#recessive traits

BOTANY

Which of the following statements about dominant and recessive traits is incorrect?

Dominant traits are not necessarily more common; frequency depends on factors like natural selection and genetic drift. This follows from latest NCERT 2026-27 principle explaining the concept clearly for NEET students in simple steps as per rationalized syllabus.

Ref: NCERT Biology Textbook - Latest Edition for Academic Session 2026-27 (Botany section, Rationalized Textbook for Class XI and XII), Chapter: Biology - Botany portion (Latest NCERT Textbooks for Academic Session 2026-27 -

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Chromosomal Theory Linkage Recombination Gene Mapping

Which of the following statements about dominant and recessive traits is incorrect?

Dominant traits are not necessarily more common; frequency depends on factors like natural selection and genetic drift.

Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Chromosomal Theory Linkage Recombination Gene Mapping

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Non-Mendelian Inheritance - Incomplete Dominance Co-dominance Multiple Alleles

Which of the following explains why some traits disappear in the F1 generation but reappear in the F2 generation?

The Law of Segregation explains that recessive traits can be masked in the F1 generation and reappear in the F2 generation.

Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Non-Mendelian Inheritance - Incomplete Dominance Co-dominance Multiple Alleles

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Pedigree Analysis

X-linked recessive traits are never transmitted from

Father transmits Y chromosome to sons and X chromosome to daughters during fertilization. Since X-linked genes reside on X chromosome, father cannot transmit X-linked allele to son who receives paternal Y instead of paternal X. Sons obtain their single X exclusively from mother. Consequently father-to-son transmission in pedigree excludes X-linked inheritance and suggests autosomal or Y-linked pattern. In X-linked recessive pedigrees, affected males must receive mutant X from carrier mother, and affected fathers pass mutant X to all daughters, making them obligate carriers, never to sons.

Ref: Hartl & Ruvolo, Genetics, 6th ed., Chapter 4: Sex Linkage and Father to Son Transmission Rule

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Pedigree Analysis

X-linked recessive traits are more commonly seen in

X-linked recessive alleles reside physically on X chromosome. Males are hemizygous with XY constitution, possessing single X copy, so any recessive allele on that X fully expresses without masking. Females possess two X chromosomes, requiring two copies to show affected phenotype, usually remaining shielded as heterozygous carriers with normal phenotype. Therefore trait appears predominantly in males across pedigree, while females serve as transmitters. This explains male bias in hemophilia, Duchenne muscular dystrophy, and red-green color blindness pedigrees where affected males connect throu

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 2: X-linked Recessive Male Predominance

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