B5 KEY TERMS

• allele - different version of the same gene
• asexual reproduction - requires only one parent, resulting in clones
• cancer - a disease that occurs as a result of cell changes that lead to uncontrolled growth and division
• clone - an organism which is genetically identical to its parent
• continuous variation - variation which can take any value between a minimum and maximum. e.g. characteristics such as weight and height, which change gradually.

  
• diploid cells - cells which contain two sets of chromosomes
• discontinuous variation - characteristics which call into distinct groups e.g. blood group, eye colour

  
• dominant allele - a version of a gene whose characteristics are always expressed if present in the genotype. represented by a capital letter
• environmental variation - variation caused by the environment
• fertilisation - the joining together of two gametes
• gametes - sex cells
• genetic cross - a technique used to show off the possible characteristics of an offspring
• genetic variation - variation caused by an organism's genetic material
• genome - all the genetic material present in an organism
• genotype - the combination of alleles present in an organism
• haploid cells - cells which contain one set of chromosomes (half of a diploid)
• heterozygous - an organism that has two different alleles of a gene
• homozygous - an organism that has two copies of the same allele
• heterozygous - you inherit a different version of a gene from each parent. They do not match.


  homozygous - you inherit the same version of a gene from each parent, so you have two matching genes
• meiosis - cell division which produces gametes (sex cells)
• mutation - a change in the sequence of DNA bases
• phenotype - observable characteristics in an organism. the appearance.
• punnett square - a diagram used to show the possible genetic makeup of offspring, based on a mother's and a father's genes

  
• recessive allele - a version of a gene whose characteristics are only shown if two copies are present in the genotype. represented through lower-case letters.
• sexual reproduction - reproduction requiring two parents, which results in variation
• zygote - a fertilised egg