Genetic Diversity (HL) (DP IB Environmental Systems & Societies (ESS)) : Revision Note

Genetic Diversity

DNA, chromosomes and genes

• DNA is the molecule that carries genetic information in all living organisms

• Genes are specific sequences of DNA that code for particular traits or proteins in an organism

  • Each gene controls a certain characteristic or function

• Chromosomes are long strands of DNA tightly coiled together

  • For example, humans have 46 chromosomes, arranged in 23 pairs

  • Each pair carries genes inherited from both parents

• The genome is the complete set of genes or genetic material in an organism

  • Every living thing has its own unique genome

• Genetic diversity refers to the variation in genes between individuals within a species

  • This diversity is very important for the survival and adaptation of populations in changing environments

How genetic diversity arises

Mutation and genetic diversity

• Mutations are random changes in the DNA sequence

  • They can occur naturally during cell division or due to environmental factors like radiation

• Mutations create new versions of genes known as alleles

  • These changes can introduce new traits into a population

  • For example, a new allele might provide resistance to a certain disease or the ability to digest a new food source

• Most mutations are neutral, meaning they have no effect on the organism

  • However, some can be beneficial (increasing survival chances) or harmful (leading to genetic disorders)

  • For example, in some human populations, a mutation in the CCR5 gene provides greater resistance to HIV infection

Sexual reproduction and genetic diversity

• Sexual reproduction combines genetic material from two parents

  • An individual's gametes are genetically distinct from each other

  • Depending on which gametes fuse together during fertilisation, the offspring created will always be genetically distinct

  • This results in offspring with a unique set of genes

• The genetic recombination that occurs during reproduction (i.e. the mixing of DNA from both parents) leads to new combinations of alleles in the offspring

  • For example, human siblings (except for identical twins) have different combinations of their parents' genes, leading to genetic variation within a family

Importance of genetic diversity

• Survival and adaptation:

  • High genetic diversity gives populations a greater ability to adapt to changing environments

  • If a new disease, new predator, new food source or climate change occurs, some individuals may have the right genetic traits to survive. For example:

    • In agriculture, maintaining genetic diversity in crops is important for resilience to pests and diseases

    • Some corals have specific genes that code for proteins helping them survive higher temperatures

    • Genetic diversity in these heat-tolerance genes can allow certain corals to withstand warming ocean temperatures, while others without these genes may bleach and die

• Reduced risk of inbreeding:

  • In populations with low genetic diversity, individuals are more likely to inherit harmful mutations due to inbreeding (mating between closely related individuals)

  • This can lead to genetic disorders or reduced survival rates

  • For example, cheetahs have low genetic diversity, making them more vulnerable to disease and reproductive issues