Question

Good notes of heridity and evolution
Give fast as you can

Answer 1

Genetics : Branch of science that deals with Heredity and variation.

Heredity : It means the transmission of features / characters/ traits from one generation to the next generation.

Variation : The differences among the individuals of a species/population are called variations.

Mendel and His Work on Inheritance

Gregor Johann Mendel started his experiments on plant breeding and hybridization. He proposed the laws of inheritance in living organisms. Mendel was known as Father of Genetics

Plant selected by Mendel : Pisum sativum (garden pea). Mendel used a number of contrasting characters for garden pea.  

Following are the seven pairs of contrasting characters in Garden Pea

(TABLE OF CONTRASTING CHARACTERS. SEVEN PARTS)

CHARACTER

DOMINANT TRAIT

RECESSIVE TRAIT

Flower colour

Violet

White

Flower position

Axial

Terminal

Seed colour

Yellow

Green

Seed shape

Round

Wrinkled

Pod shape

Inflated

Constricted

Pod colour

Green

Yellow

Height of plant    

Tall

Dwarf/Short

Mendels Experiments : Mendel conducted a series of experiments in which he crossed the pollinated plants to study one character (at a time)  

Monohybrid Cross : Cross between two pea plants with one pair of contrasting characters is called a monohybrid cross. Example : Cross between a tall and a draft plant (short).

Observations of Monohybrid Cross

1. All F1 progeny were tall (no medium height plant (half way characteristic)

2. F2 progeny ¼ were short, ¾ were tall

3. Phenotypic ratio F2 – 3:1 (3 tall : 1 short)

Genotypic ratio F2 – 1 : 2 :1  = TT : Tt : tt  

Conclusions

1. TT and Tt both are tall plants while tt is a short plant.

2. A single copy of T is enough to make the plant tall, while both copies have to be ‘t’ for the plant to be short.

3. Characters/Traits like 'T' are called dominant trait (because it express itself) and ‘t’ are recessive trait (because it remains suppressed)

Dihybrid Cross : A cross macle between two plants having two pairs of contrasting characters is called dihybrid cross.  

PARENT GENERATION  ---> ROUND GREEN SEEDS x WRINKLED YELLOW SEEDS      

Phenotypic Ratio

Observations

1. When RRyy was crossed with rrYY in F1 generation all were Rr Yy round and yellow seeds.

2. Self pollination of F1 plants gave parental phenotype and two mixtures (recombinants round yellow & wrinkled green) seeds plants in the ratio of 9:3:3:1

Conclusions

1. Round and yellow seeds are DOMINANT characters

2. Occurrence of new phenotypic combinations show that genes for round and yellow seeds are inherited independently of each other  

SEX DETERMINATION : Phenomenon of decision or determination of sex of an offspring

FACTORS Responsible for Sex Determination

1. Environmental : In some animals the temperature at which the fertilised eggs are kept decides the gender. eg. in Turtle                                                                                  2. Genetic : In some animals like humans gender or individual is determined by a pair of chromosome called sex chromosome  XX – Female and XY – Male

This shows that half the children will be boys and half will be girls. All children will inherit an X chromosome from their mother regardless whether they are boys or girls. Thus sex of children will be determined by what they inherit from their father, and not from their mother.