MENDEL’S EXPERIMENT: The first scientist to discover the basic rules governing inheritance was Gregor Johann Mendel. The inheritance of a single characteristic is called monohybrid inheritance while inheritance involving two characteristics is called, hybrid cross. At the end of his experiments he formulated the basic law of genetics.
For instance, to obtain a monohybrid cross between tall and dwarf plants. Mendel prevented self pollination by removing the stamens and using them to dust pollen grains on the stigma of the contrasting variety. Seeds obtained from these plants produced a new crop of plants, which he called the first filial generation (F1).
First Filial Generation (F1)
F1 Phenotypes: All tall F1 genotype
When he crossed the F1 plants, he obtained a mixture of tall and dwarf plants in the approximate ratio of 3:1 respectively.
Phenotype ratio: 3;1; genotype ratio= 1;2:1
Mendel concluded that distinct factors control dormant and recessive traits. The interpretation led to his first law called the law of segregation of genes which states that genes segregate into different gametes during gametes formation. The law of independent assortment states that each pair of genes segregate into gametes independently.
Chromosomes: Rod-like structures occurring in pairs in the nucleus of a cell which contain the genes.
This is the condition in a heterozygote in which alleles have equal dominance and the phenotype is a mixture of the opposing characters.
INCOMPLETE DOMINANCE / BLENDING INHERITANCE
This is a situation in a heterozygous pair where neither allele is dominant, rather the phenotype is a blend or intermediate of the two parents e.g. the rose plant with alleles for both red and white flowers produces pink flowers.
The male gametes bears either an X or a Y chromosomes. While the female gametes always bear an X – chromosome. At fertilization, if an X – chromosome carrying sperm fuses with the X – bearing ovum, a female child results. But if a Y – bearing sperm fuses with X – bearing ovum, a male child results.
This is the phenomenon in which genes are borne on the X – chromosome, which controls certain characteristics. Sex linked characteristics are characteristics associated with the sex of an individual in which the gene for expression of the character is borne on the X-chromosome.
APPLICATION OF THE PRINCIPLE OF HEREDITARY IN AGRICULTURE
1) Breeding of crops of high resistance to disease and pests.
2) Production of new varieties of crops through hybridization.
3) Production of drought resistant varieties of crops.
4) Production of early maturing varieties of crops and animals.
5) Production of high yielding varieties of crops and animals.
6) Improvement of the nutritive value of crops and animals.
APPLICATION OF THE PRINCIPLE OF HEREDITARY IN MEDICINE
1) Genetic counselling / prevention of hereditary disease.
2) Blood transfusion to needy patients.
3) Determination of the paternity of a child by use of DNA / blood group.
4) Production of insulin (to treat diabetes).
ADAPTATION FOR SURVIVAL AND ENVIRONMENT
1) Behavioural Adaptation in Social Animal Behavioural Adaptation: The intrinsic behavioural patterns of an organism which gives it a survival value.
i) Behavioural adaptation of predators.
ii) Laying in ambush / hide and wait position.
iii) Chasing and overtaking the prey with greater speed.
2) Behavioural Adaptation for Protection from Predator
i) Swaying the air e.g. bat
ii) Feigning death e.g. millipedes
iii) Secretion of offensive odour e.g. cockroach
3) Behavioural Adaptation Against Unfavourable Weather Conditions
i) Aestivation in active or dormant state in holding season e.g. snails
ii) Hibernation: Restive state of some animals during winter.
iii) Migration: Outright relocation to more suitable environment.
iv) Shedding of leaves to reduce water loss e.g. Almond tree.
HONEY BEE: Live in hives which consists of chambers called cell.
ECONOMIC IMPORTANCE OF BEES
i) They pollinate flowers and provide honey
The bee caste system include the
1) Queen: The fertile female which lays egg.
2) Drones: These are the fertile male.
3) Workers: These are the sterile females which perform several functions such as clearing the cell, feeding older larvae with honey, feeding younger larvae with royal jelly, collecting pollen and nectar.
TERMITES: Termites live in nest or anthills. The termites cast consist of the
1) Worker: These are blind wingless and sterile.
2) Soldiers: These are blind, wingless, sterile with big heads.
3) Reproductive: These consist of the queen, king and winged reproductive.
ECONOMIC IMPORTANCE OF TERMITES
i) They add humus into the soil by breaking down dead wood.
ii) They are good source of protein and fats.
iii) They aid in loosening and aerating the soil
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