5.2 - Chromosomes

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• Biologie
• Middelbare school
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• Leerjaar 3

How many chromosomes?

Male or female? Body cell or sex cell? 

Today

Recap 5.1

Checking homework

Explanation 5.2

• You can explain how each of the parents provides 50% of the chromosomes.

• You can say how the sex of a human is determined by sex chromosomes.

• You can explain how sexual reproduction causes variation in genotypes.

Self-study 

End

Which one is correct?

A

Phenotype = genotype + environment

B

Environment = genotype + phenotype

C

Genotype = phenotype + environment

D

If you look at this persons hair..

A

Phenotype

B

Genotype

C

Phenotype en Genotype

D

Put in the correct order, from small to big.

A

cell - chromosome - DNA - gene

B

gene - chromosome - DNA - cell

C

gene - chromosome -cell - DNA

D

gene - DNA - chromosome - cell

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.

Pair 23 are the sex chromosomes. 

Pair 23 are the sex chromosomes. 

Chromosomes

Contain DNA

Bundled DNA-fibre wrapped around histones

23 chromosome pairs in human body cells

Sex cells

Sex cells (gametes) 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. 

How many chromosomes?

Male or female?

45, X

How many chromosomes?

Male or female?

47, XY, +21 

fig. 3 Different information on a chromosome pair

Variation in genes

• Sex cells are created by a special form of cell division, meiosis. In meiosis, the chromosomes are split between the daughter cells (sex cells)

• Sex cells have no pairs of chromosomes. 

• only 1 copy of the chromosome ends up in the egg or sperm cell.

• result: variation in genotypes 

Variation in genotype

• Due to sexual reproduction.

• father 1/2 and mother 1/2 contribute 1 copy of chromosome.

• Chance/coincidence!

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

A

46

B

23

C

22

D

45

A person containing an XY is a...

A

man

B

woman

C

D

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

A

man

B

woman

C

D

You have 23 sex chromosomes in your body.

A

True

B

False

C

D

Write down the sex chromosomes of someone who is intersex.

Let's practice 

Read basics 5.2 Chromosomes

Hihglight all concepts and their defintions 

Make the assignments 1 to 8, yes 6 as well

Extra challenge: assignment 8, 9, 10

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