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Course: High school biology - NGSS>Unit 6

Lesson 3: Genes, traits, and the environment

Dihybrid cross and the law of independent assortment

The probabilities of different offspring genotypes and phenotypes can be determined using a Punnett square. A dihybrid cross results in a roughly 9:3:3:1 ratio of offspring phenotypes. Created by Sal Khan.

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• Is dihybrid cross = crossing of two identically heterozygous individuals? Does homozygous not work?
• Dihybrid cross is just the name given to crossing of two identically heterozygous individuals, and it happens that it results in a 9:3:3:1 ratio. You can cross any two individuals by using a Punnet square, but they would not have the same 9:3:3:1 ratio.
(1 vote)
• how can you predict the possibilities of the offspring by using ratios?
• Good question, the punnet square gives you the ratios of probabilities, however because it’s completely random what traits are together, there is a likeliness associated with it.
• at homozygous recessive phenotypes
can you say homozygous recessive genotypes instead?
• Phenotypes are just what is outwardly/visibly displayed as a trait of the organism. Because there are only recessive alleles in this grid or recessive genotypes, this gives you the freedom to say either of the two (phenotypes of genotypes)
• How do you know if a gene is dominant or not?
• **
Dominant refers to a relationship between two versions of a gene. If one is dominant, the other one must be not dominant. In that case, we call it recessive. A dominant gene, or a dominant version of a gene, is a particular variant of a gene, which for a variety of reasons, expresses itself more strongly all by itself than any other version of the gene which the person is carrying, and, in this case, the recessive. Now, it usually refers to inheritance patterns frequently used in conjunction with a Punnett square where, if an individual has two versions of a gene, and one is observed to frequently be transferred from one generation to another, then it is called dominant. Biochemically, what is going on in this case is that the genetic variation, for a variety of reasons, can either induce a function in a cell, which is either very advantageous or very detrimental, which the other version of the gene can't cover up or compensate for. In that case, you're going to have a dominant mutation, and that dominant mutation can be benign. It can refer to eye color of one sort or another; that can be can a dominant mutation. Or it can refer to a disease. Huntington's disease, for instance, is a dominant mutation where, if one is carrying that version of the Huntington gene, that mutation, that dominant mutation, will give the individual the disease regardless of what that person's other Huntington's disease gene allele is. That other Huntington's disease gene allele can be perfectly normal, but the person still has the disease because of that one copy of the Huntington's disease gene that is mutated. That is dominance.

**Not my article, but I hope this helped.

INFO CREDIT
:
https://www.genome.gov/genetics-glossary/Dominant
(1 vote)
• how do you decide which factor will be dominant and recessive?