4 public questions tagged with this topic.
A homozygous organism has two identical alleles for a trait.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Mendel's Laws - Dominance Segregation Independent Assortment
An organism possessing two identical alleles at a locus is termed homozygous, denoted TT for tall homozygous or tt for dwarf homozygous. Homozygotes breed true, producing gametes carrying single allelic type because segregation yields uniform content. Homozygosity increases through selfing, inbreeding or selection and exposes recessive alleles phenotypically, important for detecting deleterious mutations. Heterozygous carries divergent alleles, hemizygous describes single copy state in XY males for X-linked genes, polyploid refers to whole set number, distinct from allelic identity. Mastery ensures accurate interpretation of monohybrid and dihybrid progeny arrays, distinguishing dominance interactions from epistasis or linkage effects.
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 2: Homozygosity
Restriction fragment length polymorphism detects variation in restriction enzyme recognition sites through hybridization of digested genomic DNA. Since both parental alleles produce distinct fragment sizes, heterozygous individuals display a combined banding pattern of both alleles, while homozygous individuals show a single pattern. This codominant behavior permits genotype discrimination. Dominant systems like RAPD, ISSR and AFLP cannot differentiate heterozygotes because amplification depends solely on primer binding and yields a binary present or absent phenotype, masking allelic dosage essential for population genetics.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
RFLP genotyping requires a probe that actually spans the variable restriction site to differentiate alleles reliably on Southern blot. Coding probes hybridizing far away may detect fragments independent of polymorphism, missing variation. Intron or flanking probes outside restriction region might not cover site-containing junction. A polymorphic probe designed across the restriction site junction recognizes sequences that are cleaved in one allele but remain intact in another, yielding distinct band sizes. Such allele-specific hybridization enables discrimination of homozygous normal, homozygous mutant, and heterozygous individuals, essential for linkage analysis and disease diagnosis applications.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
