Question of 85
Q.a) How phenylketonuria is an example for Pleiotropy?
(2)
b) Schematically represent the sex determination in honeybee. (3)
Karnataka PUCKarnataka II PUC Board 2025Subjective· 5mImportance★★★★★
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Start your 14-day free trial to unlock the full solution →PKU shows pleiotropy because one mutated gene causes several effects; in honeybees, fertilised diploid eggs give females and unfertilised haploid eggs give males (haplodiploidy).
a) Phenylketonuria (PKU) as an example of Pleiotropy:
- Pleiotropy is the phenomenon in which a single gene influences multiple phenotypic traits.
- PKU is an inborn error of metabolism caused by mutation in a single gene that codes for the enzyme phenylalanine hydroxylase.
- The defective enzyme cannot convert phenylalanine to tyrosine, so phenylalanine accumulates and is converted to phenylpyruvic acid and other derivatives.
- These accumulate in the brain and are excreted in urine, producing several effects: mental retardation and reduced (low) hair and skin pigmentation.
- Since one mutated gene produces multiple phenotypic effects, PKU is a classic example of pleiotropy.
b) Sex determination in honeybee (schematic representation):
Honeybees follow the haplodiploid (male-haploidy) mechanism:
Queen (diploid, 2n = 32)
|
---------------------------------
| |
Egg FERTILISED by sperm Egg UNFERTILISED
(diploid, 2n = 32) (haploid, n = 16)
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Develops into FEMALE Develops into MALE (Drone)
(Queen / Worker) by parthenogenesis
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