Two copies of a gene

The idea

Sexually reproducing organisms carry two copies of the factor, now called a gene, controlling each trait; the two copies may be identical or different, depending on the parentage.

Pairs of factors

Mendel found that tallness and shortness were both present in the tall F1 plants, even though the plants looked tall.

How many copies of the factor for a trait must a plant have to explain this?

• Two
• One
• Three

Pairs of copies

Open every tab.

A pair of genes

The plant carries two copies of the gene for height. The pair can be two T's, two t's, or one of each, depending on the parents.

Sexually reproducing organisms carry two copies of the factor, now called a gene, that controls each trait. The two copies may be identical or different, depending on the parentage.

Notes

A sexually reproducing organism has two copies of the gene for each trait; they may be identical or different, depending on the parentage.

Check yourself

How many copies of the gene for a trait does a sexually reproducing organism carry?

Answer: 2

Two copies of the factor, now called a gene, control a trait.

The two copies of the gene for a trait in an organism…

What is the factor that Mendel proposed now called?

A pea plant has the two copies T and t. Are the copies identical?

• are identical. The two copies may be different. For example, one can be T and the other t.
• are different. The two copies may also be identical, as in TT or tt.
• may be identical or different, depending on the parentage — correct. Yes!
• A gene — correct. Yes!
• A chromosome. A chromosome is a separate independent piece in which a gene set is present. The factor is now called a gene.
• A protein. A protein is made using the information in a gene. The factor is now called a gene.
• Yes, both are T. One copy is T and the other is t.
• No, they are different — correct. Yes!
• Yes, both are t. One copy is T and the other is t.