The Genetics of Parenthood Essay

Abstract:

Why do people, even closely related people, look slightly different from each other? The reason for these differences in physical characteristics, or appearance, (called phenotype) is the different combination of genes (the genotype) possessed by each individual. All of your genes are segments of DNA located on your chromosomes. 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, which we call diploid or 2n) in each body cell. One pair of your chromosomes primarily determines your sex, thus, this pair is called the sex chromosomes. The other 22 pairs carry all the other genes that automatically determine everything else about you, thus, they are called autosomes.

In forming the gametes (egg or sperm), one of each chromosome pair will be given by each parent, so these cells, or gametes, have only 23 single chromosomes (haploid or n).

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; heterozygous means that in each of your body cells you carry one copy of the gene for one type of body trait and another copy of the gene for a slight difference in that trait. Which one of the two available copies you contribute to your baby through sperm and egg is random, like flipping a coin. In this lab, we are keeping it simple – there are only 30 gene pairs and 30 inheritable traits represented, but in reality there are thousands of different gene pairs, and so there are millions of possible gene combinations!

Purpose:

Several inheritance patterns are represented in this simulation. Inheritance patterns of the traits used in this simulation have been simplified to serve as a model; actual inheritance is far more complex.

Materials:

• 2 coins (for mother and father gamete contribution)
• Drawing paper or white boards
• Pens/crayons

Procedure/Data:

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

1. First, determine your baby’s gender. Remember, this is determined entirely by the father. The mother always contributes an X sex chromosome to the child. Heads = X chromosome, so the child is a GIRL (an XX genotype) Tails = Y chromosome, so the child is a BOY (an XY genotype) Fill in the results on your data sheet.

2. Name the child with a first and last name.

3. Now, determine the child’s facial characteristics by having each parent flip a coin for each of the traits on the given “Trait List” sheet.

Heads = child will inherit the dominant version of the trait (i.e. B or N1) in a pair Tails = child will inherit the recessive version of the trait (i.e. b or N2) in a pair

On the data sheet, circle which allele, or version of the trait that each parent will pass on to the child and write the child’s genotype.

4. Using the information on the “Trait List”, look up and record the child’s phenotype and record the phenotype. **Some traits follow special conditions, which are explained in the guide. 5. 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.

Fill in data table as you determine each trait described. Do not simply flip the coin for all traits before reading the “Trait List”, 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.

Analysis/Conclusion: (Copy and Complete)

1. What percentage does each parent contribute to a child’s genotype?

2. Explain how this does and does not relate to the process of mitosis.

3. How many individual chromosomes are found in every cell of the human body (except for the sperm and eggs)? How many pairs is this?

4. Now we’re going to relate what we know to a basic math concept. If we use “2n” to represent the 46 chromosomes found in normal human body cells, then how many chromosomes would “n” represent?

5. Would you use “n” or “2n” to represent 23 pairs of chromosomes? 6. Using “n” or “2n”, how many chromosomes would a cell have to have at the end of interphase, and at the start of mitotic division? 7. Using “n” or “2n”, how many chromosomes does each daughter cell have after mitosis?

8. Using “n” or 2n”, how many chromosomes does a sperm have?An egg have?

9. Explain with your reasoning why or why not mitosis would work to create sperm and eggs.

10. Write an analysis/conclusion about the lab. This will be approximately 2 paragraphs and should include a brief explanation about the purpose related to the abstract (why did we do the lab?) and an explanation of the results (what was the data?) in relation to what really occurs in reality. Teacher Resource Sheet

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
Activity ideas after completing the data sheets

1. 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. 2. Do the lab twice, comparing the genotypes and phenotypes of the resulting siblings. 3. “Marry” the children off, to produce an F2 generation (grandchildren). 4. 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.

References
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.