genetics

• 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 they 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 (AA,aa)
• Heterozygous


  When the two genes are different (Aa, aA)
• 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


  Observes the inheritance pattern of one character
• Dihybrid Crosses


  Mendel crossed varieties of peas that differed in two characteristics
• Mendel's observations and conclusions are summarized in the following three principles, or laws
• 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 - arises in a simple genetic cross when both parents are heterozygous for a dominant trait
  • 1:1 Ratio - results from the mating of a homozygous parent and a heterozygous parent
  • Uniform progeny - a cross between any two homozygous parents produces progeny all having the same phenotype
• Ratios of Genotypes


  • 1:2:1 ratio - produced by a cross between two heterozygotes
  • 1:1 ratio - produced by a cross between a heterozygote and a homozygote
  • Uniform progeny - produced by a cross between two homozygotes
• 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
• In genetic cross, the probability of the dominant trait being expressed is dependent upon its frequency. In this case, both parents possessed a dominant and recessive gene from the trait of flower color. The dominant trait is expressed in ¾ of the offspring and the recessive trait is expressed in ¼.

  
• 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 pea-plant characteristics he studied were transmitted as discrete units from parent to offspring, and different characteristics were transmitted independently of one another and could be considered in separate probability analyses.

  
• 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.
• Chi Square test


  Uses probability to detect differences between Expected and Observed Values. It can be used to infer that the simple assumptions, such as independent assortment, are not true if the observed data differ substantially from what would have been expected.

  
• Mendel's theory of inheritance includes 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.
• Modifier Gene


  A gene that influences the expression of another gene
• Gene Interaction


  The effects of genes at one locus depend on the presence of genes at other loci. The products of genes at different loci combine to produce new phenotypes that are not predictable from the single effects.
• Lethal allele


  An allele that causes death at a near stage of development, often before birth, so some genotypes may not appear among the progenies