HL IB Biology Genetics Unit Test
How does fertilization provide genetic variation?
1. it allows alleles from two different individuals to be combined 2. Combination is unlikely to ever have occurred before 3. promotes genetic variation in a species 4. genetic variation is required for evolution
DNA Profiling
1.Obtain a sample of DNA from a known source (individual, crime scene, fossils) 2.Select sequences that vary greatly among individuals and copy using PCR 3.Spilt copies into fragments using restriction endonucleases 4.Separate fragments using electrophoresis 5.Produces a banding pattern which is an individual's DNA profile 6.Compare profiles of individuals to find a match.
Making Human insulin
1.mRNA coding for insulin is extracted from human pancreas 2.Reverse transcriptase copies the mRNA 3.Sticky ends are made by adding extra G nucleotides to the ends of the gene 4.plasmids are cut open using restriction enzymes 5.sticky ends are made by adding extra c-nucleotides to the ends of cut plasmids 6.insulin genes and plasmids are mixed and link by complementary base pairing of C-G 7.DNA ligase seals nicks by making sugar phosphate bonds 8.recombinant plasmids are mixed with host cells (E. coli). The host cells absorb them. 9.GMO E.coli are cultured in a fermenter. 10.E.coli make insulin which is extracted, purified, and used for diabetics.
Risks of Down syndrome and maternal age
25 years 1/1250 risk, 30y 1/1000, 35y 1/400, 40y 1/100, 45y 1/30.
Where do cells for Karyotyping come from?
1. Amniocentesis 2. Chorionic villus Sampling (CVS)
What are the uses (in humans) of Karyograms?
1. Deducing the sex of an individual 2. Diagnosing conditions due to chromosomal abnormalities
Gregor Mendel
"father of genetics" Published work in 1866 on inheritance of traits in pea plants. Gametes: haploid cells which fuse together to start new life. Zygotes: diploid cell that results from the fusion of gametes Segregation of alleles: Two alleles of an individual segregate into different haploid nuclei during meiosis
How does meiosis provide for genetic variation?
1. Random orientation of Bivalents: the position of bivalents in metaphase I is random and does not influence the position of other bivalents 2. Crossing over: without crossing over some traits would be forever linked, allows linked genes to be reshuffled into new combinations, increases the number of allele combinations so that it is effectively infinite.
What is a genome?
All of the genetic information of an organism. Vary greatly in size but not related to the size of the organism.
What causes down syndrome?
An extra copy of chromosome 21. Individuals with this have three copies of chromosome 21 (trisomy 21) ◾One of the parental gametes had two copies of chromosome 21 as a result of non-disjunction ◾The other parental gamete was normal and had a single copy of chromosome 21 ◾When the two gametes fused during fertilisation, the resulting zygote had three copies of chromosome 21, leading to this.
When do chromosomes replicate?
In interphase before meiosis
Human genome project
finding and sequencing all the genes a humans. 1990-2003 23,000 protein coding genes most genes involved in regulation. Genomics. Current research. Old way: add defunct bases to stop sequencing at random spots, then sort segments by size, put 4 bases in order (electrophoresis) New way: use fluorescent markers for each base run in order once. A computer can read the order of the fluorescence.
Sex linkage
red-green colorblindness (aka Mrs. Browns son and Frank). Hemophilia, Blood does not clot properly, common in the Russian royal family as they were selective breeders.
Explain Non disjunction
refers to the chromosomes failing to separate correctly, resulting in gametes with one extra, or one missing, chromosome (aneuploidy) The failure of the chromosomes to separate may either occur via: ◾Failure of homologues to separate during Anaphase I (resulting in four affected daughter cells) ◾Failure of sister chromatids to separate during Anaphase II (resulting in two affected daughter cells) Trisomy 21 - Down syndrome: hearing loss, heart and vision disorders, mental and growth retardation Most other trisomies are so severe that offspring do not survive. Babies are sometimes born with trisomy 18 or trisomy 13. Klinefelter's and Turner syndrome are a result of nondisjunction of sex chromosomes.
Reduction division
the division completed in meiosis II which results in 4, different, haploid gametes
Crossing over
the exchange of information in between homologous chromosomes in Prophase I. Occurs between no sister homologous chromosomes. Chiasmata between non-sister chromatids in a bivalent can result in exchange of alleles. Crossing over produces new combinations of alleles on chromosomes in haploid cells
Karyotype
the number or type of chromosomes present in a cell or organism 46,XX (normal female) 47, XY +21 (male with down syndrome)
PCR polymerase chain reaction
used to amplify a single copy or a few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence. Allows a small sample to be used for many tests.
Cloning
•Genetically identical organisms derived from a single parent cell are called clones. •Asexual reproduction is a natural method of cloning used by many plant and some animal species. •Artificial cloning of animals: The simplest method is to break an embryo into more than one group early on in development when it consists of mostly stem cells (identical twins) •Cloning adults with known characteristics is more difficult. Most popular current method is somatic cell transfer which removes the nucleus from an egg and inserts the nucleus from a differentiated cell of the individual you wish to clone. This method was used to produce Dolly, the first cloned mammal.
Diploid chromosome numbers by species:
•Homo sapiens 46 •Pan troglodytes 48 •Canis familiaris 78 •Oryza sativa 24 •Parascaris equorum 4
Weighing the benefits and risks of GMO's
The Benefits of GMOs, BT corn specifically include: 1.Higher crop yields for human because of less pest damage. (Morrow plots research) 2.Less land needed for crop production, could preserve wildlife in areas. 3.Less use of insecticide sprays* *Roundup ready monsanto varieties are slightly different The risk of GMO's, BT corn specifically, include: 1.Insects that are not pests can be killed. Damage has been documented to monarch butterflies and bee populations. 2.Transferred genes can spread to other plants by cross pollination making more plants toxic to insects. 3.Insects may develop resistance to the Bt toxin. You can't throw shade on the corn!
Chi squared
X^2= (The sum of ) ((Observed score-Expected score)^2/Expected score)
Diploid
a cell that contains two complete sets of chromosomes, one from each parent
Karyogram
a photograph or diagram of chromosomes arranged in homologous pairs of decreasing length
Sickle Cell Anaemia
A base substitution mutation is the change of a single base in a sequence of DNA, resulting in a change to a single mRNA codon during transcription In the case of sickle cell anaemia, the 6th codon for the beta chain of haemoglobin is changed from GAG to GTG (on the non-coding strand) This causes a change in the mRNA codon (GAG to GUG), resulting in a single amino acid change of glutamic acid to valine (Glu to Val) The amino acid change alters the structure of haemoglobin, causing it to form fibrous, insoluble strands This causes the red blood cell to adopt a sickle shape The insoluble haemoglobin cannot effectively carry oxygen, causing individual to feel constantly tired The sickle cells may accumulate in the capillaries and form clots, blocking blood supply to vital organs and causing a myriad of health problems Also causes anaemia (low RBC count), as the sickle cells are destroyed more rapidly than normal red blood cells Sickle cell anaemia occurs in individuals who have two copies of the codominant 'sickle cell' allele (i.e. homozygotes) Heterozygous individuals have increased resistance to malaria due to the presence of a single 'sickle cell' allele (heterozygous advantage)
Gene Mutation
A change in the nucleotide sequence of a section of DNA coding for a particular feature.
How are chromosomes arranged during Karyotyping?
A karyotype is a visual profile of all the chromosomes in a cell The chromosomes are arranged into homologous pairs and displayed according to their structural characteristics Size smallest to largest, with sexual chromosomes (around 4th or 5th largest (except for y)) placed separately.
Define Amniocentesis
A procedure to obtain cells for Karyotyping where a sample of amniotic fluid is removed through the abdomen using a sonogram. Has a 1% risk of miscarriage.
Define Chorionic villus sampling (CVS)
A procedure to obtain cells for Karyotyping where a sample of chorion, the membrane of the placenta, can be done earlier in pregnancy than an amniocentesis. 2% risk of miscarriage.
How are Chromosomes formed?
By supercoiling. The DNA wraps itself around histones, and arranges into a 'pearl necklace' or 'beaded string' arrangement and then continuously wraps around itself until it becomes a chromosome.
What are somatic cells?
Diploid cells that have both sets of genetic information. Heart cells, Brain cells, liver cells ect. (2n)
Homologous Chromosomes
Have the same genes in the same sequence but may have different alleles (variations of the gene) Occur in pairs: maternal and paternal.
Haploid
Having only one set of genetic information
Define homologous chromosomes (bivalent)
Homologous chromosomes are chromosomes that share: ◾The same structural features (e.g. same size, same banding pattern, same centromere position) ◾The same genes at the same loci positions (while genes are the same, alleles may be different)
cell suicide
Known as apoptosis, when the telomeres reach a certain length after the cell has divided enough times, it causes the cell to do this. Failure to do this can result in uncontrolled cell division and cancer.
What makes Meiosis different from Mitosis?
Meiosis consists of two cell divisions: The first division is a reduction division of the diploid nucleus to form haploid nuclei The second division separates sister chromatids (this division is necessary because meiosis is preceded by interphase, wherein DNA is replicated)
Meiosis Facts
Most sexually reproducing animals are diploid - meaning they have two copies of every chromosome (one of maternal origin, one of paternal origin) In order to reproduce, these organisms need to make gametes that are haploid (have only one copy of each chromosome) Fertilization of two haploid gametes (egg + sperm) will result in the formation of a diploid zygote that will grow into a new organism
Karyotyping possibilities
Normal male 46 XY Normal female 46 XX 14/21 translocation carrier 45 XX, -14,-21+t(14:21) Trisomy 21 47 XX, +21 Fragile X syndrome 46 XY, fra(X)(q28) Turner syndrome 45 X Klinefelter syndrome 47 XXY Cat Cry Syndrome 46, XY, 5p-
Compare an Eukaryote and a Prokaryote.
Prokaryotes have: circular DNA, 'naked' DNA which is not wrapped around proteins, plasmids (often times), and a single chromosome. Eukaryotes have: linear DNA, associated histones (proteins), no plasmids, two or more different chromosomes.
Genetic Diseases
Recessive: Cystic fibrosis, both parents must be carriers, an ineffective chloride ion channel, 1/20 chance of carrying the gene, 1/400 of having a child with Cf. Dominant: Huntington's 1/10,000 but need only one allele, Brain degeneration starting in 30's to 50's Codominance: sickle cell anemia
What are Gamete cells?
Sex cells that are also haploid, ONLY egg and sperm cells (n)
Genome size examples:
T2 phage: 0.18 mil.bp E. coli: 5 mil.bp D. melangaster : 140 mil.bp H. sapiens: 3000 mil.bp P. japonica: 150,000 mil.b
Genetic modification
Taking a gene out of one species and inserting into another species. •FLAVR SAVR tomato! •Bt corn Causes people to question the ethical implications and to proceed with caution.
Define Meiosis
The process by which sex cells, gametes, are made in the reproductive organs
Structure of a chromosome
The centromere holds the two halves of the chromosomes together. The sister chromatids are the identical copies that are matched with one another. A gene is a heritable factor that controls a specific characteristic, consisting of a length of DNA occupying a particular position on a chromosome (locus). An Allele is One specific form of a gene, differing from other alleles by one or a few bases only and occupying the same locus as other alleles of the gene.
Outline the process of Meiosis (Know how to draw)
The process of meiosis involves two divisions, both of which follow the same basic stages as mitosis (prophase, metaphase, anaphase and telophase) Meiosis is preceded by interphase, which includes the replication of DNA (S phase) to create chromosomes with genetically identical sister chromatids Meiosis I Homologous chromosomes must first pair up in order to be sorted into separate haploid daughter cells In prophase I, homologous chromosomes undergo a process called synapsis, whereby homologous chromosomes pair up to form a bivalent (or tetrad) ◾The homologous chromosomes are held together at points called chiasma (singular: chiasmata) ◾Crossing over of genetic material between non-sister chromatids can occur at these points, resulting in new gene combinations (recombination) The remainder of meiosis I involves separating the homologous chromosomes into separate daughter cells ◾In metaphase I, the homologous pairs line up along the equator of the cell ◾In anaphase I, the homologous chromosomes split apart and move to opposite poles ◾In telophase I, the cell splits into two haploid daughter cells as cytokinesis happens concurrently Meiosis II In meiosis II, the sister chromatids are divided into separate cells ◾In prophase II, spindle fibres reform and reconnect to the chromosomes ◾In metaphase II, the chromosomes line up along the equator of the cell ◾In anaphase II, the sister chromatids split apart and move to opposite poles ◾In telophase II, the cell splits in two as cytokinesis happens concurrently Because sister chromatids may no longer be genetically identical as a result of potential recombination, the process of meiosis results in the formation of four genetically distinct haploid daughter cells
Sutton-Boveri chromosome theory of inheritance (HL)
These scientist worked independently but achieved similar outcomes. Sutton, Brachystola magna, n = 11, Kansas, published first Boveri studied Parascaris equorum n = 2 Both identified chromosomes with well defined shapes maintained shapes through generations. Sutton, "chromosomes may constitute the physical basis of the Mendelian law of heredity.
Autoradiography
Used since the 1940's. John Cairns used it to study E. coli chromosomes labeled thymine. He digested the membrane, coated it with photographic film, left in the dark for 2 months. Showed the position of DNA in E. coli, showed that the DNA was circular and 11ooum long.
Gel electrophoresis
Used to separate DNA or proteins by size, used in paternal testing.
Discrete and continuous variation
•Discrete: distinct categories (A, B, O) •Continuous: Data that fits a normal distribution like height, skin color, hair color. Approximation of a normal curve suggests that more than one gene is involved. This is called polygenic inheritance.
Linked Genes
•Gene loci are said to be linked if they are on the same chromosome. •autosomal gene linkage (genes are on the same autosome) •sex linkage
Causes of mutations
•Radiation and mutagenic chemicals increase the mutation rate and can cause genetic disease and cancer •A mutation is a random change to the base sequence of a gene. Two main things which increase mutation rates are: •radiation increases mutation rates because radiative energy causes chemical changes in DNA. Gamma rays, alpha particles, short-wave radiation, and X-rays are all mutagenic. •Some chemicals cause changes in DNA and so are mutagenic. (Benzene rings and nitrosamines sneaking into DNA) •Mutations in regulatory processes of cell division can develop into a tumor. •Mutations in body cells are eliminated when that individual cell dies. •Mutations in gametes can be passed onto offspring
Environmental Influence
•Some traits are activated by the environment skin color in humans is polygenic and influenced by exposure to sunlight. Traits can be influenced by exposure, diet content, and other factors
Inheritance (HL): Segregation and Independent assortment
•Unlinked genes segregate independently in meiosis because they tend to travel together and do not segregate independently. •Thomas Hunt Morgan discovered non-Mendelian ratios in Drosophila melanogaster. Led him to reject Mendel's theory of inheritance. Later after further examination, he realized his observations were an exception to independent assortment because he was looking at linked traits. The traits Morgan was investigating were sex linked in fruit flies. He found a single white fly in the room. Had very few F1s with white eyes but a lot of white eyes in the F2. All the white eyed flies in F2 were male.
