ESO 4 B&G 2

Heredity and Transmission

Key Information

Vocabulary: Mendelian Genetics
Locus (pl. loci)A place in a chromosome where a gene resides. Each locus contains the encoded information for a trait, such as "colour of the eyes".
AlleleOr allelomorph gene. Any of a number of the alternative varieties of a gene that reside in the same locus. Each allele contains the encoded information for a quality or a value of a trait, such as "brown colour of the eyes". All the possible alleles for the same locus form a "family of allelomorph genes".
HaploidCell or individual or species with one single set of chromosomes, such as bacteria or the human gametes.
DiploidCell or individual or species with two sets of chromosomes, such as the body cells of humans (and most eukaryotes). Each chromosome of a set is similar to one chromosome of the other set in that they carry exactly the same loci, but they are not identical, as the specific alleles of each locus can be different.
HomologousIn diploid individuals, each pair of chromosomes that carry the same loci. Humans have 22 pairs of homologous chromosomes and one pair (the sex chromosomes) which are partially homologous.
HomozygousOr "pure breed". Diploid individuals are homozygous for a locus when the alleles present in that locus are the same in both homologous chromosomes.
HeterozygousOr "hybrid". Diploid individuals are heterozygous for a locus when the alleles present in that locus are different in each homologous chromosome.
DominanceA type of relationship between two different alleles of the same family whereby one allele (said to be the "dominant" one) cancels out the phenotypic effect of the other (said to be "recessive").
CodominanceA type of relationship between two different alleles of the same family whereby both alleles express their phenotypic effects without blending. This is the case of the alleles for the "A" and "B" human blood types, whose heterozygosis yields an "AB" type.
Incomplete dominanceA type of relationship between two different alleles of the same family whereby the phenotypic effects of each allele are blended in the phenotype. This is the case of the alleles for the red and white colour for the corolla of the flowers of the snapdragon plant, whose heterozygosis yields a pink colour.
Mind Map: First artificial cell
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