Genetic Definitions Flashcards
Gene
A gene is the basic physical and functional unit of heredity. Genes are made up of DNA. Some genes act as instructions to make molecules called proteins. However, many genes do not code for proteins. A gene is a section of DNA that contains the instructions for making proteins that are passed down from parents to their children.
Locus or Gene loci:
The position of a gene on a particular chromosome is called the locus (plural = loci)
Genotype
The set of genes an organism has. Sometimes, genotype refers to the entire genome of an organism and sometimes it refers to the alleles carried at a particular locus.
Phenotype
The physical features of an organism. Phenotype may refer to any aspect of an organism’s morphology, behaviour, or physiology. An organism’s phenotype is affected by its genotype and by its environment.
Heredity
A property of systems in which intrinsic characteristics are passed from parent to offspring. This results in offspring that resemble their parent more than they resemble randomly chosen individuals of the population. In biology, heredity occurs largely through transmission of the genetic materials DNA and RNA. However, epigenetic heredity also occurs.
Dominant
Gene version with an effect that is observed even when paired with a non-identical gene version in the same individual.
Recessive
Gene version with an effect that is only observed when it is found paired with an identical version in the same individual.
Heterozygous
An individual carrying two different gene versions for a particular gene (e.g., Aa as opposed to AA).
Homozygous
An individual carrying two identical gene versions for a particular gene (e.g., AA as opposed to Aa).
Allele
One possible variant of a gene, Different forms of a gene.
Complete dominance
Complete dominance is a form of dominance in heterozygous condition wherein the allele that is regarded as dominant completely masks the effect of the allele that is recessive. For instance, an individual carrying two alleles that are both dominant (e.g. AA), the trait that they represent will be expressed.
Incomplete dominance
Incomplete dominance is a form of intermediate inheritance in which one allele for a specific trait is not completely expressed over its paired allele. This results in a third phenotype in which the expressed physical trait is a combination of the phenotypes of both alleles.
Codominance
Codominance happens when two traits are independently and equally expressed
Polygenic traits
A polygenic trait is one whose phenotype is influenced by more than one gene. Traits that display a continuous distribution, such as height or skin colour, are polygenic.
Monohybrid cross
A monohybrid cross is a mating between two individuals with different variations at one genetic chromosome of interest.
Dihybrid cross
Dihybrid cross is a cross between two different lines (varieties, strains) that differ in two observed traits. In the Mendelian sense, between the alleles of both these loci there is a relationship of complete dominance - recessive.
Punnett Squares
The Punnett square is a diagram that is used to predict an outcome of a particular cross or breeding experiment. It is named after Reginald C. Punnett, who devised the approach. The diagram is used by biologists to determine the probability of an offspring having a particular genotype.
Epistasis
The masking of one gene by another. For example, a gene causing baldness would mask the effect of a hair-colour gene
Pedigree
A diagram showing the lineage or genealogy of an individual and all the direct ancestors, usually to analyse or follow the inheritance of trait.
Chromosomes
Condensed DNA wrapped around histone proteins.
Genomes
The total genetic information in an organism.
Karyotype
An image of all the chromosomes of an organism.
Homologue - Homologous chromosomes
2 chromosomes with the same size and length, the same centromere position, and they share the same genes at the same gene loci.
Autosome
Any chromosome that is not a sex chromosome
Nitrogenous base
adenine (A) connects with thymine (T); guanine (G) connects with cytosine (C)
Haploid
A cell with a single set of chromosomes
Diploid
A cell with a single set of chromosomes.
Histone
A protein that has DNA wrapped around creating chromosomes.
Telomere
The ends of a chromosome.
Sex chromosome
23rd pair are the sex chromosomes, The X and the Y chromosomes are called sex chromosomes
Nucleic acid: compound
Nucleic acid is compound, such as DNA or RNA, built from nucleotide sub-units
Nucleotide
Nucleotide are made up of Sugar, Phosphate group and Nitrogenous base
Somatic cell
Somatic cells are the cells in the body other than sperm and egg cells (which are called germ cells). In humans, somatic cells are diploid, meaning they contain two sets of chromosomes, one inherited from each parent.
Chromatid
A chromatid is one of the two identical halves of a chromosome that has been replicated in preparation for cell division. The two “sister” chromatids are joined at a constricted region of the chromosome called the centromere.
Sister chromatids
Sister chromatids the identical daughter strands of a replicated chromosome
Short arm of chromosome
Short arm of chromsome - aka ‘p arm’ – this is the section of the chromosome that is shorter in length
Long arm of chromosome
Long arm of chromosome - aka ‘q arm’ – this is the section of the chromosome that is longer in length homologous chromosomes
Aneuploidy
Aneulploidy is when a cell or organism varies in the usual number of chromosomes in its genome by the addition or loss of a chromosome
Polyploidy
Polyploidy when an organism contains additional sets of chromosomes in its genome more common in plants - one advantage of polyploidy includes increased size and hardness in certain types of fruit
Monosomy
Monosomy is one missing chromosome (2n-1) e.g. turner syndrome - single chromosome X, fused neck
Trisomy
Trisomy is one extra chromosome (2n+1) e.g. down syndrome - extra copy of chromosome 21, delayed physical growth e.g. Klinefelter syndrome - extra X chromosome in males (XXY), small testes
Tetrasomy
Tetrasomy is two extra chromosomes (2n+2) e.g. Tetrasomy X - two extra copies of the X chromosome, mild delay in physical development
