Genetics Flashcards
Structure of a nucleotide
Sub-unit of DNA - contains a single sugar, phosphate molecule and a nitrogenous base
Species definition
A group of individuals with shared characteristics
Alleles definition
Alternative forms of a gene; inherited from their parent and control/determine characteristics
Chromosomes
DNA tightly wrapped around histones (proteins)
Homologous pairs
A pair of genes coding for a particular trait (dominant, recessive, co-dominant)
Genotype
The inherited genetic make-up of an individual
Phenotype
The observed expression of the alleles for a characteristic - determined by genotype and the environment
Monogenic inheritance
A single pair of alleles is inherited for a particular trait; eg. blood type - these traits are discrete (either there or not) and have only two phenotypes
Polygenic Inheritance
Controlled by multiple pairs of genes, thus continuous variation in trait - Alleles have an additive effect (skin colour, weight, height)
Polygenic inheritance characteristics
Each gene has 2 forms of alleles - contributing and non-contributing
No dominance
Additive effect
Skin colour - polygenic inheritance
Continuous variation in the trait; affected by environmental factors
Effect of genotype on skin colour
Varying amounts of the enzyme tyrosinase (stimulated by UV rays to produce melanin)
Effect of environmental factors on skin colour
UV light stimulates the production of tyrosine (aa forming melanin- protein)
Dark skin
High levels of tyrosinase; increased ability to convert tyrosine to melanin
More even distribution of melanin - more tanned, less susceptible to sun burn
Light skin
Low levels of tyrosinase; decreased ability to convert tryosine to melanin
Less even distribution of melanin (freckles) - less tanned, more susceptible to sun burn
Mutagens
Agents that increase the rate at which mutations occur