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Pitt BIOSC 0815 - Genes and Diseases
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BIOSC 0815 1st Edition Lecture 14Outline of Last Lecture I. Mendela. Three existing theoriesi. Spermistii. Ovistiii. Blendingb. Mendel’s approachc. HypothesesII. Organizing traitsIII. HomozygousIV. HeterozygousV. ConclusionsVI. Factors/AllelesVII. Recessive or Dominant Outline of Current Lecture I. Different Traits:a. Dihybrid cross.II. Law of independent assortmentIII. Product Law of ProbabilityIV. Human Genetic PatternsV. Patterns of Inheritancea. Autosomal Recessiveb. Autosomal DominantVI. Reading Pedigree ChartsCurrent LectureMendelian dihybrid crosses and pedigrees- Last lecture covered Mendel looking at one trait that occurs as different alleles in true breeding parents. This was called a monohybrid cross.- Different Traits:o Dihybrid cross. Mendel followed two traits in the offspring from true breeding parents with differing traits. o He was curious to see whether the traits were related (for example that all plantswith yellow seeds had to have round seeds).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.o He tested this to see seed color (Yellow and green, Y or y) and for seed shape (Round and wrinkled, R or r). He had parents that were YR and yr. He took RY and ry and crossed them. F1 was found to be all round and yellow. This tells us that round and yellow are dominant.  Allowed these RrYy F1 generation to self-breed.  9/16 were round and yellow, 3/16 were round and green, 3/15 were wrinkled and yellow, and 1/16 were wrinkled and green.- 9:3:3:1 is the ratioo The middle two were a completely new outcome with two new previously unseen phenotypes.  What happened? RRYY + rryy  RrYy RrYy+RrYy  many combinations Also observed that the two traits are not linked. Yellow doesn’t necessarily go with round or green with wrinkled. The traits can be separated.  During meiosis the homologous chromosomes. Durig metaphase I they can line up in different combinations. Chromatids give us many different varieties.  Extended punnett square.-- Law of Independent assortment:o Transmission of one gene does not influence that of anothero In a dihybrid cross there are sixteen possibilities and a phenotypic ratio is 9:3:3:1 is typical. This ratio is the basis to understand that something else might be happening that isn’t clear initially and occurs at the level of the gene. - Punnett Square:o As we increase the number of traits, constructing a punnet square can be difficult. An easier way to determine the outcome is through a probability rule.o This is done by looking at each trait separately and determining its probability of occurring. Then look at the next trait and find the probability of that, and then multiply their probabilities together. o Ex: what is the chance of getting a wrinkled green seed from RrYy X RrYyo Probability of getting wrinkle (rr): 1/4o Green (yy): ¼o ¼*1/4 = 1/16 probability of getting rryy.o This can be done with other parents. Ex: RrYy X RRyy- Product law of probabilityo The probability of 2 events happening simultaneously is the product of each of the separated probabilities. The events have to be independent of each other.- Human Genetic Patternso Little controlo Can be tracked by making a pedigree which is a family tree.o It is a chart of the genetic history of family over several generations.o scientists or genetic counselor would find out about your family history and makethis chart.o Making pedigree: Circle for female, male is square. Line is marriage. Affected by disorder: filled in symbol. X linked (a dot in the symbol) a carrier has a line through it. Deceased is a line through that person. If you are looking at a specific individual in a pedigree they are referred to as the proband. o Often in a pedigree you do not know the genotypes, as they may be carriers of the disease. o Purpose Advising parents of whether to have child or safety of child. - Patterns of inheritance;o Autosomal recessive: Ex: Albinism. (aa) to show trait. Aa is a carrier. AA is normal. Cycstic fibrosis, sickle cell anemia, phenylketonuria, tay-sachs disease.  Trait is very rare in pedigree Trait often skips generations, and is hidden in carriers.  Affects males or females equally.  Why do they persist?- Heterozygous advantage: o May help or provide a survival benefit to the carrier. Such as cystic fibrosis protects against severe diarrhea loss from cholera because of fewer ion channels. o Autosomal dominant: Anytime the dominant gene occurs there is a presence of the disorder Trait is common in the pedigree Trait is found in every generation Affected individuals transmit the trait to about half of their children regardless of sex (because it is not on related to the sex chromosome). Example: achondroplasia. Can be deadly. o A karyotype: munbering chromosomes based on size. 1-22 pair are somatic autosomes. #23 are sex chromosomes. o An autosomal trait is where the gene is located on an autosomal chromosome: aka not a sex chromosome. - Looking at a pedigree chart:o Is the disorder dominant or recessive If it is dominant one parents must have the disorderIf it is recessive neither parent has to have the disorder but they can be carriers of


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Pitt BIOSC 0815 - Genes and Diseases

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