3 Variation Ways in which Tom and James are the same (caused by genes): “Variation” is the name given to differences between individuals of the SAME species.Variation is due to GENETIC or ENVIRONMENTAL causes. For example, consider identical twins:Ways in which Tom and James are the same (caused by genes):Ways in which Tom and James are different (caused by environment):06/04/2017
6 Where is this information stored? Section of a chromosome:Genes for eye colourGenes for blood group:Genes for hair colourDifferent species have different numbers of chromosomes. Humans have 46 (23 pairs) in every cell.06/04/2017
7 GenesHuman cells have 46 chromosomes other organisms have different numbers of chromosomes.
8 Sexual ReproductionThe human egg and sperm cell (“GAMETES”) contain 23 chromosomes each.When fertilisation happens the gametes fuse together to make a single cell called a ZYGOTE. The zygote has 46 chromosomes (23 pairs).06/04/2017
12 What did we learn from this? Children inherit features from their parentsIf two parents have a certain characteristic then their child may show it even more (e.g. Mr Small + Little Miss Tiny = Mr Very Small!)Some things such as glasses, scars and muscles we get from our environment, they are not inherited.
13 Genetic informationThe instructions that make up a plant or animal comes from their parents.½ comes from the sperm and ½ from the eggThese instructions are found in the nucleus of the cells.The instructions for each characteristic are called GENES.
14 We saw that when Mr Small and Little Miss Tiny produced a child it was even smaller. What would happen if Mr Very Small had a child with Little Miss Miniscule??
15 This is called selective breeding and can be used to make larger animals and crops that produce more fruitLarge fruited MumLarge fruited DadVery large fruited child!At this point give out picture of the giant bull.
16 This is depending on the strength of the genes... Some genes have more clout when it comes to deciding a feature than others.“Stronger” genes are known as dominant“Weaker” genes are known as recessive.The gene for brown eye colour is dominant. If one of your parents have brown eyes it is very likely you will too!There’s still a small chance of blue eyes but the probability is decreased.
17 VariationLevel 4 – Recognise difference between organisms of the same speciesLevel 5 – Explain what may have caused some examples of variation within a speciesLevel 6 – Suggest why variation might increase an organisms chances of survivalLevel 7 – Explain, using variation, why certain species have become extinct
18 Variation…your taskYou have been asked to produce a poster for Year 8 students to teach them about ‘variation’.Use you LOs as your level ladder for this task and tick them off as you go Key words;VariationGeneInheritEnvironmentalSurvivalExtinctionOrganismDon’t forget to include the two typesof variation and examples of each!
19 Lets see what you’ve learned: Farmer Hemming wants to breed cows that are large and meaty so that he can sell them for more.What advice would you give him in order to produce larger cows?2. He can’t seem to breed cows with nose rings! Why not?3. How many chromosomes are in your cells?