23 public questions tagged with this topic.
Pleiotropy occurs when a single gene affects multiple phenotypic traits, such as in phenylketonuria.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Polygenic Inheritance Pleiotropy and Quantitative Inheritance
Females can inherit X-linked recessive disorders if they receive two copies of the affected allele (one from each parent).
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Non-Mendelian Inheritance - Incomplete Dominance Co-dominance Multiple Alleles
Polygenic inheritance involves multiple genes contributing to a trait, as seen in human skin color variation.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Non-Mendelian Inheritance - Incomplete Dominance Co-dominance Multiple Alleles
In co-dominance, both alleles contribute equally to the phenotype, instead of one suppressing the other.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Non-Mendelian Inheritance - Incomplete Dominance Co-dominance Multiple Alleles
In co-dominance, both alleles are equally expressed rather than one suppressing the other.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Non-Mendelian Inheritance - Incomplete Dominance Co-dominance Multiple Alleles
Huntington’s disease follows an autosomal dominant pattern, meaning only one copy of the mutant gene is needed for expression.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Non-Mendelian Inheritance - Incomplete Dominance Co-dominance Multiple Alleles
Mendel’s laws apply to all sexually reproducing organisms, not just plants.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Monohybrid Dihybrid and Test Cross
Fully penetrant autosomal dominant allele manifests phenotype in heterozygote, so individual cannot express trait without receiving mutant allele from at least one parent. Rare de novo mutations can create isolated affected individuals, but most affected persons inherit allele from one affected parent, creating vertical transmission where trait appears in each generation continuously. Normal homozygotes never produce affected child unless other parent contributes dominant allele. This inheritance contrasts sharply with recessive where affected individuals can have unaffected parents. Thus presence of affected parent in most cases supports dominant mode.
Ref: NCBI Bookshelf, Pedigree Analysis: Autosomal Dominant Criteria and Vertical Transmission
X-linked recessive carrier females are heterozygous X^A X^a possessing one normal and one mutant allele. One normal allele typically produces sufficient functional protein for normal physiology, and random X-chromosome inactivation creates mosaic tissue where roughly half cells express normal allele, preserving normal phenotype clinically. They remain healthy but carry fifty percent risk of transmitting mutant allele to sons who become affected and to daughters who become carriers themselves. Phenotypically normal carrier status explains why trait appears to skip generations through maternal line before reappearing in male relatives.
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 4: Carrier Phenotype and X-inactivation
Paternal transmission difference distinguishes sex chromosome inheritance: fathers contribute Y chromosome to sons and X chromosome to daughters, never X chromosome to sons. Genes located on X chromosome therefore cannot be transmitted from father to son; sons receive their single X exclusively from mother. Autosomal dominant and recessive traits can show father-to-son transmission via autosomes, and Y-linked traits by definition show obligatory father-to-son transmission. Absence of father-to-son transmission in pedigree serves as diagnostic clue for X-linkage, whether dominant or recessive, helping exclude autosomal modes.
Ref: Hartl & Ruvolo, Genetics, 6th ed., Chapter 4: Father-to-Son Transmission Rule for X-linkage
When pedigree displays only males affected in every generation with direct transmission from father to son along male line, Y chromosome linkage is strongly suspected. Y-linked genes pass exclusively along paternal lineage because only males possess Y and father contributes Y to all biological sons. X-linked recessive would show affected males linked through carrier females and absence of father-to-son transmission. Autosomal modes affect both sexes equally. Mitochondrial transmission requires affected mothers passing trait to all children. Hence all-male, father-to-son vertical pattern indicates holandric inheritance without female involvement.
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 4: Recognizing Y-linked Pedigrees Patterns
Red-green color blindness most commonly arises from mutations or unequal crossover in OPN1LW and OPN1MW opsin genes cluster on Xq28 encoding long and middle wavelength photopigments. Males hemizygous for mutant allele manifest dichromacy with impaired discrimination, while females require two mutant copies to become affected, so population prevalence higher in males approximately eight percent versus fraction in females. Carrier females retain normal vision. Transmission shows affected grandfathers passing via carrier daughters to affected grandsons, with no male-to-male transmission, defining textbook X-linked recessive trait.
Ref: NCBI Bookshelf, Genetics: X-linked Recessive Color Vision Deficiency Mechanism
