Environmental and Epigenetic factors

How is the phenotype determined?

Phenotype: The observable characteristics of an organism, determined by genotype and environmental factors

• Genotype has the biggest influence on the phenotype but environmental factors also affect the phenotype

What are some types of environmental factors that affect phenotype?

• UV radiation

• Chemicals and toxins

• Predators

• Pathogens

• Competition for resources

• Physical environment

• Harmful radiation

• Temperature

• Altitude

• Nutrition/diet

• Exercise

• Social changes

What are 2 key examples of how environmental factors act on the phenotype to produce the phenotype?

1. Flower colour in hydrangeas

Environmental factor: Soil pH (acidity of soil)

2. PKU - Phenylketonuria

Environmental factor: Diet/nutrition

How does the environmental factor soil pH affect hydrangea’s phenotype?

• Flower colour affected by pH of the soil (environmental factor)

• Acidic soil = blue flowers and Alkaline soil = pink flowers

• The more acidic the soil, the more pigment is made which produces pink flowers

How does the environmental factor diet influence having Phenylketonuria?

• Possessing the disease is affected by your diet (environmental factor)

• Individuals with PKU have a mutation in a gene which produces an enzyme that breaks down phenylalanine, therefore they cannot break it down

• Leads to build up in toxic levels which causes problems with brain development

• Recessive trait that newborn babies (in Australia) are tested for

• Symptoms can be prevented by modifying the diet to remove food containing phenylalanine

• Enzymes can be medically taken after eating high phenylalanine foods

What is the diseases Phenylketonuria?

An inherited disease in which phenylalanine (from the diet) builds up to toxic levels, leading to problems with brain development

What is epigenetics? What do these factors alter?

The study of factors that modify gene expression but do not alter the DNA sequence

What is the epigenome? Is it permanent?

Epigenome: The complete set of chemical tags on DNA that control gene expression without changing the DNA sequence

• Everyone has a different epigenome and many throughout their lifetime's as it changes overtime

How do epigenetics enable cell specialisation?

• All cells have the same genome, but different epigenetic tags meaning different genes get expressed in each cell type

• Allows cells to develop distinct structures and functions despite identical DNA

• These patterns are kept through cell division, so specialised cells produce daughter cells of the same type

What affects epigenetic modifications? Are these modifications the same between everyone?

• Epigenetic modifications are affected by environmental factors such as diet, stress and exposure to chemicals and toxins

• Thus epigenetic tags differ between individuals and change with age

• Unlike changes to the DNA sequence, epigenetic changes can be reversible

How can epigenetic markers be inherited?

• Epigenetic tags are modified and established throughout development

• Thus, pregnant woman's environment and diet can influence the epigenome of her developing baby

• During gamete formation and after fertilisation, most epigenetic marks are erased and reset — but some can escape this reprogramming

• Means some epigenetic information can pass from parents to offspring via gametes (inhertied)

• Yet the extent to which environmentally acquired epigenetic changes are inherited in humans remains uncertain

What are the two types of epigenetic modifications?

1. DNA methylation

2. Histone acetylation

What is the most common type of epigenetic tag?

DNA methylation: The addition of a methyl group (CH4) to a cytosine base in DNA

• The most common type of epigenetic tag that prevents gene expression

• The methyl group causes DNA to coil tighter around histones, which stops proteins from reading the gene

How does histone modification increase gene expression?

Histone acetylation: The addition of an acetyl group to a histone tail which relaxes the chromatin structure and increases the expression of the gene

• Increases accessibility for proteins and therefore gene expression

How are histone modifications different to histone acetylation?

Both DNA methylation and acetylation are types of histone modifications

Histone modifications: Chemical changes to histone proteins that control how tightly DNA is wrapped around them

• These changes alter chromatin structure, turning genes on or off without changing the DNA sequence itself