What is Mendelian Law and Mendelism?

The contribution of Mendel to genetics is called Mendelism. Mendel is called the “Father of Genetics.” He was born into a peasant family in 1822 in Austria. In 1843, he entered the monastery at Brunn, and in 1847, he was ordained as a priest.

After he finished his studies in theology, he worked as a math and Greek substitute teacher. In 1851, he was sent to the University of Vienna, where he studied science. Then he returned and worked as a teacher of physics and natural science. He spent the rest of his life as the abbot. He died in 1884.

Mendel was fond of gardening from his boyhood on. When he was working as a teacher, he performed a series of experiments with pea plants in the monastery garden. His work contains the inheritance of characters in 22 varieties of garden peas. His papers were published in 1866 and 1867 in the proceedings of the Natural History Society of Boston.

Gregor Mendel was an Austrian monk who is known as the “Father of Genetics” for his pioneering work on the inheritance of traits in plants. Mendel did a series of experiments with pea plants in the middle of the 1800s. He carefully controlled how the plants bred and wrote down the traits of the offspring. Mendel used the results of his experiments to come up with two rules about how things are passed down: the law of segregation and the law of independent assortment.

The law of segregation states that during the formation of gametes (sex cells), the two copies of each gene segregate from each other so that each gamete receives only one copy of each gene. This means that the inheritance of one gene does not affect the inheritance of other genes. The law of independent assortment states that the inheritance of one gene is not affected by the inheritance of other genes. This means that the combinations of traits in the offspring can be very different and hard to predict.

Mendel’s laws of segregation and independent assortment are the basis of what we know about genetics and inheritance, and these ideas are still important in modern genetics. His work helped people understand the basic rules of heredity and made it possible for genetics and genomics to grow into what they are today.

What is Mendelian Law?

Mendelian Law 1: Law of Dominance

Each organism is formed of a bundle of characters, and each is controlled by a pair of factors or genes (T or t). Each of the paired factors (T and t) is responsible for the expression of a particular variety (tall or dwarf) of a character’s height). The Mendelian law of dominance states that one factor in a pair may mask or prevent the expression of the other.

He called the variety that appeared in the F1 generation of his mono-hybrid cross as dominant and those which did not appear in the F1 generation as recessive. A recessive factor freely expresses itself in the absence of its dominant allele. This law is formulated based on the mono-hybrid experiment.

Mendelian Law 2: Alleles segregate equally (Law of Segregation)

According to Mendelian law – Law of segregation, he proposed as “Each character is controlled by a pair of gene“. The original experiments by Gregor Mendel involved phenotypic traits (physical, observable characteristics) controlled by single genes.  The first one we’ll consider is seed color, which can be yellow or green.

The dominant allele, denoted Y, generates yellow peas in either the homozygous (YY) or heterozygous (Yy) state, whereas the recessive allele, denoted y, generates green peas only in the homozygous state (yy).  (In plants and flies, the dominant allele is denoted by a capitalized abbreviation and the recessive allele is denoted by a lower case abbreviation.)

In a cross between two parents, one homozygous for the dominant allele (YY) and the other homozygous for the recessive allele (yy), Mendel showed that the F1 progeny were all yellow, i.e. they had had the same phenotype as the parent with the dominant allele.  The recessive allele was not contributing to the phenotype.

Had it been lost during the cross? No, when the F1 is crossed with itself, both parental phenotypes were seen in the F2 progeny.  The effect of the recessive allele reappeared in the second cross, showing that it was still present in the F1 hybrids, but was having no effect.

In the F2 progeny, the dominant phenotype (yellow) was observed in 75% of the progeny and the recessive (green) appeared in only 25% of the progeny.

Note that discrete phenotypes were obtained (yellow or green), not a continuum of phenotypes.  The genes are behaving as units, not as some continuous function.

The results can be explained by hypothesizing that each parent has two copies of the gene (i.e., two alleles) that segregate equally, one per gamete.  Since they are homozygous, each parent can form the only type of gamete (Y or y, respectively).

When the gametes join the zygotes of the F1 generation, each individual receives one dominant allele and one recessive allele (Yy), and thus all of the F1 generations show the dominant phenotype (e.g., yellow peas). This is the uniform phenotype observed for the F1 generation.

The two alleles did not alter one another when presenting together in the F1 generation, because when F1 is crossed with F1, the two parental phenotypes are obtained in the F2 generation.

The ratio of 3:1 dominant: recessive observed in the F2 is expected for the equal segregation of the alleles from the F1 (Y and y) and their random rejoining in the zygotes of the F2, producing the genotypes 1 YY, 2 Yy, and 1 yy.

Again, the genes are behaving as discrete units. These precise mathematical ratios (3:1 for phenotypes in this cross, or 1:2:1 for the genotype) provide the evidence that genes, units of heredity, are determining the phenotypes observed.

Mendelian Law 3: Different genes assort independently (Law of Independent assortment)

In the third Mendelian law, This law is based on a dihybrid experiment. According to this law, the genes for each pair of characters separate independently from those of other characters during gamete formation.

Now that we have some understanding of the behavior of the different alleles of a single gene, let’s consider how two different genes behave during a cross.  Do they tend to stay together, or do they assort independently?

Mendel examined two different traits, seed color (as described in the previous section) and seed shape.  Two alleles at the locus controlling seed shape were studied, the dominant round (R) and recessive wrinkled (r) alleles.

Mendel crossed one parent that was homozygous for the dominant alleles of these two different genes (round yellow RRYY) with another parent that was homozygous for the recessive alleles of those two genes (wrinkled green rryy) (see Figure).

Re-stating the basic question, do the alleles at each locus always stay together (i.e. round with yellow, wrinkled with green) or do they appear in new combinations in the progeny? As expected from the 1st law, the F1 generation shows a uniform round yellow phenotype, since one dominant and one recessive allele was inherited from the parents.

When the F2 progeny are obtained by crossing the F1 generation, the parental phenotypes reappear (as expected from the first law), but two non-parental phenotypes also appear that differ from the parents: wrinkled yellow and round green!

The results can be explained by the alleles of each different gene assorting into gametes independently. For example, in the gametes from the F1 generation, R can assert with Y or y, and r can assert with Y or y, so that four types of gametes form: RY, Ry, rY, and ry.  These can rejoin randomly with other gametes from the F1 generation, producing the results in the grid shown in Fig. 1.2.  The alternative, that R always assorted with Y, etc. was not observed.

Again, the genes are behaving as units, and the gene for one trait (e.g., color) does not affect a gene for another trait (e.g., shape). Further breeding shows that many non-parental genotypes are present, some of which give a parental phenotype (e.g., RrYy).

These results are obtained for genes that are not linked on chromosomes.

Independent assortment of genes

In the middle of the 1800s, Gregor Mendel was the first person to write about the law of independent assortment. It states that the inheritance of one gene is not affected by the inheritance of other genes. This means that the alleles for different genes are inherited independently of each other.

For the law of independent assortment to make sense, it helps to think about genes and alleles. Genes are the basic building blocks of inheritance, and they determine how each person looks and acts. Alleles are different versions of the same gene, and an individual can have two alleles for each gene, one inherited from each parent.

The law of independent assortment says that traits that are controlled by more than one gene are passed down in a way that is independent of each gene.

For example, an individual’s height is controlled by multiple genes, and the alleles for these genes are inherited independently of each other. This means that the inheritance of one gene for height does not affect the inheritance of other genes for height.

Overall, the law of independent assortment is a key idea in genetics. It helps to explain why traits in offspring can be different and hard to predict. It is one of the basic ideas about inheritance that helps us understand genetics and inheritance.

Modifications to Mendel’s laws

Mendel’s laws of segregation and independent assortment are the basis of what we know about genetics and heredity. However, it is important to note that these laws have been changed over time as new information has come to light. These changes help to explain some of the subtleties and complexities of inheritance that Mendel’s laws alone can’t fully explain.

One modification to Mendel’s laws is the concept of dominance and recessiveness. Dominance is the way that one allele is shown to be more important than the other. For example, if an individual has one allele for brown eyes and one allele for blue eyes, the allele for brown eyes is dominant, and the individual will have brown eyes. Recessiveness refers to the suppression of an allele by a dominant allele. For example, if an individual has one allele for brown eyes and one allele for blue eyes, the allele for blue eyes is recessive, and the individual will have brown eyes.

Another modification to Mendel’s laws is the concept of epistasis, which refers to the interaction between genes. In some cases, the way one gene is expressed can change the way another gene is expressed, which can make a trait weaker or stronger.

Mendel’s laws can be changed in these ways, and there are also exceptions, such as non-Mendelian patterns of inheritance. These patterns, like incomplete dominance and codominance, don’t follow the simple dominant and recessive patterns that Mendel’s laws describe. They can be harder to understand and predict.

Overall, while Mendel’s laws of segregation and independent assortment provide a useful starting point for understanding genetics and heredity, it is important to recognize that there are modifications and exceptions to these laws that help to explain them

The law of Seggregation

The law of segregation is a basic idea in genetics that was first explained by Gregor Mendel in the middle of the 1800s. It states that during the formation of gametes (sex cells), the two copies of each gene segregate from each other, so that each gamete receives only one copy of each gene. This means that the inheritance of one gene does not affect the inheritance of other genes.

To understand the law of segregation, it helps to know what alleles are. Alleles are different versions of the same gene, and an individual can have two alleles for each gene, one inherited from each parent.

For example, an individual may have one allele for a gene that codes for brown eye color and one allele for a gene that codes for blue eye color.

In this case, the individual would have brown eyes, because the allele for brown eye color is dominant over the allele for blue eye color.

The law of segregation applies to the inheritance of any trait that is controlled by a single gene with two alleles. For example, the inheritance of hair color, skin color, and blood type can all be explained by the law of segregation.

Overall, the law of segregation is an important concept in genetics that helps to explain how traits are inherited and how genetic variation arises within a population.

The Impact of Mendel’s work

The laws of segregation and independent assortment discovered by Gregor Mendel have made a big difference in the field of genetics and changed how we think about inheritance. Mendel’s work helped people understand the basic rules of heredity and made it possible for modern genetics and genomics to develop.

During Mendel’s lifetime, his laws were not widely known or accepted. However, his work was found again in the early 1900s, and it quickly became the cornerstone of genetics. Mendel’s laws are still important parts of genetics and are taught to biology and genetics students all over the world.

Mendel’s laws have been important throughout history, and they are still important in modern genetics research and technology.

Mendel’s laws are a good way to understand and predict how traits are passed down, and they can be used in a lot of different kinds of genetic research, like studying genetic diseases and making new medicines.

Overall, Mendel’s work has had a lasting impact on the field of genetics and has shaped our understanding of heredity and the way in which traits are inherited.