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L1 MendalianGenetics
Definitions for the middle sections regarding Mendalian genetics for Sci 1.9
| Term | Definition |
|---|---|
| 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)). |
| 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. |
| Monohybrid cross | a cross between two individuals that are both heterozygous at a particular gene locus. |
| Pedigree chart | diagram showing the phenotypes of members of a family and relatives. Pedigrees may be used to work out patterns of inheritance and to calculate the probability of children being born with a particular genetic defect like haemophilia or cystic fibrosis. |
| 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 |
| 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 |
| 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 homozygous state (ie when both alleles in the genotype of an individual are recessive) |
| Sex determination | process by which sex of the offspring is determined. A Punnett square can be used to show this. |
| Test cross | used to find the genotype of an individual with a dominant trait by crossing it with another individual which is homozygous recessive. Recessive offspring mean heterozygous parent. No recessive offspring, homozygous: need lots offspring to be certain. |