Science.7
Name: _____________________________
“Can You Roll Your Tongue?”
Date: ______________________________
Introduction
The combination of alleles inherited from your parents is called a genotype. When a person exhibits a dominant trait,
he/she probably does not know his/her genotype for that trait. Take, for example, the genetic trait of tongue rolling. A
tongue rolling allele (R) is dominant; a non-tongue rolling allele (r) is recessive. The alleles you have for that trait could be
identical. For example, you may have received a tongue rolling allele (R) from both you mom and dad; in that case, you
would also be a tongue roller, with a genotype of “RR”. Or you may have received a non-tongue rolling allele (r) from both
your mom and dad; in that case you would not be able to roll you tongue and your genotype would be “rr”. In either case,
when both alleles for a trait are identical, they are referred to as homozygous, from the Greek words “homo” (meaning
“same”) and “zygote” (from “zygoun”, meaning “to join”).
Sometimes the combination of alleles inherited from your parents is different. For example, you may have received a
tongue rolling allele from you mom, but not your dad. In this case, your genotype would be “Rr”. This combination of
alleles is referred to as heterozygous, from the Greek words “hetero” (meaning “different”) and “zygote”.
The important thing to remember is that both “RR” and “Rr” will result in a tongue rolling kid. In a simple inheritance
pattern involving two alleles, it is only necessary to receive one copy of the dominant allele to exhibit the dominant trait. A
person who exhibits a dominant trait will probably not know his/her genotype for that trait. On the other hand, a person
who exhibits a recessive trait always knows what his/her genotype is because no dominant allele is present. The trait that
you exhibit is called your phenotype or outward appearance for that trait.
When gametes (sperm or egg) are produced, these gametes have only one allele for the trait being studied. (ex. one allele
for tongue rolling). The distribution of alleles during the formation of gametes (sperm or egg) was one of the principles
described by Gregor Mendel. It is called the principle of segregation: This principle states that the two alleles of a gene
segregate, or separate, from each other so that each one ends up in a different gamete.
Questions:
1. What is the difference between a genotype and phenotype?
2. How would you explain the difference between dominant and recessive?
3. If a person is homozygous dominant for tongue rolling, what would their genotype look like? What would the genotype
look like for person that was not a tongue roller?
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Directions: Observe your traits. Use the table to determine your phenotype and genotype for each trait. Determine if your
traits are dominant or recessive.
Phenotype:
Genotype:
Dominant/Recessive:
Phenotype:
Genotype:
Dominant/Recessive:
Phenotype:
Genotype:
Dominant/Recessive:
Phenotype:
Genotype:
Dominant/Recessive:
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