Lab 6: Genetic Crosses

Spring 2014

Read Chapter 7 and print out the sample genetic cross to use as a guide.

Below is a list of the Phenotypes used in this lab.  These are all single gene traits that show complete dominance

Part I: Symbols and definitions:

1. a)  What is an allele?  Give an example of 2 alleles of any gene.  (0.5 pts)

An allele is a trait of the gene. Individuals has two copies of each gene inherent from both parents.  Example of 2 alleles for a gene could be the blood type or eye color

b) What is the difference between an organism that is a homozygote and one that is a heterozygote?  (0.25 pts)

Homozygote individual inherits the same two alleles for this gene, and Heterozygote individual inherits different alleles from each parent.

 c) What is the difference between an organism’s genotype and its phenotype? (0.25 pts)

            The Phenotype is the outward appearance of an individual, and  the Genotype is the organism’s genetic composition.

2.) For each trait indicate the genotypes that are possible.  Use the first letter of the dominant trait to indicate the trait.   (2pts)

Pick three of the crosses to complete using any 3 of the last 4 digits of your student ID.  If there are repeats, pick random numbers, so you are doing 3 different crosses.  Circle the numbers of the crosses you are doing in column 1 below. 

You must pick 3 different crosses.  If there are multiple repeated numbers in your ID, pick additional numbers of your choice.

Now you can use the charts and Punnett squares on each of the following pages to complete your crosses.

Cross 1:  Please write the number of the cross you are performing:    ______________

Then fill in the genotype and phenotype for each parent below.  Use the sample problem for a guide.

Step 1:  Determine the different gamete combinations that each parent can contribute to the offspring.  Check the hint from the sample problem when you are doing this.

Step 2: Fill in the Punnett Square below

Step 3: Find the Phenotype of each of the 16 combinations in your Punnett Square page. 

Cross 2:  Please write the number of the cross you are performing:    ______________

Then fill in the genotype and phenotype for each parent below. 

Step 1:  Determine the different gamete combinations that each parent can contribute to the offspring. 

Step 2: Fill in the Punnett Square below

Step 3: Find the Phenotype of each of the 16 combinations in your Punnett Square page. 

Cross 3:  Please write the number of the cross you are performing:    ______________

Then fill in the genotype and phenotype for each parent below. 

Step 1:  Determine the different gamete combinations that each parent can contribute to the offspring. 

Step 2: Fill in the Punnett Square below

Step 3: Find the Phenotype of each of the 16 combinations in your Punnett Square page. 

Questions:

1. Are gametes haploid or diploid?  What about the offspring, are they haploid or diploid?  (1pt)

 2. A) Can two tall and smooth seeded parents produce offspring that are short and have wrinkled seeds?   (To receive a full credit for this assignment you MUST explain your answers for part A and part B by drawing the respective Punnett squares for each of your answers).

     Explain using a Punnett square why you think this outcome is possible or not.  (1pt)

    B) Can two white flowered and green seeded parents produce offspring that have Purple flowers and have yellow seeds?