Family Traits – JSS3 Basic Science Lesson Note (First Term)

A family trait is a genetic likeness passed from parents to their children (offspring) through genes.

Behavioural objectives

By the end of the lesson, students should be able to:

1. define a family trait;
2. list traits that can be passed from parents to offspring;
3. explain dominant and recessive traits, with an example;
4. state the differences between dominant and recessive genes;
5. state the importance of family traits.

What are heredity and genes?

Heredity is the passing of characters from parents to offspring through genes.

• Gene: the hereditary unit that carries the instructions for a trait.
• Offspring: the children or young produced by parents.
• Genotype: the genes an individual carries for a trait, for example TT or Tt.
• Phenotype: the trait that can be seen, for example tallness.
• Inheritance: each parent gives one gene for a trait, so a child receives a pair.

Which traits can parents pass to their children?

Many physical features, body features and some abnormalities can be passed from parents to offspring.

1. Skin colour: dark or fair.
2. Height: tallness or shortness.
3. Colour of the hair and of the eye iris.
4. Shape of body parts: face, eyeball, mouth, eyelashes, lips, forehead, head, ears and others.
5. Method or style of walking.
6. Quantity of hair: on the head, body, eyebrows and eyelashes.
7. Voice.
8. Abnormalities: albinism, sickle cell anaemia, colour blindness and haemophilia.

What are dominant and recessive traits?

A dominant trait shows in the offspring, while a recessive trait stays hidden when the dominant gene is present.

• Capital letter: stands for the dominant gene, for example T for tallness.
• Small letter: stands for the recessive gene, for example t for shortness.

What is a dominant trait?

A dominant trait is a trait that keeps on appearing in the family in each successive generation.

• Example: a tall man with the genes for tallness (TT) marries a tall woman who carries the recessive gene for shortness (Tt).
• Result: if they have four children, all of them will be tall.
• Meaning: the gene for tallness is dominant over the gene for shortness.

What is a recessive trait?

A recessive trait is a trait present in an organism that does not show physically because of the dominant gene.

• Appearance: it may suddenly appear in later generations.
• Example, first generation: a tall man (TT) marries a short woman (tt). All their children are Tt, so they are tall.
• Example, second generation: when two Tt children marry, some of their children may be short (tt).
• Meaning: the recessive gene for shortness was carried but hidden.

What are the possible children of two Tt parents?

What are the differences between dominant and recessive genes?

A dominant gene shows its effect even when paired with a recessive gene, but a recessive gene shows its effect only when no dominant gene is present.

What are continuous and discontinuous variations?

Variations are the differences among members of the same family or species.

• Continuous variation: differences that change gradually from one end of a scale to the other, such as height and skin colour.
• Discontinuous variation: differences that fall into clear groups with nothing in between, such as blood group.

Why are family traits important?

Knowing family traits helps in health, family history and the detection of crime.

• Genetic diseases: they help us to understand some genetic diseases.
• Genealogy: they can be used to trace family history.
• Physical characters: they help to trace features such as the colour of the eye, skin and hair, body size and height.
• Crime detection: fingerprint and DNA tests can identify people.
• Good traits: useful qualities, such as intelligence, can run in a family.
• Intending couples: they can learn which inherited conditions may affect their children.

Practice questions

1. Which of the following is not a trait that is passed genetically from parents to offspring? A. Skin colour B. Height C. Colour blindness D. Smoking
2. Variations like height and skin colour among members of the same family that change from one end of the scale to the other are A. recessive B. continuous C. discontinuous D. genotype
3. Which of these is a genetic disease? A. Sickle cell anaemia B. Malaria C. Headache D. Kwashiorkor
4. A trait that appears in successive generations is called A. recessive B. dominant trait C. physical trait D. genotype
5. Family traits are important in all of the following except A. intelligence B. disease control C. resemblance D. hunger control

Answers: 1. D, 2. B, 3. A, 4. B, 5. D.

Evaluation

1. What is a recessive trait?
2. A man with genes TT marries a woman with genes Tt. What height will their children be, and what does this show?
3. List four abnormalities that can be passed from parents to children.
4. State three ways in which the knowledge of family traits is useful.

Assignment

1. (a) Define family traits and state two importances of family traits to intending couples.
   (b) State two differences between dominant and recessive genes.
   (c) State five examples of traits that can be transferred from parents to offspring.