Genetics
Definitions
Species: Group of similar organisms that can reproduce to produce a fertile offspring
Speciation: Formation of a new species until the new species cannot breed with the original to produce a fertile offspring
Heredity: Passing on of characteristics/traits from one generation to the next
Gene Expression: Process in which the code in DNA is used to make protein
Gene: Short region of DNA whcih contains the code for a particular protein
Structure of Chromosome
- Made up of coding and non-coding DNA
- Non-coding DNA is a region of the chromosome which does not code for the production of a protein
- DNA wraps around proteins called histones, which then supercoil into a chromosome: makes DNA stable
NOTE: Chromosomes only exist during mitosis otherwise they spend most of their life as chromatin
DNA Structure
DeoxyriboNucleic Acid
- Structured into a double helix, resembles a twisted ladder
- Strands are made up of alternating Deoxyribose (sugar) and phosphate molecules
- Strands are joined together by nitrogenous bases
Adenine to Thymine
Guanine to Cytosine
- Bases always attached to the sugar molecule
Detailed Structure of DNA was discovered by Watson and Crick
- Nucleotide: sugar, phosphate + base
Attorney General is Pure
- Adenine and Guanine are purines
- Thymine and Cytosine are pyramidines
RNA
RiboseNucleic Acid
- Mostly in the cytosol whereas DNA only stay in the nucleus
- Single stranded
- Uracil instead of thymine
- RNA sugar = Ribose
- RNA code is complementary to DNA code; DNA strands open up at desired gene and RNA makes a complementary copy of the gene
DNA Replication
- Occurs at the end of interphase
1) DNA unwinds and enzyme unzips DNA by breaking hydrogen bonds
2) Nucleotides enter the nucleus from the cytosol and are placed into their complementary base pairs by DNA polymerase(anabolic enzyme)
3) DNA replication is over, DNA rejoins with histones and supercoils into chromosomes
DNA Profiling
To produce a unique pattern of bands from someones DNA so that it can be used for identity purposes
- Applications: Paternity tests, forensics, testing meet products for contamination
Process
1) Cells are broken down to extract DNA
2) DNA are cut into fragments using restriction enzymes
3) Fragments are separated on a bases of size
- Gel Electrophoresis; DNA is negatively charged so it moves to the positive end
- Smaller DNA fragments move faster, so a clear pattern forms
4) Pattern of fragment distribution is analysed
Genetic Screening
A test of someones genes to identify gene mutations
- Carried out when someone is suspected of having or being a carrier of a genetic disease
1) Add salt and washing up liquid into a solution
- Salt clumps DNA which helps isolation
- Washing up liquid breaks down membranes to release DNA
2) Add finely chopped onion
3) Place in 60 degree waterbath for 15mins
- Denatures enzymes which would break down DNA
4) 5mins in ice water
- Stops DNA from breaking due to heat
5) Blend for 3 secs
- Breaks down cell walls
- Any longer would break the DNA
6) Filter through coffee filter paper
- Lab filter paper pores are too small to let DNA through
7) Add protease solution
- Breaks down the proteins (histones) associated with DNA
8) Pour cold ethanol slowly down the side of the test tube so that it forms a layer on top of the filtrate
9) DNA forms at the junction between the filtrate and filtrate
Protein Synthesis
Making or protein using Amino Acids and the code from messenger RNA
- Occurs on ribosome
- Continually occurring in living cells
- DNA contains the code for protein synthesis
*Ribosomes are made up of 2 ribosomal RNA (rRNA) subunits
Codon: Sequence of 3 bases on mRNA, each one will tell the ribosome to carry out 1 of the following
- Start codon; Ribosome to begin assembling protein
- Amino Acid
- End codon; Ribosome to stop assembling amino acids and to release the chain
Process
Transcription
- Occurs in the nucleus
- Making of mRNA from a DNA template = transcribe DNA info to RNA info
1) DNA unwinds and enzyme unzips DNA by breaking hydrogen bonds
2) Nucleotides enter the nucleus from the cytosol and are placed into their complementary base pairs by RNA polymerase(anabolic enzyme)
3) New mRNA detaches from RNA Plymerase and diffuses into the cytoplasm to interact with a ribosome
Translation
- Making of protein using the code of mRNA
* Each 3 base sequence of mRNA represents either a start codon, a particular amino acid or a stop codon
1) Transfer RNA bring amino acids to the ribosome
- tRNA is a 3 base sequence which is responsible for carrying 1 amino acid
Anti-codon: Sequence of 3 bases on tRNA which is complementary to a codon on mRNA
2) Once the tRNA has added its amino acid to the sequence it goes out to the cytoplasm to find another amino acid of the same type
Protein Folding
Last stage of protein synthesis
- Long chain of amino acids produced fol over on itself to give its final structure and it ready to carry out its function
Genetic Inheritance
Gamete: Haploid sex cells
In humans; egg cell and sperm cell
In plants: egg cell and pollen grain
- Gametes fuse together to form a diploid zygote
Definitions
Fertilisation: Fusion of 2 haploid gametes to produce a diploid zygote
Allele: Different forms of the same gene
Homozygous: 2 alleles are the same
Heterozygous: 2 alleles are different
Genotype: Sum of the alleles found in an individual
Phenotype: Physical expression of the gene
Dominance: Where one allele masks the effect of another
Recessive: An allele which is only expressed when in the homozygous condition
Incomplete Dominance: Neither allele is fully dominant so both are expressed
Inheritance of Gender
XX=Female XY=Male
- Male determines sex of offspring
-However other species are different e.g. Birds, Butterflies, Moths
XX=Male XY=Female
Genetic Crosses
On the left a monohybrid cross is shown.
Genetic mating between organisms in which one gene is studied
Genetic cross is a table showing how characteristics are inherited
Dihybrid Cross is a genetic mating between 2 organisms where 2 separate genes are studied
Linkage; Where two genes are present on the same chromosome one of these traits cannot be present without the other also being present.
- When genes are present on the same chromosome there are fewer unique gametes
Sex Linkage
Where a gene is located on a sex chromosome
- Blood clotting and colour vision genes are present on the X chromosome but not the Y
- Need to demonstrate how sex linked characteristics are inherited
N is used to represent the normal gene
n is used to represent the mutated gene
Non-nuclear Inheritance
The passing on of features from one generation to the next without the use of a nucleus
- Mitochondria and chloroplasts are inherited independent of the nucleus as they have their own DNA
-e.g. only the nucleus of the sperm cell enters the egg cell so mitochondria are inherited maternally
Variation and Evolution
Variation: Differences among members of the same species
- Important for adapting and evolving to the environment
- Sexual Reproduction: From meiosis and fertilisation, as we have one set of chromosomes from each parent
- Mutations: Rare and random changes in genetic material, Mutagens increase the rate of mutations. Chromosome mutations e.g. Downs Syndrome. Gene mutations e.g. Sickle cell anaemia
Evolution: Genetic changes over a period of time to produce a new species in response to environmental stresses
Evidence
Paleontology; fossils which are closer to the surface of the ground and therefore younger are more complex than older fossils found deeper in the ground. This shows genetic changes over time as organisms began to adapt more to their environment
Genetic Engineering
Artificial manipulation of genetic material
Process
1) Isolation: Remove DNA from the cell, identify specific gene required
2) Cutting and Ligation: Use restriction enzyme to remove gene from DNA. Use ligase enzyme to join the gene to a vector, which makes the new vector a Recombinant DNA
3) Transformation: Putting the recombinant DNA into the bacterial cell
4) Selection and Cloning: Select cells which have the recombinant DNA and clone them
5) Expression: Stimulate the cell so it will produce the protein required
Application of Genetic Engineering
GM Plants: Insect/Herbicide resistant plants, or Vitimin A fortifying plants. Makes them more useful
GM Animal: In research mainly using mice, the genes are knocked out/tampered with and the changes are observed to improve our knowledge of how genes work
GM Microorganisms: E.Coli can be modified to produce human insulin and human growth hormone. Hormones are purified and are given to patients
Gregor Mendel
Mendel's Laws
- Law of segregation
- 2 alleles for each trait
- Alleles separate at gamete formation; one allele for each gamete
- At fertilisation 2 alleles join thus giving the new organism 2 alleles for each trait
- Law of Independent Assortment
- Alleles separate without the influence of other alleles at gamete formation
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