Marble Heredity 2009
The purpose of this activity is to demonstrate the process of how genes are passed from parents to offspring, the concept of dominant and recessive traits, and the difference between genotype and phenotype. Using marbles to represent a genetic trait, you will illustrate what can happen when the genes from two parents combine to produce a new combination of genes in their offspring.
By the end of this exercise, you should be able to:
 Explain how traits are passed from parents to offspring.
 Identify what controls the inheritance of traits in organisms.
 Explain what is meant by genotype and phenotype.
Heredity
is the passing of physical characteristics, or traits, from parents to offspring.
Traits , such as stem height or hair color, vary between individuals and are determined by genetic material inherited from each parent. Scientists use the term " gene
" for the unit of genetic material that controls a specific trait. Alleles are the different forms of a gene. For example, a short pea plant displays the "short" allele for stem height, while a tall pea plant displays the "tall" allele for stem height.
An organism inherits one allele from each parent, so every gene is controlled by a combination of two alleles. A dominant allele is one whose trait always shows up in the organism when that allele is present. A recessive allele
is hidden or masked whenever the dominant allele is present. The allele combination or genetic makeup of an organism is called its genotype , while its physical appearance is called its phenotype . Genotypes are represented by 2 letters, one for each allele (i.e. AA, Aa, or aa). The dominant allele is usually a capital letter (i.e. A) and the recessive allele is usually a lower-case letter (i.e. a). A genotype may be homozygous for a trait if an organism has two identical alleles, or heterozygous
for a trait if an organism has two different alleles.
Gregor Mendel is considered the "Father of Genetics " because his studies on the inheritance of certain traits in pea plants formed the foundation for the scientific study of heredity. Mendel reached several conclusions about the "laws" of inheritance from his experiments. These conclusions are that: (1) alleles control the inheritance of traits (2) alleles occur in pairs (3) each parent contributes one allele (4) one allele can hide or mask another.
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Minority Science Programs – School of Biological Sciences – University of California, Irvine

Marble Heredity 2009
Heredity
Trait
Genetics
Gene
Alleles
Dominant allele
Recessive allele
Phenotype
Genotype
Homozygous
Heterozygous
Per group of 6:
 4 solid colored marbles
 4 clear marbles
 4 paper bags
You will be working in groups of 6. Designate four group members as "parents" and two group members as "offspring."
1. Each parent takes two marbles of the same type (i.e. both soild or both clear). These marbles represent the parents' alleles for a trait. Record the "Marble Type", "Genotype", and "Phenotype" in Table 1 for all four parents.
*2. Your instructor will tell you which parents should pair together.
3. Each parent puts both their marbles into a paper bag and shakes the bag to mix.
 Make a prediction about what kind of F1 offspring you expect from each parent pair.
4. Each parent draws one marble from their paper bag without looking. Record the result in
Table 1 under "Marble Passed to F1 Offspring."
5. Each F1 offspring inherits the two marbles drawn from one pair of parents. Record the
"Marble Type," "Genotype," and "Phenotype" for both F1 offspring in Table 2 .
6. Each F1 offspring puts both their marbles into a paper bag and shakes the bag to mix.
 Make a prediction about what kind of F2 offspring you expect from each F1 pair.
7. Each F1 offspring draws one marble from their paper bag. Record the result in Table 2 under "Marble Passed to F2 Offspring."
8. Complete the information for the F2 offspring in Table 3 based on the marbles drawn by the F1 offspring.
Name: _____________________ Period: ____
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Minority Science Programs – School of Biological Sciences – University of California, Irvine

Marble Heredity 2009
Solid marbles are dominant to clear marbles. The symbol for a solid marble allele is capital
"S", and the symbol for a clear marble allele is lower-case "s".
TABLE 1
( )
Allele Symbol
( )
(SS, Ss, ss)
( )
( )
( )
( )
( )
( )
(Solid, Clear)
( )
( )
( )
( )
TABLE 2
( )
Allele Symbol
( )
(SS, Ss, ss)
( ) ( )
(Solid, Clear)
( )
( )
TABLE 3
( )
Allele Symbol
( )
(SS, Ss, ss)
(Solid, Clear)
Name: _____________________ Period: ____
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Minority Science Programs – School of Biological Sciences – University of California, Irvine

Marble Heredity 2009
1. Make a prediction about what kind of F1 offspring you expect from each parent pair.
Solid (S), Solid (S) Solid (S), Solid (S)
Clear (s), Clear (s) Clear (s), Clear (s)
Solid (S), Solid (S) Clear (s), Clear (s)
2. Make a prediction about what kind of F2 offspring you expect from each F1 pair.
Solid (S), Solid (S) Clear (s), Clear (s)
Solid (S), Clear (s) Solid (S), Clear (s)
3. How many different kinds of offspring are possible when homozygous parents are crossed?
______________________________________________________________
4. What different kinds of offspring are possible when two heterozygous parents are crossed?
______________________________________________________________
5. On Tables 1, 2, and 3 above, circle any genotypes that are heterozygous.
6. In humans, the allele for free earlobes (F) is dominant over the allele for attached ear lobes (f). a. What possible genotypes could a person with the free earlobe phenotype have?
_____________________________________________________________ b. What possible genotypes could a person with the attached earlobe phenotype have?
_____________________________________________________________
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Minority Science Programs – School of Biological Sciences – University of California, Irvine