Variation and genetics

• The two base pairs in DNA are: Adenine and Thymine Cytosine and Guanine or C-G and T-A. They are connected by hydrogen bonds.
• DNA is composed of two coiled strands which form a double helix.
• DNA has a sugar-phosphate backbone.

  
• Humans have 46 chromosomes (arranged in 23 pairs) in all body cells aside from sperm and egg cells.
• The 23rd pair of chromosomes decides the sex of the individual.
• Locus: a particular position or place where something occurs or is situated on each pair of chromosomes.
• Alleles are different versions of the same gene.
• Homozygous: having two identical alleles of a particular gene or genes.
• Heterozygous: having two different alleles of a particular gene or genes.
• Alleles can be dominant (the effect is always observed, always shown with a capital letter) or recessive (the effect is only observed if both alleles are present, always shown with a lower case letter).
• Genotype: the genetic constitution of an individual organism.
• In the gametes, there is only 1 allele so after fertilisation, the offspring will have 2 alleles.
• Phenotype: the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.
• The phenotype includes all physical traits such as height, eye colour etc.
• Punnet squares: A diagram used to show the probability of offspring from a cross.

  
• DNA: a list of chemical instructions on how to build an organism.
• cell -> nucleus -> chromosomes -> genes -> DNA -> proteins -> cell
• The female sex chromosomes are called XX.
• The male sex chromosomes are XY.
• Karyotype: the number and visual appearance of the chromosomes in the cell nuclei of an organism or species.
• Cystic fibrosis

  ->Inherited condition

  ->Sticky mucus builds up in the lungs and digestive systems

  ->Caused by a faulty gene which affects the movement of salt and water in cells
• Gamete: A sex cell (ovum or sperm) that contains half the number of chromosomes as a normal cell.
• Diploid: (of a cell or nucleus) containing two complete sets of chromosomes, one from each parent.
• Haploid: (of a cell or nucleus) having a single set of unpaired chromosomes.
• Zygote: a diploid cell formed by the fusion of two haploid gametes.
• Gene: a short section of DNA that codes for a specific protein.
• Chromosome: A threadlike structure of DNA that carries genetic information.
• • For continuous variation, we use a line graph. These characteristics change gradually over a range of values. E.g. height, weight, temperature
  • For discontinuous variation we use a bar chart. These characteristics do not change. E.g. blood group, gender

  
• • Examples of genetic variation: eye and hair colour, skin colour, height
  • Examples of environmental variation: religion, language