#selection

Plant Breeding 3

In pedigree breeding, selection starts from:

In pedigree breeding, segregation reaches maximum in F2 after crossing two homozygous parents to create heterozygous F1. F1 meiosis produces recombination through crossing over and independent assortment, generating new genotypic combinations in gametes. Fertilization of these gametes creates F2 individuals that vary widely for both oligogenic and polygenic traits, exposing recessive alleles and transgressive segregants exceeding parental ranges. Selection pressure cannot discern these recombinants in F1 because all F1 share identical heterozygous genotype. Starting individual plant selection in F2 therefore captures useful recombinants early, allowing fixation through subsequent selfing and progressive homozygosity. F2 population size is kept large, often 2000-3000 plants, to increase probability of recovering rare favorable gene combinations due to low frequency of desired allele linkages. Early selection preserves superior alleles before they are lost to random drift in bulk advancement and maximizes genetic gains. Recombination frequency and linkage disequilibrium decay influence recovery of novel alleles, and large F2 increases chance of breaking undesirable linkages to assemble favorable multi-locus haplotypes for improvement.

Ref: Simmonds NW & Smartt J. Principles of Crop Improvement, Chapter 6. NCERT Class XII Biology, Chapter 9

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Basic Evolution

Selection maintaining mean but reducing SD is:

Stabilizing reflects key principle in quiz on section a solved pyqs, where evolutionary mechanisms shape genetic variation and adaptation. In this context, Stabilizing aligns with experimental and theoretical evidence from population genetics, behavioral ecology and molecular phylogeny. Textbooks like Campbell Biology, Futuyma Evolution and Hartl Principles illustrate supporting data. Understanding why Stabilizing fits helps integrate natural selection, environment.

Ref: Campbell Biology, Evolution Chapters, Selection Types.

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Basic Evolution

Selection increasing homozygosity is:

Inbreeding reflects key principle in quiz on section a solved pyqs, where evolutionary mechanisms shape genetic variation and adaptation. In this context, Inbreeding aligns with experimental and theoretical evidence from population genetics, behavioral ecology and molecular phylogeny. Textbooks like Campbell Biology, Futuyma Evolution and Hartl Principles illustrate supporting data. Understanding why Inbreeding fits helps integrate natural selection, environment.

Ref: Campbell Biology, Evolution Chapters, Selection Types.

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Hardy–Weinberg principle

Allele frequencies can change due to all EXCEPT:

Random mating reflects key principle in quiz on hardy–weinberg principle, where evolutionary mechanisms shape genetic variation and adaptation. In this context, Random mating aligns with experimental and theoretical evidence from population genetics, behavioral ecology and molecular phylogeny. Textbooks like Campbell Biology, Futuyma Evolution and Hartl Principles illustrate supporting data. Understanding why Random mating fits helps integrate natural selection, environment.

Ref: Hartl, Primer of Population Genetics, Hardy-Weinberg Equilibrium.

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