Why Are We All so Different? Lab Sheet Answer key
- Assuming no mutations, how many genetically different offspring can two parents with 2n = 6, 3 pairs, of chromosomes have? 8+8+8+8+8+8+8+8 = 8×8 = 64
- Humans have 23 pairs of chromosomes. Do you think two human parents can have more, less, or the same number of genetically different offspring as an organism with 3 pairs of chromosomes? Defend your answer. Humans have more pairs of chromosomes, so there is the possibility of more genetically different offspring than in an organism with three pairs of chromosomes.
- There is a process called crossing over. During meiosis, parts of homologous chromosomes can cross over each other, break off, and each reattach to the other chromosome. How do you think this affects variability in an organism’s gametes? Crossing over greatly increases the potential variability in an organism’s gametes. With crossing over, part of your grandmother’s chromosome can be incorporated into your grandfather’s chromosome. Creating a unique chromosome that has parts from two different individuals who are only related by marriage.
Bonus: There is a mathematical rule for how many different types of gametes an organism can produce. Think about this lab and how many different gametes were formed. Can you figure out what the rule is? Hint: The rule involves an exponent. 8 = 23 n = 3, from this you can determine that the answer is 2n; You can also tell that the number of possible genetically different offspring, assuming no mutation and no crossing over, will be 22n
Using the rule, you can peek at the answer if you need to, how many different types of gametes can one human make. Aren’t you glad we didn’t use two humans for this lab? For humans n = 23, therefore the number of different types of gametes one human can make is to 223 = 8,388,608; the possible combinations of genetically different offspring assuming no mutations and no crossing over would be 70,368,744,177,664.
Fraternal twins often look very different. Explain why based on the results of this lab.
There is a 1 in 70,368,744,177,664 chance that two siblings who are not identical twins will have the exact same genes.