IGCSE inheritance

What term is given to an organism that carries two identical alleles of a gene

• heterozygous

• homozygous

• dominant

• recessive

What term is given to an organism that carries two different alleles of a gene

• homozygous

• dominant

• heterozygous

• recessive

What term is used to describe the alleles that a person carries for a gene

• genotype

• dominant

• phenotype

• recessive

What word is used to describe a thread-like structure of DNA that carries genes?

• nucleus

• chromosome

• genotype

• phenotype

When carrying out a test cross, what is the organism of unknown genotype always crossed with?

• homozygous dominant (e.g. RR)

• heterozygous (e.g. Rr)

• homozygous recessive (e.g. rr)

• all three of these can be used

If an organism is pure-breeding, which of the following genotypes could it be?

I. AA

II. Aa

III. aa

• I only

• II only

• III only

• I and III only

Cystic fibrosis is a lung disease caused by a recessive allele, c.

Two healthy parents produce a child with cystic fibrosis.

Which of the following statements must be true?

• One parent must be homozygous and the other must be heterozygous

• Both parents must be homozygous

• One parent must be homozygous and the other must be heterozygous

• Both parents must be heterozygous

Albinism is a genetic condition caused by a recessive allele, a.

People with this condition are called albinos. They have white hair and pale skin.

What is the probability of two parents who are heterozygous for this condition producing an albino child?

• 0%

• 25%

• 50%

• 75%

How many alleles for each gene are carried in all body cells?

• 1

• 2

• 3

• 4

(a)