Lesson Notes By Weeks and Term - Junior Secondary School 2

SUBJECT:� BASIC SCIENCE ��� ���

CLASS:� JSS2

DATE:

TERM: 3RD TERM

REFERENCE

• Precious Seed BASIC SCIENCE FOR JUNIOR SECONDARY SCHOOLS BOOK 2

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WEEK NINE

FAMILY TRAITS

Introduction

In living things that carries out sexual reproduction, the offspring inherit their characteristics from their parents. These characteristics are passed on in the gametes at fertilisation, thereby making the offspring resemble their parents.

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Types of organism

This is when the young one of a particular organism resembles the same type of organism. For example, the human being resembles a human being not a dog, not a cow, nor a goat. Also cat reproduces cat not lion, etc.

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Qualities of a particular parent

This is when the offspring resembles a particular parent more than the other in the area of complexion, height, intelligence, etc. For example, a child may be as tall as the father and as light in complexion as the mother, who may not be so tall.

Family traits are the characteristics that are transmitted from the parents to the young ones. The transmission of such traits or the process of passing the traits to the young ones is called heredity. Heredity is an important factor that affects the growth and development of a child.

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Examples of family traits

1. Complexion
2. Sizes and colours of eyes
3. Height (whether tall, short or average)
4. Shape of nose, mouth, face, head etc
5. Intelligence
6. Blood type group
7. Body structure and posture
8. Size of ear
9. Sickle cell traits
10. Gait (ways of walking)
11. Albinism
12. Temperament, that is, how quickly they react to situations and or people.

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EVALUATION

1. Differentiate between types of organism and qualities of a particular parent
2. Mention five examples of family traits

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Meaning of dominant and recessive traits

Genes: these are molecules produced by the chromosomes which are structures in the nucleus of a cell.

Dominant traits: these are traits or characteristics which manifest or show in an individual thereby causing the individual to resemble one parent or the rather than the other.

Recessive traits: these are traits or characteristics which do not manifest when the dominant traits are present.

T� � � � � T� � � � � � � � � � � � � t � � � � t

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Tt� � � � � � � Tt� � � � � � � � Tt � � � � Tt

F1 geneartion

T � � � t � � � � � � � � � T� � � t

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TT� � � � � � � � � Tt � � � � � Tt � � � � � � � � Tt

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F2 generation

Importance of family traits

1. It helps to explain why a child is brilliant or dull.
2. It can be used to detect crime.
3. It also helps in tracing family genealogy or a particular pedigree.
4. It can reduce the occurrence of hereditary diseases such as eye defects, sickle cell�

anaemia, etc.

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The traits you have inherited from your parents, that you can see are the traits that are dominant. The trait that you have inherited from them but which are not expressed are the recessive ones.

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Some trait may be recessive by long period of time but after some time they manifest. An albino parent may have non albino child if the spouse is not albino.� Albinism is complete partial lack of pigmentation in the skin hair and eyes. This is why they react to light, and their skin is easily affected by insect bites.

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Gregor Mendel also observed there can be situations whereby it will be difficult to identify which gene is dominant or recessive. This is called partial dominance. An example is when a child is fair in complexion and the two parents are also fair in complexion.

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However, it must be noted that environmental factors have effects on whatever trait that is inherited by an individual. Examples of environmental factors are food, whether, diseases, facilities etc. A child may inherit the trait tallness of his parent but if the does not have good nutrient, he/she falls sick often, he� or she may grow well in terms of height a;so a child that inherit the trait of intelligence but does not attend school with good facilities to study may not be bright. Such differences are not passed to the next generation and this brings about variation.

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Let us look at some of the works of Gregor Mendel to explain better the meaning of dominant and recessive traits. If a pure tall breed pea was on crossed breed with a pure short breed pea. All the peas in the filia generation would be tall trait was dominant.

Stage 1: Tall(TT) and short (tt) were crossedbreed.

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Note: in F1 generation, all the offspring were tall (i.e Tt, Tt, Tt, and Tt). It means that for the trait (height) tallness was dominant while shortness was recessive.

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Stage 2: if Tt and Tt were crossbreed.

In F2 generation, three offspring were tall (i.e TT, Tt and Tt) and one offspring was short (i.e tt)

This means in the F2 generation, three offspring out of the four were carrying the traits of tallness hence the tallness was expressed and therefore was the dominant trait, while��� one offspring which is shortness was the recessive trait.

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EVALUATION

1. Define the following a. genes b. recessive traits c. dominant trait
2. State three importance of family traits

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GENERAL EVALUATION

1. Differentiate between types of organism and qualities of a particular parent
2. Mention five examples of family traits
3. Define the following a. genes b. recessive traits c. dominant trait
4. State three importance of family traits

REFERRENCE

CLASSIC BASIC SCIENCE FOR JUNIOR SECONDARY SCHOOL 3 PAGES 12-16

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WEEKEND ASSIGNMENT

1. ----------- helps to explain why a child is brilliant or dull. A. family traits�

1. propagation C. animal trait D. expected trait.

1. ------------is complete partial lack of pigmentation in the skin hair and eyes�

1. Deafness B. Dumbness C. Swollining D. Albinism

1. The traits you have inherited from your parents, that you can see are the traits that are ---------A. dominant B. recessive C. offspring D. none
2. The trait that you have inherited from parents but which are not expressed are the --------ones A. recessive B. dominant C. genetic D. none
3. --------- are molecules produced by the chromosomes which are structures in the nucleus of a cell. A. Genes B. Dominant C. Recessive D. none

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THEORY

1. Mention five examples of family traits
2. Define the following a. genes b. recessive traits c. dominant trait