Variation & Inheritance Biology Variation & Inheritance

Learning Intentions What is variation? What process leads variation? a) What is continuous & discrete variation? b) What is Polygenic & Single Gene Inheritance?

Variation is the differences between members of the same species 1. What is variation? Variation is the differences between members of the same species How many differences can you spot between these individuals?

2. What process leads to variation? Sexual Reproduction is when new offspring are made from male and female parents The offspring receive 50% genetic information from the mother and 50% genetic information from the father The combining of different genes through sexual reproduction contributes to variation within a species. Variation is important for the survival of the species so it can adapt to a changing environment

3. Continuous & Discrete Variation Type of Variation Continuous Variation Discrete Variation Description Variation that can be measured Variation that can be grouped Examples Height Weight Handspan Hair Length Eye Colour Hair Colour Male/Female Ear lobes/lobeless Number of genes controlling variation Many genes (Polygenic Inheritance) Single gene Graph to show variation Line Graph Bar Graph

Learning Intentions What is genetics & inheritance? What are chromosomes, genes & alleles? What are phenotypes & genotypes? What are dominant & recessive alleles? What is a homozygous and heterozygous individual? What are genetic crosses? Gender Determination What are mutations and how are they caused? What is a carrier? What is genetic counselling?

4. Genetics & Inheritance Genetics is the study of Inheritance and Variation The study of genetics and its transmission from generation to generation is called inheritance

5.Chromosomes, Genes & Alleles Genetic information is found in chromosomes in the nucleus of cells Chromosomes are divided up into genes, and genes are made of DNA Genes are packets of information stored along chromosomes. e.g. Eye colour gene, Alleles are different forms of the same gene e.g. Blue eye colour, Brown eye colour Every body cell contains 2 matching sets of chromosomes (one set from each parent) Every body cell contains 2 alleles for a particular gene (one allele from each parent)

6. Phenotypes & Genotypes The genotype is set of alleles that an organism possesses eg. BB The phenotype is the appearance of an organism e.g. Blue eyes, Brown Hair

7. Dominant and Recessive Alleles A dominant characteristic hides the other characteristic The allele of a dominant characteristic is always a capital letter e.g. B A recessive characteristic is the characteristic that is masked The allele of a recessive characteristic is always a small letter e.g. b Dominant alleles always show up in the phenotype (appearance) of an organism Recessive genes only show up in the phenotype (appearance) of an organism if they are paired with another recessive gene What colour eyes will each individual have?

8. Homozygous & Heterozygous Homozygous individuals have the same alleles e.g. AA or aa Heterozygous individuals have different alleles e.g. Aa Homozygous Heterozygous Heterozygous Homozygous

9a) Genetic Crosses In genetic crosses the generations are: P Parents F1 Children F2 Grandchildren A monohybrid cross is a cross involving one characteristic e.g. height Predicted F2 phenotypic ratio of a monohybrid cross is 3:1 Observed ratios are different to predicted because fertilisation is a random process involving an element of chance

9b) Genetic Crosses B b D d e E

10. Gender Determination The sex chromosomes that eggs can carry are an X or an X The sex chromosomes that sperm can carry are an X or a Y Sex chromosomes in Males is XY and in Females is XX

11. Mutations Mutations are changes to the chromosome structure or number of chromosomes e.g. Down Syndrome Examples of mutagenic agents are: Mustard Gas, X-Rays, UV Light

12. What is a Genetic Carrier? Pedigree charts can be used to study genetics within families A carrier is a person who has one copy of a disease allele but is not affected by the disease Find out about genetic disorders e.g. Cystic Fibrosis, Haemophilia, Down’s Syndrome,

13. What is Genetic Counselling? Carriers and those at risk of passing on a genetic disorder to their offspring may receive genetic counselling