Transcript Skin color activity - local.brookings.k12.sd.us

POPULATIONS
and the Bell curve
Section 15-1
50
45
Number of Lima Beans Occurring at Each Length
40
Number of Beans
35
30
25
20
15
10
5
0
5
6
7
8
9
10
11
12
13
Length of Lima Beans (in mm)
14
15
16
17
18
19
20
An individual who produces as much melanin
as humanly possible has genotype MMLLNN.
That person’s phenotype would be to have very
dark skin, so brown as to almost appear black.
MMLLNN
MLN
MLN
During meiosis the genotype MMLLNN, is reduced to the haploid genotype.
As the alleles are segregated from each other, the only possibility for the
sperm or egg is MLN.
Add the alleles from the sperm (MLN) and the alleles from
the egg (MLN) to determine the genotype of the zygote (and
the new individual), (MMLLNN)
♀/♂
MLN
MLN
MMLLNN
The genotype of all the offspring is MMLLNN.
All the offspring have the same phenotype—very dark skin.
An individual who produces as little melanin
as humanly possible has genotype mmllnn.
That person’s phenotype would be to have very
light skin, so as to appear so white that the pink
of the blood shows through.
mmllnn
mln
mln
During meiosis, the diploid mmllnn, is reduced to the haploid genotype.
As the alleles are segregated from each other, the only possibility for the
sperm or egg is mln.
Add the alleles from the sperm (mln) and the alleles from the egg (mln) to
determine the genotype of the zygote (and the new individual)
♀/♂
mln
mln
mmllnn
The genotype of all the offspring is mmllnn.
So all the offspring have the same phenotype—very light skin.
Crossing homozygous parents results in offspring with no variation.
What happens if the very dark mate with the very light?
Add the alleles from the sperm (MLN) and the alleles from the egg (mln) to
determine the genotype of the zygote (and the new individual)
♀/♂
mln
MLN
MmLlNn
The genotype of all the offspring is MmLlNn.
So all the offspring have the same phenotype—medium skin.
What happens if the medium-skinned mate with the medium skinned?
During meiosis, the diploid
(2n) genotype, MmLlNn
is reduced to the haploid
genotype. As the alleles
segregate and assort
independently, maximum
diversity results.
MLN
mln
MLn
mlN
MmLlNn
MlN
mLn
mLN
Mln
Add the alleles from the sperm (MLN) and the alleles from the egg (MLN) to
determine the genotype of the zygote (and the new individual), (MMLLNN)
♀/♂
MLN
MLn
MlN
Mln
mLN
mLn
mlN
mln
MLN
MLn
MlN
Mln
mLN
mLn
mlN
mln
If you count up the number of alleles represented by capital letters, you get the
number of alleles that code to make a person’s hair, eyes, or skin darker,
because each allele represented by a capital letter causes skin cells to make
more melanin (brown pigment)
♀/♂
MLN
MLn
MlN
Mln
mLN
mLn
mlN
mln
MLN
MMLLNN MMLLNn
MMLlNN
MMLlNn
MmLLNN MmLLNn
MmLlNN
MmLlNn
MLn
MMLLNn
MMLLnn
MMLlNn
MMLlnn
MmLLNn
MmLLnn
MmLlNn
MmLlnn
MlN
MMLlNN
MMLlNn
MMllNN
MMllNn
MmLlNN
MmLlNn
MmllNN
MmllNn
Mln
MMLlNn
MMLlnn
MMllNn
MMllnn
MmLlNn
MmLlnn
MmllNn
Mmllnn
mLN
MmLLNN MmLLNn
MmLlNN
MmLlNn
mmLLNN mmLLNn
mmLlNN
mmLlNn
mLn
MmLLNn
MmLLnn
MmLlNn
MmLlnn
mmLLNN mmLLNn
mmLlNn
mmLlnn
mlN
MmLlNN
MmLlNn
MmllNN
MmllNn
mmLlNN
mmLlNn
mmllNN
mmllNn
mln
MmLlNn
MmLlnn
MmllNn
Mmllnn
mmLlNn
mmLlnn
mmllNn
mmllnn
The number of alleles coding for the cells to make melanin
determine how genetically dark the individual’s hair, skin, or eyes
will be. Count up the alleles and total them in the first square
♀/♂
MLN
MLn
MlN
Mln
mLN
mLn
mlN
mln
MLN
MLn
MlN
Mln
mLN
mLn
mlN
mln
The number of alleles coding for the cells to make melanin determine
how genetically dark the individual’s hair, skin, or eyes will be. Count
up the alleles and total them in each square.
♀/♂
MLN
MLN
6
MLn
MlN
Mln
mLN
mLn
mlN
mln
MLn
MlN
Mln
mLN
mLn
mlN
mln
Now, count up the alleles coding for melanin production
and total them in each square of the Punnet square
♀/♂
MLN
MLn
MLN
6
5
MLn
5
MlN
Mln
mLN
mLn
mlN
mln
MlN
Mln
mLN
mLn
mlN
mln
Now, fill in the rest of the squares in the Punnet square.
Notice there is a pattern to the numbers.
♀/♂
MLN
MLn
MlN
Mln
mLN
mLn
mlN
mln
MLN
6
5
5
4
5
4
4
3
MLn
5
4
4
3
4
3
3
2
MlN
Mln
mLN
mLn
mlN
mln
Count how many sixes, fives, fours, threes, twos,
ones, and zeroes, out of 64, and write the totals in
the data table on the next slide.
♀/♂
MLN
MLn
MlN
Mln
mLN
mLn
mlN
mln
MLN
6
5
5
4
5
4
4
3
MLn
5
4
4
3
4
3
3
2
MlN
5
4
4
3
4
3
3
2
Mln
4
3
3
2
3
2
2
1
mLN
5
4
4
3
4
3
3
2
mLn
4
3
3
2
3
2
2
1
mlN
4
3
3
2
3
2
2
1
mln
3
2
2
1
2
1
1
0
Now, plot the data on the graph, with the numbers of alleles
on the x-axis and the number of individuals on the y-axis.
20
19
Number of Alleles Number of Individuals (out of 64)
18
17
16
6
15
14
13
4
3
Number of Individuals
5
12
11
10
9
8
7
6
2
5
4
1
3
2
1
0
0
0
1
2
3
Number of Alleles
4
5
6
Now, plot the data on the graph, with the numbers of alleles
on the x-axis and the number of individuals on the y-axis.
20
19
Number of Alleles Number of Individuals (out of 64)
18
17
16
6
1
15
14
4
3
13
6
15
20
Number of Individuals
5
12
11
10
9
8
7
6
2
15
5
4
1
6
3
2
1
0
1
0
0
1
2
3
Number of Alleles
4
5
6