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DIHYBRID CROSS EXPLAINED

Allele refers to 2 or more alternative forms of a gene that are found in the same place of a chromosome and code for the same thing. In humans freckles and free-hanging earlobes are dominant traits. Let’s consider that two parents each have one allele for freckles and one for free-hanging earlobes as well as one allele for not having these things. If these parents have a child, what is the probability that they do not have freckles nor free-hanging earlobes. A dihybrid cross can be used to find out multiple traits of the offspring based on the genotype of the parents, i.e. the alleles of the parents. DI means that we are considering 2 genes and hybrid means that both parents are heterozygotes. To setup the dihybrid cross we draw a 4x4 table called a Punnett square and place the alleles of one parent above the table and the alleles from the other parent to the left of the table. Then we fill in each square like so. The resulting genotype can be seen on the screen. The percentage comes from the total amount the letter combination appears in the table divided by 16 since that is the total amount of squares. To find the phenotype which lacks both freckles and free-hanging earlobes we need to find the letter combination consisting ONLY of small letters since these are recessive. The result is that these 2 parents’ probability of having a child without freckles nor free-hanging earlobes is 6.25%.