society by breaking transmission cycles, as in thalassemia where heterozygous couples are warned.
Parental (P) Generation
| Parent | Genotype | Phenotype |
|---|---|---|
| Pure black, rough | BBRR | Black, rough |
| Pure white, smooth | bbrr | White, smooth |
F₁ Generation
|
BbRr (Black, rough) |
BbRr (Black, rough) |
BbRr (Black, rough) |
BbRr (Black, rough) |
Punnett Square (F₂ Generation)
| × | BR | Br | bR | br |
|---|---|---|---|---|
| BR | BBRR | BBRr | BbRR | BbRr |
| Br | BBRr | BBrr | BbRr | Bbrr |
| bR | BbRR | BbRr | bbRR | bbRr |
| br | BbRr | Bbrr | bbRr | bbrr |
- Genotypic ratio = 1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1
- Phenotypic ratio = 9 : 3 : 3 : 1
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