How Many Human Traits Are Controlled By A Single Gene?

Polygenic Traits

Purpose: This action will demonstrate how polygenic traits piece of work and why sure traits in a population are graphically represented by a bell bend, or "normal distribution" rather than a few distinct types.

Process:

ane) In this simulation, we will model that there are iii genes (half-dozen alleles) involved in the expression of height, and that their effects are cumulative. You will flip 6 coins (3 coming from each "parent"). Each coin flip of heads will give an H₁ (the allele for alpine) while tails gives an H₂ (the allele for brusk). A person's full height is a result of the cumulative effects of these 6 codominant alleles, equally shown below:

penny penny penny penny penny penny

Coin Flip Results	Genotype	Phenotype
vi heads and 0 tails	H_aneH_iH_aneH₁H_iH_i	6 feet, 0 inches
5 heads and 1 tail	H_aneH_iH_oneH_oneH_aneH₂	five feet, 10 inches
4 heads and two tails	H₁H₁H₁H₁H₂H₂	v feet, eight inches
iii heads and three tails	H_iH₁H₁H₂H₂H₂	5 feet, 6 inches
2 heads and 4 tails	H₁H₁H₂H₂H₂H_two	5 anxiety, 4 inches
1 head and v tails	H₁H₂H₂H_iiH₂H_two	5 anxiety, 2 inches
0 heads and six tails	H₂H₂H_twoH_iiH₂H₂	5 feet, 0 inch

2) Consummate Table 1 below past recording the number of heads and tails that resulted from each prepare of 6 coin flips. Repeat this process 10 times, representing ten different children. Yes, that's 60 coin flips in total!

Results:

Table 1: Number of heads and tails flipped (out of half-dozen) for each of your ten babies. Brand a histogram as shown beneath of your results and of the class averages (if data is bachelor).

Babe #	Baby ane	Baby two	Baby 3	Baby four	Baby v	Baby 6	Babe 7	Baby 8	Baby 9	Infant x
# heads (H_one)
# tails (H₂)

histogram

Questions:

0) How did your private results compare to the class average? Why is the class average more than similar a bong curve than your individual results?

i) Each parent gives what percentage of his/her genetic cloth to their children? ____

two) If a man is 5 feet 8 inches tall, then he has 4 H₁ alleles and two H₂ alleles. He can only give 3 of his 6 alleles to his child. What are all the possible combinations?

He tin can give (__ H₁ and __ H_two) or (__ H_ane and __ H₂) or (__ H_ane and __ H₂)

3) If dad is 5 anxiety 8 inches tall and mom is 5 feet half-dozen inches tall, is it possible for them to give their child the necessary alleles to exist 5 feet 10 inches tall. (Hint: start by filling in the babe's alleles and piece of work backwards.)

Human being's Alleles: __ __ __ + Woman'southward Alleles: __ __ __ = Baby'south Alleles: __ __ __ __ __ __

iv) If both parents are 5 anxiety half dozen inches, it is possible for them to have a child that is half-dozen anxiety tall? Bear witness which alleles each parent must give to make this possible:

Man's Alleles: __ __ __ + Adult female's Alleles: __ __ __ = Baby's Alleles: __ __ __ __ __ __

5) If a man is v anxiety 4 inches tall and a adult female is 5 feet 0 inches alpine, what is the tallest height that their child could attain?

Human being'due south Alleles: __ __ __ + Woman's Alleles: __ __ __ = Infant's Alleles: __ __ __ __ __ __

half-dozen) If a human being is v feet eight inches tall and a woman is v feet 4 inches tall, what is the shortest pinnacle their child could achieve?

Homo'south Alleles: __ __ __ + Woman's Alleles: __ __ __ = Baby's Alleles: __ __ __ __ __ __

7) If elevation was controlled by a single factor, then the resulting phenotypes would be discrete (tall, medium and short) and easily distinguished. A polygenic trait is 1 that is controlled past many genes. As a event, the range of phenotypes is more continuous. Is man peel color polygenic? Based on your observations of human variation, are near traits controlled by single genes or many genes?

eight) Would two parents who are five feet 10 inches alpine tend to produce more alpine children or more short children? Why?

ix) If the depression and high limits of peak didn't change, simply height was controlled by six genes rather than the three in our model, should the gradations between heights exist more than smooth or more discrete? Why?

10) Why exercise you remember that the boilerplate height in the U.S. today is several inches more it was about 100 years agone? (Hint: it has nothing to practice with genetics!)

Calculating the odds with coins:

Each time yous flip a money, the odds of heads or tails is 1/2, or 50% The odds of getting iii heads from iii flipped coins is calculated equally (0.5)ten(0.5)x(0.5)=0.125 or (i/2)ten(ane/two)x(1/2)=1/8. Each event is independent just you multiply to determine the odds of all three happening together. Still, even if yous rolled 3 heads in a row, the odds of the next coin being heads is 50% because each event is contained. That might non sound intuitive, but think nigh information technology this manner: the money has no history and it has to state on one side or the other, so no thing what has happened before, the odds are fifty:50 for each flip. Why and so, can you lot sometimes get a run of heads or a run of tails? It's simply risk. We expect a l:50 ratio of heads to tails, and will go very close to that if we flip the coin many times, but flip it only a few times and y'all might get a run of heads or tails. In the long run though, information technology will be balanced out by a run in the other direction. In the human population, there are some families that take all boys or all girls, even so in the population as a whole, the sex ratio is very most 50:fifty. The odds of having a boy or a daughter are determined past whether the sperm that meets egg is carring an Ten or a Y chromosome, and that's more than or less a l:50 adventure because of meiosis.

Claiming: Computing the odds with genes:

Permit's do a piffling math to make up one's mind the odds in our height simulation above. If a homo has the genotype H₁H₁H_oneH₂H₂H₂ and volition contribute half of those alleles to the infant, the odds of the genotypes are calculated beneath. Remember however that we are sampling without replacement , and multiplying each probability for the combined result. Why the 3 in the second and third calculations? There are three possible ways to get this genotype.

probability of sampling three H_ane(H₁H₁H_one) from H₁H_oneH₁H_iiH_iiH₂: =(three/6)(2/5)(1/4)=vi/120=one/20=0.05=v%

probability of two H₁ and one H_two: H_oneH₁H_ii (or H₁H₂H₁ or H₂H₁H_one)=3(iii/vi)(ii/5)(iii/4)=3(18/120)=0.45=45%

probability of one H₁ and two H₂: H₁H_iiH₂ (or H_iiH₁H_ii or H₂H_iiH_ane)=3(3/6)(three/5)(two/4)=3(eighteen/120)=0.45=45%

probability of three 2s: H_iiH₂H₂=(iii/6)(2/5)(1/four)=6/120=1/xx=0.05=five%

Here's a second example. What if dad was H_iH_iH_iH₁H₁H₂? If and then, so at that place are fewer possible outcomes because he'southward only got a unmarried H₂ to requite.

probability of three H₁: H_iH_iH₁=(v/6)(4/five)(three/iv)=threescore/120=0.v=50%

probability of two H₁ and 1 H_ii: H_oneH₁H₂ (or H₁H₂H₁ or H_twoH_iH₁)=3(5/six)(4/v)(1/iv)=0.v=50%