how many type of Mendel law
Answers
3 Most Important Mendel’s Laws or Principles of Inheritance
1. Law of dominance:
When Mendel crossed a true-breeding red flowered plant with a true breeding white flowered one, the progeny was found to be red coloured.
Inheritance
The white colour suppressed and the red colour dominated. Mendel called such traits as redness of flowers dominant and their alternatives, such as whiteness, recessive. All the seven characters in peas studied by Mendel behaved in this way, one of each pair of contrasting traits appearing to be dominant and the other recessive.
Trait studied shape of seed colour of cotyledons form of pod Colour of pod Position of flower Colour of flower Height of plant
Dominant Round Yellow Inflated Green Axillary Red Tall
Recessive Wrinkled Green Constricted Yellow Terminal White Dwarf
Table 36.1:
Trait (Parent forms) F1 form F2 (Dominant)
Generation results
(Recessive)
Monohybrid ratio
1. Seed colour (Yellow × green) all yellow 6022 (yellow) 2001 (green) 3.01 : 1
2. Seed shape (round × wrinkled) all round 5474 (round) 1850 (wrinkled) 2.96 : 1
3. Flower colour (purple × white) all purple 705 (purple) 224 (white) 3.15 : 1
4. Pod colour (green × yellow) all green 428 (green) 152 yellow 2.82 : 1
5. Pod shape
(inflated × constricted)
all inflated 882 (inflated) 299 (constricted) 2.95 : 1
6. Flower position (axial × terminal) all axial 651 (axial) 207 (terminal) 3.14 : 1
7. Plant height (tall × dwarf) all tall 787 (tall) 277 (dwarf) 2.84 : 1
Later investigators have found many other characters that show similarly complete or almost complete dominance.
2. Law of segregation:
Mendel demonstrated that a hybrid between two different varieties possesses both types of parental factors, which subsequently separate or segregate in the gametes. This is known as law of segregation. In contrast to the uniformity of the first generation hybrids, the second generation produced by self-fertilization of the F1 red flowered plants which consist of two different kinds of plants—red ones like the red grandparent and white ones like the white grandparent.
Mendel counted the numbers of individuals with each of the differentiating characters which reappeared by segregation in F2. In the experiment for flower colour, for example, he raised 929 F2 plants and found that 705 of them bore red flowers and 224 bore white flowers. The simple ratio was found that 3/4 of the F2 resembled the dominant grandparent and 1/4 resembled the recessive one, i.e., 3:1.
On the basis of his experiments, Mendel concluded as follows: contrasting characters, such as the red and white flower colours in peas, are determined by something that a transmitted from parents to offspring in sex cells, or gametes. This something of Mendel is now called a gene.
To understand how the genes are transmitted and distributed they are symbolized by letters. The dominant genes are provided with capital letters and their recessive alternatives by corresponding small letters. For example, in the cross of red and white peas R stand for the gene for red flowers and r for the alternative, or allelic, form of this gene, which gives white flowers R and r are allelic genes or alleles.
Since an individual develops from the union of two gametes, it receives a gene for flower colour from both parents. The true breeding red flowered parent is, therefore, represented by RR and its gametes are R; the true breeding white parent is rr and its gametes, r, or vice versa; and the resulting hybrid zygote will have both R and r; its genetic formula will be Rr.
When a gene pair in an organism contains two identical alleles, e.g., R and R, the organism is considered homozygous for that gene pair and is called a homozygote. When two different alleles are present in a single gene pair, e.g., R and r, the organism is heterozygous for that gene pair and is called a heterozygote. The red-flowered plants obtained by Mendel in the F1 generation (Rr) were heterozygotes. They were red because the allele R is dominant over r.
3. Law of independent assortment:
‘When two pairs of independent alleles enter into combination in the F2, they exhibit independent dominant effects. In the formation of gametes the law of segregation operates but the factors assort themselves independently at random and freely.