Q.97 A female cat with a mutant phenotype was bred with a wild-type male cat. All progeny (4 males
and 4 females) show the mutant phenotype. On the other hand, all progeny (4 males and 4 females)
from the reciprocal cross between a mutant male and a wild-type female show the wild-type
phenotype. Which of the following explain the inheritance pattern of the mutation?
(A) Recessive (B) Linked inheritance
(C) Mitochondrial inheritance (D) Autosomal inheritance
Mitochondrial inheritance explains the mutant phenotype pattern in this cat breeding experiment.
This non-Mendelian pattern shows maternal transmission, where all offspring inherit the mother’s mitochondria.
Cross Analysis
In the first cross (mutant female × wild-type male), all 8 progeny (4 males, 4 females) show the mutant phenotype. This occurs because mitochondria, carrying the mutation, are inherited solely from the mother’s egg cytoplasm—sperm contribute negligible mitochondria. The reciprocal cross (mutant male × wild-type female) yields all wild-type progeny since the wild-type female provides mutation-free mitochondria to all offspring.
Option Breakdown
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(A) Recessive: Fails explanation. Recessive traits need both parents to carry alleles for progeny expression; here, wild-type parents produce only mutant offspring in one cross, not fitting recessive autosomal or X-linked recessive patterns.
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(B) Linked inheritance: Incorrect, as it implies sex linkage (X or Y). X-linked dominant from female would affect daughters more variably, and sons variably too; reciprocal should mirror if autosomal-linked, but phenotypes fully reverse.
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(C) Mitochondrial inheritance: Correct match. Cytoplasmic/maternal inheritance fits perfectly—mutation passes only from affected mother, regardless of offspring sex, explaining 100% mutant vs. 100% wild-type in reciprocal.
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(D) Autosomal inheritance: Does not fit. Autosomal dominant from mutant female would pass to ~50% progeny; recessive impossible as wild-type male yields all mutants. Reciprocal asymmetry rules out nuclear genes.
Introduction to Cat Mutant Phenotype Inheritance
Mitochondrial inheritance in cats explains unique mutant phenotype patterns in reciprocal crosses, key for GATE Life Sciences prep. A mutant female bred to wild-type male produces all mutant offspring; reverse cross yields wild-type. This mitochondrial inheritance cats mutant phenotype highlights non-nuclear maternal transmission, distinguishing from recessive, linked, or autosomal options.
Detailed Cross Results
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Mutant ♀ × Wild-type ♂: All 4 males + 4 females mutant.
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Mutant ♂ × Wild-type ♀: All 4 males + 4 females wild-type.
Mitochondria from oocyte cytoplasm drive this—sperm mitochondria degrade post-fertilization.
Why Other Options Fail
| Option | Reason It Doesn’t Fit Crosses |
|---|---|
| Recessive | Wild-type parent can’t produce 100% mutants without homozygosity. |
| Linked Inheritance | Sex linkage shows criss-cross (not full maternal), variable by sex. |
| Autosomal | Symmetric reciprocal results expected; no sex bias or full transmission. |
| Mitochondrial | Matches: Maternal-only, sex-independent, full progeny transmission. |
GATE Exam Relevance
Ideal for GATE Life Sciences PYQs on non-Mendelian inheritance. Mitochondrial inheritance cats mutant phenotype tests cytoplasmic vs. nuclear distinction—focus maternal lines.
Key Takeaway
Prioritize reciprocal crosses for maternal clues in cat mutant phenotype reciprocal cross problems. Practice builds exam speed.
