What determines who we are? Genes and Chromosomes

Evolution Evolution is the process by which species change over time. This is done by natural selection: random changes to an animal are passed on if those changes help the animal survive and reproduce. These random changes are called mutations. How do they happen?

Mutations Mutations are random changes to the genetic information of a plant or an animal and can cause the animal to grow in a new and different way. Most mutations are neutral – they do not affect an animal’s fitness positively or negatively. Some mutations are negative – such as deformed limbs or malfunctioning organs. Some mutations are positive – such as larger brains, webbed feet, or better camouflage.

Genes Genes hold your personal information They control hereditary traits like eye colour and body function Genes are segments of DNA DNA makes up your chromosomes Each human cell has 23 pairs of chromosomes

Chromosomes There are 22 autosome pairs and one pair of sex chromosomes Sex chromosomes control gender Females have 2 X chromosomes and males have an X and a Y chromosome Autosomes determine other traits

So what does this have to do with mutation? Mutation happens at the genetic level This happens when the information in the genes gets mixed up We know certain syndromes come from mutations in specific chromosomes: -for example Down’s Syndrome comes from having an extra chromosome 21 One possible mutation:

Recap (1) Cells contain chromosomes Each chromosome is made up of DNA A segment of DNA which controls a trait or body function is called a gene When the information in genes is mixed up it is called mutation Mutations may or may not change an individual for better or for worse

Recap (2) When the mutation helps, the individual is more likely to reproduce and pass on the mutation to future generations. When the mutation is harmful, the individual is less likely to reproduce. This process is called evolution by natural selection and allows species to change over long periods of time.

Dominant vs. Recessive Genes We get one set of 23 chromosomes from each parent When the gene from one set overrules the gene from the other set, that gene is called “dominant”. The other gene is called “recessive”. The gene for brown eyes is dominant.

Bibliography of images 1.gifhttp:// 1.gif mosomes.jpghttp://ghr.nlm.nih.gov/handbook/illustrations/chro mosomes.jpg online.org/images/gene_inversion.gifhttp:// online.org/images/gene_inversion.gif Evolution/defini8.jpghttp:// Evolution/defini8.jpg ges/drosophila_experiment.gifhttp://evolution.berkeley.edu/evosite/evo101/ima ges/drosophila_experiment.gif