midterms gen bio (3rd quarter)

• Non-Mendelian Genetics refers to traits that are not aligned with Mendel's law
• In the 20th century, geneticists learned that the patterns of inheritance were more complicated than what Mendel had discovered
• Characteristics of Non-Mendelian Genetics

  • When alleles are not completely dominant or recessive
  • A gene has more than 2 allele
  • A gene produces multiple phenotypes
• Complete Dominance


  One allele has completely dominated the other, following Gregor Mendel's hypothesis
• Incomplete Dominance


  Neither of the alleles is completely dominant over the other, resulting in an intermediate phenotype ("blending hypothesis")
• Incomplete Dominance


  • Curly hair (C) is incompletely dominant to straight hair (S), resulting in wavy hair (CS) in the offspring
• Codominance


  Both alleles are fully expressed, resulting in a phenotype that is a combination of the two
• Epistasis


  • One gene masks or modifies the expression of another gene
• Polygenic Inheritance


  • A single phenotypic trait is influenced by multiple genes
• Nature


  Genetic factors that influence an organism's traits
• Nurture


  Environmental factors that influence an organism's traits
• Incomplete dominance


  Neither of the alleles is completely dominant over the other, resulting in an intermediate phenotype
• Incomplete dominance


  • Curly hair (C) is incompletely dominant to straight hair (S)
• Incomplete dominance example


  An individual with curly hair is crossed with a straight haired individual, resulting in an offspring with wavy hair
• Codominance


  Two different alleles are simultaneously expressed in a heterozygous individual
• Codominance


  • Blood type, where an individual with homozygous type A blood crossed with homozygous type B blood results in offspring with type AB blood
• Epistasis


  One gene affects the outcome trait of another because of their interaction, where an allele of one gene hides the phenotype of another gene
• Epistasis


  • Coat color of golden retrievers, where the gene for black/brown pigment is hidden by the recessive allele for white pigment
• Polygenic inheritance


  Two or more genes affect the expression of a trait, resulting in a phenotypic spectrum
• Polygenic inheritance


  • Height and skin color
• Nature


  Innate biological heredity inherited from parents at birth, such as eye color, hair color, height, and genetic diseases
• Nurture


  Environmental factors that influence an individual's characteristics, such as parenting styles, culture, social relationships, soil acidity, humidity, and sun exposure
• Mendel's "hereditary factors" were genes
• Mitosis and meiosis were first described in the late 1800s
• Locus/Loci


  Specific locations of genes in chromosomes
• Chromosomes undergo segregation and independent assortment
• The behavior of chromosomes during meiosis can account for Mendel's laws of segregation and independent assortment
• Fruit flies


  • Produce many offspring, have a generation every two weeks, and have only four pairs of chromosomes, making them a convenient organism for genetics studies
• Morgan's experiments with fruit flies provided convincing evidence that chromosomes are the location of Mendel's heritable factors
• Mutant phenotypes


  Traits alternative to the wild type
• Morgan's findings on white-eyed mutant allele

  It must be located on the X chromosome
• Sex chromosomes


  In humans and other mammals, there are two varieties: a larger X chromosome and a smaller Y chromosome
• SRY gene


  Located on the Y chromosome, codes for a protein that directs the development of male anatomical features
• Sex-linked genes


  Genes located on either sex chromosome
• 1. linked genes


  Genes located on the X chromosome
• 1. linked recessive traits


  For a recessive X-linked trait to be expressed, a female needs 2 copies of the allele (homozygous), while a male needs only 1 copy (hemizygous)
• 1. linked recessive disorders


  • Color blindness, Duchenne muscular dystrophy, Hemophilia
• X inactivation


  In mammalian females, one of the two X chromosomes in each cell is randomly inactivated during embryonic development, resulting in a Barr body
• If a female is heterozygous for a particular gene located on the X chromosome, she will be a mosaic for that character
• Morgan's experiments with fruit flies showed that body color and wing size are usually inherited together in specific combinations (parental phenotypes), indicating that these genes are on the same chromosome