Genetics and Plant breeding pointers 20

•  Polytene chromosomes were first reported by - Balbiani in 1881. 
• Polytene chromosomes are also called Giant chromosomes / Salivary gland chromosomes
•  Lampbrush chromosomes were discovered by - Flemming (1882)
•  World's first chromosome map was produced by - Alfred Sturtevant (1913)
• B-Chromosomes are also called as Accessory chromosome / Super numerary chromosome.
• B-Chromosomes recorded was by Longley and Randolph in Maize (1927)
• The chromosome in which both arms are identical Isochromosome
• The chromosome that has lost one of its arms and replaced it with an exact copy of the other arm is called as Isochromosome
•  The 2n no. of chromosomes in Drosophila is-8
• Any change which alters the normal structure of a chromosome is known as Chromosomal mutations
•  Type of structural chromosomal aberration- Deletion. Duplication, Inversion, Translocation.
•   When aberrations remain confined to a single chromosome of a homologous pair, they are called Intrachromosomal aberrations.
• Loss of a portion of segment from a chromosome is referred to Deletion/ Deficiency.
•   The shifting of a part of one chromosome to another non-homologous chromosome is known as Translocation.
•  The chromosome rearrangement involving the exchange of chromosome segments between two chromosomes that do not belong to the same pair of chromosomes is referred to - Reciprocal translocation.
• Alterations in whole chromosome sets are referred to – Euploidy.
•  The additional chromosome in a telocentric chromosome is known as Telocentric trisomics.
•  There are two different extra chromosomes (2n+1+1) in -Double trisomics.
•   A basic of monoploid set of chromosomes of an individual is known Genome.
•   Improvement of crop plants through manipulation of chromosome number is called as-Ploidy breeding.
•  Any organisms with more than two sets of chromosomes or genomes is known as – Polyploid.
•   The effective method to obtain autopolyploids is- Colchicine.
•    Important triploid plants are Bananas, Watermelons and Winesap apples.
•   Examples of autotetraploids are Alfalfa, Coffee, McIntosh apples.
•  Inheritance of acquired characters was given by – Lamarck.
•   Who gave the statement "Genes must be carried on the chromosomes" Sutton & Boveri.
•   Discovery of non disjunction of X chromosomes in- Fruit fly Drosophila.
•  Two alleles separate during meiosis to form gametes - Law of Segregation
•   The each trait separates independently of each other Law of Independent Assortment
•   The genetic makeup of an organism is known as-Genotype
•    Two dominant genes exist for a single trait is known as - Codominance
•   Unit of inheritance located at a fixed position on a chromosome - Gene
•   Alternative form of a gene is known as - Allele
•   The term Homozygote and Heterozygote was given by- Bateson
•   The degree to which a genotype is expressed phenotypically is called Expressivity
•   The gene occupying a fixed position in the chromosome is referred to as Locus
•  The progeny obtained by crossing two pure breeding parents of different genotypes is known as-Hybrid
•   A cross between parents differing in a single gene are referred to as Monohybrid
•   A cross which involves parents differing for two pairs of contrasting characters are referred to as Dihybrid Cross
•   The progeny from a cross between parents differing in three genes-Trihybrid
•   A cross between hybrid and any one of the parents are referred to as backcross
•  A cross between hybrid and a recessive homozygote are referred to as Testcross
•   The second cross involving the same characters as the first but with the sexes of the parents interchanged are known as Reciprocal crosses
•  The interaction between genes belonging to different pairs of alleles, the dominant allele in one of the pairs preventing the dominant allele in the other pair from expressing itself is referred to as Epistasis
•  Non allelic interaction with modification in Mendelian ratio Dominant epistasis -12:3:1 Recessive epistasis 9:3:4 Duplicate and additive epistasis-9:6:1 Duplicate dominant epistasis-15:1 Duplicate recessive epistasis 9:7 Dominant and recessive epistasis-13:3
•  The genetic interactions occur in between the two alleles of a single gene is referred as Allelic interaction
•  The dominant allele at our locus mask the expression of both dominant and recessive alleles at another locus are known as Dominant epistasis
• The recessive allele at one locus mask the expression of both dominant and recessive alleles at another locus is referred to as Recessive epistasis
•  The dominant alleles at either of the two loci mask the expression of recessive alleles at the two loci ate known as Duplicate dominant epistasis
•   Duplicate dominant epistasis is also called Duplicate gene action
•   When recessive alleles at either of the two loci mask the expression of dominant alleles at the two loci it is called as -Duplicate recessive epistasis
•   Duplicate recessive epistasis is also called- Complementary Epistasis
•  The dominant and recessive alleles at one locus mask the expression of both dominant and recessive alleles at second locus is referred to Dominant and recessive epistasis
•  Dominant and recessive epistasis is also called-Inhibitory gene action
•   Two dominant alleles have similar effect when they are separate but produced enhanced effect when they are together, they are known as epistasis Duplicate and additive
•   Duplicate and additive epistasis is also called - Polymeric gene action
•   Single gene controlling more than one character is called as Pleiotropy
•  Inability of a viable pollen to fertilize the ovule of the same plant is called as-Self incompatibility
•   Stages of Self incompatibility Failure to germinate at stigmatic surface. Failure to penetrate stigma Slow growth of Pollen tube Embryo degenerates.
•   Self incompatibly alleles in plants are controlled by - Multiple allelic
•    The existence of more than two alleles at the same locus of a homologous chromosome is referred to as-Multiple alleles.
•  Examples of Multiple Alleles Fur color in Rabbits Wing type in Drosophila Eye colour in Drosophila Self incompatibility alleles in Plants ABO Blood group in man
•   The ability of a gene or gene combination to be expressed phenotypically to any degree is called - Penetrance
•   When all the individuals which carry a particular gene exhibit its phenotypic effect is called as Complete Penetrance
•    Heterozygous condition unable to express fully the normal phenotype are referred to as Incomplete penetrance
•   The degree of phenotypic expression of a gene in the different individuals is known as Expressivity