Heredity

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Heredity

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Transmission of biological traits from parents to offspring

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Progeny

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New individuals that result from reproduction. Offspring

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Dominant trait

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A characteristic that is expressed when one or both alleles in an individual are in the dominant form

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Recessive trait

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A characteristic that is expressed only when both alleles in an individual are in the recessive form

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Allele

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One of alternative forms of a gene. An individual must carry 2 copies of each gene that can be the same or different

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Homozygous

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Having identical alleles for the same gene

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Heterozygous

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Having different alleles for the same gene

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Genotype

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The genetic complement of an organism

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Phenotype

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The observable characteristics of an organism

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Segregation

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The separation of alleles during meiosis

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Phenotypic ratio

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The ratio of offspring with a dominant trait compared to a recessive trait

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Probability of an outcome

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Likelihood that the outcome will occur. P= (number of ways that a given outcome can occur/ total number of possible outcomes)

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Punnett square

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A chart used to determine the predicted outcome of a genetic cross

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Genotypic ratio

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The ratio of offspring with each possible allele combination from a particular cross

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Test cross

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The cross of an individual of unknown genotype to an individual that is fully recessive to find out the genotype

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Pedigree chart

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A chart used to record the transmission of a particular trait or traits over several generations. Like a family tree

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Pleiotropic genes

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A gene that affects more than one characteristic

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Wild type

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The most common allele of a gene with multiple alleles

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Mutant

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Any allele of a gene other than the wild type allele

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Incomplete dominance

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The expression of both forms of an allele in heterozygous individual in the cells of an organism, producing an intermediate phenotype- a blend of the 2 alleles (red×white=pink)

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Codominance

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The expression of both forms of an allele in a heterozygous individual in different cells of the same organism (red×white=roan or a mix of red and white fur)

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Dihybrid cross

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Genetic cross involving 2 genes, each of which has more than one allele

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Selective breeding

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The crossing of desired traits from plants or animals to produce offspring with both characteristics

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Inbreeding

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The process whereby breeding stock is drawn from a limited number of individuals processing desirable phenotypes

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Polygenic traits

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Inherited characteristics that are determined by more than one gene. Example: skin colour, eye colour, height.

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Epistatic genes

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Gene masks the expression of other genes

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Cytology

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Study of cell formation, structure and function

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Linked genes

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Genes that are located on the same chromosome

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Autosome

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Chromosome not involved in sex determination

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Sex-linked trait

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Trait determined by genes located on sex chromosomea

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Recessive lethal traits

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Trait that, when both recessive alleles are present, results in death or recessive malformation of the offspring. Occurs more frequently in males

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Barr body

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Small, dark spot of chromatin located in the nucleus of a female mammalian cell

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Linkage group

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Group of linked genes on a chromosome

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Locus

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A specific location along a chromosome where a particular gene is found

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Crossover percentage

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=(Number of recombinations/total number of offspring) ×100. Related to actual physical distance of 2 genes on the chromosome

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Marker genes

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Gene that confers an easily identifiable phenotype and is used to trace inheritance of other genes that are difficult to identify. Must be located on the same chromosome and ideally, at a very small distance from the gene being followed

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Continuity of life

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Succession of offspring that share structural similarities with those of their parents

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Bacteriophage

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A virus that infects bacteria. Attaches to outer surface of cell and injects its heredity into it

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Isotope

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1 or 2 more atoms of the same element, containing the same number or protons but a different number of neutrons

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Radioisotope

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Unstable isotope that decays spontaneously by emitting radiation

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Nucleotides

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Molecule having a 5-carbon sugar with a nitrogenous base attached to its 1' carbon and a phosphate group attached to its 5' carbon

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Deoxyribose sugar

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A sugar molecule containing 5 carbons that has lost the -OH on its 2' position

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Nitrogenous base

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An alkaline, cyclic molecule containing nitrogen

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Phosphate group

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Group of 4 oxygen atoms surrounding a central phosphorous atom found in the backbone of DNA

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Allele frequency

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Proportion of gene copies in a population of a given allele