Genetics
Lesson 1
DNA
-made up of nucleotides.
-a chemical that carries genetic code→discovered in 1869 by Friedrich Miescher.
-Info is transferred by DNA on chromosomes(made of DNA) when the cell reproduces.
-The Info in DNA codes for polypeptide→proteins→traits/characteristics.
-Traits=characteristics→hair colour, eye colour.
Structure of DNA
-Genes: a piece of DNA that codes for polypeptides of a certain trait.
-in 1953, Watson and Crick used info from Linus to construct their model of the DNA strand and found out DNA to be a double helical shape, similar to a twisted ladder.
-DNA is made from complementary nitrogenous base pairs(A→T, C→G)
-The base pairs are held together by weak chemical hydrogen bonds.
-the backbones/sides of DNA is made of alternating sugar and phosphate molecules
-The base pairs Adenine and Thymine is connected by 2 hydrogen bonds
-The base pairs Guanine and Cytosine is connected by 3 hydrogen bonds
-The four bases compose the basic structure of DNA of all living org., the differ of DNA between differ organisms is the # & arrangement of bases.
Structure of an NUCLEOTIDE
-phosphate group, pentose sugar, and nitrogenous base
Lesson 2
Chromosomes
-Strands of DNA packed together when the cell is about to divide
-subdivided into genes(pieces of DNA that codes for a certain trait)
-Chromosomes are located in the nucleus
Karyotype
-picture of chromosomes in matching pairs in order of largest to smallest
DNA in our cells
-Except red blood cells(RBS), all cells have a nucleus that contain genetic material.
-Cells in human body cells contains 46 chromosomes with the exception of sperm and egg cells(gametes→23 chromosomes, one of each pair)
Messages
-bases making DNA of chromosomes carry messages/genes that determine characteristics of an organism.
Amino Acids
-building blocks for enzymes and hormones which control characteristics of living organisms.
Gene expression
-DNA unzips and one of the strands is used as a template to make mRNA using free nucleotides.
-tRNA are the anticodons for the codons on the mRNA, they carry amino acids that forms a polypeptide.
-the polypeptide was made of the amino acids, connected by peptide bonds.
DNA replication
- double helix(DNA) unwinds(relax), which is driven by the enzyme topoisomerase
- DNA is also opened by helicase.
- Free nucleotides attach to each unzipped strand, pairing with their complement bases.
- Primase build an RNA primer attaches to each strand to initiate the process (initiation)
- DNA polymerase III adds nucleotides (elongation)
- The DNA ligase link together the newly formed strands.
- the errors are identified and repaired by DNA polymerase I.
Lesson 3
DNA, Polypeptides and Proteins
-a gene on DNA is the coded instructions for the synthesis of a polypeptide.
-polypeptide→subunit of a protein
-proteins have many functions:
- Transport channels – for nutrients and wastes to enter or leave cells
- Structural proteins – microtubules, actin and myosin in muscles, cell surface markers
- Enzymes – catalysts in cellular respiration or photosynthesis, or in digestion
- Carrier proteins – hemoglobin in RBCs
- Chemical messengers – peptide hormones such as insulin, prolactin and oxytocin
Protein synthesis
- Transcription
-DNA is too large to leave the nucleus, yet the ribosome(make proteins) are outside the nucleus in the cytoplasm.
-a copy of the gene must be made in order to start the process→mRNA or the messenger RNA is the copy.
RNA
-uses uracil instead of thymine
-single stranded
-much shorter and smaller than DNA
→3 types of RNA:
- mRNA(messenger)
- tRNA(transfer)
- rRNA(ribosomal)
- tRNA
-the site of the tRNA that binds to the mRNA was called the anticodon.
Translation
-the spliced, mature mRNA moves out of the nucleus into the cytoplasm for ribosomes
-the ribosome read the mRNA base sequence in a group of three, which is called the triplet codon.
-tRNA attach to the triplet codons by their complementary base pairing of their anticodon site, carrying amino acids that corresponds.
-the amino acids are connected to each other by a peptide bond.
DNA Replication
-before cell divides, all of its chromosomes are duplicated;
-DNA is copied through the process called DNA replication
-which will result 2 copies called the sister chromatids.
-the sister chromatids contain same genes and are connected at a region called the centromere.
-Each pair of homologous chromosomes in a human somatic cell is counted as two chromosomes(1 chromosome from each parent), since they both have a centromere.
-Watson and Crick made a hypothesis about the replication of DNA after the publish of their model.
- hydrogen bonds break as the 2 strands separate
- each old strand serves as a template for a new complementary strand(the 2 DNA product will be semi-conservative)
- free nucleotides attach and the daughter molecultes are formed
-once the hydrogen bonds break,replication bubbles begin to form ar points along the DNA strand
-DNA replication proceeds in both directions and sides of the DNA→the lagging strand and the leading strand.
When the cell divides
-when the cell divides, the sister chromatids are separated from each other.
-each of the chromatids goes into each of the 2 daughter cells.
-each chromatids are identical to the original set.
Lesson 4
-Mutation: the changing of a gene that results in variant form that’s permanent.
- it can be caused by environmental agent
- can arise spontaneously
- results in different sequences of DNA
-Down syndrome: trisomy 21
-Allele: different versions of a trait. e.g. the trait is hair, the alleles are blonnd, dark, brown.
Mutagen
-any environment agent that causes a mutation; chemical, biological, and physical.
- Chemical mutagen:
-these agents usually have similar structure as DNA.
-Prolonged exposure will result their incorporation into DNA by mistake (during DNA replication) which disrupts normal DNA sequence
- ex: tar in tobacco, aesbestos
- Biological mutagen:
-bacteria and virus can insert their DNA into host DNA
- fungi, viruses(insert their DNA into body cells) and bacterias
- Physical mutagen:
-high-energy electromagnetic radiation can penetrate cells & absorb by chemical bonds in DNA.
-the energy absorbed breaks the covalent bonds on the DNA causing a mutation.
- ultraviolet light
- X-rays
- gamma rays
Types of Mutations
- Point Mutation:
-occurs with a single bas pair in DNA:
- Insertion(frameshift): a new nucleotide is added in which causes a frameshift.
- Deletion(frameshift): a nucleotide is deleted and caused a frameshift
- Substitution: less affective than the other 2, change of nucleotide, a substitute.
- The Effects of Point Mutation:
- Nonsense Mutation: (stop) triplet codon changed to a stop codon; resultant polypeptide is cut short; major change to phenotype
- Missense Mutation: (bit of change)triplet codon changed to code for a different amino acid; resultant polypeptide is less functional; minor change to phenotype
- Silent mutation: (no change physically)triplet codon changed but codes for same amino acid; resultant polypeptide is unchanged; no change to phenotype
- Chromosomal Mutation:
-occurs with a section of genes on a chromosome
-chromosome deletion where a section breaks off and disappears
Deletion: a section of chromosome is removed
Translocation: a section of a chromosome is added to another chromosome that’s not its homologous partner
Inversion: a section of a chromosome is reversed
Duplication: a section of a chromosome is added from its homologous partner
The Effects:
likely to cause…
-a change to coding regions of DNA, as well as non-coding regions.
-amino acid sequence change in the resultant polypeptide; major phenotype change
Somatic Mutation:
-occurs in a cell that is not a sex cell.
- does not pass to offspring
- can be passed on in mitotic cell division.
- affects a localised part of the organism.
- Germline Mutation:
-occurs in cells that will become sex cells
- will be passed to offspring.
- this mutation will be in ALL cells of the offspring.
- can potentially affect the whole of the offspring.
- this mutation is a new allele in the population.
Lesson 6
Lamark
-changes during an organisms lifetime are passed onto offspring (is rejected by Darwin)
- e.g.: long necked giraffe v.s. short necked giraffes.
Greger Mendel
-Austrian monk
-experimented with pea plants and found out there are 2 different trait types:
- Dominant Trait: more commonly expressed.
- Recessive Trait: hidden, less commonly.
-Trait: pea color, gene for a characteristics
-Allele: Different alternatives of a gene. e.g., yellow or green
Punnett Squares
- Homozygous Dominant: 2 dominant trait e.g. BB
- Homozygous Recessive: 2 recessive e.g. bb
- Heterozygous: 1 dominant 1 recessive e.g.Bb
- Genotype: letters that codes for allele
- Phenotype: what is physically expressed
-the punnett square is a useful way to predict the genotype and phenotype of the offspring
Sex Determination
-humanbody cells→23 pairs of chromosomes in the nucleus
- but actually each pair of chromome is counted as 2 chromosomes(one from each parent)→human has 46 chromosomes in somatic cells.
-autosomes→22 pairs of chromosomes controls characteristics
-the 23rd pair carries genes that determine sex.
- Males: XY
- Females: XX
Genetic diagram
-like the punnett square, it shows how alleles are combined in zygotes.
-this diagram shows how biologicalli sex/gender is inherited.
Lesson 8
Mendel’s 3 Laws of Inheritance
→Law of Independent Assortment:
- genes for differ traits segregate independently of each other, meaning that separate traits are separately inherited.
- This is because during meiosis the chromosomes line up randomly before cell divides for gamete formation.
- as a result, offspring can have combinations of traits that are unique
- gives chance for new trait combinations that can show up to be advantageous
→Law of Dominance:
- suggests there are dominant and recessive traits.
- Dominant traits will always be expressed in the phenotype when the genotype in an organism is heterozygous for the trait.
- Complete Dominance: dominant allele masks/hides the recessive allele.
→Law of Segregation:
- suggests that everyone has 2 versions(alleles) for each trait; 1 from each parent.
- and these alleles segregate randomly during meiosis.
Lesson 9
Mitosis
-single cell division producing 2 identical daughter cells
-produce cells with same diploid # of chromosomes.
- used for growth and development, repair of damaged, replacement of dead cells.
Meiosis
-when eggs and sperm are created, a totally differ combination of genes is contained by each gamete
-Meiosis: the process of creating genetically different gametes→involves randomly shuffling genes in independent assortment and segregation
-starts with diploid cell, ends with haploid cells.
-The cell replicates its chromosomes once and splits twice.
-producing 4 daughter cells with half the chromosome number(1n=haploid) as the original cell.
-Somatic cells→chromosome number of 2n, DIPLOID (46)
-Gamete cells→chromosomes number of 1n, HAPLOID (23)
- Steps of Meiosis
- Interphase: chromosomes x2
- Meiosis I:
- Prophase I: chromatin shortens and thickens, chromosomes forms tetrads.
- Metaphase I: the homologous tetrads exchanges genes→results in genetic diversity.
- Anaphase I: tetrads are broken by spindles, moves to the opposite poles.
- Telophase I: cell separates, forming 2 new 2n cells.
- Meiosis II:
- Prophase II: nucleous membrane breaks down, chromosomes moves into the center.
- Metaphase II: Chromosomes line up in the center.
- Anaphase II: sister chromatids separated and moves to the opposite ends of the cell.
- Telophase II: cell split, resulting 4 new cells that are all haploid(1n)
Mitosis vs. Meiosis
- Mitosis goes from one cell that’s 2n →two cells that are 2n.
- Meiosis goes from one cell that’s 2n →4 cells that are 1n.
- Mitosis →Daughter cells genetically identical.
- Meiosis →Daughter cells genetically differentiated.
- Mitosis →x1 division.
- Meiosis →x2 divisions.
- Mitosis →The chromosomes don’t form tetrads/exchange genes.
- Meiosis →the homologous chromosomes lined in pairs & segregates, formes tetrads and exchange genes/crossing over (increases genetic variations).
- Mitosis →the replication and creation of normal somatic/body cells.
- Meiosis →the creation of sex/gamete cells.
Asexual Reproduction
- number of chromosomes stays the same
- used when organisms grow
- involves only one parent
- offspring is the clone of the parent
- less time required
Sexual Reproduction
- requires 2 parents
- more time consuming than asexual reproduction
- it results more genetic diversity in offspring
Chromosomes
- humans have 46 chromosomes
- That is 23 pairs of chromosomes
Lesson 10
Human Genome Project
-scientists maping human genome(human DNA sequence)
-completed in 2004
→but affecting the gene pool isn’t new, farmers had been affecting the gene pool for a long time; crossbreeding & selective breeding.
-selective breeding: reduces the gene pool of the population, which also results inbreeding which prone to disease or inherited defects(amplifies the recessive traits that are highly similar).
-less variation in a population.
Genetic Engineering
-modifies the actual genome of an organism to introduce desirable characteristics.
-can be done by transferring a desirable gene from a donor organism into the genome of a recipient organism.
- Insulin produced by Bacteria
the bacteria cell is used because…
- Bacterial DNA is easily manipulated
- Bacteria can reproduce rapidly
-the bacteria then have the ability to make whatever the desirbale gene codes for.
-before genetic engineering, insulin was obtained from pigs and cattle.
-due to an increase in the number of diabetes, more insulin was required than ever before.
-taking human insulin making gene and transfer it tp bacteria
- Advantages of genetically engineered insulin
- not limited by the slaughter of animals
- large quantities can be made quickly
- no risk of transferring infections
- more effective since animal insulin is different to human insulin
- no ethical issue concerning the use of animals
*GMF: genetically modified food
- GMO: genetically modified organism
pros:
-longer shelf life
-higher nutritional value
-higher yield
-disease resistant(Bt cotton)
-drought and flood tolerant crops
cons:
-decrease gene pool
-general fear of longterm consequences
-unatural
-not 100% sure
-might go against religion
- Recombinant DNA: DNA that had been genetically modified.
- vaccines are made of mRNA.
- it teaches your cells how to make copies of the spike protein and if you are exposed to the virus later, your body will recognise it and know how to fight it off.
- after mRNA delievers the instructions, your cell break it off and get rid of it.
- The vaccine usually contains: mRNA sequence, sugar, salt, lipids.
Lesson 11
GM crops
- pros and cons of GMOs
pros:
-longer shelf life
-higher nutritional value
-higher yield
-disease resistant(Bt cotton)
-drought and flood tolerant crops
-environment friendly(not require pesticide)
cons:
-decrease gene pool
-general fear of longterm consequences
-unatural
-not 100% sure
-might go against religion
- Cons of spraying pesticides
- time consuming
- expensive
- harmful for the farmers
- also kill useful insects like bees
- pesticide also damages soil and water in the environment
-Bacillus Thuringiensis→gene taken from it and put into crops.
-the gene from the bacteria makes the plant produce an insecticide that kills the pests which eat its leaves.
-crops are also modified to resist weed killers inorder to have higher yields.
- Bt Cotton
-developed using common soil bacterium Bacillus thuringiensis(Bt)
-Bt cotton produces proteins that are toxic to the specific helicoverpa specie, which is a pest that eats the plant.
-the inbuilt resistance has led to less use of pesticides, higher yields of cotton and higher profits.
- Soybean
- Maize
- Canola
- Golden rice
-beta carotene making gene taken from corn into the rice which helps absorb vitamin A more easier; bata carotene will be converted to Vitamin A in the human body.
-which gives the rice an yellow colour
-vitamin A deficiency will result blindness and higher youth mortality.