Home > Biology > Biology Cartersville Lab > Biology 1010 Genetics Handout
Printer Friendly Version

BIOLOGY 1010

LABORATORY EXERCISES IN GENETICS & GENETIC COUNSELING

PART ONE: GENETICS     Exercise 20 in your lab manual

  1. Basic Information: Read Lab 20 “Introduction” on p. 269.
  2. 20.1 One-Trait Crosses
    1. Read Back Ground Information on “One-Trait Crosses” on p. 270.
    2. Experimental Procedure: “The Color of Corn Kernels” (NOT IN BOOK-SEE BELOW)

 

Experimental Procedure: “The Color of Corn Kernels”

Mendelian genetics (often called classical genetics) is actually a subdivision of genetics which deals with the inheritance of traits.Practically speaking, Mendelian Genetics has a two-fold purpose:

 

  1. To understand the inheritance of certain traits in an organism of interest [example: How is corn kernel color (in Indian corn) passed on from generation to generation of corn plants?]

 

  1. To be able to predict the results of a particular mating and to express those results in terms of the probability of genotypes and phenotypes in the offspring. [example: What is the probability that a mating between a purebred purple-kernelled corn plant and a purebred yellow-kernelled corn plant will result in a purple-kernelled offspring?]

 

You should be able to appreciate the fact that Mendelian genetics can be of tremendous economic importance: you could essentially lan your way toward breeding a better plant or a more marketable animal!

  1. Obtain an ear of monohybrid cross corn.  This particular example of Indian corn will have both purple and yellow kernels.  Our exercise is relatively simple: we will examine the matings that ultimately created this ear of corn, and we will recognize that this ear of corn demonstrates the phenotypic probabilities that can arise from a particular mating.
  2. Where did this ear of corn come from?  A pure bred purple-kernelled corn plant was crossed with a pure bred yellow-kernelled corn plant.  If purple alleles are dominate (P) and yellow alleles are recessive (p), fill in the genotypes in the blanks below.

 

 

Parents_________________ X _________________

(purple corn plant) (yellow corn plant)

 

 

How could you describe the genotype of the purple parent? (circle the correct answer)

homozygous dominantheterozygoushomozygous recessive

 

How could you describe the genotype of the yellow parent? (circle the correct answer)

homozygous dominantheterozygoushomozygous recessive

 

  1. Given your parental genotypes above, let’s generate a Punnett Square for the mating and predict the results of the F₁ generation.  Fill in the appropriate gametes and the resulting genotypic combinations.

 

Purple Parent Gametes

 

 

F Genotype:

 

 

 

 

 

 

F Genotype:

F Genotype:

 

 

 

 

 

 

F Genotype:

 

Yellow

Parent

Gametes

 

 

 

 

 

 

 

  • Are all of the new genotype combinations the same?  YES or NO
  • Are all of the new phenotype combinations the same? YES or NO

 

In conclusion, we can state that a given mating between a homozygous purple parent and a homozygous yellow will result in a _______% probability that the offspring will be _________________ (state phenotype).

 

  1. Now let’s see what happens if we mate two of the F₁ individuals.  Incidentally, it is this particular mating that has given rise to the monohybrid ear of corn before you.

Fill in the appropriate genotypes and phenotypes of the F individuals:

F₁            _____________    X   _____________ (genotypes)

F₁            _____________    X   _____________ (phenotypes)

  1. Given your F₁ genotypes above, let’s generate a Punnett Square for the mating and predict the results of the F₂ generation.

 

F₁ Gametes

 

 

  1.  

 

 

 

 

 

 

  1.  

 

 

 

 

 

 

  1.  

 

 

 

 

 

  1.  

 

 

 

 

 

 

 

 

F

Gametes

  • Are all of the new genotype combinations the same?  YES or NO
  • Are all of the new phenotype combinations the same? YES or NO
  • What is the probability that a given mating will result in a homozygous dominant offspring? ___________%
  • What is the probability that a given mating will result in a heterozygous

offspring? ___________%

  • What is the probability that a given mating will result in a homozygous recessive offspring? ___________%

 

So where did your purple and yellow kernelled ear of Indian corn come from? We started with a cross between purebred (homozygous) parents.We then crossed two members of the F generation (heterozygous) to arrive at an F generation result.Your purple and yellow kernelled ear of Indian corn is a member of this F generation!

 

An ear of corn is the product of multiple acts of fertilization; each kernel is a single zygote.If you count the number of purple and yellow kernels on your ear of corn, the final numbers should approximate the phenotypic probabilities that you predicted above.Count the kernels and fill in the appropriate numbers below.

 

 

Yellow Kernels

 

 

Purple Kernels

 

 

Total # of Kernels

 

 

 

 

Number of Yellow Kernels / total # of kernels X 100 = ________________%

Number of Purple Kernels / total # of kernels X 100 = ________________%

 

Note: Since probability describes a statistic tendency, there is a remote chance that your counted kernel numbers might not directly coincide with your predicted probabilities.In much the same way, even if the probability of getting “heads” on a coin toss is 50%, a series of 100 coin tosses might generate a different set of results.

 

 

  1.  20.2 Two-Trait Crosses
    1. Read Back Ground information on Two-Trait Crosses, p. 276
    2. Perform Experimental Procedure: Color and Texture of Corn, p. 276-277.  Fill in the Punnett Square, fill in the table and answer the questions.

 

  1. 21.2 Genetic Inheritance
    1. Read Back Ground information on Genetic Inheritance, p. 290
    2. Perform Experimental Procedure: Autosomal Traits, p. 290-292.  Answer the questions and fill in the table.
  2. X-Linked Crosses
    1. Read Back Ground information on “X-Linked Crosses” on p. 280 and “Sex Linkage” on p. 292.
    2. Perform Experimental Procedure: X-Linked Traits on p. 293. Answer the genetics problems, p. 293-294.

PART TWO: GENETIC COUNSELING          Exercise 21 in your lab manual 

  1. Basic Information: Read Lab 21 “Introduction” on p. 285.
  2. 21.1 Chromosomal Inheritance.  Read Back Ground information on Chromosomal Inheritance, p. 286
    1. Read back ground information on “Syndromes Due to Numerical Sex Chromosome Anomolies” p. 286 (be sure you understand the process and results of nondisjunction)
    2. Perform Experimental Procedure: Gametogenesis and Nondisjunction, p. 287-289.

(Note: you will be using Red and Yellow pop beads, not Red and Blue as indicated in the manual)

  1. Genetic Inheritance: Pedigrees
    1. Read Back Ground information on “Pedigrees” and “Pedigree Analyses” on p. 294-295.
    2. Complete the problems on p. 295-296
Page last updated: January 3, 2012