BS2 - Chromosomes

• Biologie
• Middelbare school
• vwo
• Leerjaar 3

Chromosomes

Contain DNA

Bundled DNA-fibre wrapped around histones

23 chromosome pairs in humans

Body cells

The nucleus of the body cells of a human:

(ex. liver cells, skin cells, muscle cells etc) contain 46 chromosomes. 

Every chromosome carries the information for different hereditary traits. 

Chromosomes occur in pairs. 

Two chromosomes in a pair match; they carry information for the same traits. 

There are 23 pairs.

Sex cells

Sex cells are different than the body cells.

 

Sex cells contain 23 chromosomes. There are no pairs. 

Ex. Sperm cell and egg cell

Nucleus of the sex cell of a man and the nucleus of the sex cell of a woman fuse together. 

This way the child has 50% of its genetic information form the father and 50% of the mother. 

Pair 23 will determine the sex of the child. This depends of chromosome 23 of the spermcell  is a X or a Y chromosome. 

cells and chromosomes

humans have in EACH body cell: 

• 22 pairs of body cells
• 1 pair of sex chromosomes : X X = female, XY=male 

so, humans have in EACH gamete (sex cell):

• 22 body cells
• 1 sex chromosome

Variation in genes

• Sex cells = no pairs of chromosomes. 
• only 1 copy of the chromosome ends up in the egg or sperm cell.
• result: variation in genotypes 

Variatie in genotype

• Due to sexual reproduction.
• father 1/2 and mother 1/2 contribute 1 copy of chromosome.
• The part of the chromosome that is give to child from parents is different each time.
• Chance/coincidence!

Each human being has 46 chromosomes. How many did you get from your mother?

1. 46
2. 23
3. 22
4. 45

A person containing an XY is a...

1. man
2. woman

A person containing the same copy of a sex chromosome is a...

1. man
2. woman

You have 23 sex chromosomes in your body.

1. True
2. False

Write down the sex chromosomes of someone who is intersex.