Understanding Alleles and Genetic Concepts
Alleles
Alternative alleles of a gene, located at the same locus on homologous chromosomes, are responsible for different phenotypic manifestations of a trait.
Lethal Alleles
A lethal allele causes the death of a homozygous individual who possesses it.
Recessive Alleles
A recessive allele does not express itself in a heterozygote.
Multiple Alleles
Multiple alleles occur when a gene is represented by more than two alleles.
Autofecundation (Self-Fertilization)
Autofecundation is a mode of fertilization in which male and female gametes are derived from the same individual. It is predominantly observed in plants.
Codominance
Codominance is a type of dominance in which both alleles express their products (enzymes) separately in the production of the heterozygous phenotype.
Chromosomes
A chromosome is a nucleoprotein structure, and its core is located and observed during cell divisions.
Test Cross
A test cross is a cross used to identify whether an individual is homozygous or heterozygous and to verify the segregation of two or more genes.
Complete Dominance
Complete dominance is an allelic interaction in which the phenotype of the heterozygote is the same as that of the homozygote for the dominant allele.
Incomplete Dominance
Incomplete dominance is an allelic interaction in which the phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes.
Double Fertilization
In double fertilization, the reproductive core of the pollen grain is divided in two. One fertilizes the oosphere for embryo formation, and the other fertilizes the polar nuclei for endosperm formation.
Inbreeding
Inbreeding occurs when individuals related by descent mate. Maximum inbreeding occurs with self-fertilization, and it is related to a loss of vigor.
Epistasis
Epistasis is a non-allelic interaction in which the expression of one gene is inhibited by another.
F1 Generation
F1 is the first filial generation, resulting from the mating of homozygous progenitors.
F2 Generation
F2 is the second filial generation, resulting from the interbreeding or self-fertilization of individuals from the F1 generation.
Phenotype
A phenotype is the expression of a feature. It is determined by genotype and environment.
Recessive Phenotype
A recessive phenotype is the phenotype of individuals homozygous for a recessive allele.
Gametes
Gametes are reproductive cells that normally carry half the number of chromosomes characteristic of the species.
Genotype
A genotype is the genetic constitution of an individual.
Lethal Genes
Lethal genes are genes that can cause the death of the individual who possesses them.
Heterozygous
Heterozygous individuals have different alleles for the same gene.
Homozygous
Homozygous individuals have identical alleles for a gene.
Gene Interaction (Allelic or Non-Allelic)
Gene interaction is the interaction of two or more genes in the production of a characteristic.
Combined Allelic Interaction
Combined allelic interaction is the action of two alleles of the same gene in a heterozygote on the expression of its phenotype.
Mendelian Genetics
Mendelian genetics refers to the principles of inheritance, including the segregation and independent assortment of traits.
Meiosis
Meiosis is a cell division process responsible for the formation of gametes. It is characterized by reducing the number of chromosomes to half.
Mitosis
Mitosis is a cell division process responsible for increasing the number of cells in tissues. It is characterized by producing daughter somatic cells identical to the parent cell.
Mutation
Mutation is a process responsible for the production of new alleles through the alteration of the DNA base sequence.