Inheritance

• Inheritance


  Basic Laws and Test Cross
• In families the probability can be deduced by knowing how the affected person is related to a family member
• Tests can sometimes predict the risk of developing symptoms
• The disease may be much more common in some populations than others
• Some single-gene diseases have modes of inheritance, such as cystic fibrosis
• Modes of inheritance


  Patterns in which single-gene traits and disorders occur in families

  
• Huntington's disease


  Autosomal dominant
• Cystic fibrosis


  Autosomal recessive
• Mendel's experiments


  Described the units of inheritance and how they pass from generation to generation
• Mendel had no knowledge of DNA, cells, or chromosomes
• Mendel's laws of inheritance explain trait transmission in any diploid species
• Mendel conducted experiments from 1857 to 1863 on traits in 24,034 plants
• True-breeding


  Offspring have the same trait as parent
• Dominant trait


  The observed trait
• Recessive trait


  The masked trait
• Monohybrid cross


  Follows one trait
• Traits Mendel studied in pea plants

  • Seed shape
  • Seed color
  • Flower color
  • Flower position
  • Pod shape
  • Pod color
  • Plant height

  
• Monohybrid cross


  1. P1 Parental generation

  2. F1 First filial generation

  3. F2 Second filial generation
• Tall plants crossed with short plants

  Produces 3/4 tall and 1/4 short offspring in F2 generation

  
• Mendel's law of segregation


  Each element separates in the gametes
• Homozygous


  • Carry same alleles
• Heterozygous


  • Carry different alleles
• Genotype


  Organism's alleles
• Phenotype


  Outward expression of an allele combination

  
• Wild type


  Most common phenotype
• Mutant phenotype


  Variant of a gene's expression that arises when the gene undergoes mutation
• Mendel observed the events of meiosis

  
• Two copies of a gene separate with the homologs that carry them when a gamete is produced

  
• At fertilization, gametes combine at random

  
• Punnett square


  Represents how genes in gametes join if they are on different chromosomes

  
• Test cross


  Cross an individual of unknown genotype with a homozygous recessive individual
• Single-gene disorders are rare
• Phenotypes associated with single genes are influenced by other genes and environmental factors
• Melanin


  Pigment that determines eye color
• Melanosomes


  Structures that contain melanin
• OCA2


  Gene that confers eye color by controlling melanin synthesis
• HERC2


  Gene that controls expression of the OCA2 gene
• Modes of inheritance


  • Autosomal dominant
  • Autosomal recessive
• Autosomal dominant inheritance


  • Males and females affected, with equal frequency
  • Successive generations affected until no one inherits the mutation
  • Affected individual has an affected parent, unless he or she has a de novo mutation
• Autosomal recessive inheritance


  • Males and females affected, with equal frequency
  • Can skip generations
  • Affected individual has parents who are affected or are carriers (heterozygotes)