key area 7: evolution

Question 1

explain what genomic variations are

Answer 1

genomic sequences are inherited vertically. this means the genetic material is passed from parent to offspring either sexually or asexually when a species reproduces

Question 2

define evolution

Answer 2

evolution is the changes in genomic sequences in organisms result in changes to the organism over time

Question 3

describe how vertical gene transfer can take place

Answer 3

genes are transferred from parents down to their offspring. this can happen sexual reproduction or asexual reproduction

Question 4

describe how horizontal gene transfer can take place

Answer 4

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

Question 5

inheritance

Answer 5

genetic material can be inherited by; vertical transfer and horizontal transfer

Question 6

sexual reproduction

Answer 6

this involves two parents who differ from one another genetically. offspring inherit different combinations of gene from each parent.

Question 7

asexual reproduction

Answer 7

this is reproduction from a single parent. it produces offspring who are genetically identical to the parent

Question 8

transformation

Answer 8

when cells are destroyed bits of their DNA float around and can be picked up by new cells

Question 9

transduction

Answer 9

occasionally when viruses replicate some host DNA is packaged up with the virus. this then enters the new cell with the virus

Question 10

conjugation

Answer 10

a temporary connection called a conjugation tube forms between touching cells. plasmid DNA is then copied from one cell to another

Question 11

rapid evolutionary change

Answer 11

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

Question 12

spread of antibiotic resistance

Answer 12

resistance to antibiotics has occurred through the transfer of plasmids carrying antibiotic resistance genes from bacteria to bacteria

Question 13

horizontal transfer of genetic material in eukaryotes

Answer 13

although less common but can occur in eukaryotes by; from prokaryotes or from viruses

Question 14

Describe how prokaryotes can transfer DNA sequences horizontally into the genomes of eukaryotes

Answer 14

agrobacterium tumefaciens is a bacteria which infects plant cells with a plasmid that integrates into the genome of the plant

Question 15

Describe how viruses can transfer DNA sequences horizontally into the genomes of eukaryotes

Answer 15

some viruses can integrate their DNA into the host’s genome where they remain dormant until they reproduce and destroy the cells

Question 16

important events in earths history

Answer 16

700mya- the first animals evolved
530mya- first vertebrates evolved
400mya- first land plants evolved
350mya- first land vertebrates evolved

Question 17

Define natural selection

Answer 17

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.

Question 18

Give 2 examples of natural selection

Answer 18

The peppered moth

Giraffes and their long necks

Question 19

Define sexual selection

Answer 19

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

Question 20

How can sexual selection operate

Answer 20

• 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

Question 21

Explain what happens as a result of stabilising selection

Answer 21

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

Question 22

Explain what happens as a result of directional selection

Answer 22

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

Question 23

Explain what happens as a result of disruptive selection

Answer 23

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

Question 24

Explain what neutral mutations are

Answer 24

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

Question 25

Explain what the founder effect involves

Answer 25

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

Question 26

Define genetic drift

Answer 26

The random increase or decrease in frequency of genetic sequences.

Question 27

Explain why genetic drift has a greater impact on small populations

Answer 27

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

Question 28

Define a species

Answer 28

A species is a group of very similar interbreeding organisms that give rise to fertile offspring

Question 29

Define speciation

Answer 29

Is the formation of a new biological species. It is brought about by evolutionary change

Question 30

Name 3 types of isolation barriers

Answer 30

Geographical, ecological, reproductive

Question 31

Allopatric speciation

Answer 31

This occurs when gene flow between two or more populations is prevented by a geographical barrier

Question 32

Sympatric speciation

Answer 32

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

Question 33

Define a hybrid zone

Answer 33

An environment Ma contain several sub-populations of a species which cannot all interbreed

Question 34

Explain the significance of hybrid zones

Answer 34

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.