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  • Created by: Pope1912
  • Created on: 03-03-15 09:22


DNA is made up of nucleotides made up of a sugar, a phosphate and a base.

DNA is a polynucleotide because lots of single nucleotides are joined together.

Each nucleotide is made up of a pentose sugar (5 carbons), a phosphate group and a nitrogenous base.

The sugar in the nucleotides is called deoxyribose.

Each nucleotide has the same sugar and phosphate but the bases vary.

Four bases: Adenine, Thymine, Cytosine, Guanine.

Two polynucleotide strands join together to make a double-helix.

Two strands njoin together with hydrogen bonds.

Each base can only pair with a specific base (base pairing rule). Adenine & Thymine and Cytosine & Guanine. The two strands wind up to form the double helix.

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DNA contains your genetic information.

The DNA molecules are very long and are coiled very tightly so all the gentic information fits into the tiny space of the nucleus.

The paired structure of the DNA makes it much easier to copy itself. This is called self-replication. This is important for cell replication and passing genes on to the next generation.

The structure of DNA is the same in Eukaryotic and Prokaryotic cells, they store data in different ways.

Eukaryotic cells contain linear DNA molecules that exist as chromosomes.

The DNA is really long and wound up so it fits in the nucleus. The DNA molecule is wound around proteins called histones.

The histones also support the DNA.

Prokaryotes also have chromosomes but the DNA molecules are shorter and circular. They aren't wound around protiens .

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Genes are sections of DNA found on chromosomes.

Genes code for proteins.

Proteins are made of amino acids.

Different proteins have a different number and order of amino acids.

It's the order of the nucleotide bases in a gene that determine the order of the amino acids in a particular protein.

Each amino acid is coded for by a base triplet in a gene.

Different sequences of bases code for different amino acids.

genes in eukaryotic DNA contain sections that don't code for amino acids - these are called introns. Introns are removed during protein synthesis leaving only the exons.

Eukaryotic DNA also contain regions of multiple repeats outside of genes, these areas do not code.

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Enzymes increase the rate of most of our metabolic pathways. These chemical reactions determine how we grow and develop. They contribute to our development and ultimately what we look like (our phenotype).

All enzymes are proteins. The order of bases in the gene decided the order of amino acidsin the protein and what type of protein is made.

Our genes determine our nature, development and phenotype because the contain the information to produce our proteins and enzymes.

Genes can exist in more than one form called alleles.

The order of the bases in each allele is slightly different and therefore code for slightly different versions of the same characteristic.

Homologous pairs are the same size and have the same genes, although they may have different alleles. Alleles coding for the same characteristic will be found at the same locus (position) of each chromosome in a homologous pair.

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Mutations are changes in the base sequence of an organisms DNA.

Mutations can produce new alleles of genes.

A gene codes for a particular protein, so if the sequence of bases in a gene changes, a non-functional or different protein could be produced.

All enzymes are proteins. If there's a mutation in a gene that codes for an enzyme, then that enzyme may not fold up properly. This may produce an active site that's the wrong shape and so a non-functional enzyme.

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Meiosis and Genetic Variation

DNA from one generation is passed to the next by gametes. Gametes are the sperm and egg cells. They join together in fertilisation to form a zygote which divides and develops into a new organism.

Normal body cells have a diploid number of chromosomes - meaning each cell contains one maternal chromosome and one paternal chromosome.

Gametes have a haploid number of chromosomes - there is only one copy of each chromosome.

The haploid sperm and haploid egg fuse to form a cell with a normal diploid number of chromosomes.

Gametes are formed by meiosis. DNA unravels and replicates so there are two copies of each chromosome, called chromatids.

The DNA condenses to form double-armed chromosomes made from two sister chromatids.

The chromosomes arrange themselves into homologous pairs. these pairs are seperated , halving the number of chromosomes.

The pairs of sister chromatids that make up each chromosome are seperated.

Four haploid cells, gametes, thats are gentically different from each other are produced. 

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Meiosis and Genetic Variation

Crossing over of chromatids in meiosis means that each of the four daughter cells formed from meiosis contain chromatids with different alleles. 

The chromosomes of homologous pairs come together.

Chromasomes cross over. One chromosome from each pair ends up in each cell

Each cell has a different chromatid and therefore a different set of alleles. This, as a result, increases genetic variation.

Independant segregation of chromosomes. The four daughter cells formed from meiosis have completely different combinations of chromosomes. 

All your cells have a combination of chromosomes from your parents - half from mum and half from dad. 

When gametes are produced different combinations of those maternal and paternalchromosomes go into each cell. 

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Genetic Diversity

Genetic variation exists within a species. The DNA in a species varies very little though. All the members of the species will have the same genes but different alleles. 

The DNA of sifferent species varies a lot. Members of different species will have different genes. The more related a species is, the more DNA they share. 

Genetic variation in a species is caused by differences in alleles although new genes don't appear and old ones don't disappear.

Mutations in genes form new alleles.

Different alleles being introduced into a population when induviduals from another population migrate into them and reproduce. This is known as a gene flow. 

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Genetic Diversity

A genetic bottleneck is an event that causes  big reduction in the population. This reduces the number of different alleles in the gene pool which therefore reduces the genetic diversity. The survivors reproduce and a larger population is created from a few induviduals. 

The founder effect happens when just  few orgnisms from a population start a new colony. Only a small number of organisms have contributed to their alleles to the gene pool. There's more inbreeding in the new, smaller population which can lead to an increase in genetic disease. 

Selective breeding involves choosing the organisms which can reproduce. Humans select organisms with desirable characteristics that can reproduce together. Selectibe breeding can lead to a reduction in genetic diversity as only organisms with similar genes and traits can breed together.

For selective breeding:

Produces high yielding plants and animals. Produce organisms that are resistant to a disease. Increased tolerance to adverse conditions.

Against selective breeding:

Health problems. Reduces genetic diversity.

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