Getics midterm

• Gregor Johann Mendel

  July 22, 1822 - January 6 , 1884
• In the 1860 s, he introduced a new theory of inheritance based on his experimental work with pea plants
• Heredity


  The result of discrete units of inheritance, and even single unit or gene was dependent in its actions in an individual's genome
• Mendel is the Father of Genetics
• Inheritance of a trait


  Depends on the passing-on of units/genes
• Dominant trait


  The visible form
• Recessive trait


  The hidden form
• Individuals


  Inherit one gene from each parent so that the individuals have a pairing of two genes
• Alleles


  The alternate forms of genes
• Homozygous


  When the two alleles that form the pair for a trait are identical
• Heterozygous


  When the two genes are different
• Genotype


  The pair of alleles in an individual that are responsible for the expression of a certain trait
• Phenotype


  The observable characteristics of an individual
• Monohybrid crosses observe the inheritance pattern of one character
• Dihybrid crosses observe the inheritance pattern of two characteristics
• Mendel's observations and conclusions are summarized in the following three principles, or laws
• Law of Dominance


  When mating occurs between two organisms of different traits, each offspring exhibits the trait of one parent only. If the dominant alleles are present in an individual, the dominant trait will result. The recessive trait will only if both alleles are recessive.
• Law of Segregation


  Both alleles of a given gene -- one inherited from the mother, the other from the father -- are expressed equally in each offspring.
• If a plant has two copies of every gene, how does it pass only one copy of each to its progeny? And how then do the offspring end up with two copies of these same genes, one from each parent?
• 3 Phenotypic Ratios

  • 3:1 Ratio
  • 1:1 Ratio
  • Uniform progeny
• Ratios of Genotypes


  • 1:2:1 ratio
  • 1:1 ratio
  • Uniform progeny
• Law of Independent Assortment

  During the formation of the gamete, the alleles of one trait will segregate independently of another trait. Therefore, the inheritance of genes responsible for the expression of color and shape of the seeds were not dependent on each other.
• Branch diagram

  A convenient way of organizing all the combinations of characteristics. It helps keep track of all the potential combinations of traits that may appear in the progeny. It can be used to determine phenotypic or genotypic ratios for any number of characteristics.
• The rules of probability can be applied to Mendelian crosses to determine the expected phenotypes and genotypes of offspring. The three mathematical operations used are the product rule, sum rule and chi square.

  
• Probability


  A mathematical measure of likelihood or a likelihood that a particular event will occur. The empirical probability of an event is calculated by dividing the number of times the event occurs by the total number of opportunities for the event.
• Mendel demonstrated that the probability of the event "round seed" was guaranteed to occur in the F1 offspring of true-breeding parents, one of which has round seeds and one of which has wrinkled seeds. When the F1 plants were subsequently self-crossed, the probability of any given F2 offspring having round seed was now three out of four.
• Product rule

  The probability of two independent events occurring together can be calculated by multiplying the individual probabilities of each event occurring alone.
• Sum rule


  The probability of the occurrence of one event or the other, of two mutually exclusive events, is the sum of their individual probabilities.
• According to Mendel, to use probability laws in practice, it is necessary to work with large samples sizes because small sample sizes are prone to deviations caused by chance.
• Chi Square test

  Uses probability to detect differences between Expected and Observed Values. It can be used to infer if the simple assumptions, such as independent assortment, are not true.
• Mendel's theory of inheritance includes the principles of dominance, segregation, and independent assortment
• Incomplete Dominance


  Both traits are expressed but the traits are blended together rather than occurring in discrete patches
• Co-Dominance

  Alleles combine to influence the phenotype of the organism
• Sex-linked Traits

  The sex of the individual is determined by sex chromosomes
• Multiple Allelism


  More than two alleles are present within a group of organisms. Also referred to as an allelic series.
• Multiple Allelism


  • Duck feather patterns
  • ABO blood type

  
• ABO blood group

  The three common alleles are IA, IB, and i. IA and IB show co-dominance.

  
• Penetrance


  The percentage of individual organisms having a particular genotype that express the expected phenotype
• Expressivity


  Variability in the degree to which the phenotype is expressed
• Lethal Allele


  Causes death at an early stage of development, often before birth, so some genotypes may not appear among the progenies. Can be recessive or dominant.