Biology (Holt)

Before You Begin

A is a cross that involves

one pair of contrasting traits. Different ver-

sions of a gene are called .When two

different alleles are present and one is

expressed completely and the other is not,

the expressed allele is and the

unexpressed allele is.

1.Write a definition for each boldface term

in the paragraph above.

2.Based on the objectives for this lab, write a

question you would like to explore about

heredity.

Procedure

PARTA: Simulating a Monohybrid

Cross

1.You will model the random pairing of alle-

les by choosing lentils and peas from Petri

dishes. These dried seeds will represent the

alleles for seed color. A green pea will rep-

resent G, the dominant allele for green

seeds, and a lentil will represent g, the

recessive allele for yellow seeds.

2.Each Petri dish will represent a parent.

Label one Petri dish “female gametes” and

the other Petri dish “male gametes.” Place

one green pea and one lentil in the Petri

dish labeled “female gametes” and place

one green pea and one lentil in the Petri

dish labeled “male gametes.”

3.Each parent contributes one allele to each

offspring. Model a cross between these

two parents by choosing a random pairing

of the dried seeds from the two Petri

dishes. Do this by simultaneously picking

one seed from each Petri dish without

looking. Place the pair of seeds together

on the lab table. The pair of seeds repre-

sents the genotype of one offspring.

4.Record the genotype of the first offspring

in your lab report in a table like Table A

shown below.

5.Return the seeds to their original dishes

and repeat step 3 nine more times. Record

the genotype of each offspring in your

data table.

recessive

dominant

alleles

monohybrid cross

Skills Practice Lab

SKILLS

• Predicting outcomes


• Calculating data


• Organizing data


• Analyzing data

Modeling Monohybrid Crosses

OBJECTIVES

• Predictthe genotypic and
  phenotypic ratios of offspring
  resulting from the random pair-
  ing of gametes.


• Calculatethe genotypic ratio
  and phenotypic ratio among the
  offspring of a monohybrid cross.

186 CHAPTER 8Mendel and Heredity

Gamete Pairings

Trial Offspring genotype Offspring phenotype

1 2 3 4 5 6 7 8 9

10

MATERIALS

• lentils


• green peas


• 2 Petri dishes