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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 During meiosis, the diploid (2n) 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. MLN Go to Section: MLN Section 16-1 The union of one genetic halfcell, the sperm, with the other genetic half-cell, the egg, results in one genetically whole cell, the zygote MLN sperm + egg MLN fertilization Go to Section: MMLLNN zygote 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 Go to Section: MLN ♀/♂ MLN MLN MMLLNN The genotype of all the offspring, (1 out of 1, or 1/1), is MMLLNN, so all the offspring have the same phenotype—very dark skin. Go to Section: 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 During meiosis, the diploid (2n) 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. Go to Section: 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 Go to Section: mln ♀/♂ mln mln mmllnn The genotype of all the offspring, (1 out of 1, or 1/1), is mmllnn, so all the offspring have the same phenotype—very light skin. In both examples, when the very dark mate with the very dark and when the very light mate with the very light, the crosses result in no variation. What happens if the very dark mate with the very light? Go to Section: 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 Go to Section: MLN ♀/♂ MLN mln MmLlNn The genotype of all the offspring, (1 out of 1, or 1/1), is MmLlNn, so all the offspring have the same phenotype—medium skin. In all three examples, when the very extreme mate with the very extreme, the crosses result in no variation. What happens if the medium-skinned mate with the medium skinned? Go to Section: MLN mln MLn mlN MmLlNn MlN mLn mLN Go to Section: Mln During meiosis, the diploid (2n) genotype, MmLlNn is reduced to the haploid genotype. As the alleles segregate and assort independently, maximum diversity results. 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 Go to Section: MLn MlN Mln mLN mLn mlN mln Now do the same for the other possible combinations of sperm and eggs, filling in the boxes of the Punnet square ♀/♂ MLN MLN MMLLNN MLn MlN Mln mLN mLn mlN mln Go to Section: MLn MlN Mln mLN mLn mlN mln ♀/♂ MLN MLN MMLLNN MMLLNn MLn MlN Mln mLN mLn mlN mln MLn Go to Section: MlN Mln mLN mLn mlN mln ♀/♂ MLN MLN MMLLNN MMLLNn MLn MlN Mln mLN mLn mlN mln MLn Go to Section: MlN MMLlNN Mln mLN mLn mlN mln ♀/♂ MLN MLN MMLLNN MMLLNn MLn MlN Mln mLN mLn mlN mln MLn Go to Section: MlN MMLlNN Mln MMLlNn mLN mLn mlN mln ♀/♂ MLN MLN MMLLNN MMLLNn MLn MlN Mln mLN mLn mlN mln MLn Go to Section: MlN MMLlNN Mln MMLlNn mLN MmLLNN mLn mlN mln ♀/♂ MLN MLN MMLLNN MMLLNn MLn MlN Mln mLN mLn mlN mln MLn Go to Section: MlN MMLlNN Mln MMLlNn mLN mLn MmLLNN MmLLNn mlN mln ♀/♂ MLN MLN MMLLNN MMLLNn MLn MlN Mln mLN mLn mlN mln MLn Go to Section: MlN MMLlNN Mln MMLlNn mLN mLn MmLLNN MmLLNn mlN MmLlNN mln Now, fill in the rest of the squares ♀/♂ MLN MLN MMLLNN MMLLNn MLn MlN Mln mLN mLn mlN mln MLn Go to Section: MlN MMLlNN Mln MMLlNn mLN mLn MmLLNN MmLLNn mlN MmLlNN mln MmLlNn 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 Go to Section: MmLlNn MmLlNn MmllNN MmllNn mmLlNN mmLlNn mmllNN mmllNn MmLlnn MmllNn Mmllnn mmLlNn mmLlnn mmllNn mmllnn 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 the first square ♀/♂ MLN MLN 6 MLn MlN Mln mLN mLn mlN mln Go to Section: 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 6 MLn MlN Mln mLN mLn mlN mln Go to Section: 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 Go to Section: 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 Go to Section: 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 2 2 1 2 1 1 0 mln Go to Section: 3 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 Go to 1 Section: 0 0 1 2 3 Number of Alleles 4 5 6
