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Published byIsaac Stanley Modified over 6 years ago
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4.4 - Dihybrid Crosses Dealing with the mating of two individuals and tracking TWO traits or genes.
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These type of crosses can be challenging to set up, and the square you create will be 4x4.
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EXAMPLE A pea plant that is heterozygous for round, yellow seeds is self fertilized, what are the phenotypic ratios of the resulting offspring? X
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Step 1 Step 1: Determine the parental genotypes, the word "heterozygous" is the most important clue, and you would also need to understand that self fertilized means you just cross it with itself. RrYy x RrYy
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Step 2 Determine the gametes.
This might feel a little like the FOIL method you learned in math class. Combine the R's and Ys of each parent to represent sperm and egg. Do this for both parents.
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Gametes after "FOIL" RY Ry rY ry RY Ry rY ry
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Step 3 Set up a large 4x4 Punnet square
Place one gamete set from the parent on the top, and the other on the side.
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Step 4 Write the genotypes of the offspring in each box and determine how many of each phenotype you have.
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In this case, you will have 9 round, yellow; 3 round, green; 3 wrinkled, yellow; and 1 wrinkled green
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Example 2 – Guinea Pigs BB = black Bb = black bb = white
LL = short hair Ll = short hair ll = long hair
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F2 = Genotype & Phenotype
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Polygenic Inheritance
GENETIC COMPLEXIES Polygenic Inheritance
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POLYGENIC INHERITANCE
Polygenic inheritance is a fancy term for those genetic traits that are controlled by more than 1 gene. Involves 2 or more genes influencing the expression of one trait.
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With 2 or more allelic pairs found at different loci the number of possible genotypes is greatly increased. Human eye color involves the interaction of 2 genes. Human skin color involves the interaction of at least 3 genes. Skin color variation can be modified by environmental factors.
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Eye Color There are at least 15 genes that have been determined to help regulate eye color. There are 2 primary genes associated with eye color variation are OCA2 and HERC2, and both are localized on Chromosome 15.
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SKIN COLOR Skin Color is based on 3 main types of genes.
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