6 public questions tagged with this topic.
An individual with two different alleles for a gene (e.g., Tt) is called heterozygous.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Polygenic Inheritance Pleiotropy and Quantitative Inheritance
A heterozygous genotype contains two different alleles, such as Aa.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Mendel's Laws - Dominance Segregation Independent Assortment
A single locus heterozygous Aa contains two different alleles in diploid cell. During meiosis I, homologous chromosomes carrying A and a separate into different cells, ensuring each haploid gamete receives only one allele. No third allele type exists at that locus, so genetically distinct gamete classes number exactly two. This follows general formula 2^n where n is number of heterozygous loci; for n=1, 2^1 =2. Independent loci increase combinations, but monohybrid heterozygote limited to two, demonstrating segregation and explaining 1:1 gametic ratio.
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 2: Gamete Formation and the 2^n Rule
Heterozygous describes genotype containing two different alleles at a given locus, illustrated by Tt pea plants carrying tall and dwarf alleles. Maternal and paternal origins differ, and during meiosis these alleles segregate into distinct gametes, generating genetic variation. Phenotype depends on allelic interaction: complete dominance, incomplete dominance or codominance. Homozygous genotypes carry identical alleles, monoploid indicates single chromosome set, polyploid multiple sets, concepts related to genome copy number rather than allelic diversity within locus. Cytological correlation with prophase pairing, metaphase alignment and anaphase separation provides visual anchor for memorising genetic laws.
Ref: Hartl & Ruvolo, Genetics, 9th ed., Chapter 2: Heterozygosity and Dominance
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.
