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A short class with Sarah and her students. The other ways are under More.
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A gene is an instruction for making a protein. What might happen if a mutation changes that instruction?
The protein might be made wrongly, or not at all.
Yes. In cystic fibrosis, a faulty channel protein in cell membranes means mucus in the lungs becomes thick and sticky.
And in sickle cell anaemia, it's the haemoglobin that is changed?
Right. One base change alters one amino acid, and red blood cells bend into a sickle shape when oxygen is low.
So a tiny change in DNA can change the shape of a whole cell.
Exactly, and when cells fail, the organs built from them fail too.
Two parents are both carriers of cystic fibrosis: Ff and Ff. What are the possible children?
FF, Ff, Ff and ff.
So what is the chance that a child has cystic fibrosis?
Only ff has it, so one in four, or 25%.
And the chance of being a healthy carrier?
Two in four, so 50%.
Well done. Remember that the chances apply to each child separately, like separate coin tosses.
What makes a stem cell special?
It isn't specialised yet, and it can divide and turn into other kinds of cell.
Good. Which stem cell therapy has been used for decades?
Bone marrow transplants, for leukaemia.
Yes. And in 2023 a new treatment for sickle cell disease was approved: the patient's own blood stem cells are edited and put back.
Using their own cells means the immune system won't reject them.
Exactly, although such treatments are still very expensive and difficult to deliver.
A mutation can make a protein faulty, so the cells that depend on it stop working.
Recessive diseases need two faulty alleles; dominant diseases need only one.
People with one recessive allele are healthy but can pass it on; two carriers have a 1 in 4 chance of an affected child.
Embryonic and iPS cells are pluripotent; adult stem cells make a limited range of cells.
Bone marrow transplants and gene-edited stem cells can treat some blood diseases, but bring risks and ethical questions.
Cystic fibrosis: two healthy carrier parents (Ff) have a 25% chance with each pregnancy of a child with cystic fibrosis (ff).
Sickle cell anaemia: one base change in a haemoglobin gene alters one amino acid, so red blood cells sickle when oxygen is low and block small blood vessels.
A child with leukaemia receives a bone marrow transplant from a matched donor, and the donor's stem cells rebuild a healthy blood system.
Carrier meets carrier in a two-by-two square; in one box of four, the disease will be there.
A builder receives plans with one misprinted measurement. Every brick is laid perfectly, yet the wall leans, because the plan was wrong. Stem cells are the spare bricks that a skilled repair team can shape to fix the wall.
Embryonic is Everything, Adult is Assigned: embryonic stem cells can become almost any cell; adult stem cells make a limited range.
D.R.C.S. - Dominant needs one, Recessive needs two, Carriers are healthy, Stem cells can renew.
Term
What causes a genetic disease?
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Carrier
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Chance that two carriers of cystic fibrosis have an affected child
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Stem cell
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Why is the 2023 sickle cell treatment not rejected by the body?
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A disease caused by a change in a gene or chromosome.
A change in the base sequence of DNA.
A person with one copy of a recessive disease allele, who is healthy but can pass the allele on.
An allele whose effect shows only when two copies are present.
An unspecialised cell that can divide repeatedly and differentiate into specialised cells.
Able to develop into almost any type of cell in the body.
An adult cell reprogrammed in the laboratory to behave like an embryonic stem cell.
A treatment that replaces a patient's diseased bone marrow with healthy blood-forming stem cells.
Genetic diseases arise when a change in DNA makes a protein faulty or missing, so cells cannot work properly; stem cell therapy uses unspecialised cells that can divide and become specialised cells to replace or repair the cells that are damaged.
This lesson connects cell biology to medicine. It explains how a change in a gene or chromosome leads to diseases such as cystic fibrosis, sickle cell anaemia, Huntington's disease and Down syndrome, and how Punnett squares predict the chance of inheriting them. It then introduces stem cells (embryonic, adult and induced pluripotent), shows how they are already used in bone marrow transplants and in a recent gene-edited treatment for sickle cell disease, and weighs the risks and ethical questions involved.
Cell biology explains both why some diseases are passed down through families and how damaged cells might be repaired or replaced.
Every protein a cell makes is coded by a gene, a section of DNA. A mutation, a change in the base sequence, can make a protein faulty or stop it being made at all. Because cells depend on their proteins, the whole cell, and then the organs built from those cells, may stop working properly. Some genetic diseases are caused by a change in a single gene; others by a missing or extra chromosome.
For a recessive disease such as cystic fibrosis, a person needs two copies of the faulty allele (ff) to be affected. Someone with one copy (Ff) is a carrier: healthy, but able to pass the allele on. If two carriers have a child:
Each child has a 1 in 4 (25%) chance of having cystic fibrosis, a 2 in 4 (50%) chance of being a carrier, and a 1 in 4 (25%) chance of having two normal alleles. For a dominant disease such as Huntington's, one faulty allele is enough, so a parent who has it (Hh) and a parent who does not (hh) have a 1 in 2 (50%) chance of passing it to each child.
Genetic testing can show whether a person carries an allele, and many countries screen newborn babies for conditions such as cystic fibrosis and sickle cell disease with a small blood sample from the heel, so that care can begin early.
A stem cell is an unspecialised cell that can divide many times and can differentiate into specialised cells.
The best-established stem cell therapy is the bone marrow transplant (blood stem cell transplant). It has been used for decades to treat leukaemia and some inherited blood disorders: a patient's diseased bone marrow is cleared and replaced with healthy stem cells, usually from a matched donor, which then rebuild the blood system.
Stem cells and gene technology are now being combined. In 2023, regulators in the United Kingdom and the United States approved the first treatment using the gene-editing tool CRISPR, for sickle cell disease: some of the patient's own blood stem cells are collected, edited in the laboratory so that they produce a form of haemoglobin that does not sickle, and returned to the patient after their bone marrow has been cleared. Because the cells are the patient's own, they are not rejected by the immune system.
Researchers are also trying to grow replacement cells for conditions such as type 1 diabetes, Parkinson's disease and heart damage, but most of this work is still in trials.
Transplanted cells from another person can be attacked by the immune system, so donors must be closely matched. Pluripotent cells that are not fully controlled can form tumours. Obtaining embryonic stem cells destroys the early embryo, which some people consider morally wrong; iPS cells avoid this problem. Treatments can also be extremely expensive, raising questions of fair access, and some clinics sell unproven "stem cell treatments" that have not passed proper trials.