Basics of Genetics ~ Genotype and Phenotype ~ Homozygote and Heterozygote
Basic Concepts of Genetics
•Heredity is the ability of living organisms to transmit their traits through generations.
•Inheritance is the external manifestation of heredity, that is, the specific expression of traits.
•Variability is the opposite of heredity. These are changes that ensure adaptation to the environment, both of a specific organism and of a biological species as a whole.
•A trait is a specific property of an organism, such as eye color, body weight, height, and so on.
•The opposite expression of one trait is called an alternative. For example, eye color is a trait; an alternative expression is dark or light eyes (brown or blue). Height is a trait; an alternative expression is tall or short.
•Phenotype is the totality of all the traits of an organism (what can be seen externally).
•Karyotype is the diploid set of chromosomes in a somatic cell (a non-reproductive cell), characterized by a specific number, size, and shape.
•Genotype is the set of genes in a diploid set of chromosomes;
•A gene is an indivisible, elementary unit of heredity that encodes a protein. Genes are arranged linearly on chromosomes.
•Structural genes are genes that encode protein synthesis.
•Functional genes are genes that control and direct the activity of structural genes.
•The location a gene occupies on a chromosome is called a locus.
•A pair of chromosomes containing genes are homologous chromosomes and therefore are always paired in the genotype (one from the father, one from the mother).
•Genes located at the same loci on homologous chromosomes and determining a single trait are called alleles.
•Genes located at different loci on homologous chromosomes or on different pairs of chromosomes are called nonallelic.
•If alleles determine the same expression of a trait, then organisms are called homozygous for that trait (AA, aa).
•If alleles determine different expressions of a trait (A - yellow, a - green), then organisms are called heterozygous for that trait (Aa).
•Genes are designated by letters of the Latin alphabet. Capital letters indicate dominant, or repressive, genes (A, B, C), while lowercase letters indicate recessive, or repressed, genes (a, b, c).
•By phenotype, an organism can be large, small, red, green, or rough.
•By genotype, it can be homozygous (dominant or recessive) or heterozygous.
•That is, genes are designated by letters, and traits by words.
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