Mendel’s Laws: Definition, Difference, Experiment, and Apparent Deviations of Mendel’s Laws

Mendel’s Law – Sinaumed’s must have known that the genes in living things greatly affect how the “form” of their offspring will be, be it in humans, animals, even plants. Yep, the existence of genes in living things is the main subject and object in Genetics, namely a science that studies how traits are inherited from parents to offspring. Genes are also the most important aspect of living things because through them, they can reproduce and preserve their offspring. Now, to “calculate” how the embodiment of parental genes will be given to their offspring, you can use Mendel’s Law.

Even in this advanced era, the existence of Mendel’s Law does not necessarily become subject matter in the field of Biology, you know  It turns out that both Mendel’s Law I and II have been applied in Agriculture, especially to find superior seeds through crossing. Then how does Mendel ‘s Law I and II sound? What about examples of experiments carried out through Mendel’s Laws I and II? Why are genes important in the effort to inherit traits from parents to offspring? So, so that Sinaumed’s understands these things, let’s look at the following review!

What do Mendel’s Laws I and II sound like?

Just a little trivia , Sinaumed’s , Mendel’s Law which discusses the system of inheritance from parents to offspring was first coined by Gregor Johann Mendel, who was born on July 22, 1840. His first theory regarding the inheritance system was put forward in 1865, based on his cross research using varieties pea. The research results are written in a paper entitled Experiment in Plant Hybridization .

In cross-breeding research, the male and female parents are named parental (oldest) and are symbolized by the letter P. So, the results of the parental cross are named filius (children) and are symbolized by the letter F. Meanwhile, the cross between the male parent and the female parent is called P1. and the filial is called F1. Then, crosses between F1 males and F1 females that are carried out randomly will be called P2, while the filials will be called F2, and so on.

Mendel’s Law I

Mendel’s Law I has another name, namely the Law of Segregation. In the Law of Segregation it states that “In the formation of gametes (sex cells) the two genes that are partners will be separated in two daughter cells’. Well, Mendel’s Law I or the Law of Segregation applies to monohybrid crosses, aka crosses with one different trait.

Broadly speaking, Mendel’s Law I will relate to the existence of 3 points, namely:

  1. Genes have alternative forms that regulate variations in the inherited characters. This is what makes the concept of two kinds of alleles, namely a) recessive alleles (not always visible from the outside, expressed in lower case, for example w in the picture); and b) the dominant allele (visible from the outside, expressed in capital letters, for example R)
  2. Each individual carries a pair of genes, one from the male parent (eg ww) and one from the female parent (eg RR)
  3. If this pair of genes has two different alleles, the dominant allele will always be expressed (visually visible from the outside). Recessive alleles that are not always expressed will still be passed on to the gametes (sex cells) formed in their offspring.

Consider the example of a cross between a dominant red rose and a recessive white rose, below

Well, Mendel’s First Law also states that two alleles (gene variants) that regulate certain traits will separate in two different gametes (sex cells). Mendel’s Law I includes several things, namely:

  • Alleles (gene variations) for inherited trait variations. For example: the colors of two different flowers, called alleles, will occupy the locus that corresponds to the homologous pair.
  • Two alleles for a character will separate when gametes (sex cells) are produced. Example: the result of a cross containing one allele of the parent flower color (purple or white)
  • Each character in each organism will inherit two alleles, each of which comes from the parent. Example: the result of a cross that is likely to produce 1 white allele and 1 purple allele.
  • If there are two different alleles, one of them will be dominant, while the other will be recessive. Example: there is a marriage of purple flowers with white flowers, it will produce purple offspring.
See also  difference between cat5 and cat 6

Mendel’s Law II

In Mendel II’s Law or also known as the Law of Independent Assortment or the Law of Independently Grouping of Genes, it states that ‘if two individuals differ from one another in two or more pairs of traits, then the nature of that pair will be inherited, not depending on the nature of the other pair. ‘ . The existence of Mendel II’s Law applies to dihybrid crosses (with two different traits). In a dihybrid cross, for example, there is an individual with the genotype AaBb, then A and a and B and b will separate and then the pair will join freely. Through this, it is possible that the gametes (sex cells) that are formed will have AB, Ab, aB, and ab properties.

In short, Mendel’s Law II states that alleles (gene variations) with different genes do not affect each other. This also explains that the genes that determine plant height and plant color do not affect each other. Check out the following examples!

Difference Between Mendel’s Law I and II

The difference between Mendel’s Law I and II is most obvious in the traits that are crossed. In Mendel’s Law I states that the formation of gametes (sex cells) in both parental genes that are paired with alleles, will separate alias segregation. This causes each gamete to receive one gene from its parent.

Meanwhile, Mendel II’s Law states that if there are individuals who differ from each other in two or more pairs of traits, then it will inherit a pair of traits and not depend on other traits.

In conclusion, in Mendel’s Law I will experience a process of segregation or separation of cells freely. While in Mendel II’s Law will experience independent gene grouping.

Examples of Crosses in Mendel’s Laws

Mendel’s Law I

1. Monohybrid Cross

At that time, Mendel made an experiment by crossing two individuals of peas that had different characteristics, namely between peas with high stems and peas with low stems. While the ‘high’ trait is dominant over the ‘low’ trait, so it will produce:

If you look again at the theory of Mendel’s Law I which states that in the formation of gametes (sex cells) the allele pairs will separate freely. Well, this separation event will be seen when the formation of individual gametes that have a heterozygous genotype, so that each gamete (sex cell) will contain one of these alleles.

2. Backcross and Testcross

Backcross is the process of crossing or mating hybrid individuals (F1) with one of the parents. The goal is to be able to know the genotype of the parent (parental). Consider the following example by relying on the ‘high’ property of peas.

While testcross is the process of crossing an F1 individual with one of its homozygous recessive parents. The goal is to find out whether the F1 individual is homozygous or heterozygous.

Mendel’s Law II

1. Dihybrid Cross

Through this Dihybrid cross experiment, Mendel tried to involve two traits at once and concluded that in the process of forming gametes (sex cells), each pair of alleles at one locus will segregate independently with other locus allele pairs, and will combine freely with alleles from that locus. other. In short, monohybrid is a hybrid with 1 different trait, while dihybrid is a hybrid with 2 different traits.

At that time, Mendel used pea plants as his object of observation, for the following reasons:

  • Having a pair of striking or contrasting characteristics.
  • Self-pollination (autogamy), so that hereditary traits tend to remain.
  • Easy to cross pollinate.
  • Quick to produce offspring.
  • Can have many offspring.

The following are the properties possessed by pea plants, so that they are used as objects of observation for this dihybrid cross.

The process of dihybrid crosses has the following characteristics:

  • Crossing is done by paying attention to two different properties.
  • The number of gametes (sex cells) formed in each individual is 4 (2n)
  • An individual’s phenotype will be determined by 2 types of genetic traits.
  • There will be about a maximum of 16 genotypic variations in F2.

Pseudo Deviation of Mendel’s Laws

In Mendel’s law, both I and II, there will be apparent deviations, which are a form of crossing by producing different phenotypic ratios on a dihybrid basis. Even though it looks different, actually the phenotypic ratio is a modified form of the sum of the phenotypic ratios which is based on all of Mendel’s Laws.

See also  6 Aceh Heroes Enshrined in Jakarta

For example, in a marriage between 2 individuals with 2 different traits, it turns out that the F2 phenotypic ratio is not always 9 : 3 : 3 : 1. However, you will often find different comparisons, but a combination of Mendelian comparison numbers written 9: 3: 3:1 i.e.:

  • 9 : 7 = 9 : ( 3 + 3 + 1 )
  • 12 : 3 : 1 = ( 9 + 3 ) : 3 : 1
  • 15 : 1 = ( 9 + 3 + 3 ) : 1
  • 9 : 3 : 4 = 9 : 3 : ( 3 + 1 )

If it is based on Mendel’s Law II, one allele will not affect each other’s segregation of other allele pairs in determining different traits. These genes will be freely paired and give rise to certain traits in individuals. Well, that’s what is called the ‘Pseudo Deviation of Mendel’s Law’. It is called “pseudo” because the principle of independent segregation remains in effect, and is caused by the genes that carry traits in determining these particular characteristics. The following are the characteristics of ‘Pseudo Deviations of Mendel’s Laws’:

  • The resulting phenotypic ratio is different from Mendel’s Law.
  • There are certain traits in the gene that cause different results in filial 2.
  • There is interaction between genes.

Types of Pseudo Deviations of Mendel’s Laws

1. Atavism

Atavism is a process of interaction between genes that produces filial or offspring with different phenotypes from their parents. Example: atavism in chicken comb which has four types, namely rose (R-pp), pea (rrP-), walnut (RP-), and katakana (rrpp). Then it will be the following:

A homozygous rooster with rose comb is crossed with a homozygous pea comb female rooster. From the results of these crosses, it was found that all F1 had walnut combs. If the F1 is crossed with each other, the possible ratio of the F2 is 9:3:3:1

 2. Cryptomers

Cryptomerism is the hidden event of the dominant gene, especially if it is not paired with another dominant gene. So, if the dominant gene stands alone, it will become hidden, aka cryptos. Example: cryptomeri in the Linaria Maroccana flower cross which has 4 genes, namely:

  • A = formed anthocyanin pigment
  • B = no anthocyanin pigment is formed
  • C = alkaline protoplasm
  • D = acid protoplasm

Then through these 4 genes will form:

3. Polymers

Polymer is a process of interaction between genes that are cumulative or add to each other. So, these genes will interact with each other to influence and produce the same offspring. For example: polymerization in red grain wheat with 2 genes, namely M1 and M2, so that when the two genes meet, the color expression obtained will also be stronger. Pay attention to the following explanation!

4. Epistatis and Hypostatic

Epistasis-Hypostasis is an event when a dominant gene will cover the influence of other dominant genes that are not alleles. The gene that covers it is called epistasis, while the gene that covers it is called hypostasis. An example of this epistasis-hypostasis can be found in the cross between the pumpkin and the white pumpkin.

5. Gene-gene complements

Complementary is the process of interaction between dominant genes, with different but complementary traits, so that a certain phenotype will emerge. If one of these genes does not appear, then the trait in question will not appear either. Examples of these complementary genes can be found in the Lathyrus Odoratus flower cross which has 4 genes in the form of:

  • C = forming color pigments.
  • c = does not form color pigments.
  • P = forming activator enzyme.
  • p = does not knock down the activator enzyme.

Get to know the Theory of Inheritance

Inheritance of traits can also be referred to as “heredity” which refers to the inheritance of traits from parents to offspring. This heredity is also related to genetics, which is a science that studies the inheritance of traits. Well, the inheritance of these traits can be determined by chromosomes and genes. There are theories about inheritance, including:

1. Embryo theory

This theory was put forward by William Harvey who argued that all animals came from eggs. This statement was further strengthened by Reinier de Graaf as the first researcher to introduce the union of sperm cells with egg cells in the formation of embryos. Reinier also stated that the ovaries in birds were the same as those in rabbits.

2. Preformation Theory

This theory was put forward by Jan Swammerdam who stated that the egg contains all future generations, so it can be considered as a miniature of the previously formed individuals.

3. Embryological Epigenesis Theory

This theory was put forward by CF Wolf who stated that there is a vital force contained in the seeds of organisms. Through this power, it can cause the growth of the embryo based on the previous pattern of development.

4. Germplasm Theory

This theory was put forward by JB Lamarck who stated that the nature that occurs is due to stimuli from the outside (especially the environment), on the structure of organ functions which are passed on to the next generation.