Unit 4 - BIOL 402

• Genetics Pre-Mendel (1860s)

  • No knowledge of DNA
  • Inheritance was a giant (?)
  • Selective breeding was common
  • Blending hypothesis (ex: mixing blue + yellow = green)
• Mendel


  • Grew up on a farm
  • Went to university in the Czech Republic and became a teacher
  • Had anxiety
  • Failed his teaching license exam multiple times
  • Was a substitute teacher for 14 years before he became a full time teacher
• Garden Peas used in Mendel's Experiments

  • Easy to grow
  • Easy to control pollination - cross or self fertilized
  • Many varieties - visible variation of peas
• Stamen


  Male part
• Ovary


  Female part
• Pollination


  Plant sex
• Fertilization


  Fusion of sperm and egg
• Zygote


  Fertilized egg
• Basic Genetic Cross Setup

  1. Taking two plants & putting them together

  2. Remove the anthers (male portion of the plant) to leave JUST female portion

  3. Take pollen from another pea plant & fertilize the female portion

  4. This is controlled pollination
• Monohybrid


  • Cross-bred a purple and white flower, which made purple flowers
  • This is heterozygous: 1 dominant & 1 recessive allele
  • Daughter flowers continued to self pollinate, they continued to make purple flowers
• Mendel's Conclusions

  • Particulate theory of inheritance: discrete hereditary "factors" (particles)
  • Factors remain physically separated from generation to generation - no blending
  • Occur in pairs
  • Genes: heritable factors that determine traits
  • Allele: different forms (versions) of a gene
  • If the dominant allele is present, the dominant phenotype will show up
  • Mendel concluded that the purple flower was the dominant allele
• Somatic Cells


  • Non-sex cells
  • Homozygous dominant = BB
  • Homozygous recessive = bb
  • Heterozygous = Bb
  • Genotype: alleles present
  • Phenotype: physical appearance
  • Gametes: sex cells - one copy of each allele
• Mendel's Law of Segregation

  • Alleles segregate randomly during gamete formation
  • This is how we get variations from generation to generation, bc they separate randomly
• Determining Genotypes

  Use the punnet square

  
• Punnet Square


  • Put the dominant allele first
  • Mainly found 3:1 ratio
  • Some experiments did not support the 3:1 ratio, so that's why some people did not believe him at the time
  • If the 3:1 ratio did not work, that meant that "co-dominant" alleles are present (two dominant alleles)
  • 3:1 ratio = mendelian genetics
  • Not 3:1 ratio = non-mendelian genetics

  
• FOIL Method

  • First, outside, inside, last
  • This is assuming the law of segregation
• Mendel's Law of Independent Assortment


  • One pair of alleles can segregate independently of another pair during gamete formation
• Mendel used 72 peas in his experiments
• Pollen travels from bees, wind, etc.
• Inheritance was known, but they didn't know how
• Mendel was only looking at one trait at a time
• All offspring from cross pollination are purple
• There is a 3:1 ratio of purple to white flowers
• The dominant allele is present 75% of the time
• Heterozygous individuals will have brown eyes
• Dihybrid Cross


  Two genes being crossed
• Human Karyotype


  • Homologous chromosomes (1-22)
  • X chromosome = female
• Gene Locus


  • Physical location of a gene on a chromosome
  • This encodes who you are
  • Parents who have blue/green eyes will always have children with blue/green eyes
• Mitosis


  • Produces cells with 46 chromosomes
  • Diploid: two copies of each chromosome
  • Haploid: one copy of each chromosome
• Spermatogenesis


  Produces haploid sperm cells
• Oogenesis


  Produces haploid egg cells
• Phases of Meiosis

  1. Similar to mitosis

  2. Haploid cells

  3. After meiosis 1, produces 2 diploid cells

  4. After meiosis 2, produces 4 haploid cells

  
• Crossing Over

  • Occurs in prophase I
  • Exchange of DNA happens between homologous chromosomes
  • The two strands of chromosomes are LITERALLY crossing over
• Oocyte or Spermatocyte

  Diploid cell
• Certain Genes are "Linked"

  • Exchange of DNA happens at specific points
  • This is why we are not identical to our parents
• Humans have diploid cells, sex cells are haploid cells
• Sperm fertilizing egg activates egg
• DNA Replication

  • Conservative model, semiconservative model, and dispersive model were studied
  • The correct model is semiconservative model

  
• Replication is template-directed

  DNA needs a template to follow

  
• Replication needs DNA polymerases

  • 3' and 5' ends
  • Nucleotides cannot be added to the 5' ends