The Genetics of Parenthood
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!
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.
• 2 coins (for mother and father gamete contribution)
• Drawing paper or white boards
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.
Data: (Copy and Complete)
Names of Parents:________________________________________________________
Child's gender __________ Child's name ______________________________________
Fill in data table as you determine each trait described. Do not simply flip the coin for all traits before...
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.
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