chapter 3 science form 4

7/28/2019 Chapter 3 Science Form 4

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Chapter 3

Heredity and Variation

(Keturunan dan Variasi)

Prepared by: En. Shafie Bin Buyamin


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3.1: Cell Division

(Pembahagian Sel)

Cell has a nucleus

Nucleus contains chromosomes

Chromosomes is thread-like structure(struktur seperti bebenang) made up of longDNA molecule

Chromosomes come in pairs (berpasangan)

Genes are small portion of DNA molecule

Gene also come in pairs


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Mitosis

Process of cell division that occurs in allcells (somatic cell) except in sex cells

One parent cell produces 2 daughter cells

Number of chromosomes same


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Stages of mitosis

Stages of mitosis Simple explanation

- Chromosomes shorten,

thicken, more visible

(Memendek, menebal, lebihjelas)

-Replication(Replikasi) ofchromosomes

Each strand called

chromatid

centromere


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Stages of mitosis Simple explanation

-Chromosomes align (tersusun)

in the centre of cell

- Nucleus membrane

disappears

- Chromatid separate andmove to opposite ends of cell

- Cell starts to divide

-Nucleus membrane formsagain

- Two daughter cell formed

- Each progeny cell has the

same number of chromosomes


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Meiosis

Process of cell division that occurs in sexorgan

For production of gametes or sex cells

Parent cell produces 4 daughter cells (selanak)

Number of chromosomes in daughtercell(sel anak) is half(separuh) in parentcell (sel induk)


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Stages of meiosis

Chromosomes shorten, thicken(memendek, menebal)

Replication (replikasi) and crossingover(pindah silang) on chromatid

1. Chromosomes align (tersusun) in the

centre of cell (tengah sel)

2. Nucleus membrane disappears

First Division


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1. Chromosomes move to

opposite ends of the cell

2. The cell begins to divideinto two (membahagi 2)

1. Two daughter cells

produced (2 sel anak

terhasil)

2. Nucleus membranereforms


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1. Chromosomes align in

the centre of cell

2. Nucleus membrane

disappears

1. Chromatids separate

2. Cell begins to divide

Second Division


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1. Nucleus membrane is formed again

2. 4 daughter cells produced (4 sel

anak terhasil)3. Each cell has half(separuh) of the

chromosomes in the parent cell


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Comparing Meiosis and Mitosis

Meiosis Characteristics Mitosis

2 Number of division

(Bilanganpembahagian

1

Occurs during

the first cell

division

Replication

(Replikasi)

Occurs

4 Number of daughtercells (sel anak)

produced

2


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Meiosis Characteristics Mitosis

Half Number of

chromosomes in

daughter cell

compared to parent

cell

Same

Different Combination of

chromosomes in

daughter cell

compared to parentcell

Identical

Occurs Crossing over

(Pindah silang)

Not occur


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The Importance of Mitosis and Meiosis

Mitosis:

1. Produces new cells for growth

(pertumbuhan) and replace dead /damaged cells (ganti sel mati/ rosak)

2. Maintain genetic information

(Mengekalkan maklumat genetik)


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Meiosis

1. Produces gametes

2. Ensure number of chromosomes is kept

constant from one generation to another

generation

3. Ensure each gamete produced carry

different genetic constituents


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3.2 : Inheritance

(Pewarisan)

Traits: Characteristics inherited fromparents (ciri diwarisi dari induk)

Inheritance (Pewarisan): process ofpassing genetic information / traits from

parents to offspring (Proses menurunkanmaklumat genetik / ciri induk ke anak)


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Dominant and Recessive Genes1. Human have 46 chromosomes

2. Arranged in pairs (homologous)3. 23 pairs of homologous chromosomes

4. Each chromosomes carries a gene or a gene group

5. Gene / gene group carries traits

6. Each gene pairs with other gene on homologouschromosomes

7. Paired genes / gene groups carry instructions to create/ control one of characteristics

8. Example: one instruct curly hair, other instruct straighthair

9. One is dominant, other is recessive gene


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Dominant gene

Member of a pair of genes which carriesan instruction that overrules the other(recessive) gene

Curly hair gene is dominant, straight hairgene is recessive

Dominant Trait

When display the characteristics

of dominant gene


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Recessive gene

Member of a pair of genes which carries aninstruction that being overrules by the other(dominant) gene

If inherited only a pair of straight hair gene: we

would have straight hair

Recessive Trait

When display the characteristics

of recessive gene


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Mechanism of Inheritance of Traits

In meiosis, gamete only carry one genefrom each pair of gene

In fertilisation, gamete fuse to form zygote(combination both parent)

Traits inherited determined by both sets ofgenes from parent


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Parent

Meiosis

Gamete

Fertilisation

Offspring

H: Curly hair (Dominant gene)

h: Straight hair (Recessive gene)

All offspring have curly hair

HH hh

H H h h

Hh Hh Hh Hh

Schematic Diagram


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Genotype

Genetic composition of an organism(combination of genes)

Example: Genotype for individual withcurly hair can be HH or Hh Genotype for straight hair is hh


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Phenotype

Characteristic that can be observed ordetermined (Ciri yang boleh diperhatikan)

Example: Trait for hair type has 2phenotype that is curly hair and straight


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Parent Phenotype

Gamete

PhenotypeAll offspring have Yellow Seed

YY yy

Y Y y y

Yy Yy Yy Yy

Monohybrid Cross Gregor Mendel

Yellow seed Green seed

F1


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F1 : First filial generation

F2 : Second filial generation

- Experiment of a monohybrid cross by

Gregor Mendel to predict the genotype

and phenotype ratios of F1 & F2

-Used pea plant (yellow & green seed)

- Showed that yellow seed were

dominant trait


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Offspring of F1 (Dihybrid Cross)

F1 Generation

Gamete

Phenotype

Genotype ratio = 1 YY : 2 Yy : 1 yy

Yy Yy

Y y Y y

Y

Y

Yy Yy yy

Yellow seed Yellow seed

F2 generation

Phenotype ratio = 3 yellow : 1 green


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Punnett-square method

YY Yy

Yy yy

Y y

Y

y

Gamete Genotype of

offspring

* To predict genotype and phenotype ratio

chapter 3 science form 4

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