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L1 Genetics
definitions for genetics AS90944
| Term | Definition |
|---|---|
| Allele | alternative forms (version) of a gene (with different sequences of nucleotides that can occupy the same locus) |
| Characteristic | refers to a trait eg hair colour or foot size |
| 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. |
| Diploid | (2n) Cells (mostly body) which have 2 copies of each chromosome (one set from each parent) |
| DNA | Deoxyribose Nucleic Acid. Made up of nucleotides (sugar – phosphate backbone with one nitrogenous base (either A, T, G or C) attached to the sugar molecule. Form long strands, double helix with rungs joining bases in complementary fashion. Code. |
| DNA replication | copying from 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. |
| 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. |
| 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. |
| 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). |
| 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. |
| 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) |
| Peptide | Compound containing two or more amino acids bonded together using a peptide bond. A complete peptide molecule is called a protein. |
| 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. |
| 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. |
| 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. |
| Sperm | motile male sex cell (gamete) in animals. Has haploid number of chromosomes. |
| 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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