Boil 3333 1st Edition Lecture 3Genetics Mendels experiments were virtually ignored for 34 years - why!?Showed a pic of his notebook - full of numbers - botanists of his time were concerned with how the plants looked but not the careful analysis that was discussed at last classHis approach was well conceived, careful but very quantitative yet his “laws” couldn’t be placed in a firm observational/mechanistic biological contextNothing was known about the mechanics of passing genes from one organism to anotherOne of the experiments influenced by Mendel was the Fertilization and Pronuclear fusion(Hertwig 1875) - sea urchin egg with a membrane surrounding it and a ton of sperm attempting to enter - one sperm will enter - will have to first penetrate the membrane. The spermnucleus is what does this Pro nuclear fusion - the egg and sperm pro nucleus will fuze together Studies n mitosis indicated chromosomes had characteristics consistent with heritable information transfer Scientists started to associate the nucleus with chromosomes Nucleus disappears and chromosomes appear - chromosome shapes and numbers are a Species characteristic - this indicates a heritable process - what happens here? chromosomes are paired - a copy of each one is partitioned to daughter cells - nucleus reforms August Weismann (1880) - studies in early insect Embryogenesis showed a population of cellsthat arose early in development and gave rise to the gametes Showing 2 eggs - different by about an our - the first cells that begin to develop in the embryo are developing at the back region of the egg - these cells will go onto become the germ cells. In the slightly older embryo you can clearly see the cells forming These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Weismann postulated the Germ-plasm theory - that these cells are different than the regular somatic cells in the animal in terms of properties due to the fact that they will be responsible for transmitting genetic info from one generation to another - postulated that these have to be different from somatic cells in their division properties Predicted a reductional division for these specialized germ cells Correspondence of chromosome behavior and mendelian factors - both pair - then segregate - and are partitioned at random to daughter cells On fertlization, 2 copies of information are restored 1900 Mendel’s laws are rediscoveredHugo de vriesErich von TschermakCarl CorrensAll rediscovered these independently of each other - beginning of 20th century - menders work was finally recognized1902 - William Bateson created the word genetics19077- Wiljelm Joanssen Considering what we know about DNA and meiosis we expect that Mendels principle of independent assortment must hold for all genes: FALSE Why???! - During the first meiotic division - 2 chromosomes will be lining up relative to one another and separating - due to this separation - 4 different gametes are equally likely - this is because there are so many different ways that they can line up - But suppose the A/a B/b gene loci are close to one another on the same chromosome.. they willbe traveling together with the same centromere that will pull it into the same daughter cell - genes that are very close to each other - linked - will NOT show independent assortment - thats why it is false!!! How does probability play into the idea of segregation and independent assortment First thing we red to do is define probabilityProbability (p) the number of anticipated events/total number of PossibilitiesProbability of pulling an ace from a straight deck of cards 4/52 or 1/13The product rule: if events are independent of one another -they follow the product rule - for independent events the probability of events occurring is the product of their individual probabilities P (A and B) = P(A) * P(B)Probability of pulling an ace of spades from a straight deck of cards 1/13 * 1/4 = 1/52The Sum Rule:For mutually exclusive events the probability (P) of either event occurring is the sum of their individual probabilities: P (A or B) = P(A) + P(B)Ask the question: what is the probability of pulling an ace or a king out of a straight deck 1/13 + 1/13 = 2/13 Applications for Mendel’s crosses - Punnet square to represent the products in a monohybridcrossIn monohybrid crosses, the Probability of proceeding an offspring of dominant phenotype is: P(A_) = P(AA or Aa) = 1/4 + 2/4 = 3/4 Phenotypic segregation in Dihybrids follows the product rule: AaBb X AaBb - 2 different gene loci segregating during meiosis *GET PIC FROM PPTFor Aa xAa: For BbxBb3/4 A_ 3/4 B_1/4 aa 1/4 bb3/4 B_1/4 bbAaBbcc x AaBBCcIn the above cross what is the probability of producing progeny that are phenotypically dominantfor A and B but recessive for C? P(A_B_cc) = Aa xAa = 3/4 A_; BbxBB = all B_; cc X cc = 1/2 cc Aa BBCcdd x aabbCcDD P(AaBbCcDd) = 1/2 X 1 X 1/2 X 1 = 1/4 Mendelian inheritance patterns in humans: pedigree Analysis: - Often difficult to monitor gene transmission of heritable disorders in human populations small no of progenylong generation timecannot est. test crossesAssembling a fam history is importantPedigree assembly and analysis of transmission patterns Patterns of transmission of single gene traits - get pic from ppt Autosomal Dominant and Recessive Inheritance in Humans Autosome - non sex chromosome Since mutant gene is transmitted on chromosome not involved in sex determination disease segregates …Autosomal Dominant inheritance in HumansSince trait will be rare in the general population the most common marriage that all show affected progeny will be Aa x aa “a” the; norma;’ the standard or “wild type” allele Do not equate dominance with the most common gene present in the populationor 1/2 the progeny of an affect parent would be expected to inherit the trait Acondroplasia - a form of short limbed dwarfism True or false - shows all pedigree characteristic expected for an autosomal dominant trait - FALSE.Autosomal recessive inheritance in humans - since trait will be rare in the general population, the most common marriage that will show affected progeny will be Aa x