BIO1011 Lecture Notes - Lecture 12: Sexual Reproduction, Natural Disaster, Mutation
5 Jul 2018
School
Department
Course
Professor
Lecture 12: Population and Evolution Genetics
Variations
•Population : A group of the same species living in the same region at a given time.
•Variation exist in members of a population - our class is population .
•Genetic Variation: Differences among individuals in the composition of their genes or
other DNA sequences.
•Neutral Variation: Differences in DNA sequence that do not confer a selective
advantage or disadvantage.
• There are different types of variation within a population :
•Structural : Presence of hair, tail, muzzle length
•Biochemical : ABO antigens (blood), coat colour - due to production or lack of a
particular enzyme
•Physiological : People’s ability to taste, detect odours, distinguish colours
•Behavioural : differences in retrieval/herding/obedience training.
•Developmental : changes that normally occur during the life span of a species.
•Geographical : How members of a population differ due to their range.
• Geographical position
• Birds can show geographical variation - those in northern parts being smaller /
paler than those in the south
• When a trait changes gradually in a members of a population across its range =
cline
Variation in a Population
!
Monomorphic
- Members of a population that
are uniform - show no variation
in regard to a trait.
Polymorphic
- Members of a population which
show two or more variations of a
trait.
Continous Variation
• Type of a variation in which members of a
population vary across a range.
• Human Height is an example.
• Results in a “normal” distribution line
• Will have extreme values
• E.g height, skin colour, weight
Discontinuous Variation
• Types of variation in which members of a population can be grouped into a few non-
overlapping classes for a particular trait.
• E.g Human blood type - Population falls into four distinct groups (discontinuous
variation)
• E.g Gender, ether male or female.
Compare and Contrast Continous Variation
Causes of Variation
• Genetic
• Environment
Genetic Variation
✦Variation caused by the passing on of genes to offspring.
✦Monogenic Trait : Variation due to the actions of one gene ( gene = two or more alleles
which may result in numbers of variation)
✦E.g Two Alleles = Eye colour, Three Alleles = blood type.
✦Polygenic Trait : Variation due to the action of many genes - such trait show continuous
variation.
✦E.g Skin Colour
✦Genetic Variation also from :
✦Sexual reproduction (crossing over & recombination)
✦Mutations in DNA
Environmental Variation
★Environmental factors can have a significant influence on the phenotype of an organism
★Identical twins (same genotype) can differ in their phenotype (e.g height, strength, health,
IQ = these variations are due to environmental factors)
★Plant growth also varies depending on the environment in which they grow
★E.g Arrowleaf plant
★can be terrestrial and/or aquatic
★Phenotype depends on environment
★Internal environmental factors can also produce variations in a population (phenotype)
The Gene Pool
• Each population possess a gene pool
•Gene Pool: The complete set of genetic information carried by all of individuals of a
population
• Also includes all the alleles present in the population
• remember that at one gene locus there can be multiple alleles.
• Individuals within a population will have some but not all of the available alleles.
• Gene pool can be expressed in terms of the alleles frequency = the proportion of
alleles in a population
• Allele frequency can vary from 0 (no one has the allele) to 1 (everyone is homozygous
for the allele)
The total of all allele frequencies at one gene locus in a population is
ALWAYS 1.
Document Summary
Members of a population that are uniform - show no variation in regard to a trait. Members of a population which show two or more variations of a trait. Continous variation: type of a variation in which members of a population vary across a range, human height is an example, results in a normal distribution line, will have extreme values, e. g height, skin colour, weight. Variation caused by the passing on of genes to offspring. Monogenic trait : variation due to the actions of one gene ( gene = two or more alleles which may result in numbers of variation) E. g two alleles = eye colour, three alleles = blood type. Polygenic trait : variation due to the action of many genes - such trait show continuous variation. Environmental factors can have a significant influence on the phenotype of an organism. Identical twins (same genotype) can differ in their phenotype (e. g height, strength, health,
