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Yr12 Genetics

Definitions for Genetic Variation AS91157

Allele alternative forms (version) of a gene (with different sequences of nucleotides that can occupy the same locus)
Characteristic refers to trait
Co-dominance A condition in which the alleles of a gene pair in a heterozygote are both fully expressed thereby resulting in offspring with a phenotype that is neither dominant nor recessive.
Chromatid daughter strand of a duplicated (copied) chromosome, still joined at the centromere.
Chromosome long thread-like structures in the cell nucleus that carry genetic information coded as the sequence of bases in a DNA molecule.
Complementary base pairing The strands in a DNA molecule are held together by hydrogen bonds between complementary base pairs (Adenine always bonds with thymine (A-T), and guanine with cytosine (G-C))
Crossing over exchange of genetic material between homologous chromosomes during meiosis and increases genetic variation by creating new allele combinations on a chromosome.
Cultivar plant variety with special features produced by selective breeding.
Dihybrid cross is a breeding experiment between P generation (parental generation) organisms that differ in two traits.
Diploid (2n) Cells (mostly body) which have 2 copies of each chromosome (one set from each parent)
DNA Deoxyribose Nucleic Acid.
DNA replication process to copy a template (DNA) that takes place before cells can divide. The DNA unzips, free nucleotides will join to the exposed strands in complementary base pairing fashion (A-T, C-G) to produce two identical DNA semi-conservative strands
Dominant allele The version of the gene that will be expressed in the phenotype if it is present in the genotype whether homozygous or heterozygous.
F1 first filial generation (offspring resulting from the first experimental crossing (P1) of plants or animals).
F2 second filial generation (offspring produced by intercrossing or self-fertilisation of F1 individuals).
Fertilisation union or fusion of two sex cells (gametes) to produce a zygote.
Gamete haploid (n) sex cell (contains one set of chromosomes obtained via meiosis). Most organisms produce two kinds that are different (ie male (sperm/pollen) and female (ova/ovule)).
Gene refers to the unit of inheritance that occupies a particular position (locus) on a chromosome. (There are many different genes along one chromosome).
Genetic code Encoded in DNA: sequences of nucleotides in triplets (codons) of messenger RNA that specify the sequence of amino acids in a polypeptide.
Genetic variation inherited differences between individuals in a population resulting from mutation, crossover, the independent assortment of chromosomes during meiosis and the union of different haploid cells (gametes) at fertilisation.
Genotype the genetic make-up of an organism
Gonads organs in animals which produce the gametes, ie testes in males and ovaries in females.
Haploid the number for one set of chromosomes. Haploid gametes are produced by meiosis so when fertilisation occurs between two gametes, a diploid number of chromosomes is restored.
Hereditary describes materials and or information that are passed on from one generation to another. Not all hereditary information is genetic.
Heredity transmission of traits from one generation to another.
Heterozygous the genotype made up of two different alleles for a gene at the same loci on a pair of chromosomes in an individual.
Homologous chromosomes A pair of chromosomes, one of which is inherited from each parent. (Each pair have the same chromosome length, centromere position and banding pattern – these indicate the sequence of genes. The alleles may be different).
Homozygous condition of having identical alleles at a particular locus on each member of a pair of homologous chromosomes. They can both be dominant or both recessive.
Hybrid an organism produced by a cross between unlike parents.
Inbreeding sexual reproduction involving the mating of closely related parents.
Incomplete dominance a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele. This results in a combined (blend) phenotype.
Independent Assortment the random distribution of maternal and paternal chromosomes into the gametes. Genes will assort independently if they are located on different chromosomes.
Inherit to receive (a genetic character) by the transmission of hereditary factors
Karyotype describes the structure of a set of chromosomes as viewed through a light microscope. Often illustrated with diagrams showing pairs of chromosomes arranged from largest to smallest.
Locus position that a gene occupies on a chromosome or in a segment of DNA.
Meiosis the type of cell division for producing gametes with haploid number of chromosomes.
Mitosis the type of cell division for growth and repair of body cells. They have a diploid number of chromosomes. The daughter cells produced are genetically identical to each other and the original parent cell.
Monohybrid cross a cross between two individuals that are both heterozygous at a particular gene locus.
Mutagen physical or chemical agents that causes mutations eg x-ray, UV radiation, nuclear exposure.
Mutant organism with a mutant gene that is expressed in the phenotype eg white-eyed fruit fly.
Mutation an altered gene or the process of change in a gene due to a change in the base sequence of the DNA. It can occur following addition, deletion or substitution of a base.
Nucleotide one of the monomers from which nucleic acid polymers are constructed. Each nucleotide is made up of a sugar, phosphate and nitrogenous base (A, C, T, G)
Pedigree chart diagram showing the phenotypes of members of a family and other relatives. Pedigrees may be used to work out patterns of inheritance and to calculate the probability of offspring having genetic defects.
Peptide Compound containing two or more amino acids bonded together using a peptide bond. A complete peptide molecule is called a protein.
Phenotype observable characteristics of an organism produced by a combination of its genotype and its environment.
Phenotype ratio ratio of different phenotype combinations expected in the offspring from a cross between two parents
Polypeptide chain a polymer made up of amino acids – often several hundred of them – joined by covalent peptide bonds. Proteins are made up of one or more polypeptide chains organised into a specific structure/shape.
Population group of organisms of the same species sharing the same gene pool
Probability the chance of randomly picking an individual of a certain class or producing offspring of a particular phenotype/genotype
Progeny offspring from a mating
Protein large molecule made up of one or more polypeptide chains containing amino acids arranged in a particular sequence as determined by the genetic code.
Punnett square checkerboard method used to determine the genotypes of offspring obtained from crosses between specific parents
Purebred an organism that comes from a group that is homozygous for a particular gene or genes. Purebred lines are usually obtained by inbreeding ie continual mating with close relations.
Pure breeding A group of identical individuals that are bred for many generation from members of the same strain and always produce progeny of the same phenotype when selfed or intercrossed. Cf breeding line.
Recessive allele allele that is only expressed in the phenotype when the genotype is in a homozygous state (ie when both alleles in the genotype of an individual are recessive)
Selective breeding a deliberate breeding process using chosen parents with desirable traits to increase the likelihood of the offspring having those desirable traits or combination of traits.
Semi-conservative term used to describe replicated DNA strands where one strand is the original and the other is a complementary copy termed daughter strand.
Sexual reproduction the process of producing new offspring from the fusion of male and female gametes produced by meiosis. This increases genetic variation.
Sex determination process by which sex of the offspring is determined. A Punnett square can be used to show this.
Sperm motile male sex cell (gamete) in animals. Has haploid number of chromosomes.
Somatic cell a normal body cell with diploid number of chromosomes. Any changes (mutations) to these cells are not passed on.
Test cross used to find the unknown genotype of an individual that shows a dominant phenotype by crossing it with another individual which is homozygous recessive.
Trait observable characteristic in an organism, influenced by heredity.
Triplet sequence of three bases in the DNA that code for a particular amino acid.
Variation differences between the phenotype and or genotype of individuals in a group not linked by age or sex. They can be discrete (either or type eg roll tongue or not) or continuous (eg heights, foot size) and follow a bell shaped distribution curve.
Zygote a diploid cell resulting from the fusion of two haploid gametes.
Created by: kjsime
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