B5 Flashcards
What is a phenotype
Characteristics observed in an organism
What is variation
Differences in a species
What is a genotype
The combination of alleles present in an organism
What are the two main causes of variation
Genetic variation - variation caused by an organisms genetic materials (passed down from parents)
Environmental variation - variation caused by the environment
Give an example of genetic an environmental variation - one for humans and one for plants
Genetic
Blood group
Colour of flower
Environmental
Language spoken
Size of leaf
What causes the majority of variation
Most variation isnt genetic alone (in humans this is very rare)
Most variation in a species is caused by both environmental and genetic variation
What two groups can variation be divided into
Discontinuous - characteristics that fall into distinct groups (e.g Blood group)
Continuous - characteristics that fall between a maximum and a minimum (e.g height)
What is asexual reproduction
Reproduction which only requires one parent
It results in clones
What is sexual reproduction
Reproduction requiring two parents
Results in variation
What are the advantages and disadvantages of asexual reproduction?
Advantages:
-If the parent is well adapted to the environment its offspring will be to
- only one parent is needed, reproduction is faster so more offspring can ve produced quickly
Disavantage:
- advers changes to the abiotic or biotic environment can destroy the species as all organisms will be effected
What are the advantages and disadvantages of sexual reproduction
Advantages:
-Variation if offspring leads to adaptation in a species, these adaptations will help cope with changes in environmental pressures
Disadvantage:
- reproduction is slower as it requires two parents
What is meiosis
Cell division that produces gametes
4 genetically different haploid cell
What stages make up meiosis
Meiosis 1 :
Prophase 1
Metaphase 1
Anaphase 1
Telophase 1
Cytokinesis
Meiosis 2 :
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2
Cytokenisis
What happens in Meiosis 1, prophase 1
(Chromosones condense into their sister chromatid pairs)
Homologous chromosomes pair up to form a tetrad (total of four chromatids)
They exchange alleles in a process called crossing over
Nuclear membrane breaks down
Spindle fibers form
What are homologous chromosomes
A pair of chromosomes that share the same genes
What are alleles
Different variations of a gene due to different DNA bases
What happens in Meiosis 1, Metaphase 1
The pairs line up randomly on the cells equator
Line up in two rows (two sets in a pair)
What happens in Meiosis 1, Anaphase 1
The pairs of chromosomes are separated
(NOT THE SISTER CHROMATIDS)
and pulled to opposite sides of the cell
What happens in Meiosis 1, telophase 1
Spindle fibers break down
Chromosomes condense
Nuclei reforms
Cell pinches
What happens in Meiosis 1, cytokinesis
The cells divide into two genetically different diploid cells
What happens in Meiosis 2, Prophase 2
Both cells enter this phase at the same time and DNA has not been replicated
Spindle fibers form
Nucleus breaks down
Chromosomes condense
What happens in Meiosis 2, Metaphase 2
Chromosomes line up on the equator
What happens in Meiosis 2, anaphase 2
Sister chromatids are separated and the chromosomes are pulled to opposite polls
What happens in Meiosis 2, telophase 2
Spindle fibers break down
Nuclei reforms
Chromosomes decondense
What happens in Meiosis 2, cytokenisis
The cells split amd we are left with 4 genetically varied haploid daughter cells
What are sister chromatids
Identical copies of a chromosome formed by DNA replication
What are the two types of alleles and how they are represented
Dominant (Capital letter)
Recessive (lowercase letter)
Use the same letter for Dominant and Recessive alleles
What does heterozygous mean (alleles)
One recessive and one dominant allele
What does homozygous mean (alleles)
The alleles are the same type
Either homozygous dominant or homozygous recessive
What is a dominant allele
An allele (sequence of different DNA bases that codes for the same protein) where only one is required to be shown in the phenotype
What is a recessive allele
Two alleles ( sequence of different DNA bases that codes for the same protein) are needed to be expressed in the phenotype
How does genetic variation occur?
You share an allele with each parent the dominant one (if present will be observed)
During miosis alleles cross over causing you to have a different sequence of genes
Complete this genetic cross for the offspring
Male - Brown eyes
Female - blue eyes
The man is Homozygous recessive
The female is homozygous dominant
Male. Female
Pheno: brown. Blue
Genotype: bb. BB
Female
B. B Male. b. bB. bB
b. bB. bB
bB = 100% = blue eyes
The offspring will have blue eyes
What does it mean if someone is a carrier (genes)
They have a recessive gene that is not shown in the phenotype
How many genes in a Y chromosome
100
How many genes in an X chromosome
1000
What chromosomes do females have and which do males have
Female - XX
Male XY
What is a gene
A sequence of DNA bases that codes for specific proteins
What is mutation
A change in the DNA base sequence
What are the main causes of mutation
Exposure to radiation. (X - rays, Gamma rays, UV rays).
Carcinogens (cause cancer) (smoking or asbestos)
Errors in DNA replication
What are point mutations
One base that changes
What are the main ways DNA mutates
Substitution - a DNA base is swapped (Emg A for G)
Insertion - base are added
Deletion - bases are removed
Why can mutations be harmful
A change in the DNA base sequence can cause different amino acids to be used in protein synthesis
How many amino acids are there
20 amino acids
Why can one amino acid be coded by multiple DNA base arrangements (triplets)
There are 64 possible triplet combinations (4 bases triplet is free bases 4^3)
And only 20 amino acids
So most amnio acids are coded by multiple triplets
They are degenerate
What are silent mutations
When a mutation occurs but the amino acid coded is still the same
What is a genetic VARIENT
A different version of an allele caused by a change in DNA bases
What are examples of harmful mutations
Some can cause cancer
Cause the production of abnormal proteins
They can cause different shaped proteins to be made
How do mutations alter phenotype
Mutation can cause the production of irregular proteins
It can cause metabolic issues as these proteins (like an enzyme) no longer work effectively
This can cause conditions like phenylketonaria
What did gregor mendel discover
1886
Carried out an experiment on peas - observing characteristics from parent to offspring
1) characteristics were determined by hereditary units (genes)
2) Hereditary units are passed down from parents (1 unit from each)
3) Hereditary units are dominant or recessive
What did Friedrich Meischer discover
He discovered an acid in the nucleus of a cell.
This is DNA (acid called nuclein)
What did oswald avery discover
He transferred DNA from one bacteria to another (giving it an ability to pass disease)
The bacteria passed this trait to its offspring
This showed genes are made of DNA
1944
What did Erwin Chargaff discover
He found all DNA contains an equal amount of adenine, thymine, cytosine and guanine
1950
What did Maurice Wilkins and Rosalind Franklin do
They imaged DNA crystals using an x ray
1952
What did James Watson and Francis Crick do
They published their description of DNA, describing it as a double helix
1953
What was the Human genome project
A project that lasted over 20 years of identifying and sequencing around 24,000 genes - the complete set in the human body
(Ended 2003)
What does it mean if a codon is degenerate
It codes for multiple amino acids
What is natural selection
The survival and selection of advantageous alleles
This happens to something called survival of the fittest
What is evolution
A change in the phenotype of a species overtime
Natural selection drives evolution
Give an example of natural selection
Peppered Moths
During the industrial revolution many trees were covered in soot. The light coloured moths could no longer camouflage and were eaten
The darjer noths survived and were able to reproduce, passing on the dark coloured gene
What is a selection pressure
A change in the environment
What is a species
A group of organisms that are able to interbreed or reproduce to produce fertile offspring
How can the geography of areas create new species
As the same species live in different environments - so they have different selection pressures
As a result of these the allele frequency passed down increases but is different in both areas
Over many generations the organisms will adapt to best suit their environment
If the animals come back together and cant produce fertile offspring they are a different species
What is the fossil record
The fossil record shows where the fossils were found.
Older fossils are found deeper
How are organisms preserved
Animals encased in amber are preserved perfectly as there is no oxygen. So they cannot be decomposed.
Fossils show an animals bone structure
How are fossils formed?
FOSSILS ARE NOT THE ACTUAL BONES OF ANIMALS
After the skeleton is covered in sand, soil or clay it becomes mineralised over millions of years and the skeleton turns into rocks.
(Mineralisation - minerals enter the bones and remove oxygen so its bot decomposed)
The rocks shift in the Earth with the fossil trapped inside.
Eventually the fossils emerge as the rocks move and erosion takes place
What other examples are there for evolution - other than the fossil record
Rapid change in a species - as bacteria replicate rapidly scientists observe its evolution, like how a characteristic with antibiotic resistance is passed down
Extinction - Species that dont evolve or adapt will die out. 99% of all species are dead
Molecular comparison - DNA and proteins of different animals can be compared
Who created the theory of Evolution
Charles Darwin
What book was the theory of evolution first published in
On the Origins of species
How did Darwin come up with his theory
(Natural selection)
While on the Galapagos islands he noticed that on each island there was a different species of finch.
The finches were closely related but had different shaped beaks or claws.
Darwin realised that their beaks were shaped differently due to the food available on each island
He said that the birds with the wrong beaks would die and overtime the birds least suited would be able to reproduce, passing down these advantageous characteristics. Eventually all the finches would share the characteristic
What is classification
Sorting organisms into groups based on their observable characteristics
What is taxonomy
Naming and defining an organism based on sharef characteristics
What are the 8 taxonomic levels
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
What are the domains
Bacteria, archae (sometimes just prokaryotes)
Eukaryote
What are the 5 kingdoms
Prokaryotae
Protoctista
Plantae
Animalia
Fungi
What is Binomial Nomenclature
The process of naming
Using the genus and species
Homo sapiens
Homo is the genus and Sapiens is the species
What is artificial classification
Clarifying organisms by appearance (including bone structure and behaviour)
What is a problem with using artificial classification
It’s difficult to gain an accurate classification. Some species may have the same characteristics but ve conpletely different
What is natural classification
The classification of organisms based on evolutionary relations
This used similarities in DNA base sequences to see how closely related to a species another is
If the species are closely related they have shared a common ancestor more recently
What is the common ancestor all organisms evolved from
Luca - the Last universal common ancestor
Was believed to be a unicellular aquatic organism
What is phylogeny
The study of evolutionary links
What do branches in a phylogenetic tree show
Where two branches meet is where the last common ancestor was
What is a phylogenetic tree
A tree showing different organisms and the links between them.
This could be seen in any taxonomic level
Why is the fossil record incomplete
Fleshy bodied organisms are fully broken down
Tectonic movements break up fossils
