lecture 6 the nature of biological variation Flashcards
what is macro evolution
evolutionary change, over long periods of time, on a large scale
what are examples of macroevolution
origin of new taxonomic groups
evolutionary trends, e.g. convergence
new kinds of organisms penetrating new habitats, e.g. adaptive radiation
mass extinctions
what is microevolution
It is the basis of natural selection, whereby a population progressively adapts to its environment
Change at/below species level
what do we mean by population
A group of individuals of the same species living in a particular geographical location
what are some examples of microevolution
natural selection
variation based on location
genotype
– the genetic ‘makeup’ of an individual
phenotype
observable characteristics (genotype and environment)
chromosomes
gene carrying’ structures found in nucleus
what are homologous chromosomes
chromosomes that carry genes controlling the same characteristics
Most eukaryotes have pairs of homologous chromosomes; one set from each parent
what are genes made of
DNA
what are alleles
alternative forms of a gene = variation in the DNA sequence for a given gene
how many homologous pairs do humans have
23
what does it mean to be homozygous
the homologous pair have the same allele for the gene
what does it mean to be heterozygous
the homologous pair has different alleles for the same gene
alleles can be B or b
dominant or submissive
how does three meters of dna fit into every cell???????
super coiling
what is karyotyping
pair and order chromosomes
how does asexual reproduction happen
mitosis
what is mitosis
splitting of a parent cell into two daughter cells that are genetically identical to each other and the parent
4 ways asexual reproduction can occur
Fission
Budding
Parthenogenesis
vegetative reproduction and fragmentation
how much genetic variation occurs with asexual reproduction
little
what is binary fission
one cell divides into two cells of similar size with the same genetic material
what is budding
new individuals spilt off from parent cell, genetically identical but smaller
what is parthenogenesis
development of unfertilised egg
obligate in some species facultative in other species
what is vegetative reproduction
A form of asexual reproduction in plants, in which multicellular structures become detached from the parent plant and develop into new individuals that are genetically identical to the parent plant.
what is fragmentation
A form of asexual reproduction wherein a parent organism breaks into fragments, each capable of growing independently into a new organism.
what happens in sexual reproduction
haploid gametes formed by meiosis fure to form a diploid zygote
what meiosis
one cell splits into 4 daughter cells with different dna and only one half of a each homologous chromosome
how does meiosis drive variation for evolution
independant assortment
exchange of DNA between homologous chromosomes
random fertilisation
what is independant assortment of chromosomes
how the chromosomes line up in the cell each time before being seperated in meiosis
what is exchange of DNA between homologous chromosomes
by crossing over in meiosis wherein a pair of homologous chromosomes may swap sections in DNA
what is random fertilisation
Zygotes contain chromosomes from two parents
Different alleles from each parent which are chosen randomly from loadsssss of combinations
each zygote has 1 of 70 trillion possible diploid combinations + variation from crossing over
advantages of sexual evolution
in a stable environment the best genotype is perpetuated
uses less energy and is quicker
advantages of sexual reproduction
produces a lot of variation- new combinations may work better than older ones
in a changing environment veriation may promote overall survival
how are different alleles generated?
chromosomal mutations
multi level variation, what are the levels
chromosomal, alleles, single point mutations, single nucleotide polymorphisms
how do single nucleotide polymorphisms contribute to variation
hey can change an amino acid, therfore a protien, therefore a function
what is polypolidy
multiple sets of chromosomes
Occurs at cell/ tissue/ whole organism level
Common in plants (~50-70% angiosperms)
Liver cells are often polyploid
what are the two types of polypolidy
autopolyploidy and allopolyploidy
what is Autopolyploidy
error in mieosis/mitosis
- Single species genome duplication (single parent)
e.g., Chromosome number increases from a diploid to a tetraploid (4 copies per cell).
what is allopolyploidy
error in mieosis/mitosis- Two different, related species interbreed, hybridise, then chromosome number doubles- not common
what does polyploidy result in
reproductive isolation
is there substantial variation within species
yes
most DNA is non coding and was thought to be
silent DNA and not important
while it isn’t subject to natural selection, non coding DNA…
it will change by mutation and genetic drift
and it can have a functional role which affects how genes are expressed
what is the normal genotype for haemaglobin
HnHn
what happens to red blood cells if there is a single point mutation and HsHs occurs or HnHs
HsHs is fatal
HnHs can lead normal lives with blood transfusions
how does anaemia show co dominance
normal allele is not dominant over sickle allele they both are expressed
sickle cell heterozygotes are better adapted in
areas where malaria occurs
why is this “sickle cell heterozygotes are better adapted in areas where malaria occurs
Selection pressure from malaria maintains lethal sickle cell allele in the gene pool of the population
