Inherited variation

The features of organisms are called their [?] (e.g. blue eyes). Offspring normally share some [?] with their parents and brothers and/or sisters. Offspring can characteristics from their parents. Characteristics can be different and this is known as (e.g. brown eyes and blue eyes). [?] occurs in both plants and animals.



An organism’s characteristics are controlled by [?] which is found inside the nucleus of almost all of its cells. [?] is passed from parents to offspring during reproduction. In sexual reproduction, a male sex cell or (e.g. a sperm cell) and a female [?] (e.g. an egg cell) fuse. This fusing (joining together) produces a [?] egg cell which grows into the new organism. Each [?] contains [?] the amount of genetic information that a normal body cell has. So the fertilised egg cell gets half its genetic information from the male and half from the female.

In many animals, when two egg cells are each fertilised by a sperm cell, [?]-[?] twins are born. Sometimes a fertilised egg cell splits into two and [?] twins form.

Species, breeds and varieties

A [?] is a group of organisms that are able to produce offspring that are also able to reproduce. Members of the same [?] have very similar characteristics but there is some variation in these characteristics.

A group of animals may have special differences in their inherited characteristics from the rest of their species. A group like this is called (e.g. different [?] of dog). There are also [?] of plants and these are called [?].



All tigers have stripes but there is [?] in the stripes between each tiger.


Selective breeding
Farmers and plant breeders may choose or ‘[?]’ an animal or with certain [?] (e.g. good [?] production in cows). This animal or plant is then used to [?] from. The offspring that have the best of these characteristics are then [?] from again. This is called [?] and is how many new breeds and [?] are created. Sometimes two different breeds or [?] are bred together to produce offspring with characteristics from both breeds or varieties. This is called [?]-breeding.

Plant breeding
In nature, pollen grains (the male gametes) are carried by the wind or insects to the stigma of another flower. This is called . Plant breeders transfer the pollen that they want to the stigma that they choose, sometimes using a paintbrush.

A pollen grain grows a tube down through the style until it meets an . It grows into the [?] and meets an egg cell. The nucleus from the pollen grain goes into the egg cell and fuses with the egg cell nucleus. This is [?].



Many of the characteristics that plant breeders choose are visible (e.g. fruit size, yield) but some are not visible (e.g. disease [?]).

Variation caused by the environment
Some characteristics vary due to an organism’s surroundings ([?]). For example, plants growing in different areas of a field may be different heights depending on the amount of light, [?] and mineral salts that they get. These things are all [?] [?] factors.