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VARIATION - Coggle Diagram
VARIATION
SPECIATION
TWO MODES
- Allopatric Speciation
- Sympatric Speciation
FACTORS
ISOLATION
- Preceded by isolation of some
members of a population from
other members, forming 2
seperate gene pools
PREZYGOTIC BARRIERS
- Temporal Isolation
- Habitat Isolation
- Behavioral Isolation
- Mechanical Isolation
- Gametic Isolation
- Hybrid Inviability
- Hybrid sterility
- Hybrid breakdown
GENETIC DRIFT
- Random process by which allele frequencies in population change over time
CAUSES
-
BOTTLENECK EFFECT
Random changes in allele frequencies
in a population due to dramatic
reduction of population size
HYBRIDIZATION
- Production of offspring through interbreeding
between 2 subspecies or 2 very closely related species
ADAPTIVE RADIATION
- The cases where, a species
gives rise to many new
species in a relatively short
time
TYPES
CONTINUOUS VARIATION
- Sudden transition between 2 traits
with no intermediates for the
character involved
- blood group, sex, eye colour
- cannot be measured or graded
- discrete distribution curve
DISCONTINUOUS VARIATION
- Smooth gradation from one extreme
to the other for a named character
- Eg. : height, weight
- Can be measured or graded on a
scale
- Normal distribution curve
CAUSES/SOURCES
GENETIC
MUTATION
CHROMOSOMAL
MUTATION
- Change in the chromosome structure
or number
GENE MUTATION
- Change in structure of DNA
at single locus
-
-
-
-
SEXUAL REPRODUCTION
- Involves formation of gametes and
their fusion enables the reshuffling
of genes
INDEPENDENT ASSORTMENT
Metaphase I (meiosis), each bivalent
lined up on the equator is made up
of 2 homologous chromosomes
from 2 different parents
CROSSING
OVER
Prophase I (meiosis), when bivalents
first formed, 2 homologous
chromosomes joined in bivalent will
swap bits of the chromosomes with
the corresponding bits of another
-
ENVIRONMENTAL
- Variation caused by the surroundings
NATURAL SELECTION
1. Stabilizing Selection
Environmental pressure act to eliminate
2 extreme groups
2. Directional Selection
A form of natural selection in
which extreme type is
favoured
3. Disruptive Selection
A form of natural selection in
which 2 extreme types are
selected but act against the
intermediate group
ARTIFICIAL SELECTION
1. Inbreeding
Mating between closely related individuals
where the gametes of the close relatives
get fused
2. Out breeding
Carried out by selective and
controlled crossing among
individuals from 2 different
population, subspecies or
closely related species