Chromosomes pg 112

What are Chromosomes? When can you see them?

Chromosomes are very long, thin strands that carry information which helps the cell to function properly. They are normally found in the nucleus of the cell. You can see them when the cell is dividing becasue they became smaller and thicker.

How do the chromosomes in human sperm cells differ from those in ova?

Human sperm cells contain either an X or a Y chromosome, whereas in ova the cells contain an X chromosome.

Look at the table of the number of chromosomes in different organisms on pg 108. Notice that they are all even numbers. What is the reason for this?

The reason that they are all even numbers is that they are all presents as pairs.

The Smiths have three sons. Mrs Smith is pregnant and believes she is having another son. Mr Smith disagrees and says that becasue they have three sons the next child has a greater chance of being a daughter. Who is correct? Explain your answer.

They are both wrong. The combination of a sperm and a ova is a random event and each child has an equal chance of being a boy or a girl.

The father's sperm determines the sex of the child. Is this statement true or false? Give a reason for your answer.

This statement is true becasue each sperm cell will contain an X or a Y chromosome. Becasue all ova cells contain an X, it is the sperm which determines whether the new cell (called a zygote) is male or female.

Cosmo said to his friend, 'I inherited my red hair from my grandmother.' What does he mean by this?

You can assume that Cosmo has red hair bu neither his mother nor father does, but carry the gene. Probably, the only other person in his family to have red hair is his grandmother. What he says is true becasue he got the gene for red hair from his grandmother via his parents

In humans most cells contain 23 pairs of chromosomes. In which parts of the body would you find cells with 23 single chromosomes?

You would find only 23 chromosomes in the sex cells. In females these are the ova in the ovaries and in males they are the sperm in the testicles.