Genetics and Plant breeding pointers 23 ✓

 

• In groundnut dark plumule disorder occur due to - Calcium deficiency.
• The sample taken by seed inspector is known as - Official sample.
• The sample taken by seed certification officer from the seed lot is called Certified sample.
• Single cross (AxB) in Bajra, Brinjal, Carrot, Castor, Chillies, Cotton and Cucurbits.
• Double cross (A×B) x (CD) in -Maize and Sugar beet.
• Three way cross (AxB) x C in Sweet maize.
• Double Top cross (A×B) OPV in -Maize.
• All types of hybrid can be found in- and sugarcane and Potato.
• The plants of the same kind growing naturally from seed that remains in the field from a previous crop is called as- Volunteer Plants
• Plant that differs in morphological characters from the rest of the populations of a crop variety is called as - Off Type
• A line is Male sterile line.
• B line is Maintainer line.
• R line is Restorer line.
• Genetic variability is a prerequisite for crop improvement.
• If heritability of a trait is high, selection for the trait will be effective.
• In general, selection will be easy in case monogenic characters.
• Polygenic characters show variable magnitude of heritability, and environment plays an important role in their development
• As the number of genes governing becomes smaller, its improvement becomes easier
• Natural populations of self-pollinated species are ordinarily homozygous and heterogenous.
• Cross-pollinated populations are heterozygous and heterogeneous
• Selfing reduces heterozygosity to 50% of that present in the previous generation
• Back-crossing reduces heterozygosity at same rate as selfing.
• Recurrent back-crossing replaces the genes of nonrecurrent parent by those recurrent parent at the same rate as reduces heterozygosity.
• Land races of self-pollinated crops are homozygous, but heterogeneous.
• Genetic variability is created by sexual hybridization, mutagens, polyploidy, somaclonal variation, and genetic engineering
• Mass selection is based on phenotypic performance.
• The proportion of is additive genetic variance is  greater in self  pollinated crops
• In self-pollinated crops the proportion of additive genetic variance is lower in the early segregating generations (F2, F3 etc) than in late generations ( F6 and F5)
• Pureline selection is applied to self pollinated crops
• Mass selection is used for nucleus seed production of pure line varieties of self-pollinated crops
• Selection pressure is lower in case of mass selection than in pure line selection
• A pure line variety is genetically uniform.
• Progeny testing reveals the genetic worth of a plant.
• Pedigree, bulk and SSD method and backcross are used for handing of segregation generation of self-pollinated crops
• Selection of quantitative traits begins in F2 segregation generation.
• Selection begins in F1 generation of three way cross.
• Maximum variation will be released in F­2 generation of cross provided repulsion phase linkage is not important
• In case of pedigree method usually the objective is to obtain transgressive segregants
• Nilson Ehle provided the genetic basis for transgressive segregation in oats and wheat
• Transgressive segregation denotes production of plants in an F2 generation that are superior to both parents for one or more characters.
• In case of bulk method of breeding usually artificial selection is not done during period of bulking.
• In case of bulk method, mass selection may be done for certain traits, e.g., maturity date. seed size, etc, during the period of bulking
• Generally, selection for characters with low heritability, e.g., yield, is not effective in early segregating generations.
• In bulk populations, natural selection usually tends to reduce the frequencies of undesirable types and increase those of desirable types.
• Selection for quantitative traits is easier and more effective, when their heritability is high.
• Natural selection favours those genotypes that are good competitors irrespective of their agronomic desirability.
• Single seed (SSD) method was proposed by Goulden in 1940 and named so by Johansen and Bernard in 1962.
• Backcross refers to crossing of F1 with one of its parents.
• In test cross, F₁ is crossed with a strain that possesses recessive forms of the concerned traits (irrespective of whether this line is one of the parents of the F, or not).
• Transfer of a monogenic trait through back- cross procedure is much easier as compared to that of a polygenic trait.
• When the trait being transferred is governed by a dominant gene, selection is done in each backcross generation.
• When the trait being transferred is governed by a recessive gene, selection is confined to the F₂ generations produced, usually, following first, third and fifth backcrosses.
• During the transfer of a polygenic trait through backcross method, F₁ and F₂ generations are raised after each backcross generation.
• Backcross method was proposed by Harlan and Pope in 1922.
• Strict selection for the gene(s)/character(s) being transferred is essential during back- crossing.
• In backcross method, the objective of repeated backcrosses is to restore in the progeny the genotype of recurrent parent, except for the gene/cytoplasm being transferred from the donor parent.
• Recurrent selection is more easily applied and is more effective in cross-than in self. pollinated crops.
• Recurrent selection aims to increase the frequency of desirable genes and genotypes in the population.
• One cycle of recurrent selection requires two/three years since all the different operations have to be carried out in different years on different progenies/generations.
• In recurrent selection, intermating among progenies is done to restore heterozygosity and to allow recombination to break undesirable linkages.
• Diallel selective mating design (DSM) was proposed by Jenson in 1970.
• In diallel selective mating design, any new germplasm can be incorporated into the breeding population at any selective series/ stage.
• Selfing leads to severe inbreeding depression in cross-pollinated and clonal crops.
• Selfing releases a large amount of genetic variability in cross-pollinated crops.
• In case of cross-pollinated crops, inbreeding is usually associated with detrimental effect.
• Some cross-pollinated species show little or no inbreeding depression.
• In case of recurrent selection for GCA/SCA, the tester serves as the eye of breeder.
• The testers for GCA have broad genetic base, e.g., a heterogeneous line like an open- pollinated variety.
• Testers for SCA have narrow genetic base, e.g. inbred lines, or F₁ generation from a single cross.
• The objective of reciprocal recurrent selection is to improve two populations simultaneously for their ability to combine well with each other.
• In case of reciprocal recurrent selection, the two populations serve as testers for each other.
• The performance of inbred lines depends mainly on additive genetic variance.
• GCA of inbred lines is tested by top-cross Synthetic and composite varieties exploit mainly the additive variance.
• Synthetic and composite varieties exploit only a part of heterosis, while hybrid varieties exploit the full expression of heterosis,
• Heterosis can be fixed only when it is the consequence of additive x additive type of epistasis
• The population of a single cross hybrid is heterozygous, but homogeneous. Triple cross or double cross hybrids are heterozygous and heterogeneous.
• GCA of the constituent parental lines is evaluated during the development of hybrid and synthetic varieties; it is not done in the case of composite varieties,
• A farmer has to purchase every year fresh seeds of a hybrid variety, but this is not required in the case of synthetic and composite varieties. GCA is more important in synthetics, while SCA is more important in the case of hybrids.
• Synthetics and composites are essentially open-pollinated populations constituted by breeder.
• In case of synthetics, the greater is the number of parental lines, the smaller is the amount of inbreeding depression in the Syn2and later generations.
• Asexually reproducing crop species are highly heterozygous and show severe inbreeding depression.
• Linkage increases the proportion of homozygous genotypes for one or the other allele of the linked genes, but does not change the percentage of homozygous gene pairs, that is, percentage of homozygosity.
• A major advantage of self-incompatibility over male sterility is that the F1 hybrid seeds can be harvested from both the parents.
• Genotypic and phenotypic ratios are the same in the case of incomplete dominance or co-dominance.
• According to a survey. -86% of seed moves from farmer to farmer in A.P., India.
• KRL-19 is a salinity tolerant variety of wheat.
• Kharchia local wheat is the primary source of salinity tolerance.
• An RFLP is detected by a combination of a DNA probe and a restriction enzyme, it detects polymorphism in the lengths of the fragments generated by a restriction enzyme in the genomic segment identified by the probe.
• RFLP is a codominant marker and follows Mendelian inheritance, te, shows a 1:2:1 ratio in F2
• RAPD is a PCR-based molecular marker.
• RAPD is a dominant marker.
• Southern blotting is used for the detection of specific DNA fragments.
• Northern blotting is used for the detection of RNA fragments.
• Western blotting is used for the detection of proteins of a particular antigenic specificity.
• Pulsed-field gel electrophoresis (PFGE) is used for separation of large-sized DNA molecules, sometimes representing whole chromosomes. Using the technique of pulse-field gel electrophoresis and more refined technique of countour clamped homogeneous electric field electrophoresis (CHEFE), genomes of several fungi could be resolved into chromosomal bands and used for mapping of DNA sequences on specific chromosomes.
• Methylation and demethylation is the defence mechanism of organisms against restriction enzymes.
• Methylation of promoter sequences suppresses gene expression.
• The chances of breaking linkage between desirable and undesirable genes are more with backcrossing than with selfing.
• Genepool represents the entire genetic variability or diversity available in a crop species
• Germplasm includes cultivated and wild relatives of crop plants.
• Germplasm can be collected from centres of diversity, gene sanctuaries, gene banks. tribal communities, farmer fields, markets and seed companies.
• Gametophytic self-incompatibility reaction is determined by the genotype of pollen.
• self-incompatibility reaction is Sporophyte by the genotype of sporophyte (pollen producing plant). 
• In case of sporophytic self-incompatibility. pollen germination or pollen tube growth is inhibited on the stigma.
• In case of gametophytic self-incompatibility. pollen tube growth is usually inhibited in style or ovary.
• Genetic constitution of plants is determined by their mode of pollination.
• Pure lines and inbred lines usually have narrow adaptation.
• Heterogeneous populations have wider adaptability and stable performance under different environments.
• Heterozygous populations have greater buffering against environmental fluctuations.
• Mass selected varieties have wider adaptation and more stable performance against environmental fluctuations due to their heterogeneity.
• Mass selection is applicable to self-as well as cross-pollinated crops. However, it is more commonly used in cross-pollinated crops.
• Transgenic plants are those plants, which carry one or more genes transferred through genetic transformation.