Download Biology 3 - Polygenic Inheritance

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Biology 3 - Polygenic Inheritance
TASK 1 - CLASS ACTIVITY
1. Without speaking to each other, create a histogram of the class showing the height distributions of
members of the class. You have 5 minutes to accomplish this with the materials given.
POLYGENIC INHERITANCE
Polygenic inheritance is a pattern responsible for many features that seem simple on the
surface. Many traits such as height, shape, weight, color, and metabolic rate are governed by the
cumulative effects of many genes. Polygenic traits are not expressed as absolute or discrete
characters, as was the case with Mendel's pea plant traits. Instead, polygenic traits are recognizable
by their expression as a gradation of small differences (a continuous variation). The results form a
bell shaped curve, with a mean value and extremes in either direction.
Height in humans is a polygenic trait, as is color in wheat kernels. Height in humans is NOT
discontinuous. If you line up the entire class a continuum of variation is evident, with an average height and extremes in
variation (very short and very tall). Traits showing continuous variation are usually controlled by the additive effects of
two or more separate gene pairs. This is an example of polygenic inheritance. The inheritance of EACH gene follows
Mendelian rules.
2. “poly” meaning: ________________________________________________________________________
3. What is polygenic inheritance?
TASK 2 – PAIR ACTIVITY
Let’s see how polygenic inheritance works through an example.
4. Collect three pairs of coins. Each pair of coins represents a gene and each gene is composed of a pair of alleles (one
from the mother and another from the father). Assume that heads represent dominant alleles and tails represent
recessive alleles.
Alleles from the mother (egg) represented by coins
Alleles from the father (sperm) represented by coins
A/a
B/b
C/c
How many genes will control our fictional trait? _____
A/a
B/b
C/c
How many alleles? _____
5. In this example, both mother and father are heterozygous for all genes involved.
a. What is the probability that the offspring will inherit only recessive alleles (aabbcc)? ________
b. What is the probability that the offspring will inherit only dominant alleles (AABBCC)? ________
6. Carefully flip all six coins on a flat surface to simulate the laws of segregation and independent assortment in
determining the genotype of the offspring.
7. Complete Table 1 by recording the number of heads and tails that result from flipping the same set of coins ten
times.
Table 1 – Group results
FLIP
1
2
3
4
5
6
7
8
9
10
NO. OF TAILS (dom)
NO. OF HEADS (rec)
8. Familiar so far? Now comes the process that sets polygenic inheritance apart from Mendelian inheritance. Each
dominant allele contributes to the intensity of the character. Add up all the dominant alleles of the genes
involved to determine the actual trait displayed by the individual.


Complete Table 2 by adding up the number of times the following situations occurred.
0 Tails and 6 Heads
 2 Tails and 4 Heads
 4 Tails and 2 Heads
1 Tail and 5 Heads
 3 Tails and 3 Heads
 5 Tails and 1 Head

6 Tails and 0 Heads
9. Record your results from Table 2 on the board with the class results and copy the totals below.
Table 2 – Group and class results
0T, 6H
1T, 5H
2T, 4H
3T, 3H
4T, 2H
5T, 1H
FLIP SITUATION
No dom
1 dom
2 dom
3 dom
4 dom
5 dom
GROUP TOTAL
CLASS TOTAL
6T, 0H
6 dom
10. Construct a bar graph from the class data. The number of heads and tails will go on the X axis (the independent
variable), while the number of times the situation occurred will go on the Y axis (the dependent variable).
11. Describe the shape of the graph generated in #7. Why does the data have this particular shape?
12. How can you solve for the probabilities of the situations outlined below? Will your method enable you to do it in 5
minutes or less?
a. The offspring inherits 2 dominant alleles.
b. The offspring inherits 3 dominant alleles.
c. The offspring inherits 4 recessive alleles.
d. The offspring inherits 3 recessive alleles.
Hint: Remember that Pevent = number of desired outcomes/total number of outcomes.
Hint: There are only two possibilities for each allele: dominant or recessive.
Special Math 7 Hint: Does the order in which the alleles are chosen matter in this case?
Conclusion: Use the following Height Table and the example below to
answer the rest of the questions. Write your answers at the back of this
sheet.
A man is 5 feet 7 inches tall, has 3 heads (dominant alleles) and 3 tails (recessive
alleles). He will give 3 alleles to his child. These 3 alleles can be given randomly.
 He can give 3 dominant alleles and no recessive alleles
 He can give 2 dominant alleles and 1 recessive gene
 He can give 1 dominant gene and 2 recessive alleles
 He can give 0 dominant alleles and 3 recessive alleles
These are all the possible combinations that he can give his child. The height of
the mother will dictate the alleles that she will give to the child. The combination
of the mother's alleles and the father's alleles will decide the height of the child.
Coin Situation
Height
O Tails and 6 Heads
6 feet 1 inch
1 Tail and 5 Heads
5 feet 11 inches
2 Tails and 4 Heads
5 feet 9 inches
3 Tails and 3 Heads
5 feet 7 inches
4 Tails and 2 Heads
5 feet 5 inches
5 Tails and 1 Head
5 feet 3 inches
6 Tails and 0 Heads
5 feet 1 inch
1) If a male is 5 feet 9 inches tall, it means that he has 4 dominant alleles
and 2 recessive. He will only give 3 alleles to his child. What are the possible combinations of alleles that he can
give?
2) The male is 5 feet 7 inches and the female is 5 feet 5 inches. Is it possible for them to give their child the necessary
alleles so the child can be 5 feet 11 inches tall? Explain your answer. Diagrams are often useful.
3) If 2 parents are 5 feet 7 inches, is it possible to have a child that is 6 feet tall? Explain.
4) If the male is 5 feet 5 inches tall and the female is 5 feet 3 inches tall, what is the tallest height that their child could
attain? What is the shortest height their child could attain? Explain.
5) List 3 other polygenic traits.
6) How are polygenic traits different from the traits we have studied so far (i.e. traits that only require 2 alleles)?
7) Why do you think tha t some children are taller than their parents?
8) Given AaBbCc x AaBbCc parents, give the probability that the offspring would have the heights specified in the height
table.
How is polygenic inheritance different from classical Mendelian inheritance?