Chromosome: Structure in the nucleus of a cell, composed of DNA
DNA: A double helix structure made of nucleotides
Deoxyribose sugar: one of the three nucleotides of DNA
Gene: a section of DNA that carries the code for a particular characteristic
Nitrogenous base: part of a nucleotide, four types: ademine, thymine, guanine and cytocine
Nucleotide: the building blocks of DNA, composed of a Deoxyribose sugar, Nitrogenous base and phosphate
Phosphate: one of the components of a nucleotide
Trait: a characteristic inherited by an organism
Autosome: all chromosomes other than sex chromosomes
Centromere: point where the two chromatids join together
Chromatid: one of the strands of a chromosome following replication
Diploid Number: number of chromosomes in the cell of an organism, represented as \(2N\). \(2N=46\) in humans
Gamete: sperm or egg cell
Haploid Number: number of chromosomes in the gametes of an organism, represented as \(N\). \(N=23\) in humans
Homologous Chromosomes: chromosomes with genes for particular characteristics at the same location
Meiosis: A type of cell division where gametes are produced
Mitosis: A type of cell division that produces two daughter cells which are identical to the parent cell
Allele: Different forms of the same gene located at the same point of homologous chromosomes
Dominant Allele: allele for a trait that is observed in the outward appearance when the trait is heterozygous
Genotype: genetic information carried by an individual
Heterozygous: having two different alleles on homologous chromosomes
Homozygous: having two identical alleles on homologous chromosomes
Mutation: the alteration of the nucleotide sequence in the genome of an organism
Phenotype: observable characteristic dictated by the genotype
Recessive Allele: allele for a trait that is hidden in the outward appearance when the trait is heterozygous
Genome: genetic information carried by a haploid set of chromosomes
Single Nucleotide Polymorphism (SNP): difference of only one base pair between two organisms
A fossil is evidence of past life.
Fossils can be part of an organism, such as its bones, teeth, feathers, scales, branches or leaves.
Fossils can also be traces, such as footprints, burrows and other evidence that an organism existed in an area.
Fossils provide evidence that life has changed over time. Some life forms that used to exist on Earth no longer exist.
Studying the fossil record also provides evidence that life forms have become more complex over time.
The study of fossils is called Palaeontology.
Major Milestones in the History of Life
Merger between mitochondria and anaerobic organisms
Formation of the KT Boundary (Extinction of the dinosaurs)
Motion of tectonic plates
Land animals developing eggs
Animals moving onto Land
Formation of life on Earth
Planet Earth forms
Core and Crust forms
First Life (Cyanobacteria or Archea)
Oxygen accumulates in the atmosphere
First Vertebrates (Fish)
First land plants
Dinosaurs go Extinct
Theory of evolution
All life on Earth shares a common ancestor.
All the different species on Earth underwent mutations in the past to better suit their environment.
Evolution (Not Theory of Evolution) means “descent with modification”
Darwin’s Theory of Evolution states that all life shares a common ancestor, and that the differences between life forms is explained by Survival of the Fittest
Natural selection is the concept of survival of the fittest.
There are 4 conditions for natural selections: variation between individuals, heredity, reproduction and variation of fitness
Selective pressures are phenomena that impact on an organism’s fitness
Stages of Natural Selection
A species becomes separated by an environmental factor e.g. formation of a river
A mutation occurs in one of the isolated groups
If the mutation improves fitness, the mutation is passed on to the next generation
After several generations, the isolated group has a majority of individuals carrying the mutation, and these individuals are considered to have evolved.
Law of Superposition
Because upper layers are younger than the ones beneath them, the law of superposition states that a fossil’s age can be determined by the age of fossils around them. This only applies to UNDISTURBED rock.
Relative age: age of the fossil based on the Law of Superposition, e.g. Fossil A is older than Fossil B but younger than fossil C.
Absolute age: the actual age of the fossil, e.g. Fossil A is 6000 years old.
Analysing the Fossil record
Faulting can cause projections of rock through other layers.
Folding results in layers of rock being moved away from each other.
Why are fossils important?
Fossils allow us to determine early biodiversity
Fossils can be compared to modern day organisms
Fossils improve our understanding of previous conditions on Earth
Fossils support our estimates for the age of the Earth
Fossils provide evidence for Evolution
Fossils provide evidence of continental drift
Mitosis is the process by which one parent cell splits into two identical daughter cells.
Mitosis is the most common method of reproduction for single-celled organisms.
There are 5 main stages of mitosis:
Prophase: number of chromosomes in the cell double up
Metaphase: chromosomes wind up and align along the equator of the cells
Anaphase: Chromatids (Not Chromosomes, this is explained later) are drawn towards the ends of the cell by spindle fibers
Telophase: Cell nuclei forms, chromosomes form and unwind
Cytokinesis: Cell splits into two, completing the process of mitosis
In the human body, all cells other than sex cells (sperm and ova) are generated through mitosis.
DNA stands for DeoxyriboNucleic Acid
DNA takes the shape of a Double Helix
The DNA molecule is made up of repeating components known as NUCLEOTIDES
Each nucleotide has three components:
One of four nitrogenous bases:
A - Ademine
T - Thymine
G - Guanine
C - Cytocine
Adenine (A) can only pair with Thymine (T), while Guanine (G) can only pair with Cytocine (C)
DNA contains all the instructions to make POLYPEPTIDES (Proteins)
The nitrogenous bases bond with each other via hydrogen bonds
DNA is read in groups of three, known as CODONS or TRIPLETS
A MUTATION is the alteration of the nucleotide sequence in the genome of an organism
A MUTAGEN is a physical or chemical agent that changes the genetic material (Usually DNA) of an organism, increasing the frequency of
Most mutations are harmless (neutral)
Mutations that IMPROVE survivability are known as BENEFICIAL MUTATIONS
Mutations that DECREASE survivability are known as DETRIMENTAL MUTATIONS
Chromosomes contain genes, which dictate traits
An Allele is any of the possible forms of a gene, e.g. Tall/short
Alleles tend to be either Dominant or Recessive. Dominant alleles are represented by a capital letter, while recessive alleles are represented by the same letter, but lower case.
Every chromosome pairs up with another chromosome. The alleles in each pair of chromosomes dictates the properties of the organism. One chromosome is inherited from the organism’s male parent, while the other is inherited from the female parent.
When an organism has a pair of Homozygous Alleles, both chromosomes for that trait have the same allele (Both Dominant or both recessive)
When an organism has Heterozygous Alleles, one chromosome has the Dominant allele, while the other has the recessive allele. An organism with Heterozygous Alleles will display the characteristics of the Dominant Allele.
A Punnett square is a graphical representation of the chances of an organism having a specific trait.
In the image above, yellow coloring is the dominant allele, while green coloring is the recessive allele.
The yellow parent in the image is Heterozygous for the color trait, while the green parent is Homozygous Recessive for the color trait.
The chart shows that there is a 50% chance of a heterozygous plant, and a 50% chance of a homozygous recessive plant.
Punnett squares can be used for many visible traits (handedness, curly/straight hair, ability to roll tongue, detached earlobes), while other traits, such as some genetic diseases, require more in-depth methods.
A pedigree chart is a diagram that shows the occurence and appearance of phenotypes of a particular gene from one generation to the next.
Pedigree charts can be used to find the presence or absence of traits in a bloodline (e.g. CCR-5:Δ32 HIV Immunity)