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Variation

Last updated Jun 19, 2023 Edit

# Genetic Causes of Variation

Genetic cause of variation	What happens?	Why does it cause variation?	Example?
Alleles	Different versions of genes	Produces different proteins and therefore different structures and effects	Blood group
Mutations	Mistake in DNA	Changes in protein that are coded for	Cystic fibrosis
Meiosis	Gametes form which have half the genetic material of parent cells. Crossing over and independent assortment also occur to make every gamete genetically different.	Different gametes have different mix of alleles	Variation in gametes
Sexual reproduction	Inherit genes from both parents	Individual produced is genetically different from parents	Children
Chance	Chance which gametes fertilise	Unique combination of genetic material for each offspring	Siblings different from each other

# Environmental Causes of Variation

Environmental cause of variation	What happens?	Why does it cause variation?	Example?
Conditions for plant	Plants in different conditions grow to different sizes Plants in different pH soils can grow different coloured flowers Lack of nutrients for plant	More sunlight for photosynthesis to make glucose for respiration and growth Acidic soil makes blue flowers. Alkali makes pink flowers Proteins	Rose bush in higher light intensity grows bigger Different coloured flowers of hydrangeas Nitrates
Injury/Disease	Damaged tissue	Damages cell, leaves marks on skin	Scars

# Combined Environmental and Genetic Causes of Variation

Environmental and genetic effect of variation	How do genetics play a part?	How does environment play a part?
Height	Inherited genes from parents	Malnourishment
Skin colour	Genes instruct melanin levels	Sunlight can increase melanin production

# Discrete Variation

Discontinuous/discrete variation is normally only controlled by a single gene (or very few).
There are no in-between values, only specific ones.
Normally represented through a bar chart.

# Continuous variation

A characteristic that can take any value in a range (quantitative) is said to show continuous variation.
Characteristics that show continuous variation such as height show a normal distribution pattern
These characteristics are usually controlled by a number of genes (polygenic) and influenced by the environment