human biology ATAR 12 - sickle cell anaemia and thalassemia

genetic mutation

changes in a single gene so that the traits normally produced by that gene are changed or destroyed

how does sickle cell anaemia occur

caused by a specific single nucleotide mutation in the beta globin gen which results in sickle-shaped red blood cells.

what is sickle cell anaemia

a genetic blood disorder that affects hemoglobins - the oxygen transporting moles in red blood cells

the different base sequence means that the amino acid is added instead of a glutamic acid, which results in a different form of protein which alters the haemoglobin produced which can distort the shape of the red blood cells

treatment for sickle cell anaemia

currently limited but frequent blood transfusions and medication to relieve pain or reduce symptom frequency are used.

effects of sickle cell anaemia

sickle shaped red blood cells are also inflexible and can become stick in the blood vessels which can cause a blockage.

fatigue, jaundice, organ damage, high blood pressure and heart failure.

how is sickle cell anaemia passed on

autosomal recessive: the child has to inherit a copy of the sickle cell gene from both parents.

what is thalassemia

a disorder that alters the amount of hemoglobins causing the body to have less hemoglobins and too much iron.

people with thalassemia cannot carry as much oxygen in their blood.

what is alpha thalassemia

due to a mutation in the HBA gene on chromosome 16, this reduces the level of alpha globin in haemoglobins.

how does alpha thalassemia effect allele frequency

increases

due to the selective advantage of alpha thalassemia in malaria-endemic regions, the frequency of alpha thalassemia alleles in the gene pool increases. Over generations, this can lead to a higher proportion of the population carrying one or more copies of the thalassemia allele.

what is beta thalassemia

due to the mutation in the HBB gene on chromosome 11, this reduces the level of beta globin in haemoglobins.

treatment for thalassemia

depends on the severity of the case. It can include:

• Medication which can help the body get rid of the extra iron.

• blood transfusions which involve receiving injections of red blood cells through a vein to restore normal levels of healthy blood cells.

• Stem cell or bone marrow transplants which involves getting healthier stem cells or bone marrow from a donor which is given via a drip into the patient’s veins.

what is malaria

a life-threatening disease spread to humans by some mosquitoes.

the infection is caused by a parasite and cannot be spread from person to person

treatment for malaria

artemisinin based combination therapies (ACTs)

type of medication depends on the type of parasite

natural selection

* with example

the process through which populations of living organisms adapt and change.

survival of the fittest – the most favourable traits will survive.

example: one species of moth is black and can blend with the black smoke of industrial evolution so white moth stand out to be eaten by animals.

stages of natural selection

variation: there is variation between individual species.

isolation: populations of the same species are isolated without gene flow.

selection: each population is subjected to different selective agents.

speciation: the allele frequency changes until they become so different that the two groups are no longer able to interbreed.

how does natural selection impact allele frequency

Natural selection changes gene pools by favouring individuals with traits that help them survive and reproduce better in their environment.

Some ways include:

variation in traits: populations have different traits due to genetic variation.

survival and reproduction: Individuals with traits that give them an advantage in their environment are more likely to survive and have offspring. These advantageous traits are passed on to the next generation.

changes in allele frequency: the genes or alleles responsible for these beneficial traits become more common in the population.