The Genetics of Parenthood

Lenore Kop and Thomas Crowley
1994 Woodrow Wilson Collection

This is a simulation that easily captures student interest and can be varied to meet different ability levels. Making the assumption that the P (parental) generation is heterozygous at all loci and that independent assortment occurs (no linkages), students flip coins to determine which allele they will pass on to the F1 generation, and draw the resulting child's face. Emphasize the variation which occurs, reminding the students that these children are genetic siblings since all parents have identical genotypes.

Several inheritance patterns are represented in this simulation, and it is important to review these with the students beforehand. Inheritance of the traits used in this simulation have been simplified to serve as a model; actual inheritance is far more complex and students may need to be reminded about this in case they get overly concerned about their own traits.

  • Dominant: allele which masks the expression of another; represented by capital letters (R, V)

  • Recessive: allele which is expressed only if both parents contribute it; represented by small letters (r, v)

  • Incomplete dominance: phenotype of the heterozygote is an intermediate form; represented by capital letters and subscripts (C1, C2); an example is red color tints in the hair

  • Polygenic: several genes contribute to the overall phenotype; an example is skin color

  • Sex-linked: commonly applied to genes on the X chromosome, the more current term is X-linked; genes on the Y chromosome are holandric genes; no examples in this activity

  • Epistasis: one gene masking the effects of another; an example is hair color to red color tints

Target Age/Ability Group

High School Biology, all levels

Class Time Required:

At least 1-2 class periods


Preferably male/female pairs, but other configurations like same sex pairs, trios and single parents have also been used, depending on the students; use your discretion.


  • 2 coins (preferably different kinds to keep track of mother/father contribution)

  • The Genetics of Parenthood Guidebook

  • Drawing paper or white boards

  • Pens/crayons (Crayola has a "My World Colors" set for various skin/eye colors)

Activity ideas after completing the data sheets

  1. Each student draws the child's face; compare "mother's" and "father's" perception of characteristics.

  2. One student draws the child's face; partner writes a biography of the child at age 30 - what is the child like, what have they accomplished, what are their dreams...this can also bring about interesting discussions on how the students feel about their parents and their perceptions of parenthood.

  3. Do the lab twice, comparing the genotypes and phenotypes of the resulting siblings.

  4. "Marry" the children off, to produce an F2 generation (grandchildren).

  5. Instead of drawing the face, decorate an egg or a five pound package based on the child's traits. It can then be used in the activity "Problem Solving in Genetic Disorders" by Nikki Chen, or "One + One = One" by Dorothy Josephine Cox.


Adapted from materials from Joan Carlson, Jack Doepke, Judy Jones and Randyll Warehime.

Lewis, Rikki. 1994. Human Genetics: Concepts and Applications. Wm. C. Brown Publishers.

Stine, Gerald J. 1989. The New Human Genetics. Wm. C. Brown Publishers.


The Genetics of Parenthood Data Sheet

Parents _____________________________ and ______________________________

Child's gender _____ Child's name _________________________________

Fill in data table as you determine each trait described in the Guidebook. Do not simply flip the coin for all traits before reading the guide, because some traits have special instructions. Believe it or not, it will make your life easier if you follow directions. In the last column, combine the information and draw what that section of the child's face would look like.


  1. What percentage does each parent contribute to a child's genotype?
  2. Explain how/what part of your procedures represents the process of meiosis.
  3. Using examples from this activity, explain your understanding of the following inheritance patterns:

      a. dominant
      b. recessive
      c. incomplete dominance
      d. polygenic
      e. epistasis

  4. Compare the predicted phenotype ratio (Punnett squares) to the actual ratio (class data) for the following traits:

      a. trait # 2 (chin size)
      b. trait #8 (hair type)

  5. All the children had 2 heterozygous parents. Use the law of independent assortment to explain why there were no identical twins produced.


The Genetics of Parenthood Guidebook

Why do people, even closely related people, look slightly different from each other? The reason for these differences in physical characteristics (called phenotype) is the different combination of genes possessed by each individual.

To illustrate the tremendous variety possible when you begin to combine genes, you and a classmate will establish the genotypes for a potential offspring. Your baby will receive a random combination of genes that each of you, as genetic parents, will contribute. Each normal human being has 46 chromosomes (23 pairs - diploid) in each body cell. In forming the gametes (egg or sperm), one of each chromosome pair will be given, so these cells have only 23 single chromosomes (haploid). In this way, you contribute half of the genetic information (genotype) for the child; your partner will contribute the other half.

Because we don't know your real genotype, we'll assume that you and your partner are heterozygous for every facial trait. Which one of the two available alleles you contribute to your baby is random, like flipping a coin. In this lab, there are 36 gene pairs and 30 traits, but in reality there are thousands of different gene pairs, and so there are millions of possible gene combinations!


Record all your work on each parent's data sheet.

  • First, determine your baby's gender. Remember, this is determined entirely by the father. The mother always contributes an X chromosome to the child.

      Heads = X chromosome, so the child is a GIRL

      Tails = Y chromosome, so the child is a BOY

    Fill in the results on your data sheet.

  • Name the child (first and middle name; last name should be the father's last name).

    Determine the child's facial characteristics by having each parent flip a coin.

      Heads = child will inherit the first allele (i.e. B or N1) in a pair

      Tails = child will inherit the second allele (i.e. b or N2) in a pair

    On the data sheet, circle the allele that the parent will pass on to the child and write the child's genotype.

  • Using the information in this guide, look up and record the child's phenotype and draw that section of the face where indicated on the data sheet.

  • Some traits follow special conditions, which are explained in the guide.

  • When the data sheet is completed, draw your child's portrait as he/she would look as a teenager. You must include the traits as determined by the coin tossing. Write your child's full name on the portrait.

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