IB Bio Unit 3 SL

DNA Molecule

comprised of a pair of antiparallel strands with linear sequences of nucleotides

Gene

A particular section of DNA that can be transcribed and translated to form a specific polypeptide. Is an inheritable factor that controls a specific characteristic.

Allele

A slightly different form of a gene. Slightly diferent base sequences between allels of one gene

Codon

a triplet of nucleotides within an mRNA molecule

Base Substitution Mutation

The incorrect insertion of a nucleotide, the incorrect sequence is then translated and transcribed

Locus

The location of a gene on a chronosome

Genome

All the genetic information of an organism

Human Genome Project

mapped all the genes in the human body located specific genes helps analyse evolutionary relationships discovery of proteins and function **morals

Sickle Cell Anemia

base substitution mutation recessive carriers cannot have malaria

GAG is the normal codon GTG in sickle cell patients

transcribed to GTG instead of normal GAG. GTG forms valine (amino acid) normal is glutamic acid --> this results in a change in the sequence of the hemoglobin protein

cells are sickle shape, don't carry oxygen well, clog veins more, person is more tired.

Genome size

the total amount of DNA the total number of nuclotide base pairs within one cope of a single genome. complexity is not proportional to size NOT the number of genes

Gene number examples

Homo Sapiens - 23,000 genes Ecoli - 3,000 genes thaliana plant - 25,000 genes

Chromosomes

Are made up of lengths of DNA They carry the organism's genetic information

Prokaryotic DNA

circular chromosomes

free in the cytoplasm, not compartmentalised

extra genetic material in plasmids

cell has only 1 chromosome

no histone proteins holding the chromosomes

Eukaryotic DNA

Chromosomes are wrapped around 8 histones and sealed with the 9th

2+ chromosomes

Sealed form the rest of the cell in the nucleus by a double membrane

no plasmids

Linear chromosomes

Interphase

Eukaryotic chromosomes coil then replicate so that after the first division both daughter cells will be diploid.

Somatic Cell

A normal body cell. Not a sex/gamete cell

Gamete

sex cell (sperm or egg)

Homologous Chromosomes

Chromosomes carrying the same genes at the same locus, but not the same allels

Karyogram

A chart of all the homologous chromosome pairs in the organism, ordered by decreasing size.

Karyotype

The number and type of chromosomes in the nucleus

Sex Chromosomes

X and Y chromosomes. Determine the sex of an organism

Haploid and Diploid

Diploid:

has homologous pairs of sister chromatids joined at the centromere

Haploid:

has one set of chromosomes, sister chromosomes joined at the centromere.

Once split, these sister chromatids are considered chromosomes

Genome size comparison

T2 Phage (virus) - 3569 (first RNA genome sequence) E.coli - 4.6 x 10^6 fruit fly - 130 x 10^6 human - 3200 x 10^6 Japanese pale petal - 150,000 x 10^6 (largest known of plants)

Meiosis

A reduction division of one diploid nucleus to form four haploid nuclei. Allows for a full nuclei of chromosomes after fertilization

Meiosis stages (SL)

Interphase: chromosomes are replicated

Prophase 1

chromosomes supercoil, homologous pairs line up, crossing over takes place, microtubules form, nuclear envelope breaks down

Metaphase 1

Homologous pairs line up along the equator, microtubules attach to centromeres, random alignment of maternal/paternal chromosomes to increase genetic variety

Anaphase 1

microtubules contract towards either end of the cell, sister chromatids remain together, homologous pairs are separated

Telophase 1

Spindle fibers break down new nuclear envelopes form around each new group of chromosomes

Cytokenisis

The cell pinches together and separates the two cells

Prophase 2

New spindlefibres form by replication, chromosomes recoil, nuclear envelope begins to break down

Metaphase 2

nuclear envelope finishes breaking down, chromosomes line up along the equator, spindle fibres attach to the contromeres.

Anaphase 2

Spindlefibres contract to wards either end of the cell, separating the sister chromatids, spindle fibres pull the sister chromotides to opposite sides of the cell

Telophase 2

new nuclear envelopes form around the separated chromatids, chromosomes uncoil

Cytokenisis: cell pinches and divides into 4 haploid cells.

Genetic variation comes from…

fertilisation, crossing over, random orientation, mutation

Non-disjunction

When sister chromatids or homologous pair have not separated properly.

More common in elderly parents. Prenatal screening can be important in locating this.

Genotype

An organism's alleles represented by a letter. The come in pairs (one from each chromosome

Phenotype

The characteristics of an organism, external or internal. Eg. Colour, hair, sickle cell anaemia

Dominant allele

The allele that shows whether homozygous or heterozygous. Has a capital letter.

Recessive allele

The allele that only has an effect when it is homozygous. Has a lower case letter

Codominant allele

Pairs of alleles that both effect the phenotype in a heterozygous state. Eg. White and red = pink.

Homozygous

Having two identical alleles. Eg. TT or tt.

Heterozygous

Having two different alleles. Eg. Tt.

Test cross

Testing a dominant phenotype to determine if it is heterozygous or homozygous. Eg testing TT or Tt with tt, so see what the children get to determine what the parents have.

Carrier

Someone with a recessive allele, but is heterozygous so does not suffer from the disease.

Pure breeding

Two people with the same phenotype breeding to have kids with the same phenotype.

Sex Linkage

The pattern of inheritance that is characteristic for genes located on the X chromosome. Only the X chromosome is big enough to carry extra genes. So males cannot be homozygous or heterozygous by sex-linked genes, so cannot be carriers. Women have two X chromosomes, and can be heterozygous or homozygous, meaning they can also be carriers. Eg. Red-green colour blindness, or haemophilia.

Pedigree charts

Displays of the family tree to trace back genetic conditions. Shows birth order, marriages, siblings, and generations. circle = female square = male coloured = affected empty = unaffected

Genetic diseases

Diseases present in non-sex chromosomes or from mutations. Usually recessive and pass through the generations. Eg. Sickle-cell disease (chromosome 11), cystic fibrosis (chromosome 7).

Cystic fibrosis

chromosome 7 autosomal recessive

Huntington's Disease

Dominant Autosomal

Mutation Rates

Mutations are spontaneous permanent changes in the base sequence of DNA. Mutation rates can be increased by mutagenic chemicals, ionising radiation, and tobacco tar (by mutagens). Eg. After Chernobyl and Hiroshima nuclear incidents resulted in increase in rate of cancer in people nearby. Only mutagens in cells that produce gametes will be passed on.

Blood Inheritance

A (IA) and B (IB) are co-dominant O (i) is recessive

Chiasmata

The point where crossing over occurs

Haemophilia

X linked recessive life threatening more in males women can carry blood can't clot

Red-green colour blindness

x linked recessive males more likely females can carry gene for photoreceptor proteins difficult to distinguish between red and green

Recombinant DNA

DNA that has been artificially changed. Can join genes from different species.

Plasmid

An independent chromosome small circle of DNA often found in bacteria. Good vector for genetic engineering

Restriction Endonuclease/Enzyme

An enzyme used to cut nucleic acids at specific sequences of bases (to break DNA for gel electrophoresis)

DNA Ligase

Enzymes that link okazaki fragments during DNA replication Also used to join double- stranded DNA fragments at their sticky ends

Sticky ends

Some restriction enzymes cut the double stranded DNA to produce short single-stranded section of overhanging DNA. This is the sticky end

Reverse Transcriptase

An enzyme that can synthesis DNA from RNA

Short Tandem Repeats

repeating sequences of DNA.

• each STR is shared by 5-20% of unrelated people, can be used to identify people

Gene Modification

Transfer of genes from one species to another Made possible by the universal shared genetic code.

Genetically modified organisms

can have pros and cons for - enviroment, agriculture, health. risk assessment morals

Clone

A genetically identical organism to a group of cells derived from a single parent organism.

Plants can do it naturally by asexual reproduction (eg. roots or stems or runners growing and making new plants)

Animals can be produced fro embryos after in vitro fertilisation. a ball of cells from a dividing zygotes is taken and separated to form several identical embryos.

Somatic Cell Nuclear Transfer

fusion of an ovum with a sheep's nucleus. Created a replica of the sheep that provided the nucleus.

DNA profiling

matching a DNA sample to a person paternity should be 50% crime scene should be 100%

Polymerase Chain Reaction (PCR)

Makes more DNA from a small bit.

95 degrees - Double stranded DNA sample hydrogen bonds are broken to seperate the two strands.

60 degrees - sample is cooled, then DNA primers attached to the strands. Free nucleotides and DNA polymerase is added

70 degrees - the DNA polymerase catalyses the synthesis of complementary DNA strands, replicating a section.

Repeated 30 times

Gel Electrophoresis

To separate DNA fragments to investigate charge and size.

PCR sample taken

Restriction enzymes used to cut the DNA into fragments at specific base sequences.

Florescent marker binds to a triplet in the DNA so it can colour the results

samples of DNA placed in wells in electrophoresis chamber.

electrical field applied, fragments move to positive end.

Lighter fragments move further, displaying a banding pattern.

Genetically Engineered Insulin

Human insulin gene located within donor DNA

Gene is cut with restriction enzyme, producing sticky ends.

Suitable vector (plasmid) is cut using same restriction enzyme.

Gene is put into the plasmid, matching base pairs.

Sticky ends joined by Ligase.

Plasmid is put into E.coli

E.coli grown in presence of antibiotic, and forms resistant to the antibiotic due to marker gene.

E.coli cloned then insulin protein extracted and purified.