AQA GCSE Inheriting disorders(Biology)

Inheriting disorders

Inherited disorders are conditions caused by genes passed from parents to offspring. They are caused by different versions of genes called alleles. Some alleles can cause disease.

An inherited disorder is caused by the inheritance of a faulty allele.

Dominant vs Recessive Alleles

A dominant allele only needs one copy to show the disorder.

A recessive allele needs two copies (one from each parent).

Dominant alleles are always expressed if present, whereas recessive alleles are only expressed if two copies are inherited.

Example: Polydactyly

Polydactyly is a condition where a person is born with extra fingers or toes. It is caused by a dominant allele. This means only one copy of the allele is needed to have the condition.

For a person to have polydactyly they will have a genotype of DD or Dd.

If a person does not have polydactyly, their genotype will be dd.

In the diagram below, it will show two punnett squares one where the 1st parent is DD, and the 2nd where the 1st parent is Dd.

Example: Cystic Fibrosis

Cystic fibrosis is a disorder affecting cell membranes. It causes thick, sticky mucus in the lungs and digestive system. It is caused by a recessive allele. A person must inherit two copies to have the disease.

Embryo Screening

Embryo screening is used to check embryos for genetic disorders before birth. It helps prevent inherited diseases.

There are two main methods that are used for sampling

1.Amniocentesis involves taking a small sample of amniotic fluid to analyse the baby’s genes.

2. Chorionic villus sampling (CVS) involves taking a small sample of cells from the placenta to test for genetic disorders.

Embryo screening can reduce suffering but raises ethical concerns about selecting embryos.

Advantages of embryo screening	Disadvantages of embryo screening
Helps to prevents serious genetic diseases	Some people think it is wrong to select embryos
It can reduce suffering	It may lead to “designer babies”
Allows parents to make an informed decision about whether to continue or terminate the pregnancy.	Some religious groups believe that life begins at fertilisation, so destroying embryos is wrong.
	Screening can be expensive, so not everyone has equal access.

Using IVF and Embyro screening

IVF is used for artificial fertilisation in the lab

Sperm are collected from the male

Eggs are collected from the female.

Then the method below is used to test the embryo that develops after fertilisation.

Stages of embryo testing in a lab

1.A sperm will fuse with an egg in a petri dish.

2. Fertilised egg cell will divide by mitosis to form an embryo.

A sample from each embryo is taken and tested for the genetic disorder.

If the embryo tests positive for the disorder it is discarded.

If the embryo tests negative for the disorder, it can be implanted into the female uterus to develop into a baby.

Gene Therapy

Gene therapy involves inserting healthy genes to replace faulty ones. It could treat inherited disorders in the future.

The gene can be inserted using a virus. After the gene has been inserted the correct protein will be produced.

Gene therapy may treat genetic disorders but raises ethical and safety concerns.

Advantages of gene therapy	Disadvantages of gene therapy
Can treat or potentially cure genetic disorders (e.g. cystic fibrosis)	Very expensive, so not widely available
Targets the cause of the disease (the faulty gene) rather than just symptoms	Long-term effects are unknown (may cause unexpected problems)
May provide long-term or permanent effects	Genes may be inserted into the wrong place in DNA, causing issues
Can improve quality of life	May not work in all cells, so treatment might be incomplete