DNA, genes and inheritanceIB MYP Sciences: Flashcards

Exam questions on DNA, genes and inheritance

1. A science museum in Seoul has an exhibit about the nucleus of a human body cell. It explains that the nucleus contains 46 chromosomes arranged in 23 pairs, and that each chromosome is made of one very long molecule that is tightly coiled.
   Explain what is meant by the term allele and why a body cell contains two alleles of each gene.2 marks
2. A pet breeder in Brazil crosses two hamsters that both have black fur. Black fur is controlled by a dominant allele (B) and brown fur by a recessive allele (b). Some of the offspring in the litter have brown fur.
   Use a Punnett square to show the cross between the two black parents, and state the ratio of black to brown offspring that is expected.2 marks
3. A genetic counsellor in Toronto meets a couple who do not have cystic fibrosis, but whose first child does. Cystic fibrosis is caused by a recessive allele (f). The dominant allele (F) allows the body to work normally.
   Explain how two parents who do not have cystic fibrosis can have a child who has the condition.3 marks