block 4 - genetics NEW

What is a quantitative trait?

Continuous variation, influenced by many genes + environment.

Continuous variation

A phenotype that shows a range of values with no distinct categories, caused by many genes + environment

→ Simple: values blend smoothly (like height, not blood groups)

Give examples of quantitative traits.

Height, BMI, blood pressure, skin colour.

Why don't quantitative traits follow Mendelian ratios?

Controlled by many genes (polygenic).

What is polygenic inheritance?

Many genes contribute to one trait.

What is the additive model?

Each gene adds a small equal effect.

What are QTLs?

Genomic regions controlling quantitative traits.

Polygenic Inheritance - What are 2 loci additive traits?

A quantitative trait controlled by 2 genes (2 loci) where each allele adds a small effect

What is the F2 ratio for 2 loci additive traits?

1 : 4 : 6 : 4 : 1.

What happens as loci increase?

More phenotypes → continuous distribution.

How are traits described statistically?

Frequency distribution (often normal).

What is phenotypic variance (Vp)?

Total variation in a population.

What is the equation for phenotypic variance?

Vp = Vg + Ve.

What is genetic variance (VG)?

differences due to genes

Ve

differences due to environment

What is heritability (H²)?

Proportion of variation due to genetics.

What does heritability NOT tell you?

Not individuals; not differences between populations.

How is heritability estimated?

Family + twin studies.

What % genes are shared between parent and child?

50%.

What % genes are shared between identical twins?

100%.

Why compare MZ vs DZ twins?

To separate genetic effects from environmental effects, if MZ are more similar than DZ → the trait is genetic

What is population genetics?

Study of genetic variation in populations.

What is a population?

Interbreeding individuals in same space/time.

What is panmixia?

Random mating.

What causes population structure?

Geographic barriers, environment, behaviour (assortative mating).

What is a locus?

Position in genome.

What are alleles?

Different gene forms.

What are SNPs?

Single base pair changes.

What are STRs?

Short repeating DNA sequences.

Why are STRs useful?

Highly variable → identification.

What are CNVs?

Copy Number Variants = differences in the number of copies of a DNA segment between individuals

What is PCR?

DNA amplification using cycles.

What is the amplification pattern of PCR?

2ⁿ (exponential).

What are key components of PCR?

Primers, Taq polymerase, dNTPs.

What is RFLP?

Restriction Fragment Length Polymorphism = DNA is cut by restriction enzymes, producing different fragment lengths depending on the allele