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.