How do the events of meiosis explain Mendel's law of indpenedent assorment???

Question

How do the events of meiosis explain Mendel's law of indpenedent assorment???

Answer 1

Let me offer an example.  Let's start with two plant parents that are heterozygous for a specific trait (doesn't matter what it is).  A stands for the dominant allele and a is the recessive one.  So each parent has the genotype Aa.  In each somatic cell of the parent plant (pea, for instance) each chromosome exists in duplicate.  So in this case, each parent has the A allele on one chromosome and the recessive a on the other chromosome of the pair.  

Now, during meiosis the two chromosomes part company and each goes to a separate cell called a gamete.  A gamete is a reproductive cell (like egg and sperm).  One gamete from each parent will join up to make a zygote that eventually becomes a new plant.  In our example each parent makes an equal number of gametes carrying the A allele and the a allele.  Each gamete from one parent will randomly unite with a gamete from the other parent.  So, one half of the gametes from the first parent carry the A allele and one half of these will find a gamete from the second parent carrying the A allele.  So, one fourth of the progeny will be AA.  The other half of the A gametes from the first parent will unite with a gamete carrying a.  Likewise, one half of the gametes carrying the a allele from the first parent will find the A allele from the second parent.  Thus, one half of the progeny will be Aa.  Lastly, one half of the gametes of parent 1 carry a and these have a one half probability of finding an a gamete from the second parent.  Hence, one fourth of the progeny will be aa.  

parent 1 gametes- A and a:    parent 2 gametes- A and a

(equal frequency of each allele in gamete populations)

Cross  Aa  x   Aa

Progeny-  AA   Aa   Aa   aa

Answer 2

During meiosis there are structures formed called chiasmata. These are the physical evidence that there is recombination due to crossing over. Crossing over occurs between homologous chromosomes. During crossing over, alleles can be exchanged thus, varying the traits that a chromosome carries.

Also, during meiosis, the homologs are divided such that each of the four resulting cells carries one p and q arm of the chromosome.