genetics III

• Breeding pea plants


  Reproduce sexually
• Fertilization


  Gametes form zygote (fertilized cell)
• Pollination


  Pollen grains from male to female
• Monohybrid Cross


  • Mendel crossed a short plant with a tall plant (P Generation)
  • All offspring (hybrids) were tall (F1 Generation)
  • 2nd Generation (F2) - tall plants from 1st generation to self-polinate
• What is F and P
• Organisms


  • Always have two alleles (one on each chromosome)
  • Alleles can be either dominant or recessive
  • Dominant trait - masks the presence of other traits for the same characteristic
  • Recessive trait - is masked by dominant trait for the same characteristic
• Law of Segregation


  1. There are alternate versions of genes called alleles

  2. For each characteristic, an organism inherits two alleles

  3. Alleles interact in a number of ways

  4. The two alleles for a trait separate during gamete production

  
• Vocabulary


  • Homozygous: the two of the same alleles
  • Homozygous dominant: two dominant alleles (TT)
  • Homozygous recessive: two recessive alleles (tt)
  • Heterozygous: two different alleles (Tt)
  • One is dominant and one is recessive

  
• Law of Independent Assortment

  1. Inheritance of one trait will not affect the inheritance of another

  2. Only true for traits not linked
• Punnett Squares


  • Reginold Punnet (1905) developed punnett squares
  • Monohybrid Cross
  • Shows probability, yet not exact outcomes (genetics follows rule of chance)
• Mendel's Principles


  • Genes are passed from parents to their offspring
  • If two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant or others may be recessive
  • In most sexually reproducing organisms, each adult has two copies of each gene. These genes are segregated from each other when gametes are formed
  • Some alleles are neither dominant or recessive, and many traits are controlled by multiple alleles or multiple genes

  
• Incomplete Dominance


  • When one allele is not completely dominant over another it is called incomplete dominant
  • The heterozygous phenotype is between the two homozygous phenotypes. It is a form of intermediate that results in a third phenotype

  
• Incomplete Dominance


  • A cross between flowers of red (RR) and white (WW) four o'clock plants produces pink-colored flowers (RW)
• Codominance


  • Both alleles contribute to the phenotype
  • In certain varieties of chicken, the allele for black feathers codominant with the allele for white feathers
  • Heterozygous chickens are speckled with both black and white feathers. The black and white colors do not blend to form a new color, but appear separately
• Multiple Alleles


  • Genes that are controlled by more than two alleles are said to have multiple alleles
  • An individual can't have more than two alleles. However, more than two possible alleles can exist in a population
• Multiple Alleles


  • Blood type is an example of a common multiple allele trait. There are three different allele for blood type (A, B, & O)
  • A is dominant to O. Therefore, A is dominant and O is recessive
  • B is also dominant to O. Therefore, B is dominant and O is recessive
  • A and B are both codominant
• Polygenic Traits


  • Traits controlled by two or more genes are said to be polygenic traits
  • Skin color in humans is a polygenic trait controlled by more than four different genes

  
• Epistatic Gene


  • Can interfere with other genes
  • It can mask the phenotype effect of another gene
• The environment interacts with genotypes

  Phenotypes is a combination of genotype and environment
• Phenotype affected by environment

  • The sex of sea turtles depends on both genes and the temperature of the nest (cooler temps produce males, warmer temps produce females and a pivotal temp that would produce equal)
  • Height and weight is another example of phenotype affected by the environment (nutrition and exercise)
• Nature vs nurture
• Mendel's First Law: Law of Segregation


  Members of each gene pair must separate into different gamete cells during the formation of eggs and sperm. Each gamete has an equal chance of possessing either member of a pair of homologous chromosomes

  
• Mendel's Second Law, Law of Independent Assortment

  Genes on nonhomologous or different chromosomes will be distributed randomly into gametes