Biology (Holt)

6.Based on each offspring’s genotype,

determine and record each offspring’s

phenotype.

PARTB:Calculating Genotypic and

Phenotypic Ratios

7.In your lab report, prepare a data table

similar to Table B shown below.

8.Determine the genotypic and phenotypic

ratios among the offspring. First count

and record the number of homozygous

dominant, heterozygous, and homozygous

recessive individuals you recorded in

Table A. Then record the number of off-

spring that produce green seeds and the

number that produce yellow seeds under

“Phenotypes” in your data table.

9.Calculate the genotypic ratio for each

genotype using the following equation:

phenotypic ratio =

number of offspring with a given genotype

total number of offspring

10.Calculate the phenotypic ratio for each
phenotype using the following equation:
phenotypic ratio =
number of offspring with a given phenotype
total number of offspring

11.Now pool the data for the whole class, and
record the data in your lab report in a
second table like Table B.

12.Compare the class’s sample with your
small sample of 10. Calculate the geno-
typic and phenotypic ratios for the class
data, and record them in your data table.

13.Construct a Punnett square showing the

parents and their offspring in your lab

report.

14. Clean up your materials before
    leaving the lab.

Analyze and Conclude

1. Summarizing Results What trait is
   being studied in this investigation?


2. Analyzing DataWhat are the genotypes
   of the parents? Describe the genotypes of
   both parents using the terms homozygous
   or heterozygous, or both. Did Table B
   reflect a classic monohybrid-cross pheno-
   typic ratio of 3:1?


3. Drawing Conclusions If a genotypic
   ratio of 1:2:1 is observed, what must the
   genotypes of both parents be?


4. Predicting PatternsShow what the
   genotypes of the parents would be if 50
   percent of the offspring were green and 50
   percent of the offspring were yellow.


5. Further Inquiry Construct a Punnett
   square for the cross of a heterozygous black
   guinea pig and an unknown guinea pig
   whose offspring include a recessive white-
   furred individual. What are the possible
   genotypes of the unknown parent?

CHAPTER 8Mendel and Heredity 187

http://www.scilinks.org

Topic:Genetic Code

Keyword:HX4089

Do You Know?

Do research in the library or media center

to answer these questions:

1.How are hybrids of plants such as

orchids produced?

2.What is hybrid vigor?

Use the following Internet resources

to explore your own questions about

genetics.

Offspring Ratios

Genotypes Total Genotypic ratios

Homozygous dominant (GG)

Heterozygous (Gg) ____ : ____ : ____

Homozygous recessive (gg)

Phenotypes Phennotypic ratios

Green seeds

________ : ________

Yellow seeds