Biology Forums - Study Force

Relate Mendel's law of independent assortment and law of equal segregation to chromosome behavior during meiosis

Mendel's law of segregation states that the two alleles for a character separate (or segregate, hence the name) during the formation of gametes (sex cells), so that each gamete only carries one allele for each character. So if an organism had a characteristic R and the alleles it had for that character were Rr, the allele R would end up in a different gamete from r.

Mendel's law of independant assortment states that during gamete formation in an F2 cross, a particular allele for one character can be paired with either allele of another character. An example would be a cross between two plants with two characters, R and Y. If their genotypes are RRYY and rryy, R can be paired with Y or y and r can be paired with Y or y.

Both describe the movement of alleles during meiosis but they are not the same. Independent assortment describes the movement of alleles relative to other alleles. Segregation describes the movement of alleles relative to gametes.

Independent assortment says that for each pair of alleles, how one of dad's alleles is inherited is independent of all of the other alleles from dad. And the same from mom's alleles. So if you are just talking about two alleles, a particular gamete could get both of mom's, both of dad's or one of each with equal likelihood.

Segragation says that each gamete will get one of each allele. It says nothing about the type of combination of mom's and dad's alleles.

Mendel summarized his findings in two laws; the Law of Segregation and the Law of Independent Assortment.
The Law of Segregation states that the members of each pair of alleles separate when gametes are formed. A gamete will receive one allele or the other.(Due to chromosomes spliting into 2 chromatids at meiosis 2 anaphase)

The Law of Independent assortment states that two or more pairs of alleles segregate independently of one another during gamete formation.(Due to chromosomes lining up randomly at meiosis 1 metaphase)

In independent assortment the chromosomes that end up in a newly-formed gamete are randomly sorted from all possible combinations of maternal and paternal chromosomes. Because gametes end up with a random mix instead of a pre-defined "set" from either parent, gametes are therefore considered assorted independently. As such, the gamete can end up with any combination of paternal or maternal chromosomes. Any of the possible combinations of gametes formed from maternal and paternal chromosomes will occur with equal frequency. For human gametes, with 23 pairs of chromosomes, the number of possibilities is 2^23 or 8,388,608 possible combinations. The gametes will normally end up with 23 chromosomes, but the origin of any particular one will be randomly selected from paternal or maternal chromosomes. This contributes to the genetic variability of the offspring.

Mendel's law of segregation, states that allele pairs separate or segregate during gamete formation, and randomly unite at fertilization.

Mendel's Law of segregation: Allele pairs segregate during Meiosis I and the paired condition is restored by the random fusion of gametes during fertilization.

Mendel's Law of Independent Assortment: Each allele pair segregates independently from other allele pairs during Meiosis I.

Genes separate in both, but in the law of segregation, they separate when gametes form, but the new offspring gets both genes after fertilization. During independent assortment, the gametes stay segregated, which allows for genetic variation.

Both processes occur during gamete (sperm & egg) maturation. Both involve a separation of alleles.

Differences:

Segregation (means separation): Alleles for the SAME trait (like height) separate (segregate )into different gametes; i.e.: one sperm gets a "t" and the other gets a "T".

Indep. Assortment: Alleles for DIFFERENT traits separate (in this case we say assort) independently from each other. This can best be seen in gamete formation of a dihybrid.

• Example: TtYy will produce four different kinds of gametes. A "big T" doesn't have to be in the same gamete as a "big Y." You can have TY,tY Ty or ty. The two different alleles for T and Y assorted independent of each other.