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KGS N4N5 Unit 2 – Variation & Inheritance Learning Outcomes Variation Variation is the differences between members of the same species Continuous variation is a factor that can be measured e.g. height, weight, hand span Discrete variation is a factor that can be sorted into groups e.g. hair colour, skin colour Continuous variation is controlled by many genes (Polygenic inheritance) Discrete variation is controlled by a single gene During sexual reproduction, the new member of the species receives 50% genetic information from its mother and 50% genetic information from its father The combining of different genes through sexual reproduction contributes to variation within a species Inheritance Genetics is the study of Inheritance and Variation The study of genes and their transmission from generation to generation is called inheritance Genetic information is found in chromosomes in the nucleus of cells Chromosomes are divided up into genes, and genes are made of DNA The chromosome complement is the number of chromosomes you find in each body cell of a species eg. Human chromosome complement = 46; Kangaroo chromosome complement =12 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 chromsomes (one set from each parent) Every body cell contains 2 alleles for a particular gene (one allele from each parent) 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 A dominant characteristic hides the other characteristic The allele of a dominant characteristic is always a capital letter e.g. B A recessive allele 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 alleles only show up in the phenotype (appearance) of an organism if they are paired with another recessive gene Homozygous individuals have the same alleles e.g. BB or bb Heterozygous individuals have different alleles e.g. Bb 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 fertilsation is a random process involving an element of chance 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 Carriers and those at risk of passing on a genetic disorder to their offspring may receive genetic counselling 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 Mutations are changes to the chromosome structure or number of chromosomes Examples of mutagenic agents are: Mustard Gas, X-Rays, UV Light