Chapter 3: Heredity and Variation

3.1 Cell Division

1. In the nucleus of the cell, there are _____________ that carry genetic materials.

2. ________________ are thread-like structure which carry genetic information that

controls various __________ of the cell.

3. Chromosomes are very small and can only be seen when the cell undergoes

______________.

4. A chromosome is made up of ______________________________.

5. Each chromosome is carries thousands of ________.

6. A _______ is a small segment of the ______ molecule in a chromosome which contains

genetic information that controls a ________ received from parents.

7. ____________ is the passing down of traits from parents to offspring.

8. All multicellular organisms begin their lives as a single cell and then divides over and

over again to produce ______ cells.

9. There are two types of cell division. They are called ____________ and ____________.

10. There are a few types of cells that do not carry out cell division. They are nerve cells or

________________ and ________________ cells.

Mitosis

11. Mitosis is a type of cell division in which a cell divides into _______ cells.

12. Occurs in

a. Humans and animals – _____________ cells

b. Plant cells – __________ and __________

The process of mitosis

10. Chromosomes in the nucleus ____________,

____________, and become more

____________.

11. The chromosomes replicate themselves to form

two _____________.

7. The centrioles move to two separate ends of the

cell.

8. ________________ emerge.

9. Nuclear membrane start to _______________

6. Chromosomes align themselves in the _________

of the cell

3. Then the chromatid __________ and _________

to the opposite ends of the cell

4. The cell starts to ____________

5. Two nuclear membranes are formed _________

the chromosomes at the _______ of the cells.

1. Two daughter cells are ____________

2. Each cell has the _______ number of

chromosomes as the parent cell.

Characteristics of Mitosis

1. Mitosis is the process by which a mature cell divides into _________ new cells.

2. Each new cell possesses the ________ number of chromosomes as the parent cell.

3. ______ cells divide by mitosis except _____________________.

4. Mitosis is carried out at the ends of plant ___________ and ____________.

Importance of Mitosis

1. Mitosis produces new cells for:

a. _______________________

b. _______________________ old or damaged cells

2. For example, after fertilization, a newly formed zygote, which is a _________________

organism will go through mitosis to become a ___________________ organism.

3. Also, skin cells on the surface of our body are constantly ____________ and need to be

__________________ with new identical cells.

4. Besides that, it also enables certain organisms to ________________ lost parts of their

body. For example, a __________ that loses its tail is able to grow a new tail.

5. Mitosis enables organism to reproduce themselves (not sexually):

a. Using __________________ reproduction. For example, amoeba uses

________________ and yeast uses _______________.

b. Using _________________ reproduction. For example, tapioca plant reproduces

from its ______________, lotus grows through its _____________, bryophyllum

grows using its ______________.

6. Mitosis ensures that the new cells produces have the ____________ number of

chromosomes as the parent cells.

a. This ensures that the daughter cells have the same _______________ as the

parent cells.

Meiosis

1. Cell division also occurs during the formation of __________________ cells or

_______________.

2. In human beings, the gametes are the _____________ produced by the male

reproductive organs ( _______________ ) and the ______________ produced by the

female reproductive organs ( __________________ ).

3. In plants, the gametes are in the __________________ contained in the male

reproductive organs ( ______________ ) and the _________________ contained in the

female reproductive organs ( ____________________ ).

4. Other cells which are not reproductive cells are called _______________ cells.

5. Meiosis is the process of cell division for the formation of _________________.

6. When meiosis occurs, the end result is four cells which have ___________ the number

of chromosomes of the parent cells.

7. Meiosis occurs in ________ stages: Meiosis _____ and Meiosis _____.

Homologous chromosomes are

__________________ chromosomes.

Diploid number of chromosomes is

chromosomes having ______chromosomes

or ______ pairs

Haploid number of chromosomes is

chromosomes having ______ chromosomes

only

1. Parent cells have _______ pairs of chromosomes

2. Chromosomes ______________ themselves

3. Nuclear membranes begin to ____________

14. Homologous chromosomes __________ and arrange

themselves in the __________

15. _______________ takes place in which genetic

material is __________________

13. Homologous chromosomes __________ and go to the

opposite ends of the cell

11. Two _____________ cells are formed

12. They have a ____________ number of chromosomes

9. In each daughter cell, the chromosomes arrange

themselves in the _____________.

10. The chromosomes are not ______________.

8. Each chromatid _______________ and moves to the

opposite ends of the cell.

4. ________ daughter cells are formed

5. They all have __________ genetic information

6. Each daughter cell contains __________ the number

of chromosomes in the ____________ cell.

7. They have a ___________ number of chromosomes

in each cell.

Mitosis and Meiosis

where it occurs

number of times the

nucleus divides

number of daughter cells

produces

genetic contents of

daughter cells

number of chromosomes

crossing-over

variation

importance

Mitosis Meiosis

Similarities

both involve the ____________ of nucleus and cytoplasm

both involve the replication of ______________

both ensure the ____________ of organisms

both ensure the passing down of ___________ material from __________ to

_____________

Differences

3.2 Inheritance

1. Genes are hereditary units which carry _______________ that determines the different

traits of an organism.

2. Hence, the _______________ of a person are determined by his genes.

3. Our chromosomes exist in ________ called _______________ chromosomes.

4. The gene for a certain characteristic may be _____________ or _______________.

5. A ______________ gene is powerful and can mask the effect of a less powerful gene.

6. The ______________ gene is weak and cannot show its effect if paired with a

_______________ gene.

7. Example:

8. Example:

a. Brown eyes are _____________ over blue eyes.

b. The dominant gene for brown eyes is represented by _____.

c. The recessive gene for blue eyes is represented by _____.

d. A person with _____ has brown eyes with ____ dominant genes for brown eyes.

e. He is ______________.

f. A person with _____ has blue eyes with ____ dominant genes for blue eyes.

g. He is also ______________.

h. A person with _____ has _________ eyes because the dominant ________

gene is more powerful than the recessive ________ gene.

i. This person is ________________.

9. Dominant traits and recessive traits

10. Schematic diagram for inheritance

Dominant traits Recessive traits

Phenotype Genotype Phenotype Genotype

Right handed

Short

Black hair

Straight hair

Brown eyes

Blue eyes

With ear lobes

Cannot roll tongue

Skin has pigment

Colour blind

Has dimples

Short eye lashes

3.3 Sex Determination 1. There are two types of cells in the body: __________ cells and _____________ cells.

2. ___________ cells are ordinary body cells. These cells do not take part in the

____________ system of the body.

3. ___________ cells are also called _____________. They contribute to the _____________ system of the body.

4. An _______ in the _________ gamete.

5. A ________ is the ________ gamete.

6. There are two types of chromosomes in every cell: _____ chromosomes and _____

chromosomes.

7. Non-sex chromosomes are called _____________.

8. Autosomes determine our ___________ and ____________.

9. Sex chromosomes determine our ______.

10. In women, the pair of ____ chromosomes is called ____.

11. In men, the pair of ____ chromosomes is called ____.

Chromosomes in a man

Chromosomes in a woman

12. During meiosis, each gamete receives ____ ordinary chromosomes ( ____________ )

and ____ sex chromosome.

13. Each ovum receives ________ chromosomes.

14. Each sperm receives ________ chromosomes or ________ chromosomes.

15. From the above diagram, we know that the sex of the zygote is decided during ____________. The occurrence of twins

1. There are two types of twins: ___________ and __________ twins.

2. ____________ twins are twins that have the same _______________ and the same _____.

3. They have the same characteristics because they have the same ______________ and

_________.

4. ____________ twins are twins that have different ____________ and ____________.

5. They have different characteristics because they have different _____________ and _________.

6. Identical twins come from a zygote that _______ into two.

7. Non-identical twins comes from the formation of _____ zygotes.

MAN WOMAN

Somatic cell Sperm Somatic cell ovum

Autosomes

Sex chromosomes

Total

Identical and non-identical twins

Number of gametes

involved

Fertilization

Zygote

Number of placentas

Chromosomes and genes

Sex of twins

Characteristic features

Identical twins Non- identical twins

Similarities

Two fetuses develop in the uterus at the _______ time

Two babies are ______ at the same time

Differences

3.4 Mutation

1. A mutation is a ________ in a gene or chromosome.

2. This results in change in _________ of the organism.

3. Mutations can happen but it is _________.

4. A mutant gene or chromosome can be __________ to future generations. Types of mutation

1. Mutations that occur in genes are called _____________. 2. Mutations that occur in chromosomes are called ______________.

3. Gene mutation

a. Gene mutation occurs when the genes are ___________ spontaneously

b. Mutant genes can cause changes in the _____________ and _____________ controlled by the genes

c. Examples are ____________ and _____________

4. Chromosome mutation

a. Chromosome mutation is caused by changes in the ____________.

b. The changes may alter the ___________ of the chromosomes or the

__________ of chromosomes.

c. Mutant chromosomes can cause changes in the ______________ and __________ of a person.

d. For example, _____________ and _____________