polymorphism exam study

🌱 What Is Polymorphism?

Polymorphism = When a gene exists in 2 or more versions (alleles) in a population.
To be polymorphic, each allele must be in more than 1% of the population.

🔍 Where Do Alleles Come From?

Caused by mutations (tiny DNA changes).
Most mutations are rare and random.
If a mutation gives a survival or reproductive advantage, it can become more common (thanks to natural selection).

💡 Balanced Polymorphism

A type of polymorphism where:
- There are 2 or more alleles.
- People with one of each allele (heterozygotes) do better than people with two of the same (homozygotes).
About 28% of human genes are polymorphic!

🧬 Real-Life Example: Sickle Cell Trait

Hemoglobin Basics:

Hemoglobin = Protein in red blood cells that carries oxygen.
Made of 4 parts: 2 alpha chains + 2 beta chains.

The Mutation:

A single DNA change in the beta chain causes cells to become sickle-shaped.

Sickle Cell Disease (SS):

Health problems include:
- Anemia
- Slow growth
- Pain and organ issues
- Shortened life span

Treatment Options:

Pain medication
Bone marrow transplant
Gene therapy

🌍 Why Does the Sickle Cell Allele Still Exist?

Malaria Connection:

In Africa and Asia, malaria is common.
People with one sickle allele + one normal allele (AS):
- Are healthier
- Get less malaria

How It Helps:

In AS people, malaria-infected cells die off quickly.
Parasites can't survive = fewer malaria symptoms.

🌾 Evolution + Environment

AS (carriers) survive best in malaria areas = more likely to pass on their genes.
Farming may have spread malaria, helping this gene become more common.

🧬 Other Helpful RBC Polymorphisms

Thalassemia:

Helpful if you have one copy.
Two copies = health issues.

G-6-PD Deficiency:

Usually no symptoms.
Also helps fight malaria!

🌎 Summary

Polymorphisms exist because they can offer advantages in tough environments.
Traits like sickle cell, thalassemia, and G-6-PD persist because they protect against malaria.
Evolution is about using what works best for survival!