Basic Genetics

Dhirendra khare Plant Breeding and Genetics JNKVV, Jabalpur (India) 1

2

A living thing has specific number of . 3 A Say One organism has 10 . 4 This is the diagram of 7th number chromosome. 5 Chromosome is a two armed structure. 6 The size of arm may differ from each other. 7 Arms are separated by a point known as centromere. has specific location on particular chromosome. 1 In the given diagram the chromosome has two arms A and B. 2 The number given 1 to7 on arm A and 1 to 6 on B 3 shows location of gene. 4 B

5

6

7th chromosome 1 1

2 2 3 Each chromosome is present in pair it means 3 The one more chromosome of same size of arm and 4 A 4 is also present. It is known as homologous 5 5 chromosome. 6 6 If we deal with gene number 5 present on Arm A of 7th chromosome. Say this gene is responsible for 7 7 flower colour. Then in all the plants of the species under study will have gene responsible for flower colour on 1 1 location 5th of Arm A of 7th chromosome in both the chromosome of the pair. 2 2 The location of the gene is known as . 3 3 4 B 4

5 5

6 6

7th chromosome 1 1

2 2 3 It means at locus 5th of arm A of 7th gene responsible for flower colour is located. 4 A 4

We may give any symbol to this gene say F F F

In the species under study three to four flower 6 6 colour may present say purple, yellow, white and pink 7 7 The gene govern that flower colour is F In all the plant of that species flower colour has fixed location, to differ these we may designate them as F1, 1 1 F2, F3 and F4. 2 2 These are different form of F known as allele 3 3 These genes are also known as allelic gene 4 B 4

5 5

6 6

7th chromosome There are five types of allelic gene interaction

Epistatis Genotype

AA Aa aa

3 1 Complete dominance

1 2 1 Incomplete dominance

1 2 1 Over dominance Better Best poor

1 2 1 Co-dominance

1 2 1 Lethal factor Lethal 1 1 Complete dominance 2 2 3 If one plant species has plants with two different 3 flower colour say red and white 4 A 4 If we make cross between plant of white and red F 1 F2 flower colour by the process of emasculation and 6 6 pollination. 7 7 If the plant formed by sowing of this seed bears red colour flower

1 1

2 2

3 3

4 B 4

5 5

6 6

7th chromosome 1 1 Complete dominance 2 2 3 In one pair of chromosome two different alleles of 3 the same gene may present 4 A 4 In such case the expression of the gene that is F 1 F2 depleted on flower of the plant formed by crossed seed 6 6 is known as dominant gene 7 7 The gene for flower color present on the chromosome but not able to express itself is known as recessive gene.

1 1

2 2

3 3

4 B 4 Dominant 5 5 Recessive 6 6

7th chromosome 1 1 Complete dominance 2 2 3 We may use capital letter to show dominant gene 3 and small letter of the same alpha bet for recessive gene 4 A 4 Say gene F is responsible for flower colour F f F is responsible for red colour 6 6 f is responsible for white colour 7 7 If both the alleles are of dominant type say FF then it is known as HOMOZYGOUS dominant

If both the alleles are of recessive type say ff then it is 1 1 known as HOMOZYGOUS recessive 2 2 If one allele is of dominant type and other one is 3 3 recessive type then it is known as HETEROZYGOUS B 4 4 5 5

6 6

7th chromosome 1 1 Complete dominance 2 2

3 3

4 A 4 we make cross between plant of white and red flower colour F f by the process of emasculation and pollination. 6 6 These plants are known as parent 7 7 Female parent plant on which emasculation is performed

Male parent plant of which pollen is used for pollination

The seed thus formed is known as Hybrid seed 1 1 This seed and plant formed by this seed is known as F1 (filial=generation) 2 2

The further self fertilized generation is known as F2, F3 -- Fn 3 3 4 B 4

5 5

6 6

7th chromosome 1 1 Complete dominance 2 2 3 If we make cross between red and white flowered 3 plant 4 A 4 F 1 F2 F1F1 F2F2 6 6

7 7 F1F2

When flower colour of one paret appears as such 1 1 in F1 then it is known as complete dominance. 2 2

FF ff 3 3 4 B 4 Ff 5 5

6 6 It shows that F is completely dominant over f

7th chromosome 1 Complete dominance 1 2 2

3 3 4 FF X ff 4 A F f

6 Ff F1 6 7 7 When F1 seed is sown and self fertilization occurs

Then 3:1 ratio is formed in F2

3 red 1 1 1 white 2 2

Gamete 3 3 F f 4 B 4

F FF Ff 5 5 6 6 f Ff ff 7th chromosome 1 Incomplete dominance (semi-dominance) 1 2 2 3 If we make cross between red and white flowered 3 plant 4 A 4 F 1 F2

6 6 F2F2 F1F1 7 7 F1F2

When intermediate colour appears in F1 then it is 1 1 known as incomplete dominance. 2 2

FF ff 3 3 4 B 4 Ff 5 5

6 6 It shows that F is incompletely dominant over f

7th chromosome 1 Incomplete dominance (semi-dominance) 1 2 2 3 FF X ff 3 4 A 4 F f Ff F1 6 6 When F1 seed is sown and self fertilization occurs 7 7 Then 1:2:1 ratio is formed in F2

1 Red: 2 Pink :1 white

Gamete 1 1 F f 2 2

F FF Ff 3 3 4 B 4

f Ff ff 5 5

6 6 In heterozygous condition dominant gene is not able to express completely therefore intermediate effect th appears recessive gene not performed at all 7 chromosome 1 1 Over dominance 2 2 3 If we make cross between 30cm and 20cm tall plants 3 4 A 4

F 1 F2

6 6

7 7

1 1

TT Tt tt 2 2 3 3 The F1 thus formed performs better than both the 4 B 4 parent it is of more height then it is known as Over dominance 5 5

It is mainly due to enhancement in biochemical pathway 6 6

It shows that T is over dominant on t 7th chromosome 1 1 Over dominance 2 2 3 TT X tt 3 4 A 4 F f Tt F1 6 6

7 7 When F1 seed is sown and self fertilization occurs

Then 1:2:1 ratio is formed in F2

1 1 Gamete F f 2 2

3 3 F FF Ff 4 B 4

5 5 f Ff ff 6 6

7th chromosome Co-dominance 1 1

2 2 3 Alleles which lack dominant and recessive 3 relationships In heterozygous condition both the gene are 4 A 4 able to express with the same intensity F 1 F2

6 6

7 7

The performance of heterozygous genotype is 1 1 different than either of the homozygous genotypes than it known as co-dominance 2 2 M M 3 3 L L LN LN

4 B 4

5 5 LMLN 6 6 It shows that LM and LN are co dominant 7th chromosome Co-dominance 1 1

2 2

3 3 M M L L N N 4 X L L 4 A

F f M N L L 6 6

7 7

The allele governing M_N blood group in human are co-dominant

It is symbolized by LM and LN 1 1 The letter L is assigned in honour to discoverer Landsteiner and Levine) 2 2

3 3

4 B 4 Two antisera i.e., anti-M and anti-N are used to distinguish three genotypes and their corresponding 5 5 three blood groups 6 6

7th chromosome Co-dominance 1 1

2 2

3 3 M M L L N N 4 X L L 4 A

F f M N L L 6 6

7 7

Agglutination is represented by + and non agglutination by -

Genotype Reaction with Blood group 1 1

Anti-M Anti- N Phenotype 2 2

M M M 3 3 L L + - 4 B 4 M N MN L L + + 5 5 N N N 6 6 L L - +

7th chromosome

Lethal alleles 1 1 2 2 3 Some combination of allelic gene leads to death of 3 individual prior to maturity is known as lethal gene 4 A 4 Combination of lethal gene that may lead to death F 1 F2 may be 6 6 Homozygous dominant 7 7 Homozygous recessive A fully dominant gene for lethality rarely arise that may kill individual in homozygous and heterozygous state 1 1 2 2

3 3

4 B 4

5 5

6 6

7th chromosome 1 1 Lethal alleles 2 2 3 Homozygous dominant lethality 3 4 When dominant gene is present in homozygous state 4 A than only lethality expressed F 1 F2

6 6 Ll X Ll 7 7

L l L l 1 1

Gamete 2 2 L l 3 3 B L LL Ll 4 4 Lethal 5 5 6 6 l Ll ll

7th chromosome 1 1 Lethal alleles 2 2 Homozygous recessive lethality 3 3 When recessive gene is present in homozygous state A 4 than only lethality expressed 4 F 1 F2

6 6 Ll X Ll 7 7

L l L l 1 1

Gamete 2 2 L l 3 3 B L LL Ll 4 4 5 5

l Ll ll Lethal 6 6

7th chromosome Lethal alleles 1 1 2 Homozygous recessive lethality 2 3 The amount of chlorophyll in snapdragons is controlled by an 3 incomplete recessive gene which exhibits lethal effect on 4 A 4 homozygous recessive state and a distinctive phenotypic F2 effect in heterozygous state F 1 6 6 Cc X Cc 7 7

C c C c 1 1

Gamete 2 2 C c 3 3 B C CC Cc 4 4 5 5

c Cc cc 6 6 Lethal

7th chromosome Multiple alleles 1 1 2 An individual ( polyploidy?) may possess maximum two 2 alleles at one locus in a normal condition. 3 3

But several alternate may exist in the population as allele 4 A 4 of that gene. F 1 F2 When more than two alleles are known for one gene locus 6 6 than the case is considered as of multiple allelism. 7 7 Example Blood group system of human

Human has four major type of blood group

1 1

2 2

3 3 A B AB O 4 B 4

5 5

6 6

7th chromosome Multiple alleles The red blood corpuscles of man contain pertinacious substance on their body known as antigens.

These antigens are A and B type.

• It means few person contain A type,

• few B type

• some contain both A and B type

• whereas still few contain no antigen.

Antigen Antibody Blood group

1 A For B A

2 B For A B

3 AB NONE AB

4 No A and B O Antibody coagulates the incompatible blood group on mixing it means blood group A has antibody to coagulate blood group B Multiple alleles

Antigen Antibody Blood group

1 A For B A

2 B For A B

3 AB NONE AB

4 No A and B O

Antibody coagulates the incompatible blood group on mixing it means blood group A has antibody to coagulate blood group B

Antibody a produced by plasma cells in response to foreign substances (antigen) and capable of coupling substances that are chemically very similar to the antigen

Antigen a foreign substance that, upon introduction, stimulate the production of homologous antibodies