Genetic Information, Variation and Relationships Between Organisms

Nucleus contains long, linear DNA molecules with associated proteins as chromosomes, DNA is wound around histones (proteins) for strength and so it can fit, coiled very tightly to make compact chromosomes

Have their own DNA, circular and shorter and not associated with proteins

Carry DNA as chromosomes, shorter, circular, not associated with proteins, condenses to fit in cell by supercoiling

A base sequence of DNA that codes for: The amino acid sequence of a polypeptide A functional RNA

3

20

64

Universal - same bases for all species Non-overlapping - read in triplets Degenerate - different triplet codes for the same amino acid

RNA molecules other than mRNA (e.g. tRNA and rRNA) which perform special tasks during protein synthesis

Introns - removed by splicing Exons - do code for amino acids

Different versions of the same gene

Pairs of matching chromosomes, same size and same genes, but could have different alleles

The fixed position of a gene on each chromosome in a homologous pair

Complete set of genes in a cell

Full range of proteins a cell is able to produce

Single polynucleotide strand, contains uracil instead of thymine

Made during transcription, carries genetic code from DNA to ribosomes, where it is used to make a protein during translation, single polynucleotide strand, groups of 3 adjacent bases = codons

Involved in translation, carries amino acids used to make proteins to ribosomes, single polynucleotide folded, H-bonds hold it in shape, have specific anticodon and amino acid binding site

Nucleus

Ribosomes in cytoplasm, directly produces mRNA from DNA (no splicing occurs)

1. RNA polymerase attaches to DNA at beginning of gene, breaks H-bonds, separating strands

2. RNA polymerase lines up free nucleotides, complementary mRNA formed, T is replaced with U, RNA polymerase joins together free bases, forming an mRNA strand

3. RNA polymerase moves down DNA, mRNA assembles, H-bonds reform

4. RNA polymerase reaches stop signal and detaches

5. In eukaryotes, splicing occurs, introns are removed

Ribosomes in cytoplasm

1. mRNA attaches to ribosome and tRNA molecules carry amino acids to it, ATP provides energy for bond between amino acid and tRNA to form

2. tRNA (carrying amino acid) with complementary anticodon attaches to mRNA, a second tRNA does the same

3. The 2 amino acids join by a peptide bond

4. Process continues as ribosome moves along mRNA, produces polypeptide chain, until it reaches a stop signal

5. Polypeptide chain is complete

Diploid (2n)

Haploid (n)

Diploid = 46 Haploid = 23

2 gametes joining together at fertilisation to form a zygote, which divides and develops into a new organism

Haploid egg fuses with haploid sperm, to make a cell with normal diploid number of chromosomes (1/2 from father, 1/2 from mother)

1. Before meiosis starts, DNA unravels and replicates, so there are 2 copies chromosome = sister chromatids

2. DNA condenses to form double-armed chromosomes, each made from 2 sister chromatids joined by centromeres

3. First division - chromosomes arrange themselves in homologous pairs then homologous pairs separated, halving the chromosome number

4. Second division - Pair of sister chromatids are separated (centromere divides)

5. 4 haploid cells that are genetically different from each other are produced

In reproductive organs of multicellular, eukaryotic organisms

Change in DNA base sequence of chromosomes

One or more bases added, changes whole code

One or more bases deleted, changes whole code

One base is substituted for another, only 1 triplet will be changed, sometimes changes degenerate code

Increase probability of a mutation occurring

UV radiation, ionising radiation, some chemicals, some viruses

When meiosis goes wrong, cells produced contain variations in numbers of whole or parts of chromosomes, leads to inherited conditions

Homologous pairs fail to separate

Zygote haas 3 copies of a chromosome

1. During meiosis 1, homologous chromosomes pair up

2. Chromatids twist and entangle (form chiasma) and swap over same length of genes

3. New combinations of alleles formed

When homologous pairs are separated in meiosis 1, it is completely random which chromosome from each pair ends up in which daughter cell, so the 4 daughter cells have different combinations of alleles, leads to genetic variation

Difference between same species organisms

Total number of different alleles of genes in a population

Total number of organisms in a habitat

Frequency of specific alleles in a population

If a population has low genetic diversity, it might not be able to adapt to a change in the environment and the whole population could be wiped out by a single event

Mutations in DNA forming new alleles, gene flow (different alleles being introduced into a population when individuals from another population migrate into it and reproduce)

An event that causes a big reduction in a population, reduces number of different alleles in a gene pool which reduces genetic diversity, the survivors reproduce and a larger population is created from a few individuals

When a few organisms from a population start a new colony and there are only a small number of different alleles in the initial gene pool, genetic diversity is reduced

It increases proportions of advantageous alleles within a population

1. Presence of advantageous alleles

2. Survival of the fittest

3. More likely to survive, reproduce and pass on genes to offspring

4. Frequency of allele increases

5. Leads to evolution

The gradual change in species over time, leads to diversity of living organisms on earth

Where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce, this could be in response to an environmental change

Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce, occurs when environment isn't changing and it reduces the range of possible characteristics

The study of evolutionary history of groups of organisms

Closely related species diverged away from each other more recently

The science of classification, naming organisms and putting them into groups

The production of a new species

Organises species on how closely they are related

Domain Kingdom Phylum Class Order Family Genus Species

More groups, but fewer organisms in each group, organisms in each group become more closely related

Discoveries of new species and new evidence about known organisms (e.g. DNA sequencing data)

Genus and species, universal

First - genus, second - species, in italics or underlined, 1st letter - uppercase, 1st letter of second word - lowercase

Behaviour carried out by organisms to attract a mate of the same species

Releasing a chemical using sound, visual displays

Dancing, building

Male or female, may sometimes involve both sexes

Courtship behaviour is species specific, the more closely related a species is, the more similar their courtship behaviour

Number of different ecosystems and communities of organisms, number of different species and degree of genetic diversity within those species

Place where an organism lives

All the different species that live together in a habitat

A measure of the number of different species in a community

Relationship between number of species in a community and number of individuals in a species

Woodland clearance, hedgerow removal, pesticides, herbicides, monoculture

1. Frequency of measurable or observable characteristics

2. Base sequence of DNA / immunology

3. Base sequence of mRNA

4. Amino acid sequence of proteins encoded by DNA and mRNA