Hereditary and Variation – JSS2 Intermediate Science Lesson Note (Second Term)

Heredity is the passing of characteristics from parents to their offspring through genes, while variation is the difference between individuals of the same species.

Behavioural objectives

1. Define heredity and variation.
2. State how genes, chromosomes and DNA carry features from parents to children.
3. List common inherited traits in humans.
4. Distinguish between morphological and physiological variation.
5. Distinguish between continuous and discontinuous variation.
6. State the importance of variation.

What is heredity?

Heredity is the process by which characteristics are passed from parents to their offspring through genes.

• Offspring: the children or young produced by parents.
• Everyday sign: people say “You have your father’s nose” or “You smile like your mother”. This is heredity at work.
• Result: a child is a mixture of features from both parents, not a copy of one person.

How does heredity work?

Heredity works through genes, which are carried on chromosomes inside the cells of the body.

1. Every cell nucleus contains chromosomes.
2. Chromosomes are made of DNA.
3. Genes are short sections of DNA. Each gene carries instructions for a feature.
4. The father’s sperm cell carries half of the instructions.
5. The mother’s egg cell carries the other half.
6. Fertilisation happens when the sperm joins the egg. The two sets of instructions combine.
7. The new cell grows into a baby with a mixture of both parents’ genes.

What are the key terms in heredity?

What are inherited traits?

Inherited traits are features that are passed from parents to offspring in the genes.

• They are present from the moment a baby is conceived.
• They cannot easily be changed.
• Not everything about a person is inherited. Skills such as playing the guitar are learned, so children are not born knowing them.

What are examples of inherited traits?

1. Eye colour: dark brown, black or even blue.
2. Hair texture: naturally curly, coily or straight.
3. Skin colour: the amount of melanin in the skin is passed down from parents.
4. Height: parents’ genes decide the potential height. Good food helps a child reach it.
5. Blood group: every person belongs to one of four groups: A, B, AB or O.

What is the difference between inherited and learned features?

What is variation?

Variation is the differences that exist between individuals of the same species.

• No two people look exactly the same, except sometimes identical twins.
• Brothers and sisters in the same family also differ.
• Genes: different gene combinations from parents cause differences.
• Environment: food, climate and way of life also cause differences. Two identical twins with the same genes can grow to different weights.

What are the types of variation?

There are two types of variation by kind of feature: morphological and physiological.

What is morphological variation?

Morphological variation is the difference in how individuals look on the outside.

• Height: tall and short people.
• Fingerprints: every person has a unique pattern.
• Weight and body shape: people are slim, medium or heavy.

What is physiological variation?

Physiological variation is the difference in how the body works on the inside.

• Blood groups: some people are group O, others group A, B or AB.
• Tongue rolling: some people can roll the tongue into a “U” shape, and others cannot.
• Taste sensitivity: some people find certain foods very bitter, and others do not notice.

What is the difference between continuous and discontinuous variation?

Continuous variation is a gradual range of differences with no clear groups. Discontinuous variation is a set of differences that fall into clear, separate groups.

Why is variation important?

Variation is important because it helps individuals and species to be recognised, to survive and to adapt.

1. Identity: unique faces and fingerprints let people recognise one another.
2. Survival: if a new disease comes, some people may have a natural resistance and survive it.
3. Adaptation: over many years, variation helps plants and animals to cope with places such as deserts and cold regions.

Evaluation

1. Define heredity in your own words.
2. List three traits that a person can inherit from parents.
3. Why can a skill such as playing the guitar not be inherited?
4. What is the difference between morphological and physiological variation?
5. Give one example each of continuous and discontinuous variation.

Assignment

Make a table of five traits of your own, such as height, blood group and tongue rolling. For each trait, state whether it is continuous or discontinuous variation, and whether it is morphological or physiological.