Biology IB Genetics

A heritable factor that consists of a length of DNA and influences a specific characteristic.

Specific characteristics.

Is the specific position of the gene on the chromosome.

The different forms of a specific gene (that differ from one another by a few bases)

All individuals carry the same gene on the same loci of the same chromosome. Alleles that differ from one another by a few bases cause variation.

A random, rare change in the sequence of bases of the gene.

• Is the insertion of an incorrect nucleotide
• This either has no or major influences on the organism’s physical characteristics.

• Beneficial: increases survival rate, likely to be passed on
• Detrimental: decreases survival rate, unlikely to be passed on
• Neutral: does not influence the survival rate.

Taking a beneficial gene from someone who carries it and putting it into someone who does not have it (a virus may be used)

• The whole of the genetic information of an organism.
• Not the number of genes but the total amount of DNA
• (The number of genes is not proportional to the amount of DNA)

• Number: 1 in prokaryotes, 2 or more in eukaryotes.
• Shape: circular in prokaryotes and linear in eukaryotes
• Pairs: no in prokaryotes yes in eukaryotes
• Histones: no in prokaryotes (except for archaea) yes in eukaryotes
• Plasmid: sometimes in prokaryotes never in eukaryotes

• Radiation from a substance is captured from film or by sensors.
• John Cairns produced the first images from E. coli by the growth of a culture containing thymidine containing a radioactive isotope of H (thymine + pentose sugar)
• Through this, he found that
• E Coli DNA is circular
• Semi-conservative replication is supported

• Representation of the chromosomes found in the cell according to a standard format.
• (stained cells are photographed during mitotic metaphase)

A specific number and appearance of the chromosomes of a cell

• 1 division in mitosis and 2 in meiosis
• Diploid cells produced in mitosis and haploid produced in meiosis
• No crossing over in prophase 1 in mitosis
• No chiasmata formation in mitosis
• Homologous pairs don’t line up in metaphase of mitosis
• Sister chromatids separate at anaphase 1 in mitosis

• Alleles are exchanged between homologous chromosomes
• Homologous chromatids break at the same point, twist around each other and connect to the other’s initial location
• Happens during prophase 1

Spots where two homologous chromosomes going through crossing over connect to exchange genetic material.

Exchange of DNA to recombine and produce new combinations of alleles

They form during prophase 1 through synapsis of homologous chromosomes

Homologous chromosomes randomly line up in the center of the cell during metaphase 1 and metaphase 2, leading to variation.

• DNA replication
• Chromatin condenses into chromosomes (2 sister chromatids joined by the centromere)
• Further growth, organelle replication

• Homologous chromosomes go through synapsis to from tetrads.
• Nuclear membrane dissolves
• Crossing over occurs
• Centrioles migrate to opposite poles of the cell. Microtubule spindle attaches to each centromere of the chromosomes

• Tetrads line up at the equator
• Random orientation of chromosomes leads to variation

• Microtubule spindle contracts.
• Homologous chromosomes pairs are separated.
• Reduction division occurs. Chromosome number at each pole of the cell is halved.

• Cell elongates, cleavage furrow forms.
• Cytokinesis begins
• Nuclear envelope reappears
• Chromosomes uncoil
• Spindle begins to disintegrate
• MANY PLANTS DO NOT HAVE TELOPHASE 1

• Interphase or S phase does not occur before this.
• Nuclear membrane disintegrates
• Chromatin supercoils to form chromosomes
• Centrioles move to opposite poles (perpendicular to prophase 1)

• Chromosomes line up at the equator in random orientation
• Spindle attaches to centromeres

• Spindle contracts, splitting chromosomes into 2 sister chromatids.
• An equal number of chromosomes are pulled towards opposite poles.
• Random orientation of sister chromatids leads to further variation

• Nuclear envelope reappears
• Chromosomes uncoil
• Cell elongates as cleave furrow or cell plate forms
• Cytokinesis 2 begins

Nondisjunction of the 21st chromosome during anaphase 1

• Crossing over during prophase 1
• Random orientation during metaphase 1 and metaphase 2 (n over 2)
• Fertilization (allele combinations)

XO

XXY

Observed the inheritance of single traits and deduced the law of genetics.

Pair of alleles which are both expressed when present (expressed as over a letter such as I or C, example being ABO blood type)

Combination of alleles.

Testing a dominant phenotype to determine if it’s homozygous or heterozygous by crossing it with homozygous recessive,

Individuals of the same phenotype, that we crossed, produce individuals of the same phenotype.

• Albinism
• Cystic fibrosis
• Sickle cell
• Tay Sachs

• Hemophilia
• Color blindness

• 3 or more genes influence a trait
• (ABO)

Two genes found on the same chromosome are linked genes

A group of genes inherited together

The segregation of a pair of alleles between gametes is independent from the segregation of another unless they’re linked genes.

• Independent assortment
• Not preferable over each other
• Equally distributed between gametes

• Two or more genes influence the expression of a trait.
• Most common human traits are too complex to be influenced by one gene.

Polygenic traits show continuous variation.

• (O-E)^2 divided by O
• Summed
• Degree of freedom - 1 is your critical value

• He worked with drosophila flies. He induced some mutations using chemicals and radiation and observed whether the mutations were inherited by doing cross breeding.
• He discovered that:
• 1)linked genes exist
• 2)Traits can be sex linked
• 3) crossing over occurs

• Agents that cause mutations
• chemicals (carcinogens)
• Some viruses
• High energy radiation
• UV Light (breaks AT bond and bonds Ts together)

• Genes where a mutation leads to cancer through
• Lack of apoptosis
• Uncontrolled cell division due to abnormal cell cycle
• What is DNA Profiling?
• The process of matching an unknown sample of DNA with a known sample to see if they correspond.
• A sample of DNA is taken
• Sequences that vary significantly between individuals are selected and copied by PCR
• The sequence is determined through gel electrophoresis

• Polymerase chain reaction is used to get the sufficient amount of DNA to analyze
• A sequence is selected using a primer that binds to the start of the desired sequence
• The DNA is heated to 95 degrees, breaking the double helix apart
• At 55 degrees, primers anneal to the template strand
• At 72 degrees, Taq polymerase and extra nucleotides add complementary strands to the desired sequence selected by the primer
• Cycle is repeated 20-30 times to get desired amount of DNA

• Restriction enzymes chop up the DNA into fragments
• DNA fragments are placed into wells
• The gel is exposed to electric current (positive at one side and negative at the other) as the negatively charged DNA moves to the positive side.
• The smaller and less charged particles move faster, showing bands in the gel.

A known sequence of complementary DNA that binds to a specific gene that can be used in gel electrophoresis to determine the presence of a specific gene.

• Paternity testing
• Criminal investigation
• Evolutionary biology (cladograms)
• Identifying bodies

• Transfer of genes from one species to another to produce a variety of organisms with desirable traits.
• Possible because of universal gene code

• Plasmid is removed from bacteria
• Restriction enzyme (endonuclease) is used to cut open the plasmid
• The same restriction enzyme is used to remove the desired gene from the donor.
• DNA ligase splices the genes and Sticky ends with complementary base sequences are used to bind the DNA.
• The recombinant plasmid is inserted back into the host cell
• Note: When insulin producing E. Coli is being produced, reverse transcriptase is used to convert mRNA to cDNA (complementary DNA) which is then inserted into the host,

• Sheep producing milk with anti-clotting protein which is used for example to prevent fatal clotting during childbirth
• Bt corn produces a protein that kills harmful larvae

• Allergies in humans
• Gene jumps resulting in superweeds resistant to herbicides
• Gmo plants will outcompete wild plants and change the gene pool
• Negative economic events
• May save from hunger in the short term but the problem is the distribution of food not the production of it
• Green revolution (60s) high yielding varieties of grains and modernization of agricultural practices led to the prevention of the starvation of a billion people.

Genetically identical organisms derived from a single parent organism.

• Natural clones
• Reproductive clones
• Therapeutic clones

• Vegetative propagation
• Such as rhizomes (horizontal underground growth of many grasses)
• Runners (horizontal aboveground stems (stolons)
• Potato tubers
• Grafting (disadvantage, potato famine)

Parthenogenesis, in vitro fertilization, twins and triplets

Using stem cells

• Somatic cell from donor sheep was collected. Nucleus of one of the cultured cells is removed,
• Unfertilized egg from another sheep is collected and its nucleus is removed.
• The nucleus of the somatic cell and the egg cell are fused through electrical current.
• After being developed in vitro, the embryo is placed into a surrogate sheep.