Genetics 1 - Monohybrid Crosses

  1. What are the objectives of this lecture?
    understand Mendel’s experiments on inheritance

    understand the significance of his work to genetics and biology

    understand and correctly use genetic terminologypredict the phenotypes and genotypes of the offspring in a cross involving one contrasting trait when the parents are known

    determine the genotypes or phenotypes of the parents in a cross from the phenotypes and ratios of the offspring
  2. Mendel's first law, The Principle of Segregation, states what?
    During the formation of gametes, the paired unit factors separate, or segregate, randomly so that each gamete receives one or the other with equal likelihood.
  3. What is a gene?
    A gene is the basic biological unit of heredity.
  4. What is an allele?
    Any gene that gives rise to more than one version of the same trait.

    Example: The height trait has two possible alleles - short and tall.
  5. What is a genotype?
    The genetic makeup of a certain trait; the genetic constitution of an organism.
  6. What is a phenotype?
    The physical expression of a certain trait; the observable characteristics of the organism.
  7. Homozygous means..
    Organisms with two identical alleles.

    Example: tt/TT
  8. Heterozygous means..
    Organism with two opposing alleles for a single gene.

    Example: Tt
  9. Genotypes set the range of possible __________.
  10. The environment determines _______________________________.
    where in that range the phenotype ends up.
  11. Reciprocal Crosses:
    If the results of reciprocal crosses are the same,
    it means that the inheritance of the trait doesn't depend on the sex
  12. The cross SS x ss gives you what?

    all Ss or 4/4 Ss

    • __S__S__
    • s| Ss Ss
    • s| Ss Ss
  13. The cross Ss x Ss gives you what?

    • __S__s__
    • S| SS Ss
    • s| Ss ss

    • 1/4 SS,
    • 2/4 Ss,
    • and 1/4 ss

    or 3/4 S_ and 1/4 ss
  14. The cross Ss x ss gives you what?

    • __S__s__
    • s| Ss ss
    • s| Ss ss

    1/2 Ss and 1/2 ss
  15. The cross Ss x SS gives you what?

    • __S__s__
    • S| SS Ss
    • S| SS Ss

    all (or 4/4 or 1) S_
  16. The cross SsYy x SsYy results in what?

    (Also remember that for this cross you'll be using the branch diagram.)
    A 9:3:3:1 ratio (out of 16) where

    • 9/16 are S_Y_,
    • 3/16 are S_yy,
    • 3/16 are ssY_, and
    • 1/16 are ssyy
Card Set
Genetics 1 - Monohybrid Crosses