Biology B1 GCSE Revision Notes OCR (higher)

HideShow resource information
  • Created by: Anouschka
  • Created on: 09-05-11 17:50

SIZE, LARGEST TO SMALLEST


Organism. Organ. Cell. Nucleus. DNA. Chromosome. Gene. Molecule. Atom.

 

CHROMOSOMES

A "normal" human cell nucleuscontains 46 chromosomes (23 pairs)

Females - XX
Males - XY

All normal egg cells produced by a human ovary carry the X chromosome.

Half of the sperm carries an X chromosome, and half carries Y chromosome.

The baby's gender is determined by the sperm that fertilises the egg. If the sperm carries the X chromosome, it will be a girl, and if a Y, a boy.

50/50 chance.

*Sex Cells are known as gametes.

ALLELES

  • Different versions of the same gene
  • Eg. the gene for eye colour has an allele for blue eyes and an allele for brown.
  • For any gene, a person may have the same two alleles or two different ones
  • Can be recessive or dominant

Heterozygous
of an organism which has two different alleles of a given gene

Recessive
only shows if the individual has two copies of it. Eg. Blue/green eyes.

Dominant
Always shows, even if the individual only has one copy of it. Eg. Brown eyes.

FOR EXAMPLE:

(http://www.abpischools.org.uk/res/coResourceImport/modules/genome/en-images/eyecolour2.gif)

Even if both the parents have brown eyes, if they are both carriers of the blue-eyed allele, they would have a 1 in 4 chance of having a blue eyed child.
Even if…

Comments

marina

there could be some tables in here

but other than that very good.

Callum Stuart Hepburn

This is very good :D

Similar Biology resources:

See all Biology resources »See all resources »