Chromosomes

The idea

Each gene set exists as separate independent pieces called chromosomes; a cell has two copies of each, one from each parent, and a germ-cell takes one from each pair, of either origin, so traits are inherited independently.

Cutting a gene set

Imagine the genes of a cell are in separate independent pieces, not one long thread. A germ-cell takes one piece from each pair.

Could a germ-cell then have a mix of pieces from both parents?

• Yes, a mix is possible
• No, it takes all from one parent
• No, it takes none from either parent

Make germ-cells

Choose which copy goes into the germ-cell for each pair.

Pieces called chromosomes

The gene set is not one long thread. It is in separate pieces called chromosomes. A germ-cell takes one chromosome from each pair, so the traits can be passed on independently.

Each gene set exists as separate independent pieces called chromosomes. A cell has two copies of each, one from each parent. A germ-cell takes one chromosome from each pair, of either maternal or paternal origin, so traits are inherited independently.

Notes

Gene sets exist as chromosomes; a germ-cell takes one from each pair, of either origin, so traits are inherited independently.

Check yourself

A gene set is present as…

From each pair of chromosomes, how many does a germ-cell take?

Answer: 1

A germ-cell takes one chromosome from each pair.

The chromosome a germ-cell takes from a pair may be…

What allows different traits to be inherited independently?

• one single long thread of DNA. The gene set is not present as a single long thread. It is in separate independent pieces.
• separate independent pieces called chromosomes — correct. Yes!
• a single gene. A gene is a section of DNA for one protein. A gene set is present as separate pieces called chromosomes.
• always the paternal one. It may be of either maternal or paternal origin.
• always the maternal one. It may be of either maternal or paternal origin.
• of either maternal or paternal origin — correct. Yes!
• The gene set is in separate independent chromosomes — correct. Yes!
• The gene set is one long thread of DNA. If a whole gene set were inherited as one piece from each parent, traits would be linked to each other and could not be inherited independently.
• A germ-cell takes both chromosomes of every pair. A germ-cell takes one chromosome from each pair.