What are the mendelian laws? and explain each one.
Answers
Answer:
Mendel’s Laws
Mendel discovered that by crossing true-breeding white flower and true-breeding purple flower plants, the result was a hybrid offspring. Rather than being a mix of the two colors, the offspring was purple flowered. He then conceived the idea of heredity units, which he called “factors”, one of which is a recessive characteristic and the other dominant. Mendel said that factors, later called genes, normally occur in pairs in ordinary body cells, yet segregate during the formation of sex cells. Each member of the pair becomes part of the separate sex cell. The dominant gene, such as the purple flower in Mendel’s plants, will hide the recessive gene, the white flower. After Mendel self-fertilized the F1 generation and obtained an F2 generation with a 3:1 ratio, he correctly theorized that genes can be paired in three different ways for each trait: AA, aa, and Aa. The capital A represents the dominant factor while the lowercase a represents the recessive.
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Figure 12.3A.1 : Mendel’s Pea Plants: In one of his experiments on inheritance patterns, Mendel crossed plants that were true-breeding for violet flower color with plants true-breeding for white flower color (the P generation). The resulting hybrids in the F1 generation all had violet flowers. In the F2 generation, approximately three-quarters of the plants had violet flowers, and one-quarter had white flowers.
Mendel stated that each individual has two alleles for each trait, one from each parent. Thus, he formed the “first rule”, the Law of Segregation, which states individuals possess two alleles and a parent passes only one allele to his/her offspring. One allele is given by the female parent and the other is given by the male parent. The two factors may or may not contain the same information. If the two alleles are identical, the individual is called homozygous for the trait. If the two alleles are different, the individual is called heterozygous. The presence of an allele does not promise that the trait will be expressed in the individual that possesses it. In heterozygous individuals, the only allele that is expressed is the dominant. The recessive allele is present, but its expression is hidden. The genotype of an individual is made up of the many alleles it possesses. An individual’s physical appearance, or phenotype, is determined by its alleles as well as by its environment.
Mendel also analyzed the pattern of inheritance of seven pairs of contrasting traits in the domestic pea plant. He did this by cross-breeding dihybrids; that is, plants that were heterozygous for the alleles controlling two different traits. Mendel then crossed these dihybrids. If it is inevitable that round seeds must always be yellow and wrinkled seeds must be green, then he would have expected that this would produce a typical monohybrid cross: 75 percent round-yellow; 25 percent wrinkled-green. But, in fact, his mating generated seeds that showed all possible combinations of the color and texture traits. He found 9/16 of the offspring were round-yellow, 3/16 were round-green, 3/16 were wrinkled-yellow, and 1/16 were wrinkled-green. Finding in every case that each of his seven traits was inherited independently of the others, he formed his “second rule”, the Law of Independent Assortment, which states the inheritance of one pair of factors (genes) is independent of the inheritance of the other pair. Today we know that this rule holds only if the genes are on separate chromosomes
Answer:
Between 1856-1863, Mendel conducted the hybridization experiments on the garden peas. During that period, he chose some distinct characteristics of the peas and conducted some cross-pollination/ artificial pollination on the pea lines that showed stable trait inheritance and underwent continuous self-pollination. Such pea lines are called true-breeding pea lines.
Also Refer: Mendel’s Laws of Inheritance: Mendel’s Contribution
Why was Pea Plant Selected for Mendel’s Experiments?
He selected a pea plant for his experiments:
The pea plant can be easily grown and maintained.
They are naturally self-pollinating but can also be cross-pollinated.
It is an annual plant, therefore, many generations can be studied within a short period of time.
It has several contrasting characters.
Mendel conducted 2 main experiments to determine the laws of inheritance. These experiments were:
Monohybrid Cross Experiment
Dihybrid Cross Experiment
While experimenting, Mendel found that certain factors were always being transferred down to the offspring in a stable way. Those factors are now called genes i.e. genes can be called the units of inheritance.
Mendel’s Experiments
Mendel experimented on a pea plant and considered 7 main contrasting traits in the plants. Then, he conducted both the experiments to determine the aforementioned inheritance laws. A brief explanation of the two experiments is given below.
Monohybrid Cross
In this experiment, Mendel took two pea plants of opposite traits (one short and one tall) and crossed them. He found the first generation offsprings were tall and called it F1 progeny. Then he crossed F1 progeny and obtained both tall and short plants in the ratio 3:1. To know more about this experiment, visit Monohybrid Cross – Inheritance Of One Gene.
Mendel even conducted this experiment with other contrasting traits like green peas vs yellow peas, round vs wrinkled, etc. In all the cases, he found that the results were similar. From this, he formulated the laws of Segregation And Dominance.
Dihybrid Cross
In a dihybrid cross experiment, Mendel considered two traits, each having two alleles. He crossed wrinkled-green seed and round-yellow seeds and observed that all the first generation progeny (F1 progeny) were round-yellow. This meant that dominant traits were the round shape and yellow colour.
He then self-pollinated the F1 progeny and obtained 4 different traits wrinkled-yellow, round-yellow, wrinkled-green seeds and round-green in the ratio 9:3:3:1.Conclusions from Mendel’s Experiments
The genetic makeup of the plant is known as the genotype. On the contrary, the physical appearance of the plant is known as phenotype
The genes are transferred from parents to the offsprings in pairs known as allele.
During gametogenesis when the chromosomes are halved, there is a 50% chance of one of the two alleles to fuse with the other parent.
When the alleles are the same, they are known as homozygous alleles and when the alleles are different they are known as heterozygous alleles.
Also Refer: Mendelian Genetics
Mendel’s laws
The two experiments lead to the formulation of Mendel’s laws known as laws of inheritance which are:
Law of Dominance
Law of Segregation
Law of Independent Assortment
Law of Dominance
This is also called Mendel’s first law of inheritance. According to the law of dominance, hybrid offsprings will only inherit the dominant trait in the phenotype. The alleles that are suppressed are called as the recessive traits while the alleles that determine the trait are known as the dormant traits.
Law of Segregation
The law of segregation states that during the production of gametes, two copies of each hereditary factor segregate so that offspring acquire one factor from each parent. Key Points on Mendel’s Laws
The law of inheritance was proposed by Gregor Mendel after conducting experiments on pea plants for seven years.
The Mendel’s laws of inheritance include law of dominance, law of segregation and law of independent assortment.
The law of segregation states that every individual possesses two alleles and only one allele is passed on to the offspring.
The law of independent assortment states that the inheritance of one pair of genes is independent of inheritance of another pair.
