Question

Review the description of meiosis (see Figure 13.8) and Mendel’s laws of segregation and independent assortment (see Concept 14.1). What is the physical basis for each of Mendel’s laws?

Short answer

The separation of homologous chromosomes during anaphase I of meiosis is the physical basis for the law of segregation.

While the alternative arrangements of the homologous chromosomes pairs during metaphase I is the physical basis for the law of independent assortment.

Step-by-step solution

Mendel’s law

Based on the experiments conducted on pea plants, Mendel observed that the allele pairs, which are the alternative forms of a gene, separate from each other during gametogenesis. As a result,the gametes produced contain only one allele of the pair. This is known as the law of segregation.

During the dihybrid cross, Mendel observed that the alleles of different genes that code for traits in an individual are sorted and inherited independently of each other during meiosis. This means alleles of one gene do not influence the inheritance of alleles of other genes. This is known as the law of independent assortment.

Meiosis

A process of cell division includes two sequential nuclear divisions. This produces haploid daughter nuclei that contain only one member of each pair of homologous chromosomes. Thus,this division process that reduces the number of chromosomes to half is called meiosis.

Meiosis comprises two cell divisions; meiosis I and meiosis II. In meiosis I, homologous chromosomes separate from each other to form two diploid daughter cells. These cells undergo meiosis II, similar to mitosis, where the sister chromatids of chromosomes separate to form four haploid daughter cells.

Physical basis of the law of segregation

The physical basis of the law of segregation is Meiosis I.During anaphase of meiosis I, the homologous chromosomes separate from each gene are segregated into daughter nuclei.

The homologous chromosomes behave during anaphase I account for the separation of the alleles to form gametes. Thus, the chromosome separates and segregates to form different gametes during meiosis.

This means the alleles of the gene separate, and each gamete inherits one allele of the gene.

Physical basis of the law of independent assortment

The physical basis of the law of independent assortment is also Meiosis I. In metaphase I, the bivalents chromosomes are arranged at the equator. The way the maternal and paternal chromosomes of each bivalent appear on the metaphase I plate is random.

The maternal and paternal chromosomes of a bivalent have an equal chance of facing either pole.Thus, when chromosomes separate during anaphase I, each pole receives a random assortment of parental chromosomes.

Thus, the alternative arrangement of homologous chromosomes in metaphase I demonstrate the physical basis of the law of independent assortment.