Genetics - Final Exam Flashcards
Law of Independent Assortment
Two different genes will randomly assort their alleles during the formation of haploid cells. Linked genes do not sort independently. More chromosomes = more diversity.
Phenotypic Ratio
Divide each total number of characteristic by the lowest number characteristic (usually the most recessive trait(s))
Genetic Recombination
Offspring receives a combination of alleles that differs from those in the parental generation.
2n
2 = one pair of chromosomes, while n = number of pairs.
Law of Segregation
The two copies of a gene segregate or separate from each other during transmission from parent to offspring. Only one copy of each gene is found in a gamete. At fertilization, two gametes combine randomly.
Loss-of-function
Defective copy of a gene that affects the phenotype. Recessive allele is usually loss-of-function.
Recessive Pattern of Inheritance
Must inherit two copies of mutant allele. Two heterozygous individuals will have 1/4 of offspring affected. Offspring of two affected individuals will be affected.
Dominant Pattern of Inheritance
Affected individuals will have inherited mutant allele from at least one affected parent.
Probability
P = Number of times outcome occurs / total # of possible outcomes.
Product Rule
EX: What is the probability that the couple’s first three offspring will have congenital analgesia? 1. Calculate individual probability of phenotype (1/4). 2. Multiply individual probabilities (1/4x1/4x1/4)
Product Rule Used for Combination of Different Offspring
EX: What is the probability that the first offspring will be unaffected, the second affected, and the third unaffected? (3/4 x 1/4 x 3/4)
Product Rule Used for Two or More Genes
EX: Individual with genotypes Aa Bb CC crossed with Aa bb Cc. What is probability of offspring having AA bb Cc? Do monohybrid cross for each genotype then multiply probabilities (1/4 x 1/2 x 1/2)
Binomial Expansion
Used to determine probability that certain proportion of offspring will be produced particular characteristics. What is the probability that two of five children have blue eyes?
Chi Square Test
Used to determine if a genetic hypothesis is consistent with the observed outcome of a genetic cross.
How to Set Up Chis Squared
- Determine hypothesis: is it segregated or assorted independently? 2. Calculate expected values: Determine ratio and determine probability. 3. Multiply probability with total. 4. Determine chi squared value and use chi square table. A P value less than 5% means the hypothesis is rejected.
X-Linked Inheritance`
Many genes found on X chromosome rather than Y chromosome. Genes on X chromosome govern eye color in fruit flies.
Chromosome Theory of Inheritance
Inheritance pattern of traits can be explained by transmission patterns of chromosomes during meiosis and fertilization. 1. Chromosomes contain genetic material that is transmitted from parent to offspring and from cell to cell. 2. Chromosomes replicate and are passed from generation to generation from parent to offspring. Each cell retains its individuality during cell division and gamete formation. 3. Nuclei of cells contain homologous pairs of chromosomes and are diploid. At meiosis, one of the two homologs segregates into a daughter cell nucleus. Gametes contain one set of chromosomes - they’re haploid. 4. During formation of haploid cells, nonhomologous chromosomes segregate independently. 5. Each parent contributes on set of chromosomes to offspring. Each set carries a full complement of genes.
Phases of Mitosis
Prophase, Prometaphase, Metaphase, Anaphase, Telophase
Prophase
After the chromosomes are decondensed (less tightly compacted) from interphase, mitosis begins with this stage. Chromosomes have replicated, resulting in 12 chromatids joined as 6 pairs of sister chromatids. Nuclear membrane begins to dissociate into vesicles. Nucleolus becomes less visable. Chromosomes move apart and mitotic spindle begins to form.
Prometaphase
Centrosomes move to opposite sides of cell. Spindle fibers interact with sister chromatids. Microtubules grow and are “captured” by kinetechores. Mitotic spindle is completely formed.
Metaphase
Sister chromatids align along metaphase plate. Metaphase begins once chromatids have alligned. Each pair of chromatids are attached to both poles by kinetechore microtubules.
Anaphase
Connection that holds sister chromatids together is broken. Each chromatid or monad, is linked to only one of the two poles. Chromatids move towards the pole they’re attached to. Kinetechore microtubules shorten. Poles themselves move farther apart due to elongation of polar microtubules and motor proteins.
Telophase
Chromosomes reach their perspective poles and decondense. Nuclear membrane reforms. Two nuclei with six chromosomes each.
Cytokinesis
Two nuclei and organelles are segregated into separate daughter cells. In animal cells, this occurs shortly after anaphase and a cleavage furrow is formed. In plants, a cell plate.
Meiosis
Diploid eukaryotic cells divide into haploid cells which contain a single set of chromosomes.
Prophase of Meiosis I
Replicated chromosomes condense. Synapsis begins in which chromosomes recognize each other and align. Bivalents or tetrads, contain two pairs of sister chromatids and crossing over occurs. Synaptonemal complex dissociates.
Crossing Over
Exchange of chromosome pieces. In animals, a chromosome can undergo slightly more than two cross overs, while in plants, 20 or more. Connection that occurs as a result is a chiasma.
Prometaphase of Meiosis I
Spindle appapratus is complete and chromatids are attached to kinetechore tubules.
Metaphas of Meiosis I
Bivalents organized at metaphase plate. Pairs of sister chromatids are aligned in a double row. Random alignment of homologous chromosomes increases diversity. One pair of sister chromatids is linked to one of the poles.
Anaphase of Meiosis I
Two pairs of sister chromatids separate. Connection that holds chromatids does not break. Two dyads in a tetrad separate from one another and migrate to opposite poles.
Telophase of Meiosis I
End result is two cells with three pairs of sister chromatids but cells are considered to be haploid.
Meiosis II
Two cells that begin meiosis II each have six chromatids that are joined as three pairs of sister chromatids or three dyads. Analogous to mitosis. Produces four haploid cells.
Meiosis vs Mitosis
Mitosis produces two diploid daughter cells with six chromosomes each. Meiosis produces four haploid daughter cells with three chromosomes each.
Incomplete Dominance
A condition in which the phenotype is intermediate between the corresponding homozygous individuals. Can display a 1:2:1 ration.
Overdominance
Phenomenon in which a heterozygote has greater reproductive success compared with either of the corresponding homozygotes. EX: Sickle Cell Anemia. Heterozygotes are more resistant. Explanations of overdominance: disease resistance, homodimer formation, variation in funcional activity.
Multiple Alleles
Within a population, genes are typically found in three or more alleles. EX: ABO group of antigens that determine blood type.
Codominance
Two alleles are expressed in the heterozygous individual. EX: Ia and Ib alleles for blood type.
Lethal Allele
An allele with the potential to cause death within an organism. Absence of specific protein results in lethal phenotype. Gain of function can be more harmful then a loss of function when a gene is abnormally expressed.
Conditional Lethal Alleles
Can be temperature sensitive, or sensitive to an environmental agent.
Gene Interaction
Allelic variations of two different genes affect a single trait. A single trait was determined by two different genes. EX: A rose comb chicken.
Epistasis
Inheritance pattern in which the alleles of one gene mask the phenotypic effects of the alleles of a different gene. Occurs when two or more different proteins participate in a common function.
Hemizygous
Single copy of an X-linked gene in the male. A male mammal is said to be hemizygous for X-linked genes.
Recombinant
- Combination of alleles or traits that are not found in the parental generation. 2. DNA molecules that are produced by molecular techniques in which segments of DNA are joined to each other in ways that differ from the original arrangement in their native chromosomal states. EX: Cloning of DNA into vectors, which are small segments of DNA used as carriers for other segments of DNA.
Crossover Frequency
RF = (Recombinants / total #) x 100. If percent of recombinant offspring approaches 50%, value becomes progressively more inaccurate measure of actual map distance. Greater distance = more crossovers.
3-Point Testcross
Three genes with two alleles each (2 x 2 x ) = 8 possible combinations of offspring. If assorted independently, all eight combinations would occur equally. In crosses with linked genes, parental phenotypes occur most frequently in offspring. Double crossovers are always the least frequent. 1. Determine the map distance between two linked genes of the recombinant offspring. 2. Determine map distance between double crossovers. 3. Find how many offspring are produced as a result of a double cross over. 4. Find interference value.
Positive Interferance
Occurrence of a crossover in one region of a chromosome decreases the probability that a second crossover will occur nearby. First cross over interferes with second.
Unordered Tetrad
Ascus allows tetrads or octads of spores to randomly mix together.
Ordered Tetrad
Tight ascus prevents spores from randomly moving around.
First-Division Segregation
Crossover has not occured. Linear arrangement. Four haploid cells carry A allele are adjacent to four haploid cells with a allele. 4:4 ratio. A and a alleles have segregated from each other after first meitotic division.
Second-Division Segregation
If crossover occurs between the centromere and the gene of interest, the ordered tetrad will deviate from 4:4 pattern. Depending on locations of two chromatids, the ascus will contain a 2:2:2:2 or 2:4:2 pattern. A and a alleles do not segregate until the second meiotic division.
What type of segregation is used to calculate the map distance between the centromere and the gene of interest.
Second-Division Segregation
Parental Ditype
Following meiosis, tetrad can contain four spores with the parental combinations of alleles. No crossing over.
Tetratype
Ascus contains two parental cells and two nonparental cells. Single crossover.
Nonparental Ditype
Ascus contains four cells with nonparental genotypes. When genes assort independently, the number of parental ditype equals nonparental, thus yielding 50% recombinant spores. Double crossover.
Conjugation
Direct physical action between two bacterial cells. One bacterium acts a donor and the other a recipient.
Who and what experiment was done to determine conjugation?
Bernard Davis used a U-Tube to determine that without physical contact, bacteria cannot transfer genetic material to one another.
F Factors
F+ bacteria have the the F factor gene. Make Sex Pili. Transfers F factor to F- bacteria.
Conjugation Bridge
Allows passageway for DNA transfer.
Hfr Strain
High frequency of recombination. Forms when F factor integrates with cell’s chromosome. Longer segments for longer periods of time allow for more amino acids.
Interrupted Mating
Bacteriophages are sheared from the surface of E. coli cells if spun in a blender. Detach from surface but the bacteria remain healthy and viable. Treatment could also be used to separate bacteria during conjugation.
Who discovered interrupted mating?
Wollman and Jacob
Goal of Interrupted Mating
Interruptions at different times would lead to various lengths of the Hfr chromosome.
Who determined bacterial DNA was circular?
Cairns, Lederberg and Tatum
Transduction
Virus infects bacteria and then transfers genetic material from that bacterium to another.
Transformation
Genetic material released into environment when bacteria dies. Material can bind to living bacteria where it can be absorbed.
Lytic Cycle
Phage injects DNA. Phage DNA directs synthesis of new phages and the host DNA is degraded. Cell lyses and releases new phages. New phages can bind to other bacterial cells.
Propage
Integrated phage DNA
Lysogenic Cycle
Phage DNA integrates with host chromosome. Prophage DNA is copied when cells divide. On rare occasions, prophage may be excised from host chromosome.
Temperate Phage
Bacteriophage that exists in lysogenic cycle. Temperate phages do not produce new phages and do not kill the host bacterial cell.
Homologous DNA
The exchange of DNA segments between homologous chromosomes. Occurs during cross over in meiosis. Helps repair DNA and ensures proper segregation of chromosomes. Bacteria can have more then one copy of a chromosome, which can exchange genetic material. During DNA replication, replicated regions may also undergo homologous recombination.
Competent Cells
Bacterial cells that are able to take up DNA.
Competence Factors
Cells that take up DNA naturally carry genes that encode proteins. Proteins facilitate the binding of DNA fragments to the cell surface, uptake of DNA into cytoplasm, and incorporate into bacterial chromosome.
Factors that influence competence
Temperature, ionic conditions and nutrient availability can affect competence.
Steps of Transformation
- DNA fragment binds to a cell surface receptor. 2. Endonuclease cuts DNA into smaller fragments. 3. One strand is degraded and a single strand into cell via uptake system. 4. DNA strand incorporated into bacterial chromosome via homologous recombination. 5. Heteroduplex repaired.
Heteroduplex
During homologous recombination, alignment of the lys- and lys+ results in a heteroduplex with a number of mismatches. DNA repair enzyme recognize complex and repair it.
AT-rich region
DNA binding proteins (HU, IHF) causes DNA to bend around the complex of DNA proteins and results in separation of AT base pairs because of only two hydrogen bonds instead of the three at CG.
Helicase
Breaks the hydrogen bonds between two double-strands, thereby generating two single stands. Seperate in two directions creating two replication forks. Bidirectional Replication.
Topoisomerase II (gyrase)
Travels in front of DNA and alleviates positive supercoiling.
Single-strand binding proteins
Binds to the strands of parental DNA and prevent re-forming of double helix.
Primase
Forms RNA primers about 10-12 bp long. One primer in the leading strand and there are multiple made in the lagging strand.
DNA polymerase III
Alpha subunit catalyzes covalent bonds between adjacent nucleotides. Sigma subunit allows for proofreading in the 3’ to 5’ direction. Beta subunit clamps polymerase and prevents it from falling off DNA. Synthesizes nucletotides in 5’ to 3’ direction. Template strand is read in 3’ to 5’ direction.
DNA polymerase I
Removes RNA primers and fills in gaps with DNA.
DNA ligase
Covalently attaches adjacent Okazaki fragments
DNA polymerase II, IV, and V
Play a role in repair and replication of DNA.
DNA replication in eukaryotes begins with…
Assembly of prereplication complex and origin replication complex. Binding of MCM helicase starts DNA replication.
Flap Endonuclease
DNA polymerase gamma elongates the left okazaki fragment and causes flap to form on the right. Flap endonuclease removes the flap. Continues until lagging strand is formed.
Topoisomerase I
Removes negative supercoiling.
Transcription in Bacteria
Sigma factor recognizes a promoter and RNA polymerase forms closed complex. Open complex is made and short RNA is made. Sigma factor releases and core enzyme proceeds down the DNA. RNA polymerase moves in a 3’ to 5’ direction but synthesizes 5’ to 3’.
Termination in Bacteria
Once a p recognition site is reached, RNA polymerase forma a stem-loop and then proceeds to terminator. Stem-loop pauses RNA poly. During this pause, p protein catches up and seperates RNA-DNA hybrid. U-Rich (weak U and A bonds) sequence is unable to hold hybrid together and disassociates.
Core promoter
Short DNA sequence necessary for transcription to take place. Consists of TATA box. Produces low level of transcription called basal transcription.
Transcription in Eukaryotes
Transcriptional binding proteins promote RNA polymerase II. Closed complex is formed. TFIIH forms an open complex. CTD breaks contack with proteins and they’re released.
Termination in Eukaryotes
RNA polymerase II transcribes gene past the polyadenation signal. RNA is cleaved past the signal and RNA polymerase continues synthesizing RNA.
Allosteric vs. Torpedo Model
Elongation or termination factors causes RNA polymerase to disassociate (Allosteric). Exonuclease catches up to RNA polymerase II and causes termination (Topedo).
Genetic Code
Ability of mRNA to be translated into a specific sequence of amino acid relies on this. Sequence of bases provides coded information that is read in groups of three known as codons.
Sense Codons
Codons that code for a particular amino acid.
Nonsense Codon
Also called termination or stop codons.
Maternal Effect
Inheritance pattern for certain nuclear genes in which the genotype of the mother directly determines the phenotype of her offspring. Gene products of nurse cells, which reflect genotype of mother, influence early developmental stages of the embryo.
Genomic Imprinting
Inheritance pattern that involves a change in a single gene or chromosome during gamete formation. Depending on when the modification occurs during spermatogenesis or oogenesis, imprinting governs whether an offspring will express a gene that has been inherited from its mother or father.
How does Genomic Imprinting work?
A marked gene allows for only the parternal gene to be expressed, rather then the maternal silenced gene. After fertilization, imprint is maintained and silenced gene will not be expressed. During gametogenesis, the imprint is erased and the female mouse produces eggs in which the gene is silenced and the male contains either an active allele or a silenced allele resulting in a normal sized or a dwarf sized mouse.
Lac Operon - No lactose in the environment
In the absence of the inducer allolactose, the repressor protein is tightly bound to the operator site, thereby inhibiting the ability of RNA polymerase to transcribe the operon.
Lac Operon - Lactose present
Allolactose binds to the repressor. This alters the conformation of the repressor protein, which prevents if from binding to the operator site. Therefore, RNA polymerase can transcribe the operon.
Lac Operon Cycle
- Lactose becomes available and a small amount is taken up and converted to allolactose. Allolactose binds to repressor and falls off operator site. 2. Lac operon proteins are synthesized. This promotes the efficient uptake and metabolism of lactose. 3. Lactose is depleted and allolactose levels decrease. Allolactose is released from the repressor allowing the it to bind to the operon site. 4. Proteins involved with lactose utilization are degraded.
Effects of Lactose and Glucose
The presence of lactose allows the binding of allolactose to the repressor keeping it from binding to the operon. If glucose is present, cAMP is unable to bind to CAP which means slower rate of transcription.
What occurs when Trp levels are low?
Trp does not bind to trp repressor protein, which prevents the repressor from binding to the operator site. RNA polymerase can transcribe the operon, which leads to expression of trpE, trpD, trpC, trpB, trpA genes. Genes code for enzymes involved in trp synthesis.
What happens when Trp levels are high?
Trp acts as a corepressor that binds to the trp repressor protein. The tryptophan-trp repressor complex then binds to the operator site to inhibit transcription. Attenuation can also occur, which is when RNA is transcribed only to the attenuator sequence , and then transcription is terminated. Inhibits further production of tryptophan.
Activator
A transcriptional regulatory protein that increases the rate of transcription.
Enhancer
DNA sequence that functions as a regulatory element. The binding of a regulatory transcription factor to the enhancer increases the level of transcription.
Repressor
Regulatory protein that binds to DNA and inhibits transcription.
Mediator
Protein complex that interacts with RNA polymerase II and varioius regulatory transcription factors. Depending on its interactions with regulatory transcription factors, mediator may stimulate or inhibit RNA polymerase II.
Transcription Factors
Broad category of proteins that influence the ability of RNA polymerase to transcribe DNA into RNA.
Steroid Hormone
May influence the ability of a transcription factor to bind to the DNA. Binds to glucocoricoid response element that is next to a particular gene. Binding to these receptors activates transcription of adjacent target gene.
Peptide Hormone
Synthesized in cells from amino acids. Increase cAMP within cells.
Chromatin Remodeling
Changes within structure of chromatin.
Closed Conformation
Transcription may be difficult to impossible.
Open Conformation
More easily accessible to transcription factors and RNA polymerase so transcription can occur.
Acetylation
DNA becomes less tightly bound to the histone proteins via histone acetlytransferase, which removes acetyl groups. Acetyl group eliminates positive charge on the lysine side chain, thereby interrupting attraction between histones and DNA backbone.
DNA Methylation
Occurs via DNA methyltransferase, which attaches a methyl group to the number 5 position of the cytosine base. Inhibits transcription of eukaryotic genes. Methylator of a CpG island may inhibit binding of a transcriptional activator protein to the promoter region. Methyl-CpG-binding protein to a CpG island may recruit other proteins such as histone deacetylase that convert chromatin to a closed conformation.
CpG Islands
Found in vertebrates and plants. Occur near promoter. Expression of some genes may be silenced by methylation of CpG islands.
Bioremediation
Use of living organisms or their products to decrease pollutants in environment.
Gene Replacement
Cloned gene undergoes homologous recombination and replaces normal gene. EX: Glofish
Gene Addition
Cloned gene may recombine nonhomologusly at some other chromosomal location. EX: Chimeras - An organism with cells from two different individuals.
Gene Redundency
One type of gene is inactivated, another gene with a similar function may be able to compensate for the inactive gene.
Gene Knockin
Gene of interest has been added to a particular site in the genome.
Totipotent
Fertilized egg. Gives rise to all cell types in an adult organism.
Embryonic Stem Cells
Are pluripotent. Can differentiate into almost every cell type within the body. Found within early mammalian embryo.
Multipotent
Differentiates into several cell types but far fewer then an ES cell. Many adult stem cells are multi or unipotent.
