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What are the 2 key principles/concepts of evolution

1. Descent with modification ie all species have descended without interruption from an original form
2. Natural Selection
It is the causal agent of adaptive evolutionary change where more offspring are produced then can survive and less well adapted individuals have a lower reproductive success than better adapted


What are the three area where evidence for evolution can be found

In fossil records which hold history and patterns of evolution
In livining organisms through comparing traits and studying their form and functions to infer evolutionary associations
Experimental evolution can be used to manipulate selection or genetic drift to test theories and predictions


Types of fossils 4

• Trace fossils – e.g. footprints, burrows, bite marks
• Chemical fossils – e.g. lipids from algae found in oils
• Unaltered remains - frozen in ice, trapped in amber


Problems of fossils

Fossilization is inherently unlikely – record is extremely incomplete due to
Biological factors such as rarity or not made of suitable fossil material
Non-biological - sediments do not always solidify into rock, and that rock must persist and the be found
Dating is can also be inaccurate
Also little about how fossilised organisms were created in the first place


Why are fossils useful

allow us to characterise timeline of life on earth and show intermeidiate or stages characteristics between different groups such as Archaeopteryx – bird-like organism but with
dinosaur features
This can be interpreted as evolutionary change


Flaw with studying evolution through living things

There is a limited ability to view evolutionary processes due to time factor


Define Macroevolution (inferred from e.g. fossil record)

Large evolutionary changes e.g. origin of new organisms, body plans


Define microevolution

Smaller-scale changes such as alterations of gene frequency within a population (e.g. changes in frequency of human
blood group types)


What does DNA stand for

DeoxyriboNucleic Acid


What is DNA

Double helix made of two polymers of nucleotides (pentose sugar + phosphate + base)


What are the 4 DNA bases and how do they

Adenine and Guanine (purines)
Cytosine and Thymine (Pyrimidines)


What are the two types of nuclear DNA

Autosomal chromosomes which are diploid, each contain two copies of each chromosome
Sex chromosomes XX and XY


Two types of cytoplasmic DNA

Mitochondria - uni parental inheritance ie it is maternally inherited in egg cytoplasm
Chloroplast uni parental inheritance maternally (in the egg) in some species, paternally inherited (in pollen) in others


Define Locus

(plural loci) is the specific location of a gene or DNA sequence on a chromosome


Define allele

One of the different forms of a gene that can exist at a single locus


Difference between heterozygote and homozygote

Heterozygote possesses two different alleles at a particular locus whilst a homo has two identical


Define linkage

The tendency for loci to be inherited together when near one another on the same chromosome as they are less likely to be separated by recombination


What is a codominant allele

When neither allele is dominant so the phenotype is a mixture of the two


What two things determines an organisms phenotype

genotype and environment


Example of pleiotropy

phenylketonuria = mutation in a single gene - reduced hair and skin pigmentation + mental retardation


Define epistasis

The effect of one gene is modified by another e.g genomic level, where one gene could code for a protein preventing transcription of the other gene or phenotypic level, the gene causing albinism would hide the gene controlling color of a person's hair.


Which is the sense strand and which is the antisense

sense strand is coding and is transcribed
the antisense is the non coding strand


How can DNA change over time

Through mutations caused by chemicals, irradiation, viruses or occurs during replication (enzymes make a mistake)


How are mutations limited

Body has mechanisms to repair mutations using the other strand as a template


What are large scale DNA mutations

Chromosome breakages, rearrangements, duplications


What are small scale changes to DNA

Single base difference (point mutation)


What is transcription

Transcription is the first step in gene expression. It involves copying a gene's DNA sequence to make an RNA molecule.


What enzyme is transcription performed by

is performed by enzymes called RNA polymerases, which link nucleotides to form an RNA strand (using a DNA strand as a template).


What is the goal of transcription

to make a messenger RNA copy of a gene's DNA sequence


What is a non-synonymous substitution

A mutation that causes a change in an amino acid sequence