"Father of Genetics: Mendel"**He wa Born on 22July 1822
**He Graduate in physics and post graduate in economics.Monk in a monastry.
**He Devoted 12 years for hybridisation experiments.
**Heworked on Pisum sativum for 7 years.
**He published his findings in the form of a research paper named "Experiments of Plant Hybridisation" in "Natural history of Science Society Brunn,Austria".
**He died due to Kidney disorder in 1884 .
**Mendel also worked omHieracium(Hawk weed) and Lab Lab(broad bean) but failed to get same result as in Pisum sativum.
**Pea was also selected by Gross and Knight as an experimental tool,but they faip to explain genetics.
Rediscovery of Mendelism
By
1) Carl Correns (germany)
He worked on Mirabilis jalapa and Antirrhinum majus
2) Isthermark(Australia)
He worked on Pisum sativum
3)Hugo de Vries(Holland)
He worked on Oenothera lamarckiana
.............Mendel work ...........
**Mendel studied 7 characters in pea plant using 17 pure breeding varieties .
**Mendel.initially took 34 varieties then 22 and finally 17 varieties.
**Initially it was believed that the genes of 7 characters present on 7 different chromosomes.Later Blixt reported that genes for 7 characters present on 4 different chromosomes.
Suitability of pea plant as experimental tool:
**Cross as well as self fertilisation both possible in .
**It possess many contrasting characters.
**It produce large number of seeds or offsprings.
**It have short life span of 3-4months .Hence, many generation can be studied within a single year.
pea have 2n=14 chromosomes
n=7 chromosomes
Reason of Mendel success:
**Mathematical approach and statistical analysis of results.
**Large sampling size;he perform same experiment in large number of plants.
**Accurate data and record of each experiment.
**Formualtion of theoretical explanation of each results(postulates).
**Study one character at a time.
Mendel monohybrid cross:
Crossing between two individuals differing from each other only in single character.
Parents Male Female
TT tt
Gametes T , T t ,t
F1 All are Tt (tall)
generation:
On selfing F 1 generation Tt×Tt
Phenotypic ratio:
Tall :dwarf
3 : 1
Genotypic ratio:
TT : Tt : tt
1 : 2 : 1
On basis of Mendel monohybrid cross ,he proposed 3 postulates:
1)Postulates of Unit Factor: Each character is controlled by a pair of unut factor which are stable ,discrete nad unblending.
2)postulates of Dominance : when two dissimilar unit factor present together only one of them is expressed which is called dominant while other factor remain hidden which is called recessive.
3)Postulates of segregation: Two dissimilar unit factors present together in an individual don't get mixed and there is no blending between them at the time of gamete formation.They segregate from each other ,due to their segregation recessive character is also expressed in F2 generation which remain hidden in F 1 generation.
Laws of Inheritance:
Carl Corrensce shaped up the postulates im the form of law of inheritance.
1)Law of dominance :Postulate 1+postulate2
exception- Multiple allelism
. Codominance
Incomplete dominance
Pleiotropy
2)law of segregation/Law of purity of gametes: Postulate 3
universally accepted,no exception
Mendel Dihybrid Cross:
Cross between two individuals differing from each other only in 2 characters.
*To study the inheritance of two characters at a time.
Characters:
Seed shape anad seed colour
Phenotypic ratio of dihybrid cross:
Round yellow: Round green: Wrinkled
yellow:Wrinkled green
9: 3: 3: 1
Parental frequency: Round yellow and wrinkled green = 9+1/16 =10/16
Recombinant frequency: 3+3/16 =6/16
Seed shape: Round:Wrinkled
(9+3) : (3+1)
12 : 4
3 : 1
Seed colour: Yellow : Green
(9+3) : (3+1)
3 : 1
Genotypic ratio: RRYY:RRYy:RRyy:RrYY:RrYy:Rryy:rrYY:rrYy:rryy
1 : 2 : 1 : 2 : 4 :2 :1 :2 :1
Number of genotypes: 3n(n is in the formof power);where n is number of heterozygous pair=9
**On the basis of Dihybrid cross,Mendel proposed only 1 postulate:
4)Postulate of Independent Assortment:
When a cross is made between two individuals differ from each other in two characters then both segregate independently and due to their independent assortment recombinations are also formed alongwith the parental recombinations..
Carl Corrensce shaped the postulate 4 as Law of independent assortment. Ecception-Linkage.
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