What does independent assortment produce

However, many of these combinations are identical at the genotype and phenotype level. For example, as was mentioned at the top of the page, 4 of the 16 are crested males. Punnett squares are useful for showing where the alleles came from to make the possible allele combinations.

But with crosses that involve increasing numbers of genes, they become awkward and not very useful. Imagine plotting a Punnett square of a cross involving sex, crest, and pattern. Each parent would have 8 possible gametes, and there would be 64 possible offspring! In female birds and male mammals , sex-linked genes like color do not segregate independently. Genetically linked genes also do not segregate independently.

This is true in both males and females. Using multiplication, we can calculate 1 the number of possible allele combinations for a given cross, and 2 the probability of an offspring having a particular allele combination. Notice that the denominator also tells you the number of possible combinations.

To see where these numbers came from and to check the calculation, you can look back at the first Punnet square near the top of the page. We can also add crest to our calculations. At the end of prophase I, the pairs are held together only at the chiasmata; they are called tetrads because the four sister chromatids of each pair of homologous chromosomes are now visible.

During metaphase I, the tetrads move to the metaphase plate with kinetochores facing opposite poles. The homologous pairs orient themselves randomly at the equator. This event is the second mechanism that introduces variation into the gametes or spores. In each cell that undergoes meiosis, the arrangement of the tetrads is different.

The number of variations is dependent on the number of chromosomes making up a set. There are two possibilities for orientation at the metaphase plate.

The possible number of alignments, therefore, equals 2 n , where n is the number of chromosomes per set. Given these two mechanisms, it is highly unlikely that any two haploid cells resulting from meiosis will have the same genetic composition.

In humans, there are over 8 million configurations in which the chromosomes can line up during metaphase I of meiosis. It is the specific process of meiosis, resulting in four unique haploid cells, that results in these many combinations.

This independent assortment, in which the chromosome inherited from either the father or mother can sort into any gamete, produces the potential for tremendous genetic variation. Together with random fertilization, more possibilities for genetic variation exist between any two people than the number of individuals alive today.

Sexual reproduction is the random fertilization of a gamete from the female using a gamete from the male. A sperm cell, with over 8 million chromosome combinations, fertilizes an egg cell, which also has over 8 million chromosome combinations. That is over 64 trillion unique combinations, not counting the unique combinations produced by crossing-over.

The result is 4 haploid daughter cells known as gametes or egg and sperm cells each with 23 chromosomes — 1 from each pair in the diploid cell. At conception, an egg cell and a sperm cell combine to form a zygote 46 chromosomes or 23 pairs. This is the 1st cell of a new individual.

The halving of the number of chromosomes in gametes ensures that zygotes have the same number of chromosomes from one generation to the next. This is critical for stable sexual reproduction through successive generations. Replication of DNA in preparation for meiosis. After replication, each chromosome becomes a structure comprising 2 identical chromatids. The chromosomes condense into visible X shaped structures that can be easily seen under a microscope, and homologous chromosomes pair up.

Recombination occurs as homologous chromosomes exchange DNA. At the end of this phase, the nuclear membrane dissolves. The pairs of chromosomes separate and move to opposing poles. Either one of each pair can go to either pole. Moreover, the probability of having one gene does not influence the probability of having the other. What stage of meiosis does independent assortment occur?

Independent assortment in meiosis takes place in eukaryotes during metaphase I of meiotic division. It produces a gamete carrying mixed chromosomes. Gametes contain half the number of regular chromosomes in a diploid somatic cell. Thus, gametes are haploid cells that can undergo sexual reproduction at which two haploid gametes are fused together forming a diploid zygote having the complete set of chromosomes.

The physical basis is the random distribution of chromosomes during the metaphase in relation to other chromosomes. Why is independent assortment important? Independent assortment is responsible for the production of new genetic combinations in the organism along with crossing over. Thus, it contributes to genetic diversity among eukaryotes.

To define independent assortment, you should understand the law of segregation first. The law of segregation states that in meiosis, different gamete cells get two different independently assorted genes. On the other hand, the two maternal and paternal DNA are randomly separated allowing for more diversity in genes. The law of independent assortment is apparent during the random division of the maternal and paternal DNA sources.

Due to random assortment, the gamete may get maternal genes, paternal genes, or a mixture of both. The genetic distribution is based on the initial stage of meiosis where these chromosomes are lined up randomly. Gregor Mandel carried out several experiments on pea plants. How does independent assortment occur? Independent assortment occurs spontaneously when alleles of at least two genes are assorted independently into gametes.

Consequently, the allele inherited by one gamete does not affect the allele inherited by other gametes. Mendel noted that the transmission of different genes appeared to be independent events.

In independent events, the probability of a particular combination of traits can be predicted by multiplying the individual probabilities of each trait. In independent events, the inheritance pattern of one trait will not affect the inheritance pattern of another. For example, when Mendel crossed plants with round yellow peas to plants with wrinkled green peas, all of the F1 peas expressed the dominant traits round and yellow.

In the F2, along with round yellow and wrinkled green peas, he observed round green and wrinkled yellow peas. The four possible combinations of color and shape appeared in the ratio of , which represents the independent assortment of the genes for the two pairs of traits into the gametes. The proportions of the other three combinations can be similarly calculated. Later, after the discovery of chromosomes, and of their behavior in meiosis , it was possible to explain independent assortment as a consequence of the independent movement of each pair of homologous chromosomes during meiosis.