Why is independent assortment important

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. Nuclear membranes reform. Cell divides and 2 daughter cells are formed, each with 23 chromosomes.

There are 4 new haploid daughter cells. In males, 4 sperm cells are produced. In females, 1 egg cell and 3 polar bodies are produced. Polar bodies do not function as sex cells. During fertilisation, 1 gamete from each parent combines to form a zygote. Because of recombination and independent assortment in meiosis, each gamete contains a different set of DNA. Today we know that this rule holds only if the genes are on separate chromosomes. In a heterozygote, the allele which masks the other is referred to as dominant, while the allele that is masked is referred to as recessive.

Most familiar animals and some plants have paired chromosomes and are described as diploid. They have two versions of each chromosome: one contributed by the female parent in her ovum and one by the male parent in his sperm.

These are joined at fertilization. The ovum and sperm cells the gametes have only one copy of each chromosome and are described as haploid. Recessive traits are only visible if an individual inherits two copies of the recessive allele : The child in the photo expresses albinism, a recessive trait.

Rather than both alleles contributing to a phenotype, the dominant allele will be expressed exclusively. The recessive trait will only be expressed by offspring that have two copies of this allele; these offspring will breed true when self-crossed. By definition, the terms dominant and recessive refer to the genotypic interaction of alleles in producing the phenotype of the heterozygote. The key concept is genetic: which of the two alleles present in the heterozygote is expressed, such that the organism is phenotypically identical to one of the two homozygotes.

It is sometimes convenient to talk about the trait corresponding to the dominant allele as the dominant trait and the trait corresponding to the hidden allele as the recessive trait.

However, this can easily lead to confusion in understanding the concept as phenotypic. This will subsequently confuse discussion of the molecular basis of the phenotypic difference. Dominance is not inherent. One allele can be dominant to a second allele, recessive to a third allele, and codominant to a fourth. If a genetic trait is recessive, a person needs to inherit two copies of the gene for the trait to be expressed. Thus, both parents have to be carriers of a recessive trait in order for a child to express that trait.

Instead, several different patterns of inheritance have been found to exist. Apply the law of segregation to determine the chances of a particular genotype arising from a genetic cross. Observing that true-breeding pea plants with contrasting traits gave rise to F 1 generations that all expressed the dominant trait and F 2 generations that expressed the dominant and recessive traits in a ratio, Mendel proposed the law of segregation. The law of segregation states that each individual that is a diploid has a pair of alleles copy for a particular trait.

Each parent passes an allele at random to their offspring resulting in a diploid organism. The allele that contains the dominant trait determines the phenotype of the offspring.

In essence, the law states that copies of genes separate or segregate so that each gamete receives only one allele. For the F 2 generation of a monohybrid cross, the following three possible combinations of genotypes could result: homozygous dominant, heterozygous, or homozygous recessive. The equal segregation of alleles is the reason we can apply the Punnett square to accurately predict the offspring of parents with known genotypes.

The behavior of homologous chromosomes during meiosis can account for the segregation of the alleles at each genetic locus to different gametes. As chromosomes separate into different gametes during meiosis, the two different alleles for a particular gene also segregate so that each gamete acquires one of the two alleles. Independent assortment allows the calculation of genotypic and phenotypic ratios based on the probability of individual gene combinations. Use the probability or forked line method to calculate the chance of any particular genotype arising from a genetic cross.

The independent assortment of genes can be illustrated by the dihybrid cross: a cross between two true-breeding parents that express different traits for two characteristics. Consider the characteristics of seed color and seed texture for two pea plants: one that has green, wrinkled seeds yyrr and another that has yellow, round seeds YYRR. Therefore, the F 1 generation of offspring all are YyRr. For the F2 generation, the law of segregation requires that each gamete receive either an R allele or an r allele along with either a Y allele or a y allele.

The law of independent assortment states that a gamete into which an r allele sorted would be equally likely to contain either a Y allele or a y allele.

Thus, there are four equally likely gametes that can be formed when the YyRr heterozygote is self-crossed as follows: YR, Yr, yR, and yr. These are the offspring ratios we would expect, assuming we performed the crosses with a large enough sample size. Independent assortment of 2 genes : This dihybrid cross of pea plants involves the genes for seed color and texture. Because of independent assortment and dominance, the dihybrid phenotypic ratio can be collapsed into two ratios, characteristic of any monohybrid cross that follows a dominant and recessive pattern.

Ignoring seed color and considering only seed texture in the above dihybrid cross, we would expect that three-quarters of the F 2 generation offspring would be round and one-quarter would be wrinkled. Similarly, isolating only seed color, we would assume that three-quarters of the F 2 offspring would be yellow and one-quarter would be green. The sorting of alleles for texture and color are independent events, so we can apply the product rule. These proportions are identical to those obtained using a Punnett square.

What does independent assortment mean? The law of independent assortment means that separate traits of different alleles are inherited by the zygote independently from each other. Where the random selection of one allele for a certain trait is not connected by any means to the selection of another allele for a different trait. What is an independent assortment? Independent assortment states that the inheritance of various genes occurs independently of each other.

In the law of independent assortment, the combination of genes and their probability is calculated and assumed by multiplying the probabilities of each gene. 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.

It is important to note that there is an exception to the law of independent assortment for genes that are located very close to one another on the same chromosome because of genetic linkage.

Further Exploration Concept Links for further exploration gene principle of segregation allele genotype phenotype dihybrid cross gamete diploid chromosome haploid meiosis recombination linkage Principles of Inheritance principle of uniformity. Related Concepts You have authorized LearnCasting of your reading list in Scitable.

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