Missense Mutation Non-sense Mutation The mutation where the codon for one amino acid is changed into a codon for another amino acid. The mutations where codon for one amino acid is changed into a termination or stop codon.

(i) Back cross is a cross of F, hybrid with any one of the parental genotypes. 
(ii) They are of two types - Dominant back cross recessive back cross.

A true breeding lines means it has undergone continuous self pollination having stable trait inheritance from parent to off spring. 

Gymnosperms - Pollination is said to be direct as the pollen are deposited directly on the exposed ovules  Angiosperms - Pollination is said to be indirect as the pollen are deposited on the stigma of the pistil.

Dichogamy stamens and stigmas mature at different times (protandry, Protogyny) Herkogamy - Stamens and stigmas are arranged in such a way, self pollination become impossible.

Hofmeister described the structure of pollen tetrad

(i) Sutton and Boveri independently proposed the chromosome theory of inheritance.
(ii) Somatic cells of organisms are derived from the zygote by repeated mitotic division. These consist of two identical sets of chromosomes. One set is received from female parent and the other from male parent which constitute the homologous pair.
(iii) Chromosomes retain their structural uniqueness and individuality throughout the life cycle of an organism.
(iv) Each chromosome carries specific determiners or Mendelian factors which are now termed as genes.
(v) The behaviour of chromosomes during the gamete formation provides evidence to the fact that genes are located on chromosomes.

It is based on independent, self-replicating extra chromosomal unit called plasmogene located in the cytoplasmic organelles, chloroplast & Mitochondrion.

Supplies nutrition to the developing microspores contributes sporopollenin through, ubisch bodies. This plays an important role in pollen wall formation. The pollen kit material is contributed by tapetal cells, and is later, transferred to the pollen surface. Exine protein responsible for rejection reaction are derived from tapetal cells.

In Bryophyllum, the leaf is succulent and notched on its margin. Adventitious buds (epiphyllous buds) develop at these notches. They develop into new plants forming a root system. They become independent plants when the leaf gets decayed.

The diagrammatic representation of position of genes and related distances between the adjacent genes is called gene mapping. 
Uses 
(i) Used to determine gene order.
(i) Identify the locus of a gene.
(i) Calculate the distance between genes.
(i) Useful in predicting results of dihybrid and trihybrid crosses.
(i) Allows the geneticists to understand the overall genetic complexity of particular organism.

The widely accepted model of DNA recombination during crossing over is Holliday's hybrid DNA model.

Steps involved are:
1. Homologous DNA molecules are paired side by side with their duplicated copies of DNAs
2. One strand of both DNAs cut in one place by the enzyme endonuclease.
3. The cut strands cross and join the homologous strands forming the Holliday structure or Holliday junction.
4. The Holliday junction migrates away from the original site, a process called branch migration, as a result heteroduplex region is formed.
5. DNA strands may cut along through  the vertical (V) line or horizontal (H) line.
6. The vertical cut will result in heteroduplexes with recombinants.
7. The horizontal cut will result in heteroduplex with non recombinants.

(i) Incomplete linkage

Rano : 1:2:1

(i) Polygenic inheritance - Several genes combine to affect a single trait.
(ii) A group of genes that together determine (contribute) a characteristic of an organism is called polygenic inheritance. It gives explanations to the inheritance of continuous traits which are compatible with Mendel's Law.
(iii) The first experiment was demonstrated by H. Nilsson - Ehle (1909) in wheat kernels.
(iv) He crossed the two pure breeding wheat varieties dark red & white.
(v) Dark red genotypes R₁R₁R₂R₂ and
(vi) white genotypes are r₁r₁r₂r₂ 
(vii) In the F₁ generation medium red were obtained  R₁r₁R₂r_2.
(viii) F₁ wheat plant produces four types of gametes R₁R_2, R₁r_2, r₁R_2, r₁r_2.
(xi) The intensity of the red colour is determined by the number of R genes in the F₂ generations.
(x) Four R genes -  Dark red kernel.
(xi) Three R genes - Medium dark red kernel 
(xii) Two R genes - Medium red kernel
(xiii) One R gene - Light red kernel.
(xiv) Absence of R gene - White kernel.


F₂ 

1	6	15	20	15	6	1
Dark red	Moderate red	Red	Intermediate red	light red	very light red	white

(xv) In F₂ generation plants have kernels with wide range of colour variation. 
(xvi) This is due to that the genes are segregating and recombination takes place.
(xvii) The cumulative effect of several pairs of gene i interaction gives rise to many shades of kernel colour.

(i) The production and development of seedless fruit is called parthenocarpy.
(ii) Fruit like structures may develop from the ovary without the act of fertilization. Such fruits are called parthenocarpic fruits
Examples: Seedless-Banana, Grapes, Papaya
(i) Parthenocarpy is of three types
1) Genetic Parthenocarpy
(i) Arises due to hybridization or mutation. 
2) Environmental Parthenocarpy
Environmental conditions like frost, fog, low or high temperature induce Parthenocarpy.
Example - low temperature for 3-19 hours induces parthenocarpy in Pear.
3) Chemically induced Parthenocarpy
(i) By the application of growth promoting hormones like auxins and gibberellins.
Significance:
(i) Seedless fruits - Significance in Horticulture have commercial value useful for the preparation of jarns, jellies, sauces, fruit drinks,
(ii) High proportion of edible part is available