65e806c5627be0001873d5e6_##_Principle of Inheritance and Variation in 1 shot_ Class Notes

Introduction

Genetics: study of heredity & variation.
Heredity: transfer of characters from parent to offspring.
Variation: offspring differ from parents.
Terms:
- Genetics: Bateson
- Gene: Johannsen
- Factor: Mendel
Inheritance: transmission of characters from parent to offspring.

Gene

Definition: Segment of DNA which forms protein & this protein control particular character.
Character: Plant height
Traits: Tall, dwarf
Allele: slightly different form of same gene present on same locus/position on Homologous chromosance.
Homozygous: Both allele/trait are same (TT or tt).
Heterozygous: Both allele/trait are different (Tt).
Dominant allele: Which trait express in both homozygous (TT) & heterozygous (Tt) condition.
Recessive allele: Which trait express only in homozygous condition (tt).
$2n$ : chromosome number.
- $2n = TT$ : Homozygous dominant allele, Tall.
- $2n = Tt$ : Heterozygous dominant allele, Tall.
- $2n = tt$ : Homozygous recessive allele, dwarf.

Conclusion from Table

Dominant allele can express
- In both Homozygous & Hetrozygous condition
- In presence of identical (TT) & non-identical allele (Tt)
Recessive allele can express
- Only in Homozygous condition
- Only in presence of its identical allele (tt)

Mendelism

Born: 22 July 1822
Place: Austria
Worked: Augustinian monastery
Name of Plant: Pea (Pisum sativum)
How many years: 7 years
He started experiment in: 1856
Experiment work till: 1863 (1856-1863)
Scientist of which century: 19th century.
Total plant variety: 14
Total character studied: 7
Total pair of contrasting trait: 7pairs = 14 Trait

Selection of pea plant

Annual plant: which complete their life cycle in one year, 3-4 months
Life cycle & offspring: short, maximum offspring can be produced in one year
Bisexual: Natural self pollination present
Cross pollination Can Be performed by Removal of anther (Emasculation) & Bagging (Female plant)
Cultivation : easy to cultivate.

Reason for Mendel success

First time: Mathmetical Tools & stastics.
Record: He kept Record of His work.
Sampling Size: Large, He Repeated same experiment on 100 to 1000 plant
Result proved By experiment Technique.
- Emasculation
- Bagging
Experiment: He studied one or Two Character at a Time.
He was lucky Because He didn't find LINKAGE.

Chromosome/allele/gene/Factor

Formation of Gamete: segregation or seperation.
Number and Type of gamete.
- $2n=TT$ : No. of Gamete: 1, Type of gamete: T
- $2n=Tt$ : No. of Gamete: 2, Type of gamete: T, t
- $2n=tt$ : No. of Gamete: 1, Type of gamete: t

True Breeding

True Breeding show stable Trait for many generation.
- TT × TT
- tt × tt
Gamete
- T (n)
- t (n)

Inheritance of one gene

one gene = one character (Plant Height) = Two Trait.
MONOHYBRID CROSS
2 parent /2 plant = 2 variety: Tall & dwarf.
True Breeding / Homozygous.

Monohybrid Cross

Parent: (TT) Tall × (tt) dwarf.
Gamete: T & t.
$F_1$ generation: Tt = Tall.
Selfing: Tt × Tt.
Punnett square: graphical Representation to Find out the offspring.
Scientist: RC Punnett, Butsch Geneticst.
Phenotypic ratio: 3(Tall): 1(dwarf)
No. of phenotype : 2 (Tall, dwarf)
Genotypic ratio: 1(TT): 2(Tt): 1(tt)
No. of genotype: 3
Phenotype: Physical appearence.
Genotype: genetic constitution of organism.

Monohybrid Cross Formula

n: no. of Hetrozygous.
No. of gamete: $2^n$
No. of phenotype: $2^n$
No. of genotype: $3^n$
No. of zygote/offspring: $(game)^2 = (2)^2$

Gamete Formation

Calculate number of gametes, phenotype and zygote formed.
- Gamete no. $=2^n$
- Zygote no. $=2n \times 2n$

Question Based on Gamete formation

Different types of gametes from different genotypes (TT, Tt, tt, AABB, AaBB, AaBb).

Segregation of alleles

Segregation of alleles is a random process so the chances of a gamete containing either allele is 50%.

Sexual reproduction in F1 individual

If $F_1$ individual of genotype (Tt) go through sexual reproduction, then it's gamete with genotype (T) have 50% chances to pollinate eggs of the genotype (T).

Pure tall and pure dwarf plant cross

A pure tall and a pure dwarf plant were crossed to produce offsprings. Offsprings were self crossed, then the ratio between true breeding tall to true breeding dwarf is 1:1.

Homozygous tall plant cross with a dwarf plant

If a homozygous tall plant is crossed with a dwarf plant, the ratio of plants in offsprings is All heterozygous tall.

Gametes formed by F1 progeny

The number of different types of gametes that can be formed by $F_1$ progeny resulting from the cross: AA BB CC x aa bb cc is 8.

Monohybrid cross question

In $F1$ -generation with genotype (AABbCC) on selfing of this plant what is the phenotypic ratio in $F2$ -generation is 3:1.

Types of gametes from the organism

The number of types of gametes are expected from the organism with genotype AABBCC is One.

TTRr x ttrr cross

Due to the cross between TTRr x ttrr the resultant progenies showed 50% plants would be tall, red flowered.

Aa BB X aaBB cross

A cross between Aa BB X aaBB yields a genotypic ratio of 1 AaBB: 1 aaBB.

True breeding line

The odd one w.r.t. true breeding line is Shows expression for few generations only.

Test Cross

Find out genotype of Unknown parent in $F_2$ gen".
Unknown parent x Recessive Parent
Phenotypic ratio: 1:1 (Tall: Dwarf)
No. of phenotype : 2
Genotypic ratio: 1(Tt): 1(tt)
No. of genotype : 2
Phenotypic & genotypic Ratio are same.

Test Cross Example

Examples of Test Cross (NCERT)
Flower colour in pea:
- Violet (D) white (R)
- Find out genotype of Onknown parent.
- all violet Flower
- 1:1

Law of Inheritance

On Basis of monohybnd cross. Some Rules are given principle of inhentence
- 1st Law: Law of dominance
- 2nd law: Law of segregation

Law of Dominance

Characters are controlled by discrete units called factors/gene.
Factors occur in pairs (TT/Tt/tt).
In a dissimilar pair of factors one member of the pair dominates (dominant) the other (recessive).
The law of dominance is used to explain the expression of only one of the parental characters in a monohybrid cross in the $F1$ , and the expression of both in the $F2$ .
It also explains the proportion of 3:1 obtained at the $F_2$ .
It is not Universal law, Some Exception is there.

Law of Segregation

This law is based on the fact that the alleles do not show any blending and that both the characters are recovered as such in the $F2$ generation though one of these is not seen at the $F1$ stage.
Though the parents contain allele do not show Blending
Universal law
Melosis: gamete formation:
Chromosome: seperate/segregate in such a way So that each gamete Receive only one Chromosome / one allele/ one factor
Homozygous & Hetrozygous produce different gametes.

Ratio of monohybrid test cross:

The genotypic and phenotypic ratio is 1:1.

Terminologies

Mendel's experiments, colour of seed, colour of flower, position of flower, colour of pod, height of stem, are called Phenotype.

Mendel's Principle of segregation

Mendel's Principle of segregation means that the gamete cells always receive one of the paired alleles.

Result of test cross:

More than one option is correct, Equal number of genotypes and phenotypes in progeny, Phen = 2 =Tall, dwarf and Geno= 2 = Tt, tt

Select the incorrect match:

Alleles = Slightly different forms of two genes (incorrect), Alleles = slightly different forms of same gene.

law of dominance Exception of Mendelism

Incomplete Dominance
Example Antirrhinum majus/dog Flower/snapdragon
- Mirabilis Jalapa/4 o'clock plant
None of Two allele are domment
$F_1$ do not show Resemblance to any parent
Mixing of allele/colour/Blending Intermediate
Both phenotypic & genotypic Ratio are Same (1:2:1).

Multiple Allele

More than Two allele for a gene control one character.
Out of three allele: only two present on Homologous chromasome.
Human Blood group (phenotype) = 4
Human Blood group (genotype) = 6
Character : ABO Blood group

Types of Blood Group

Types of blood which can express in both homozygous and heterozygous condition.
Type of blood group which express in homozygous condition
Type of blood group which can express only in homozygous condition

Codominance

Both allele equally express, independently,
\F_1 Resemble to Both parents equally,
No mixing of allele / No Blending
Co-Dominance Examples:
- Coat Colour in cattle
- Sickle cell anemia

Mother and Father blood group-related Questions

If mother is B: Hetrozygous and Father is A: Heterozygous, possible blood groups in offsprings?
If Mother is O and Father is A: Homozygous, possible blood groups in offsprings?

ABO Blood group:

ABO Blood group controlled by one gene I, controlled by three allele $I^A$ , $I^B$ , $I^O$ , Follow codominance $I^AI^B$ , Follow multiple allele

Concept of Dominance

Dominant allele or Wild allele or Normal allele produce Normal enzyme that control particular phenotype (Character).
Modified allele/mutant allele either produce Non-Functional enzyme or No enzyme, so phenotypic character is change/altered. This is Recessive allele.

Pleiotropy

One gene control more than one character.
Ex: Starch synthesis in pea plant
SEEDS Size Control.
Shape of Seed.
Dominance is not autonomais feature of gene.
A Same gene control: more than one character.
size of seed (phenotype): Study: incomplete donnance
shape of seed (phenotype): study: Complete dominance

Inheritance of Two gene

Study of 2 gene = 2 character = 4 Trait.
DICOTYLEDONOUS CROSS
Male & female parent
Phenotypic Ratio 9:3:3:1
Genotypic Ratio 1:2:1:2:4:2:1:2:1

Dihybrid Cross

Round, yellow Seed Colour (RRYY) x Wrinkled green seed Colour (rryy).
$F_1$ = RrYy (Round yellow).

Ratio of trait

Two dominant trait controlled by same gene in DC: False.
Two recessive trait controlled by same gene in DC: False.
Ratio of two dominant trait controlled by two different gene is 12:4 = 3:1.
Ratio of two recessive trait controlled by two different gene is 12:4 = 3:1.
The number of plant which are heterozygous for both trait is 4.

Law of Independent assortment

Law of Independent assortment Can't Be explained by Monohybind cross ,given on Basis of Dihybind cross.
Exception: LINKAGE

Dihybind cross basis

On Basis of Dihybnd cross Law of Dom", Law of segregation and law of indep ass. Can be exp.

Monohybrid condition Questions:

Which is monohybrid condition (One: Hetrozygous)

Dihybrid condition questions:

Which represent dihybrid condition 2 Hetrozy

Fgeneration question

Total number of plants in Fgeneration where all alleles are in identical condition (Dihybrid cross).
Total number of plants in $F2$ generation which resemble with $F1$ generation phenotypically (Dibybrid cross).
Total number of