1. Lesson Starter How many chromosomes does almost all human cells have?
How many chromosomes does human sex cells have?
What does the word allele mean?
Give an example of variation in humans
Give an example of variation in plants

2. Inheritance
Lesson 2

3. Learning Intention- lesson 2
To learn about environmental variation

4. Environmental Variation
Characteristics can be affected by factors other than just genetics
Think of examples of environmental differences between people

5. Environmental variation: copy
Characteristics can be affected by factors other than just genetics
Variation caused by surroundings is called ENVIRONMENTAL VARIATION
Examples include: - Language spoken
- Religion
- Hair length
- Weight
- Piercings
- Tattoos

6. Genetic Inheritance
Sex cells (gametes) contain only one set of chromosomes.
After fertilisation takes place the new cell (zygote) contains two sets of chromosomes.
One set is from the father and the other set from the mother.

7. Genetic Inheritance
Each parent contributes one piece of information to it’s offspring for each characteristic
THEREFORE every inherited characteristic is controlled by two pieces of information
The pieces of information can be the same or different

8. Genetic Inheritance
Pieces of information are called genes (stored in chromosomes)
Different versions of gene called alleles
You inherit one allele from your Mum and one from your Dad for each gene- your genotype

9. Task: write down 3 characteristics that are inherited from the parents and 3 that are environmental

10. Task: write down 3 characteristics that are inherited from the parents and 3 that are environmental

11. Task: write down 3 characteristics that are inherited from the parents and 3 that are environmental

12. Task: write down 3 characteristics that are inherited from the parents and 3 that are environmental

13. Video What does the DOMINANT gene do to the RECESSIVE gene?
What is the chromosome type of a girl and of a boy?
What is haemophilia?
What is the difference between normal RBC and RBC affected by thalassaemia?
Where is there a successful screening programme for thalassaemia?

14. Genetic inheritance We receive two copies of the same gene (allele)
Some genes are stronger than others. These genes are dominant.
The weaker genes are recessive.
Dominant genes can hide (mask) other genes that are not so strong.

15. Genetic Inheritance
If an individual inherits a dominant gene for brown eyes from one parent and a recessive gene for blue eyes from the other, that person will have brown eyes.
However, they would still carry a recessive gene for blue eyes which can be passed on to their offspring.

16. Genetic Inheritance: copy
We receive two copies of the same gene (allele) however some genes are stronger than others.
The stronger genes are called dominant and the weaker genes are recessive.
Dominant genes can mask the recessive genes
Eg: If you inherit a dominant gene for brown eyes from mum and a recessive gene for blue eyes from dad then you will have brown eyes.
However, you would still carry a recessive gene for blue eyes which can be passed on to their offspring.

17. Genetic Crosses
Dominant genes always appear in the physical characteristics (phenotype) of an organism- you only need one of them to have the characteristic. ​
However, a recessive gene is always hidden by a dominant one, and if you are to have that characteristic, you need to get two copies of the gene.​

18. Genetic Crosses: copy
When carrying out genetic crosses, each gene is represented by using a letter.
The letter used is a capital if the characteristic is dominant and lower case if the characteristic is recessive.

19. Phenotype Blue eyes x Brown eyes Genotype bb BB Gametes passed:
Parents
Phenotype Blue eyes x Brown eyes
(recessive genes) x (dominant genes)
Genotype bb BB
Gametes passed:
All b All B
Offspring
Genotype: all Bb
Phenotype: all Brown eyes B B b Bb Bb b Bb Bb

20. Examples Dad has brown hair (Bb) and mum has blonde hair (bb)
- What is the GENOTYPE of the offspring and what is the PHENOTYPE?