The rule of independent assortment states that alleles of one gene can segregate

Question

The rule of independent assortment states that alleles of one gene can segregate independently of alleles of other genes. In other words, the allele you pass on for one trait (for example, eye color) does not have any effect on the allele you pass on for some other trait (for example, height). Imagine you have conducted the following cross using a type of pea plant similar to Mendel.

P1 Round/Yellow (RR/YY)
P2 Wrinkled/Green (rr/yy)


a) What is (are) the phenotype(s) and genotype(s) of the F1 generation?

b) You cross the F1

Explanation / Answer

Mendel's Laws: 1. Law of Unit Characters: Mendel deduced that there were units in the cell that were responsible for these traits, and that these units came in pairs. Since sexual reproduction was the mode of gene transfer, he figured that each offspring received one unit from each of the two parents. 2. Law of Segregation: During gamete (sex cells) formation gene pairs separate. This is evident in meiosis. When a sperm or egg cell is being produced it under goes a reduction in the number of chromosomes by 1/2. This will allow the normal number of chromosomes to occur in the offspring at fertilization. 3. Law of Independent Assortment: Mendel deduced the first 2 laws by using a monohybrid cross. This is a genetic cross containing 1 trait. Mendel was lucky in choosing the characteristics he worked with, since the were not linked and found on separate chromosomes. In a dihybrid cross, 2 trait cross, there are many possible chromosome combinations during gamete formation. Each chromosome seems to have a mind of its own when choosing which sperm or egg cell to enter. Each chromosome does not have a mind but the rules of chance take over in determining where they are to go. This is called independent assortment. Let us look at a simple example: RrYy represents one parent with the characteristics R and r for skin texture and Y and y for hair texture. The parent is heterozygous for both characteristics. During gamete formation one of the R's and one of the Y's need to be in each sperm cell. If this does not happen the offspring will have too many Y's or too few R's and visa versa. The possible gametes must have one R and one Y to be effective. RY, rY, Ry, and ry are the only possible combinations allowed. This individual has the possibility of producing any one of these gametes from the original RrYy cell. If the other parent has the same genotype ( arrangement of genes) the gametes would be the same. If a genetic cross were made there would be 16 possible combinations of offspring from that mating. 9 would be dominant for both characteristics, 3 would be dominant for R and recessive for y, 3 would be dominant for Y and recessive for r, and 1 would be recessive for both characteristics. This can only occur if 2 or more traits are being used and they are on separate chromosomes. 4. Law of Dominance: Within any characteristic one allele appears more often than the other. This may give the appearance that that allele is stronger and the other is weak. The fact is that it has nothing to do with strength. The dominant allele is naturally selected to appear more often than the other allele. In some cases the dominant allele is lethal and in a homozygous condition kills the offspring during some point in its life cycle. The recessive allele appears least often and in many cases is less selective of the two alleles. In some cases a trait may have more than one allele representing the characteristic. This is called multiple alleles. An example of this condition is Human ABO blood typing. A and B type blood are co-dominant while blood type O is recessive to both A and B. Hence your genotypes for A type blood are: AA and AO; B type blood: BB and BO; AB blood is AB, and O type is OO.

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.