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#Mendelian inheritance

18 public questions tagged with this topic.

BOTANY

In Mendelian inheritance, what is the expected genotypic ratio of the F2 generation in a monohybrid cross?

The expected genotypic ratio in a monohybrid cross (F2 generation) is 1:2:1 (homozygous dominant: heterozygous: homozygous recessive). This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.

Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Principles of Inheritance and Molecular Basis of Inheritance, Topic: Genetics and molecular biology in plants.

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Mendelian Inheritance

The phenotypic expression of a heterozygote in Mendelian inheritance shows

In Mendelian inheritance with complete dominance, heterozygote carries one dominant and one recessive allele but produces sufficient dominant gene product to achieve dominant phenotype threshold, such as enzyme activity or structural protein. Consequently phenotypic expression of heterozygote shows dominant trait, identical to homozygous dominant, e.g., tall Tt same as TT. Recessive trait appears only in tt lacking dominant allele. Blended or intermediate trait characterises incomplete dominance, not Mendelian complete dominance where heterozygote fully expresses dominant phenotype. Cytologica

Ref: Snustad & Simmons, Principles of Genetics, 7th ed., Chapter 3: Heterozygote Expression

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Mendelian Inheritance

Which cross gives information about types of gametes formed?

Cross revealing types of gametes formed is test cross where individual of interest mated to homozygous recessive tester. Because tester contributes invariant recessive allele, phenotype of each progeny directly reflects gamete received from tested individual, uncovering parental versus recombinant classes and frequencies. Self cross or back cross to dominant parent masks recessive gametes, reciprocal cross compares parental sex effects not gamete content. Test cross therefore provides information about gamete spectrum, recombination frequency and genotype composition essential for linkage mapp

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 4: Gamete Types Test Cross

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Mendelian Inheritance

If all F2 progeny show dominant phenotype, the genotype of F1 was

If all F2 progeny exhibit dominant phenotype after selfing, parental F1 could not have contributed recessive allele to any zygote, genotype must be homozygous dominant TT producing only T gametes. Heterozygous Tt would have generated 25 percent recessive tt progeny giving 3:1 ratio, tt would produce all recessive, mixture Tt and TT would also produce some recessive when Tt mothers contribute t. Uniformly dominant F2 therefore indicates fixation of dominant allele in F1, genotype TT only capable of such outcome. Conceptual clarity supports solving numerical problems involving segregation ratios

Ref: Hartl & Ruvolo, Genetics, 9th ed., Chapter 2: Homozygous Dominant F1 Identification

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Mendelian Inheritance

The purpose of a reciprocal cross is to test

Purpose of reciprocal cross is to test sex linkage versus autosomal inheritance. Swapping male and female parental phenotypes, such as tall female by dwarf male versus dwarf female by tall male, yields identical results for autosomal genes because transmission independent of parental sex. For X-linked genes results differ due to hemizygous male inheritance and dosage, revealing criss-cross pattern. Gene purity assessed by test cross, independent assortment by dihybrid ratio, mutation rate not addressed, reciprocal design specifically diagnoses sex-linked transmission. Understanding this mechan

Ref: Pierce, Genetics, 7th ed., Chapter 4: Sex Linkage Test via Reciprocal Cross

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Mendelian Inheritance

In a monohybrid self-cross, total possible genotype combinations are

Monohybrid self-cross Tt by Tt generates two gamete types per parent T and t. Combining in Punnett square produces four possible fertilisation events representing total genotype combinations regardless of identity, namely T fertilised by T, T by t, t by T and t by t. Two middle events share genotype Tt, resulting in distinguishable genotypes three but combinations four. Count two reflects allele number, three distinct genotypes, eight would require three segregating genes, accurate total possible zygotic combinations four underlies 1:2:1 genotypic ratio. This principle is routinely tested in N

Ref: Snustad & Simmons, Principles of Genetics, 7th ed., Chapter 3: Punnett Combinations

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