analysing evidence

history of dna

individuals involved - j watson, f crick and roselind franklin

rosalind franklins image of dna - image 51, proved the double helix structure

technique used to image dna - x-ray

genetic structures - overview

a chromosome is made of 1 DNA strand, along this chromosome is multiple genes, these structures are in the nucleus   

dna

• deoxyribonucleic acid

• the genetic material of an organism, all of an organisms body cells will have the same DNA

• found in the nucleus

• set of genetic instructions used to build, grow and maintain living organisms

dna - structure

double helix strucutre

- two strands

monomer

small single simple molecules that can join together

polymer

large molecules made up of the smaller monomer units together in a repeating chain

polynucleotides

• a single strand of DNA that are long chains of nucleotide monomers linked together , known as a polynucleotide - made of subunits called nucleotides

polymer - polynucleotide

monomer - nucleotide

nucleotide - parts

3 parts

• deoxyribose sugar - as its pentose sugar

• negative phosphate group (PO4³-)

• nitrogenous base (varies) : adenine, guanine, cytosine or thymine

bonds within a strand (nucleotides)

strong sugar phosphate bonds join nucleotides to create a polynucleotide strand

• between the negative phosphate group and the deoxyribose sugar

• covalent bonds

dna backbone

deoxyribose sugar, negative phosphate group

dna - base pairing and bonds

four bases : adenine (A), thymine (T), guanine (G), cytosine (C)

bond on a complementary base pairing system - joined by hydrogen bonds

• A will always bond to T (2 bonds)

• G will always bond to C (3 bonds)

not as strong as sugar phosphate bond

chargaff’s rule

in DNA the number of

• A = T

• G = C

applies when considering both DNA strands, not one

strawberry practical - why did we crush the strawberries

• to break the cell walls and tissue of the strawberries

• exposes the individual cells so that the detergent and salt can reach them

what did the exactraction mixture contain

salt and detergent

what does the salt do

• neutralizes the DNA’ charge so that the DNA strands are able to clump together

• The salt provided positively charged sodium ions and these ions are attracted to the negative charges on the strawberry’s DNA phosphate backbone.

•  This allows the tiny DNA to stick together to aggregate and form visible clumps.

what does the detergent do

• breaks the membranes (cell and nucleus)

• acts as a chemical lysing agent - a substance used to break open cells by disrupting their outer membranes or walls

what does the ethanol do

• precipitates the DNA (allows it solidify)

what purpose does the ice serve

• to keep the solution cold which slows down the activity of the degrading enzymes of the strawberry called DNases, which can break down the DNA

• so DNA does not break down

genes

a sequence of DNA bases which codes for your traits/proteins

• proteins control the function and structure of an organism

• all your physical attirbutes are a result of the sequence of bases in you DNA

• traits can be determined by multiple genes

• there are segments of DNA that do not code for a trait

genes are passed onto subsequent generations - genes of offspring are derived from their parents

genome

the complete set of genes in an organism

chromosomes

a chromosome is compacted DNA - found in the nucleus of eukaryotic cells

• eukaryotes - organisms with nucleus and organells

1 chromosome is composed of 1 DNA double helix, humans have 46 chromosomes (23 pairs)

karyotype

an image of an individuals complete set of chromosomes

human chromosomes

• 1 pair of sex chromosomes (X or Y)

• 22 homologous pairs of autosomal chromosomes (1-22)

autosomal chromosomes (autosomes)

non sex-chromosomes

you have 2 of each autosome - homologous pair

sex chromosomes

determine sex of indivudal

• XX = female , 23 homologous pairs

• XY = male , 22 homologous pairs , 2 non homologous sex chromosomes

each parent contributes 1 chromosome to each of the 23 pairs of chromosomes

homologous

having the same or similiar structure, position, or origin, after coming from a common ancestor

homologous pairs - chromosomes

chromosomes pairs with the same

• genes

• gene position (locus/loci) / bands

• length

linked genes

genes on the same chromosome

dna replication - importance

DNA must be replicated to produce new cells (new DNA molecules are made from existing DNA) - ensures new cells have correct number of chromosomes

by using existing DNA strands as templates, we can ensure that new DNA is identical to the original

dna replication - enzymes

dna helicase - breaks hydrogen bonds between DNA strands / bases (unzipped)

dna polymerase - add nucleotides to template strands to create new strands

dna replication - process

1. DNA helicase moves along the DNA, breaking the hydrogen bonds between bases

2. DNA polymerase adds complementary nucleotides to the template strands to create new strands, 1 nucleotide at a time - helix will reform when strand is complete

semi conservative process

semi - half

conservative - to retain , keep the same

the way dna creates an identical copy of itself

because new DNA is made from existing DNA strands, half of each new DNA helix is from the original

DNA replication - after

before replication - single strand chromosomes

after replication - double strand chromosomes

chromatids

• 1 chromosome strand

• DNA replication produces chromosomes with 2 chromatids

sister chromatids - on the same chromosome, chromatids attached by a centromere with the same genetic information

centromere

joins the chromatids

diploid vs haploid

diploid - 2 complete sets of chromosomes, body cells

haploid - single set of unpaired chromosomes (1 set for humans), gametes (sex cells, sperm and egg cell)

cell division - mitosis

• process - 1 parent cell divides into 2 diploid daughter cells, identical to the parent (original) daughter cells = new cells

• occurs in somatic cells (body cells)

purpose of mitosis

• growth and development

• replacing old or damaged cells

mitosis seperations

before mitosis

• dna replication must occur first, ensures each daughter cell can have enough chromosomes

during mitosis

• sister chromatids seperate into each daughter cells

cell division - meiosis

process - 1 parent cell divides into 4 unique haploid daughter cells

• occurs in germ line cells to form gametes (sex cells) - diploid to haploid

purpose of meiosis

why gametes have to be haploid

purpose

• to produce gametes for sexual reproduction

• so that when 2 haploid gametes fuse during fertilisation each contributing a set of chromosomes of 23, the resulting offspring receives the correct diploid number of chromosomes

• form a zygote with the correct number of chromosomes

meiosis seperations

pre meiosis - dna replication must occur first

2 stage process

• meiosis I - seperation of homologous chromosomes, produces 2 haploid daughter cells with sister chromatids

• meiosis II - seperation of sister chromatids, produces 4 haploid daughter cells with 23 chromosomes (chromatids)

meiosis variations, name

extra processes during meiosis I to ensure the 4 daughter cells are not identical

• independent assortment

• crossing over

variation by independent assortment

• homologous pairs line up randomly when split

variation - daughter cells have different chromosome combinations of parent chromosomes

variation by crossing over

• dna exchange between homologous pairs of non sister chromatids

homologous pairs have the same genes but could have different base sequence

gene expression

the process of producing proteins from genes

• transcription: DNA to mRNA

• translation: mRNA to protein

RNA

• ribonucleic acid

• single stranded nucleic acids involved in protein synthesis - made up of nucleotides

composed of

• ribose sugar

• negative phosphate group

• cyclic nitrogenous base

RNA vs DNA differences

RNA has uracil (U) instead of thymine (T)

• A binds with U

• G binds with C

transcription

objective - produce a strand of mRNA from a gene of DNA

location - nucleus

mRNA - messenger RNA

• capable of exiting the nucleus to act as a template for a protein

• produced by RNA Polymerase

transcription process

1. RNA polymerase binds to template strand causing DNA to unwind

2. RNA polymerase runs along the strand to produce mRNA using complementary base pairs

3. at end of gene, RNA polymerase and mRNA are released

4. mRNA exits the nucleus

proteins and amino acids

polymer: protein, proteins are larger complex polymers and are made up of long chains of amino acids

monomer: amino acids, amino acids are the monomer of proteins just as nucleotides are the monomers of DNA and RNA

translation

objective: produce a protein from mRNA (proteins are formed from a sequence of amino acids one at a time)

location: ribosome - protein factory

tRNA - transfer RNA

• carry amino acids to the mRNA based on the complementary base pairing

codons

sequences of 3 bases on mRNA

translation process

1. tRNA transport amino acids to the mRNA based on completementary base pairing

2. the amino acids are joined as they are added

3. once the stop codon is reached, the amino acid chain (protein) is released

redundancy

multiple codon sequences code for a single amino acid

tips for translation

1. look for start codon (AUG)

2. write full name of amino acid

3. don’t write stop

mutations

a change to the sequence or structure of DNA

typically occur during DNA replication

can be inherited from parents

cause of mutations

mutagens - environmental factors which increase the frequency of mutation

genetic (single gene) mutation - point substitution mutations

point substitution mutations: 1 base is changed

• missense : an amino acid is changed

• silent: no amino acid change

• nonsense: early stop codon is produced

genetic (single gene) mutation - frameshift mutations

frameshift mutations: bases added or removed (changed reading frame of codons)

• insertion; base added to a gene

• deletion: base removed from a gene

amino acid sequence functionality

• changed amino acid sequence = protein no longer functional

• unchanged amino acid sequence = protein still functional

chromosomal structural mutations

segments of chromosome is changed

• deletion - chromosome segment removed

• duplication - chromosome segment repeated

• translocation - chromsome segment moved to another chromosome

• inversion - chromsome segment is flipped

chromosomal number mutations =

total no. of chromosomes changes

aneuploidy

abnormal no. of specific chromsome

• trisomy 21 - down sydrome

polyploidy

abnormal no. of chromosome sets

alleles

• different forms of a gene

classified as

• dominant (uppercase)

• recessive (lowercase)

genotype

someone allele combination for a trait

• homozygous dominant - 2 dominant alleles

• homozygous recessive - 2 recessive alleles

• heterozygous - 1 of each allele (known as a carrier)

dominant allele masks the recessive allele when present

phenotype

the observed traits in an organism (depends on genotype and environment)

human somatic cells - parent alleles

diploid - 2 sets of chromosomes

• one set inherited from each parent, so each parent contributes 23 chromosomes

• each parent contributed an allele to all of your genotypes

• your alleles/genotype were dependent on your parents genotypes

punnett square

determine genotype of offspring

• genotype ratio - 1 Dd : 1 dd

• phenotype ratio - 1 detached earlobes : 1 attached earlobes

law of dominance - mendels experiments conclusions

dominant alleles mask recessive alleles

law of segregation - mendels experiments conclusions

alleles are seperated during meiosis

law of independent assortment - mendels experiment conclusions

alleles for different traits are inherited independently of one another

x linked traits - sex linked traits

traits coded by a gene on the x chromosome

• alleles can be dominant or recessive

x linked dominant traits - more likely?

more females affected

• inherit 2 X chromosomes while males only inherit 1

x linked recessive traits - more likely?

more males affected

• only inherit 1 X chromosome

• no chance of having dominant allele to mask the recessive

Y linked traits

traits coded by a gene on the Y chromosome

• affect biological males

human genome project

• International collaborative project​

• Timeline: 1 October 1990 – 14 April 2003 (13 years)​

• Cost: 3 billion dollars total​

• Goal - map and understand the genes in the human genome​

discoveries of human genome project

• 3 billion base pairs​

• 20,500 genes​

• Which chromosome each gene is on​

• Location of each gene on a chromosome​

• Function of each gene​

bioethical principles

beneficence - who can benefit from this technology

• Rationale: Biotechnology should only be developed if it can benefit society in some way​

Non-maleficence - Who might be harmed by this technology/ can the harm be minimised?

• ​Rationale: Biotechnology should not be developed if it is extremely harmful​. Or it should only be developed if the positives outweigh the negatives​

Individual Rights/ Respect - Are the rights of all individuals involved considered and respected?

• ​Rationale: use of the technology should not breach individual’s rights​

Justice/ Equity - Are interests of communities considered/ discrimination prevented?​

•  Rationale: use of the technology should not discriminate against any cultural or socioeconomic group (should be fair for everyone)​​

Integrity- Is technology developed with honesty and allowing for scrutiny?

• Rationale: discoveries and faults of the technology must be honest​​

genetic screening and testing - purpose and importance

purpose - to check how likely someone is to have a condition/disease

importance - early detetion can improve quality of life

future potential: gene therapy

modification of genes within an individual to treat or prevent disease

• once tech advances, may be possible to modify specific genes/sections of dna to remove detrimental diseases/conditions

  • issue - would require the dna in all the cells of an individual to be modified

use genetic screening/testing to identify genetic conditons and then use gene therapy to modify dna to eliminate conditions

genetic screening and testing - methods

methods

• gene test - analyses specific genes

• dna test - alayses whole dna

• biochemical test - analyses proteins

• can occur at any point in life

other info obtained

• sex determination, carrier screening for recessive traits, diagnosing and predicting genetic diseases

genetic screening

routine analysis of many people regardless of family history of a genetic disorder - random check

• early detection of these conditions can greatly increase the quality of life of affected patients

genetic screening e.g 1

• heel prick - blood extracted from the heel of newborns to test for conditions

  • cytosis fibrosis - confirmed by high IRT protein

  • phenylketonuria (pku) - confirmed by low phenylalanine

  • hypothyroidism - confirmed by low thyroid

genetic testing

analysis of specific people with a history of genetic disorder - targeted and specific check

genetic testing - e.g 1

• prenatal chromosome count - checks NO. chromosomes via a karyotype

  • can identify aneuploidy

    • Chorionic villus sampling (10-12 week foetus) – collects actual foetus cells

    • ​Amniocentesis (14-16 week foetus) – collects uterine fluid containing foetus cells​

genetic testing e.g 2

• dna sequencing - determines the base sequence (ATCG) in dna

  • diagnosis - confirm if someone has a condition

  • carrier testing - check if someone is a carrier (heterozygous) for a disease

genetic testing e.g 3

• dna profiling - seperate and organise DNA into fragments (using gel electrophoresis)

  • diagnosis - confirm if someone has a condition

  • paternity testing - confirm the father of a child

  • forensics - confirm if someone was present at a crime scene

pros of genetic screening/testing

• Early detection of diseases to inform medical Treatments​

• Informed decision making​

• Identification of carriers​

• Advance Medical Research ​

cons of genetic screening/testing

• Psychological impact on patients​

• Privacy and equity concerns (discrimination due to having a confirmed disease)​

• Cost and accessibility ​

cloning

genetically identical copy of a gene, cell, tissue or organism

• not only limitied to a whole organism

cloning - reproductive

copying whole organisms

process: somatic cell nuclear transfer (somatic cell - body cell, nuclear - nucleus containing dna)

reproductive cloning - individuals

individuals required ​

• Nucleus donor - gives DNA for the clone , will be identical to the nucleus donor ​

• Egg contributor - gives an egg tocarry the clone DNA​

• Foster mother - carries the embryoto develop into the clone​

reproductive cloning - process

1. Diploid somatic cell is extracted ​- Haploid egg cell is extracted​

2. Diploid nucleus is isolated from somatic cell​ - Haploid nucleus is removed from egg cell​

3. Diploid nucleus is fused with enucleated egg cell with electric shock​

4. Fused cell replicate to form an embryo​

5. The embryo is implanted in the foster mother’s uterus​

6. Embryo develops and is birthed as a clone of thenucleus donor​

pros - reproductive cloning

• medical advancements

• biomedical research advancements

• species preservation

• offsrping for idnividuals who cannot have children

• reviving extinct species

cons - reproductive cloning

• poor welfare of surrogates

• shortened lifespan/ welfare of clones

• loss of genetic diversity

therapeutic - cloning

copying cells / tissue

process: somatic cell nuclear transfer

goal: harvest embroynic stem cells

therapeutic cloning: stem cells

cells which specialise into other cells

• adult stem cells can only specialise into a small range of cell types - mulitpotent

embryonic stem cells can:

• divide indefinitely

• specialise into any cell type (totipotent) - can be used to treat various conditions through transplant

therapeutic cloning: process

same as reproductive cloning except embryo is not implanted in uterus

• instead - further divides in a dish

• is harvested as stem cells (after around 5 days)

these clones can be used for transplants for the donor