HEREDITARY VARIATION AND CAUSES
Hereditary variation is the differences among individuals which can be passed from the parents to their offspring (progenies).
NOTE: No two offspring inherit exactly the same set of characteristics from parents except in identical twins. Hereditary variation arises because of
- Genetic reshuffling during meiosis due to independent assortment and segregation before the final combination results in a totally new individual
- Crossing over during meiosis, the chromatids get in contact with powder at the prophase stage of cell division. The homologous chromosomes break and rejoin at a point called This results in crossing over of genetic materials hence, variation in the off spring.
Transmittable characters in animals
These include: body stature, shape or size of the head, nose and ear, colour of skin, hair colour, eye colour, intelligence, height, and characteristic voice of speech, blood group, baldness, tongue rolling, sickle cell anaemia, haemophilia, colour blindness, finger prints and ability to taste phenylthiocarbamide (PTC)
Transmittable characters in plants
These include height, weight or shape of plants, its fruit, leaf, fruit taste, food content, colour of leaf or flower, fruit or seed, resistance to environmental factors like disease, pest and wind, leaf texture, life span etc.
How characters get transmitted
Only characters controlled by genes are transmissible. Diploid organisms produce gametes by meiosis in their reproductive organs, therefore the male gamete (sperm cell) and the female gamete (ovum) are haploid organisms containing one set of chromosomes in their cell (one copy of each gene from homologous pair.
When fertilization takes place during sexual reproduction, the gametes (spermatozoon and ovum) fuses together to form a zygote.
Each zygote is a diploid organism having two set of chromosomes. Hence two copies of each gene (a copy donated by each gamete)
Hence, characters determined by genes are transmitted from parents to offspring through gamete