HEREDITY HEREDITY

ANDAND

VARIATION VARIATION

By :Reynaldo ThomasBy :Reynaldo Thomas

What Are Genes? Each cell in the human body contains

approximately 25,000 to 35,000 genes.

Your genes has the information which determines your features or characteristics passed to you (inherited) from parents.

For example, if both of your parents have blue eyes, it is possible you might inherit blue eyes from them.

Where are Genes Found? Are very small and can not be seen with the naked eyes.

Genes are found along threadlike structures called chromosomes.

What are Chromosomes Chromosomes are found in the nucleus of

cells.

Each chromosomes contains hundred of genes

Chromosomes comes in pairs.

Humans have 46 individual chromosomes or 23 pairs in each normal body cells.

This is called the diploid number.

Each Gametes has 23 chromosomes and is called the haploid number.

Hence when the sex cells fuse during fertilization each nucleus gives 23 chromosomes.

Chromosomes come in various striping patterns and lengths.

Chromosomes are lined up by their sizes and similar striping pattern.

First twenty two pairs of Chromosomes are called autosomes.

The last pair of chromosomes are known as the sex chromosomes, X and Y.

This pair of chromosomes will determine if a child is boy or girl.

Male have one X and one Y chromosomes.

While female have two X chromosomes.

Homologous ChromosomesThese are matching chromosomes.

The chromosomes in the picture have been arranged in order of size.

One chromosome from the father and the other from the mother. Homologous chromosomes are similar but not identical.

Homologous chromosomes Contain the same genes in the same places.

DNAChromosomes and genes are made up of DNA.

Individual chromosome contains a single long DNA molecule.

DNA molecule look like a Twisted ladder.

Mitosis Life starts as a single cell.

The cell then divides over and over until all body cells are produce.

As a result of mitosis each new cell receives 46 chromosomes.

Same as the original cell.

The new cells are genetically identical

(clone).

The two news cells are called daughter

cells.

Mitosis is a types of cell division .

Use to make new cells for growth and repairs.

Stages of MitosisOne The cell first makes an exact copy of

each chromosome. The two copies are called chromatids.

The chromatids are held firmly together by centromere.

Stage Two

Chromosomes become shorter and fatter.

Stage 3 The chromosomes line up in the middle of

the cell.

Stage 4 The two chromatids will break apart and

pulled by spindles to opposite ends of the cell.

Stage 5

Chromatids are now separated.

Stage 6

Finally the two cells will form.

Making of Gametes (Sex Cells) For sexual reproduction two gametes are

fuse together to make a zygote.

This new zygote must have two full sets of chromosomes (46 in total). Hence each gamete must have only one set of chromosomes.

When fused together, the zygote Will have two sets.

MeiosisMeiosis Sex cells are made in the testes Sex cells are made in the testes and ovaries.and ovaries.

In meiosis each newIn meiosis each new cell contain only onecell contain only one set of chromosomes. set of chromosomes.

Meiosis cut the number of Meiosis cut the number of chromosomes by half chromosomes by half (46 to 23)(46 to 23)..

Stages of MeiosisStage 1

Cell will first make a copy of each chromosome, as in mitosis.

Stage 2 Homologous chromosomes in the cell will

pair up with each other.

Stage 3Stage 3 The chromosomes line up at the center of

the cell in pairs.

Stage 4Stage 4

The chromosomes are pulled apart, to opposite sides of the cell.

Stage 5 Stage 5

The cell now divide into two new cells with each having 23 chromosomes ( Haploid number).

Stage 6

Each of the two new cells will now divide again, just as they would in mitosis.

The final result will be four new cells, each having 23 chromosomes.

Variation You and your classmates belong to the

same species, as you all humans.

However you are not the same.

This is an example of variation between you.

Types of Variation Discontinuous Variation

These are clear cut variations.

Each individual falls into a particular category.

Example , the person blood group can be A,B,AB, or O.

Each person has one of these four blood group.

For discontinuous variation there are no in-between categories.

The person either has the characteristic or not.

Characteristics normally qualitative and cannot be measured.

Discontinuous variation are cause by genes only and cannot be change by your environment.

Continuous This variation is not clear- cut.

Each individual lies somewhere on a continuum.

Height is an example of continuous variation.

You can be any where between the lowest and the highest extremes.

Normally quantitative and can be measured. Cause by both genes and environment.