Mendel & Inheritance

Gregor Mendel

  • An Austrian Monk (1822-1884)
  • He was interested in how traits (characteristics that organisms have) were passed on from generation to generation.
  • He used pea plants for his studies.
  • He crossed (mated) *__true breeding__ peas.

  *Pea plants that inherited the same traits from generation to generation.

Misconception of the Time

  • Initially it was thought that traits “blended together”.
  • However, in Mendel’s study, yellow and green pea plants only made yellow when crossed.

  Yellow x Yellow = 75% yellow, 25% green

Solving a Genetic Problem?

How is this possible?

Step 1. Make a let statement

Let Y = yellow (in pea plants, yellow is dominant)

Let y = green (in pea plants, green is recessive)

Step 2. State the parental genotypes

P: YY x yy

YY = true-breeding, homozygous, dominant

yy = true-breeding, homozygous, recessive

Step 3. Perform meiosis to determine the possible gametes

 This is how you "perform meiosis" to find possible gametes.

Step 4. Determine the genotypes of their children (F1) using a Punnett square.

 The Punnett square determines the genotypes. Use that to determine the phenotype, which is a statement of what the F1 will look like physically.

Mendel uses the results discovered from the F1 to determine the next generation (F2).

 

Conclusion

  • Traits are encoded by genes on chromosomes
  • Genes always come in pairs

Mendel’s Law: The Law of Segregation

  • Every person has a pair of alleles for any trait.
  • Each parent passes a random copy of alleles to the offspring when fertilization occurs

The Law of Independent Assortment

  • When a gene is passed to the offspring during gamete formation, it does not affect how the gene for another trait is passed (as long as they are not linked)