Inherited disorders Flashcards – AQA GCSE Combined Science: Trilogy (8464) — Biology — Foundation

For a gene with two copies, what is the difference between homozygous and heterozygous?

Homozygous: the two alleles are the same. Heterozygous: they are different.

When is a dominant allele expressed in the phenotype?

When at least one copy is present, including in a heterozygote.

In a two-copy model, when is a recessive allele expressed in the phenotype?

When both alleles are recessive.

What does dominance describe about alleles?

Their relationship in their effect on a characteristic.

Does dominance mean that an allele is more common?

No. Dominance does not indicate how common an allele is.

Does a dominant allele remove a recessive allele?

No. A dominant allele does not remove the recessive allele.

What is polydactyly?

The presence of extra fingers or toes.

How many copies of the allele causing an inherited form of polydactyly can produce the characteristic?

One copy; the allele is dominant.

What allele combination causes a person to have cystic fibrosis?

Two cystic fibrosis alleles; the alleles are recessive.

What is an unaffected carrier of cystic fibrosis?

A person with one cystic fibrosis allele and one unaffected allele who can pass the recessive allele to offspring.

How do cystic fibrosis alleles affect cell membrane function?

They disrupt chloride transport across cell membranes.

What effect does disrupted chloride transport have in cystic fibrosis?

It leads to thick, sticky mucus, particularly in the lungs and digestive system.

What is embryo screening?

Testing cells from early embryos for particular genetic variants before implantation, usually during in vitro fertilisation.

How can embryo screening results inform reproductive decisions?

They can help decide which embryos to transfer.

What is the potential benefit and key limitation of embryo screening for inherited disorders?

It can reduce the risk of a child having a particular inherited disorder, but testing and pregnancy outcomes are not guaranteed.

What should an informed judgement about embryo screening weigh?

Evidence and different viewpoints.

What economic considerations are relevant to embryo screening?

The costs of testing and treatment, and the allocation of healthcare resources.

What social considerations are relevant to embryo screening?

Effects on families, access to screening, and possible stigma towards people with genetic conditions.

What ethical considerations are relevant to embryo screening?

Reproductive choice and differing beliefs about creating, selecting, storing or disposing of embryos.

How might people differ in their evaluation of embryo screening?

They may assign different importance to each consideration.