key area 7: evolution Flashcards
explain what genomic variations are
genomic sequences are inherited vertically. this means the genetic material is passed from parent to offspring either sexually or asexually when a species reproduces
define evolution
evolution is the changes in genomic sequences in organisms result in changes to the organism over time
describe how vertical gene transfer can take place
genes are transferred from parents down to their offspring. this can happen sexual reproduction or asexual reproduction
describe how horizontal gene transfer can take place
in prokaryotes genetic material can transferred from one cell to another through horizontal gene transfer. horizontal gene transfer can occur in three ways; transformation, transduction and conjugation
inheritance
genetic material can be inherited by; vertical transfer and horizontal transfer
sexual reproduction
this involves two parents who differ from one another genetically. offspring inherit different combinations of gene from each parent.
asexual reproduction
this is reproduction from a single parent. it produces offspring who are genetically identical to the parent
transformation
when cells are destroyed bits of their DNA float around and can be picked up by new cells
transduction
occasionally when viruses replicate some host DNA is packaged up with the virus. this then enters the new cell with the virus
conjugation
a temporary connection called a conjugation tube forms between touching cells. plasmid DNA is then copied from one cell to another
rapid evolutionary change
in early evolution of prokaryotes there was a lot of horizontal gene transfer because obtaining a gene from a neighbour is much faster than waiting from one to evolve. this allowed rapid evolution of prokaryotes
spread of antibiotic resistance
resistance to antibiotics has occurred through the transfer of plasmids carrying antibiotic resistance genes from bacteria to bacteria
horizontal transfer of genetic material in eukaryotes
although less common but can occur in eukaryotes by; from prokaryotes or from viruses
Describe how prokaryotes can transfer DNA sequences horizontally into the genomes of eukaryotes
agrobacterium tumefaciens is a bacteria which infects plant cells with a plasmid that integrates into the genome of the plant
Describe how viruses can transfer DNA sequences horizontally into the genomes of eukaryotes
some viruses can integrate their DNA into the host’s genome where they remain dormant until they reproduce and destroy the cells
important events in earths history
700mya- the first animals evolved
530mya- first vertebrates evolved
400mya- first land plants evolved
350mya- first land vertebrates evolved
Define natural selection
Organisms produce more offspring than the environment can support. All members of a species show variation from each other.Only those who are better adapted to the environment will survive and breed. The adaptions pass on to their offspring and gradually change the characteristics of a species.
Give 2 examples of natural selection
The peppered moth
Giraffes and their long necks
Define sexual selection
Sexual selection is a special case of natural selection where selection is driven by the organisms ability to get a mate. It is the process of selection for traits that increase reproductive success
How can sexual selection operate
- male to male competition. They compete aggressively to defend territories and get access to females. Larger, stronger males or males with better weapons win mating rights and pass those alleles on.
- female choice. Females select males which they consider high quality depending on the traits they display
Explain what happens as a result of stabilising selection
This form of selection exerts its pressure against the extreme variations and favours the intermediate versions of the trait. It leads to a reduction in genetic diversity without a change in the mean value. It operates in an unchanging environments and maintains the status quo for the best adapted genotype so in the population
Explain what happens as a result of directional selection
This type of selection is most common during a period of environmental change. It favours a version of the characteristic that was initially less common form and results in a progressive shift in the populations mean value for the trait
Explain what happens as a result of disruptive selection
When extreme versions of a trait are favoured at the expense of the intermediates. It results in the population becoming split into two distinct groups each with its own mean value. Under natural conditions it occurs when 2 different habitats or types of resources become available
Explain what neutral mutations are
Change the nucleotide sequence of a gene but do not change the amino acids coded for. They are not subject to natural selection but are affected by genetic drift
Explain what the founder effect involves
If a population becomes isolated and is not large enough to contain the entire gene pool, gene frequencies will be different in that population.an example of the founder effect can be seen in the different groups blood group allele frequencies in different human populations
Define genetic drift
The random increase or decrease in frequency of genetic sequences.
Explain why genetic drift has a greater impact on small populations
The total of all the different genes in a population is called the gene pool. If a series is under no selective pressure, frequencies of individual alleles will stay the same from generation to generation
Define a species
A species is a group of very similar interbreeding organisms that give rise to fertile offspring
Define speciation
Is the formation of a new biological species. It is brought about by evolutionary change
Name 3 types of isolation barriers
Geographical, ecological, reproductive
Allopatric speciation
This occurs when gene flow between two or more populations is prevented by a geographical barrier
Sympatric speciation
Two or more populations live in close proximity in the same environment but still become genetically isolated . This happens due to a behavioural or ecological barrier or by the occurrence of polyploidy
Define a hybrid zone
An environment Ma contain several sub-populations of a species which cannot all interbreed
Explain the significance of hybrid zones
Each sub-population can breed with its neighbour but may not be able to breed with more distant members of the species. Hybrid zones exist where interbreeding is possible and as a result genes are able to flow between the sub-population.
