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Let the frequency of allele Abe represented by q. p + q = 1p2+ 2pq + q2 = 1Apply the probability of marrying parent carrying gene of interest to pedigree problems.Downloaded by Nat Kp ([email protected])lOMoARcPSD|2850388
Week 3 Lecture 5 Variation in Chromosome Number and Structure:chromosome •a DNA molecule with part or all of the genetic material (genome) of an organismsister chromatid •pieces of identical DNA that are crucial in the process of cell replication and divisionhomologue •a chromosome that is similar in physical attributes and genetic information to another chromosome with which it pairs during meiosisnondisjunction •results in daughter cells with abnormal chromosome numbers (aneuploidy) - failure of a pair of homologous chromosomes to separate in meiosis I, failure of sister chromatids to separate during meiosis II, and failure of sister chromatids to separate during mitosisaneuploidy•the presence of an abnormal number of chromosomes in a cellpolyploidy •containing more than two paired (homologous) sets of chromosomesDiploid 2n:mitosis •cell division initiates by doubling each chromatid, then chromatids are packaged and divided between daughter cells - if 2n = 46, 4n = 92 after DNA duplicationmeiosis I •gamete production initiates by doubling each chromatid, then maternal and paternal chromatids stay together (bivalents) and segregate together - if 2n = 46, 4n = 92 after DNA replicationmeiosis II •no DNA replication, segregation of sister chromatids before divisionDownloaded by Nat Kp ([email protected])lOMoARcPSD|2850388
Cytological Techniques •geneticists use stains to identify specific chromosomes and to analyze their structures, often focuses on chromosomes in dividing cellsGiesma banding •lyse cell, stain with GiesmaQuinacrine •lyse cell, stain with quinacrineChromosome painting •ﬂuorescent dyes stain only some chromosomesIdeogram •identification of chromosome, result of staining bandsKaryotype •depiction of duplicated chromosomes of a cell arranged for cytogenic analysisMonoploidy n •only one set of chromosomes - male ants, bees, waspsDiploidy 2n •2 sets of chromosomes - most plants and animal speciesPolyploidy 3n,4n, … •more than the normal number of sets of chromosomes30-35% of ﬂowering plants are polyploids.Polyploidy is rare in the animal kingdom.Seedless varieties of fruits have an odd number of sets of chromosomes (like triploids or pentaploids). Meiosis is impaired because the organism will produce gametes with different number of chromosomes. The organism will be sterile. Instead, plants have omnipotent cells - cells that can differentiate into all cell types - any cell can form a whole new plant.Problems with Polyploidy - Triploid 3n: unbalanced segregation of bivalents in meiosis I•the number of chromosomes in a gamete can vary•gametes that have extra chromosomes or lack certain chromosomes are not viable•the gamete pairs that will re-create the 3n plants is extremely rareMeiosis in bananas! 3n = 33, 3 trivalentsfor every chromosome:Then consider the segregation possibilities for each set!