genetic Diversity Flashcards
haploid
one copy of each chromosome in a cell
diploid
two copies of each chromosome in a cell
meiosis
cell division that creates genetically different gametes
there are two nuclear divisions in this process
results in four haploid daughter
cells
independent segregation
homologous pairs of chromosomes randomly line up opposite each other at the equator of the cell
when they separate it creates a
large number of possible
combinations of chromosomes
in the daughter cells produced
crossing over
homologous pairs of chromosomes line up opposite each other at the equator in meiosis 1
parts of the chromatids twist, break and recombine with another chromatid
results in new combinations of alleles in the gametes
How does meiosis introduce variation
Crossing over
Independent segregation
Types of gene mutations
Deletion
Substitution
What is a frame shift
The removal of one base
Changes all subsequent codons
All bases shift back one position
Chromosome mutation
Change in the number of chromosomes
Occurs during meiosis
Deletion mutation
A gene mutation
a base is removed from a sequence
causes a frameshift
Substitution mutation
a gene mutation
a base is swapped for a different one
Non-disjunction
The chromosomes or chromatids dont split equally during anaphase
Polyploidy
changes in whole sets of chromosomes
e.g. when organisms have three
or more sets of chromosomes
mainly occurs in plants
Aneuploidy
a change in the number of individual chromosomes
e.g 3 copies of chromosome 21
Downs syndrome
causes by a chromosome mutation
an example of aneuploidy
3 copies of chromosome 21
Genetic diversity
The measure of how many different alleles there are for each gene
Gene mutations
a change in the base sequence of DNA
substitution or deletion
When in the cell cycle do gene mutations occur
Interphase (s phase)
this is when DNA is replicated
Natural selection
the process that leads to evolution in populations
results in species becoming better adapted to their environment
Gene pool
All the genes and alleles in a population at a particular time
Allele frequency
the proportion of organisms within the population carrying a particular allele
Evolution
the change in allele frequency over many generations in a population
Selection pressure
factors that affect the survival of an organism
the driving force of natural selection
Types of selection
Stabilising
Directional
Directional selection
one of the extreme traits has a selective advantage
occurs when there is a change in the environment
the modal trait changes
Stabilising selection
the middle (median) trait has a selective advantage and continues to be the most frequent in the population
represented by a normal distribution graph
range decreases as the extreme
traits are lost over time
Example of directional selection
Abiotic resistance
Example of stabilising selection
Human birth weight
