Basics Flashcards
What is genetics?
Genetics is the study of genes, genetic variation, and heredity in living organisms
Allele
Variation of a gene
An allele is the variant form of a given gene. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation. However, most genetic variations result in little or no observable variation.
Most multicellular organisms have two sets of chromosomes; that is, they are diploid. These chromosomes are referred to as homologous chromosomes. If both alleles at a gene (or locus) on the homologous chromosomes are the same, they and the organism are homozygous with respect to that gene (or locus). If the alleles are different, they and the organism are heterozygous with respect to that gene.
In many cases, genotypic interactions between the two alleles at a locus can be described as dominant or recessive. Many traits defy this simple categorization and the phenotypes are modeled by co-dominance* and polygenic inheritance.
*Co-dominance occurs when the contributions of both alleles are visible in the phenotype.
Gene
A gene is a locus (or region) of DNA which is made up of nucleotides and is the molecular unit of heredity.
Genes can acquire mutations in their sequence, leading to different variants, known as alleles, in the population. These alleles encode slightly different versions of a protein, which cause different phenotype traits.
Genotype and phenotype
Genotype is the part (DNA sequence) of the genetic makeup of a cell, and therefore of an organism or individual, which determines a specific characteristic (phenotype) of that cell/organism/individual.
Genotype is one of three factors that determine phenotype, the other two being inherited epigenetic factors, and non-inherited environmental factors.
The set of alleles for a given organism is called its genotype, while the observable traits of the organism are called its phenotype.
When organisms are heterozygous at a gene, often one allele is called dominant as its qualities dominate the phenotype of the organism, while the other allele is called recessive as its qualities recede and are not observed. Some alleles do not have complete dominance and instead have incomplete dominance by expressing an intermediate phenotype, or codominance by expressing both alleles at once.
Locus
A locus (plural loci) in genetics is the position of a gene on a chromosome. A variant of the similar DNA sequence located at a given locus is called an allele.
