SIZE, LARGEST TO SMALLEST
Organism. Organ. Cell. Nucleus. DNA. Chromosome. Gene. Molecule. Atom.
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.
*Sex Cells are known as gametes.
- 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
of an organism which has two different alleles of a given gene
only shows if the individual has two copies of it. Eg. Blue/green eyes.
Always shows, even if the individual only has one copy of it. Eg. Brown eyes.
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.