Standard Grade Biology

Inheritance TopicChromosome Mutations

2

Inheritance

By the end of this lesson you should be able to:

•Describe one example of a human condition caused by a chromosome mutation•Explain what amniocentesis is

3

Chromosome Mutations

Almost 1% of all babies born have some sort of abnormality which has been caused by accidental damage to their chromosomes.

These changes to chromosomes are called mutations.

Mutations often produce changes in the characteristics of the individual affected.

4

Chromosome Mutations

A mutant is an organism with a changed phenotype due to a mutation.

Most mutations cause inferior versions of the phenotype which can be fatal.

Mutations are Rare Spontaneous

5

Down’s Syndrome

An example of a mutation that affects humans is Down’s Syndrome.

Children with Down’s Syndrome have slanting eyes and flattened noses.

Other symptoms include an enlarged and protruding tongue and thickening of the hands and feet.

Children with Down’s Syndrome can be very affectionate and with help can lead a full and happy life.

6

Down’s Syndrome

Children with Down’s Syndrome are also mentally deficient.

Down’s Syndrome is caused by an egg with 24 chromosomes fusing with a normal sperm with 23 chromosomes.

The zygote has 47 chromosomes instead of 46.

7

Down’s Syndrome

Insert the “Chromosome Sets” diagram into your notes. Circle the chromosomes numbered 21

8

Chances of having a Down’s Syndrome baby

Usually, the chances depend upon the age of the mother.

Mother’s age (years)

Chance of Down’s Syndrome baby (%)

23 0.05

30 0.08

35 0.25

40 1.11

45 3.12

50 12.5

Draw a linegraph to

show theseresults

9

Down’s syndrome

What is recommended to detect Down’s Syndrome?

Until recently, the answer was to offer amniocentesis to all pregnant women aged 35 or older and to those women who had a previous child with Down Syndrome.

Now some doctors recommend screening tests for all pregnancies.

10

Down’s Syndrome

What is amniocentesis?

With amniocentesis a needle is passed through the mother’s belly into the womb to sample foetal cells in the amniotic fluid.

These cells are then sent for chromosome analysis.

The test is usually done between 14 and 18 weeks of pregnancy.

11

Down’s Syndrome

What is amniocentesis? cont….

Although fairly safe there is a small risk of miscarriage.

If the result is positive for Down’s Syndrome the parents may decide to terminate the pregnancy.

Insert the “Amniocentesis” diagram into your notes.

12

Inheritance

Can you do it?

•Describe one example of a human condition caused by a chromosome mutation•Explain what amniocentesis is