1. Variation & Inheritance
Biology
Variation & Inheritance

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

3. 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?

4. 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

5. 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

6. 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?

7. 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

8. 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)

9. 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

10. 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?

11. 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

12. 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

13. 9b) Genetic Crosses B b D d e E

14. 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

15. 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

16. 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,

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