1. Passing on the Code
Inherited characteristics are determined by genetic information carried by genes. Chromosomes are long pieces of coiled up DNA which contain many genes.
The Rule of 23:
Sex cells (Gametes) carry half the total number of chromosomes of each parent. In humans, they carry 23 chromosomes each. During fertilisation, they combine to produce 46 chromosomes (23 pairs) in the embryo.
Mixing Genes:
There is a mixing of genes, which is why offspring look similar but not identical to parents. There is more than one version of a gene.
Example: A child may inherit a "tall" gene from the mother and a "short" gene from the father.
2. Genetic Mutation
A mutation is a change in the structure of DNA. This can happen through deletion, duplication, or substitution of genes.
Common Causes:
- ☢️ Ionising Radiation
- 🧪 Dangerous Chemicals
- 🦠 Viruses
While most mutations are harmless, some cause cells to multiply abnormally, creating tumours which can lead to cancer.
3. Predicting Traits
Task: Smooth vs Wrinkled Peas
Cross two smooth pea plants that carry a wrinkled gene (Ss x Ss).
Probability Calculator:
What is the probability of Wrinkled (ss) peas?
If 200 peas were produced, how many were wrinkled?
4. Sex Determination
Human sex is determined by chromosomes. Males carry XY and females carry XX. Since eggs always provide an X, the sperm determines the sex of the child by providing either another X or a Y.
SPERM
EGG
50% / 50%
Male or Female probability
Plenary: Summary Task
Coiled up DNA is known as . Human sex cells, also known as , contain chromosomes each. During reproduction, the offspring inherits a of genes from both parents.
A change in the structure of DNA is known as a . This can be caused by exposure to ionising , dangerous chemicals, or viruses. To predict the probability of a child inheriting characteristics, scientists use a square.
In humans, sex is determined by chromosomes. The sex chromosomes are XY, while the female are .