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The Genetics of Eye Color

based on 6 ratings
Author: Crystal Beran

Grade Level: 7th - 11th; Type: Life Science

Objective

To discover a person’s eye-color genotype.

The purpose of this project is to discover eye-color genotypes that could be present in a given population. This study will take into account simple brown/blue dominant and recessive traits.

Research Questions:

  • How are genes passed down from parents to their offspring?
  • How many eye-color alleles does each person have?
  • How many eye-color alleles can one person pass to their offspring?
  • Are dominant or recessive genes passed down more frequently?
  • Why can two brown-eyed parents have a blue-eyed baby?
  • Why can’t two blue-eyed parents have a brown-eyed baby?
  • What is the difference between genotype and phenotype?
  • How can you determine possible genotypes?
  • Which genotype for eye color can you be absolutely certain of?
  • Are blue eyes or brown eyes more common?

Mendel first identified simple dominant and recessive traits in his famous experiments on pea plants. In human beings, a baby receives one set of genes from its father and another set from its mother. The combination of all of these genes, and the often complicated interactions between them, give the baby many of its physical characteristics, including its eye-color. Though there are many color variations in a human’s eyes, the colors brown and blue fall into this same simple dominant and recessive trait chart that Mendel first discovered. Brown eyes are dominant and blue recessive, which means that two parents with brown eyes could potentially have a baby with blue eyes, but the reverse is not possible. 

The following example shows the possible genetic outcomes for a father with Bb and a mother with Bb. 

Father’s Genotype

Bb (one gene for dominant BROWN and the other for recessive blue)

Father’s Phenotype

Because only on gene must be dominant to show the dominant trait, the father has brown eyes.

 

Mother’s Genotype

Bb (one gene for dominant BROWN and the other for recessive blue)

Mother’s Phenotype

Because only on gene must be dominant to show the dominant trait, the mother has brown eyes.

As each parent will only pass down one of their two alleles to their offspring, we can determine what combinations are possible using a chart such as this:
 
Father à

BROWN (B)

blue (b)
Mother ↓
 
 

BROWN (B)

BB (brown eyes)

Bb (brown eyes)

blue (b)

bB (brown eyes)

bb (blue eyes)

 

 

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