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Yr12 Genetics
Definitions for Genetic Variation AS91157
| Term | Definition |
|---|---|
| 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. |
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