GENETIC VARIATION

Genetic Variation• Meiosis and sexual reproduction ensure that variation

occurs in individuals within a population/species.

Genetic Variation• Meiosis and sexual reproduction ensure that variation

occurs in individuals within a population/species. • Individuals produced by sexual reproduction are different

from one another and their parents- this is because mixing of genetic material occurs during:

-

Genetic Variation• Meiosis and sexual reproduction ensure that variation

occurs in individuals within a population/species. • Individuals produced by sexual reproduction are different

from one another and their parents- this is because mixing of genetic material occurs during:

-the production of gametes in meiosis

Genetic Variation

• Meiosis and sexual reproduction ensure that variation occurs in individuals within a population/species.

• Individuals produced by sexual reproduction are different from one another and their parents- this is because mixing of genetic material occurs during:

-the production of gametes in meiosis

-Fertilisation when the zygote receives half its chromosomes from the male and half from the female.

Meiosis ‘juggling the genes’• Variation between closely related individuals results from

the random way in which chromosomes (and therefore their alleles) line up in meiosis.

Meiosis ‘juggling the genes’• Variation between closely related individuals results from

the random way in which chromosomes (and therefore their alleles) line up in meiosis.

• When chromosomes separate, it is chance which chromosome/alleles will come together in a gamete (eg sperm or egg)

Meiosis ‘juggling the genes’

Fertilisation• Occurs when a sperm fuses with an egg – it is a chance

event as to which sperm fertilises the egg (both have a unique combo of alleles)

Identical Twins• Develop from the same fertilised egg, so the DNA in their

cells is the same.

Identical Twins• Develop from the same fertilised egg, so the DNA in their

cells is the same.• Differences between identical twins occur from ageing

processes, and environmental events.

Sex determination• Sex is determined by the X and Y chromosomes

Sex determination• Sex is determined by the X and Y chromosomes• Males have XY and females are XX

Sex determination• Sex is determined by the X and Y chromosomes• Males have XY and females are XX• Genes on the sex chromosomes control the manufacture

of sex hormones, which bring about secondary sexual characteristics such as breast development (females) and the growth of facial hair (males)

Sex determination• Sex is determined by the X and Y chromosomes• Males have XY and females are XX• Genes on the sex chromosomes control the manufacture

of sex hormones, which bring about secondary sexual characteristics such as breast development (females) and the growth of facial hair (males)

• The X chromosome is much larger than the Y – therefore contains more genes.

Sex determination• Sex is determined by the X and Y chromosomes• Males have XY and females are XX• Genes on the sex chromosomes control the manufacture of

sex hormones, which bring about secondary sexual characteristics such as breast development (females) and the growth of facial hair (males)

• The X chromosome is much larger than the Y – therefore contains more genes.

• Each gamete only receives only one sex chromosome.- From a male, half the sperm receive an X chromosome and

half receive a Y chromosome

Sex determination• Sex is determined by the X and Y chromosomes• Males have XY and females are XX• Genes on the sex chromosomes control the manufacture of sex

hormones, which bring about secondary sexual characteristics such as breast development (females) and the growth of facial hair (males)

• The X chromosome is much larger than the Y – therefore contains more genes.

• Each gamete only receives only one sex chromosome.- From a male, half the sperm receive an X chromosome and half

receive a Y chromosome- Since females have only X chromosomes, all eggs have one X.

Sex determination• Whether a child is male or female is determined the

moment of fertilisation by the sperm.

Sex determination• Whether a child is male or female is determined the

moment of fertilisation by the sperm.• If an X sperm fertilises the egg, the offspring will be

female

Sex determination• Whether a child is male or female is determined the

moment of fertilisation by the sperm.• If an X sperm fertilises the egg, the offspring will be

female• If a Y sperm fertilises the egg, the offspring will be male

Sex determination• Whether a child is male or female is determined the

moment of fertilisation by the sperm.• If an X sperm fertilises the egg, the offspring will be

female• If a Y sperm fertilises the egg, the offspring will be male

• 50% chance either a male or female will be born every time.

X X

X XX XX

Y XY XY