B5

Properties of continous variation

Properties of continous variation

Can take any value within a range eg. height
Caused by genetic or environmental factors
Controlled by multiple genes (or none)
Represented by Line graph or histogram

Properties of discontinous variation

Only results in discreet, specific values eg. blood type
Caused by genetics only
Controlled by one or a few genes
Represented by a barchart

How are features passed on?

Phenotype influenced by interaction between genome and environment
Genome is an organisms entire genetic material
During reproduction, copy of some (or all) of organism’s genome passed to its offspring
Either sexually or asexually

Properties of Asexual reproduction

One parent
No mixing of genetic material due to no gametes
No variation eg. bacteria

Properties of sexual reproduction

Two parents
Gametes involved so mixing of genetic material
Offspring are genetically different to parents
Variation eg. crickets, humans

Advantages and disadvantages of Asexual reproduction

+ If parent well-adapted to environment, genetically identical offspring will be too
+ Only 1 parent is needed so it is faster and more offspring can be produced

- Population more vulnerable to environmental change due to lack of adaptation

Advantages and disadvantages of sexual reproduction

+ Variation in species makes them less vulnerable to environmental change as some individuals may have adaptation

- Requires two parents so reproduction is slower and less offspring

Difference between Haploid and Diploid

Haploid- One set of chromosomes
Diploid- Two sets of chromosomes
Eg. Egg + Sperm = Zygote (diploid)

Outline the process of Meiosis

Prophase 1- Chromosomes pair up
Metaphase 1- Pairs of chromosomes line up across middle of cell
Anaphase 1- Pairs of chromosomes separate. Half of chromosomes go to each end of the cell
Telophase 1- Cell divides into two cells
Telophase 2- Two cells divide again to form 4 cells

Define Allele and what are the two types of Alleles

Alleles- Different versions of the same gene

Dominant (Always expressed) and Recessive (only expressed if two copies present eg. tt)

Difference between Genotype and Phenotype

Genotype is the combination of alleles present whilst phenotype is the characteristic observed

Difference between Homozygous and Heterozygous

Homozygous is an organism with two copies of the same allele whilst heterozygous has different alleles of a gene

Why are test crosses used?

Determine an unknown genotype
Genetic counsellors can predict the likelihood of a genetic disease

What causes mutations?

Occur spontaneously eg. error during replication
Chances of mutations increased by mutagenic agents (eg. tobacco, Ethanol, Denzene, UV, X-rays, Gamma rays)

What effects do mutations have?

All genetic variations arise from mutations
Creates different versions of alleles
Position in the DNA squence determines the effect it will have
Coding DNA- May cause change in the protein made
Non-coding DNA- May cause change into transcription of a gene or change in cell cycle

How does a mutation affect the phenotype?

If mutation within a gene, wrong amino acid could be assembled, causing wrong protein to be made or protein may fold incorrectly and be the wrong shape.

Why are mutations in non-coding DNA dangerous?

Gene may not be transcribed so no protein produced
Mutations in this region can also cause cancer
Only affects organisms phenotype if present in all cells
Needs to be present in gamete from which organism was formed
When passed on, leads to variation in species

What did Gregor Mendel do and find

Experimented on peas and observed characteristics passed on from parents to offspring
Characteristics decided by hereditary units (genes)
Passed on from both parents, one unit from each
Hereditary units can be dominant or recessive

Steps of Natural selection

Presence of natural variation + Overproduction of offspring + competition for limited resources + Change in environment/Beneficial mutation
Best adapted survive
Inheritance of successful adaptations
Formation of new species (Speciation)

Outline the process of fossilisation

Organism dies and quickly buried by soft materials like mud
Soft parts of organism decay
More layers of sediment form above
Water seeps in and dissolves bones
Minerals in water form rock in space left behind

What is the fossil record

Fossils found within different rock layers are different
Most recent fossils found in uppermost layers
Fossil layers form sequence showing how organisms gradually evolve
Supports idea that simple life forms gradually evolved into more complex ones

Why are there gaps in the fossil record?

Many organisms soft-bodied and decay quickly so no fossil formed
Many fossils destroyed
Many fossils not yet discovered

Other evidence for Evolution?

Rapid change in a species- eg. Peppered moths
Extinction- Species that don’t adapt die out, >99% of species that have ever lived now extinct
Molecular composition- Look at order of amino acids in protein or bases in DNA. More similar = closer related

What did Darwin observe and where

Galapagos Islands- noticed different islands lead to variation (Finches have different sized beaks and claws and Tortoises have different shaped shells)

What conclusions did Darwin arrive at

Different designs link to food available on each island.
More suited species would survive longer
Leads to more offspring and eventually every member of species would have that characteristic

What did Wallace observe and where

Borneo in Malay Archipelago- Imperfections in vestigial structures (Whale flipper bones)
Animals without pouches live on the West (Asia)
Animals with pouches live on the East (Australia)

What conclusions did Wallace arrive at

Species came from pre-existing species which lived nearby
Every species a modified version of older species
Theory of natural selection

How did Darwin and Wallace make their ideas public

Proposed theory of evolution in join presentation of 2 scientific papers to Linnean Society of London
Darwin published “On the origin of species”
Wallace published “Darwinism”

Why were their ideas revolutionary?

Most common belief was theory of Special Creation
People eventually accepted his theory and now it is widely accepted and increasing evidence found often

What is classification and why do scientists classify

Classification- Process of sorting living organisms into groups (Organisms in same groups share similar features)

Order to identify species, predict characteristics, find or show evolutionary links

What are the different classification systems

Artificial- based on observable characteristics, Don’t take evolutionary relationships into account, makes accurate classification difficult

Natural- Takes into account evolutionary links, DNA sequencing used to link relationship between organisms, Links used to form groups based on common ancestor

What is phylogeny

Study of evolutionary links
Established by studying similarity and differences in DNA between species
More similar DNA, more closely related they are

What are the different Taxonomic levels

Kingdom- Animalia
Phylum- Chordata
Class- Mammalia
Order
Family- Equidae
Genus- Equus
Species- Burchelli (Zebra)

Who was Carl Linnaeus and what did he invent

Scientist who developed the Binomial nomenclature- two part Latin name: Genus and species

Shorter, standardised and universally recognisable way of naming organisms
Laid foundation for modern biology and evolutionary studies