- Assortive mating is the mating between individuals with similar
phenotypic traits or characters.Assortive mating is also known as
homogamy.Similar phenotypic traits include body size,skin
colouration ,pigmentation etc.This mating increases the genetic
similarity within a family.In assortative mating,mating of
individuals with dissimilar phenotypes is rare.So this helps to
maintain the races as matings will be within the race.
- Human skin colour is variable around the world.It is different
for different region.The colour of skin is due to the pigment
melanin.Melanin is produced by the cells located in the epidermis
known as melanocytes.These cels have photosensitive receptors and
detect he ultraviolet rays from the sun.In response to this ,they
produce melanin.With the increase in UV rays ,more melanin is
produced that result in various skin colur.People in northern
latitudes have dark skin colour due to the abundant melanin
production.Melanin protects our body from the harmful effects of UV
rays (like sun burn,skin cancer ). Moreover folate (derived from
folic acid) gets broken down in too much UV rays.Melanin preserves
the folate from being broken down. Some amount of UV rays is
required for the production of vit D.So people with dark complexion
find difficult to live in northern latitudes as they cannot produce
vit D . So people in different latitudes have different skin Colour
in terms of vit D and folate levels.
PLANT BIODIVERSITY
- The four phyla of plants are :Bryophyta (mosses and
liverworts),pteridophyta(ferns),gymnosperms (conifers)and
angiosperms.(flowering plants)
- Significance of seeds than spores are:
1.seed coat protects the inside of the seed
2.seed contains endosperm that gives nourishment to the
developing embryo.
3.seed contain fully developed embryo and and many seeds go
through a dormancy period.So in right conditions only seeds
germinate.having a developed embryo provides more chances of
Survival than spores.
4.seeds donot need water.In dry conditions large seeds can hold
water .while spores require water for germination.
- Non vascular plant phyla is the bryophyte that include mosses
and liverworts.They donot have a root system.or stem.Leaves lose
the water.Vascular plant phyla are pteridophyta,gymnosperms and
angiosperms.
- Vascular system in plants is an association of conducting
tissues and supportive fibres.Conducting tissues include xylem and
phloem.Thgis helps in the easy transport of water,minerals to the
leaves and food from leaves to all parts of the plant.