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Monday, December 4, 2017

Genetics and Genetics Terminology

•    Genetics is the science of hereditary and variations in living organisms.
•    Gregor John Mendel is known as the Father of Genetics.
•    His findings of Genetics are called Mendel’s Law.
•    Mendel summarized his findings in two laws: the Law of Segregation and the Law of Independent Assortment.



The Law of Segregation or The First Law


The Law of Segregation states that every individual possesses a pair of alleles (assuming diploidy) for any particular trait and that each parent passes a randomly selected copy (allele) of only one of these to its offspring. The offspring then receives its own pair of alleles for that trait. Whichever of the two alleles in the offspring is dominant determines how the offspring expresses that trait e.g. the color of a plant, the color of an animal's fur, the color of a person's eyes.

Law of Independent Assortment or The Second Law


The Law of Independent Assortment, also known as "Inheritance Law", states that separate genes for separate traits are passed independently of one another from parents to offspring. That is, the biological selection of a particular gene in the gene pair for one trait to be passed to the offspring has nothing to do with the selection of the gene for any other trait.

Genetics Terminology


•    Haploid - the condition of having only one set of chromosomes per cell (n)

•    Diploid - the condition of having two sets of chromosomes per cell (2n)

•    Gamete - a haploid (n) sex cell in plants and animals (egg or sperm)

•    Zygote - diploid (2n) cell resulting from the union of two gametes in sexual reproduction

•    Chromatin - the complex of DNA, RNA and proteins that makes up uncondensed eukaryotic chromosomes.

•    Chromosome - structures within the nucleus of eukaryotic cells composed of chromatin and visible at cell division (condensed chromatin).

•    Homologous chromosomes – These are chromosomes similar in morphology i.e. shape and form and genetic structure. In animals one set comes from the father and the other set comes from the mother.

•    Chromatids - one of the two halves of a duplicated chromosome

•    Recombination - exchange of genetic material between chromosomes

•    Synapsis - the pairing of homologous chromosomes during prophase I of meiosis.

•    Genotype - the genetic make-up of an individual.

•    Phenotype - the physical or chemical expression of an organism’s genes.

•    Gene - a discrete unit of hereditary information.

•    Alleles - genes governing variations of the same characteristic which occupy corresponding positions on homologous chromosomes.

•    Homozygous - possessing a pair of identical alleles for a particular locus (gene).

•    Heterozygous - possessing a pair of unlike alleles for a particular locus (gene).

•    Carrier - a heterozygous individual not expressing a recessive trait but capable of passing it on to its offspring.

•    Parent generation (P) - the generation that supplies gametes to the filial generation.

•    Filial generation (F,) - the generation that receives gametes from the parental generation.

•    Hybrid - An offspring resulting from the mating between individuals of two different genetic constitutions.

•    Dihybrid cross - a genetic cross that takes into account the effect of alleles at two separate loci or two different genes.

•    Monohybrid cross - a genetic cross that takes into account the effect of alleles at a single locus or single gene.