principles of inheritance & variations 12th | digital notes
Definations:-
Heredity - transfer of character from parent to offspring.
Inheritance - process responsible for transfer of character - parent
to offspring
Variation - difference in offspring from parent
Genetics - Branch of science that deals with the study of
heredity and
variation.
- term genetics given - batson
- father of genetics - gregor johann mendal(death - 1884 without recognition of his work)
- father of modern genetics - bateson
- father of experimental genetics - T H Morgan
- father of human genetics and biochemical - A.Garrod
Mendelian genetics
- father of genetics - gregor johann mendal
- birth 22 July 1822
- pisum sativum 7years(1856-1863) without recognation of his work.
Mendels works were reproduced by 3 scientits later:-
1.Hugo de vries (holland)
2.carl carrens (germany)
3.erich von tshermak sesenegg(austria)
why mendel select pea plant for experiment?
1.Small
2.Short life span
3.Can easily grow in backyard
4.Single fertilization produce large number of seed.
5.Bisexual flower - bisexual flower
--> self fertilization and
cross fertilization.
6.contain
7 morpholoogical characters,14 different varities/traits
of pea plants.
| character | trait |
|---|---|
| -features of an individual is k/a character. | -distinguishable feature of any character is k/a trait. |
eg.
|
eg.
|
8.Pure lines / pure breeding lines are easily to produce .
pea(tall)---(self cross)----> offspring(tall)
when we self cross the parent plant and get same trait in offspring for the
characters, then such breed is k/a
pure line breed.(doubt)
Tt, tt, YY, yy .etc
Why wrinkled seeds have such shape?
Note:
3.Pisum sativum total 14 chromosomes (7 pair) are present.
4.for any trait one allele/gene is responsible.but mendel utilised term unit
factor(for allele) or factor (for gene).
5.Allels are alternative form of a gene.Allels are present on homologous
chromosomes.
6.Morphologically,similar pair of chromosomes are called homologous
chromosomes.
In homologous chromosomes
1.similarty occurs w.r.t shape and size
2.similarity occurs w.r.t position of centromere
3.similarity occur w.r.t locus of genes/alleles
7.genes are present in specific location(position) of chromosomes k/a
Locus.(singular locii)
8.MAX.m characters selected by mendel in pea plant were present on chr. no 4.
- Term Allele = Bateson
- Term Gene = Johanson
Hybridization Experiment performed by mendel:-
3 steps followed in all experiments were :-
1)slection of parents
2)cross fertilization
3)self hybridization
Multiple allelsism
one gene more than two alternative forms
ABO blood group
ABO blood group has 3 alleles.
IA,IB,I0
Discovered by Carl Landsteiner
Gene for ABO blood group is present on 9th chromosome(Autosome).
IA and IB both are equal dominant (hence,codominant) & both are dominant
over I0/i allele.
Formula for Multiple alleles:-
- where n = no. of multiple allele
Phenotype - (n+1)
Genotype - n/2(n+1)
Eye colour of drosophila n= 15
Coat colour of drosophila n=4
to study all the alleles of a Multiple allelic gene, it is required group
study/popuation analysis.
Pleiotropy
Some case 1 gene is regulate more than one character such process is k/a
Pleiotropy.
SBE gene i.e starch branching enzyme(responsible for conversion of glucose
into starch.)
1)cystic fibrosis
2)Phenyl Ketone Urea(PKU)
3)SCA(sickle shape anaemia)
4)Huntington's chorea
Chromosomal theory of inheritance
- Unit factors alleles
- alleles are present on chromosomes,this was not given by mendel give by
sutton & Bovery
- chromosomes are the carrier of genes/alleles & chromosomes get
degregate during gamet formation which again get paired on fertilization in
diploid organism.
Similarities
Proposal chromosomal theory of inheritance was given sutton and Bovery.
Experimental proof was given by TH Morgan - fruit fly as an experimental
material.
Why morgan selected fruit fly for his experiment?
Linkage
Genes present on one chromosomes are called linked gene.
Linkage was first discovered by Bateson and punnet.
Mechanism of linkage was given by Morgan.
Note:-
Dominant wild type.
Recessive allele is k/a Mutant type/Modified allele.
Chromosomal theory of linkage:-
Linkage:-
Linkage have the tedency to stay together but they can segregate from
chromosomes by the process of Crossing over/recombination.
Theory of recombination of genes over a chromosomes is k/a Chromosomal
theory of linkage.
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