Biology » Reproduction


Key Words

DNA - contains deoxyribonucleic acid a chemical that all of the genetic material in a cell is made up from. It is also a polymer.

Chromosomes - really long molecules of DNA. Chromosomes come in pairs.

Gene - a small section of DNA found on a chromosome.

Genome - the entire set of genetic material in an organism.

Nucleotides - repeating units that make up the DNA strands.

mRNA - a molecule which acts as a messenger between the DNA and the ribosome.

Enzymes - biological catalysts that speed up chemical reactions in the body.

Hormones - carry messages around the body.

Mutations - random changes in an organism's DNA. These can sometimes be inherited. Three types of mutation are:

  • Insertions - a new base is inserted into the DNA base sequence.
  • Deletions - a random base is deleted from the DNA base sequence.
  • Substitutions - a random base is changed in the DNA base sequence.

Sexual reproduction - genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to the parent.

Asexual reproduction - carried out by mitosis. There is only one parent so the offspring are genetically identical to that parent.

Gametes - contain 23 chromosomes. Instead of having two of each chromosome, a gamete has just one.

Meiosis - produces cells which have half the normal number of chromosomes.

X and Y chromosomes - males have an X and a Y choromosome (XY), females have two X chromosomes (XX).

Alleles - different versions of genes.

Homozygous - when an organism has two alleles for a particular gene that are the same.

Heterozygous - when an organism has two alleles for a particular gene that are different.

Dominant allele - the allele for the characteristic that's shown when two alleles are different.

Recessive - the allele for the characteristic that is not shown when two alleles are differnet.

Genotype - combinations of alleles you have.

Phenotype - the characteristics you have.

Recessive allele - people with one copy of the allele (a carrier) won't have the disorder. However for a child to have the disorder both parents will have to be carriers.

Cystic Fibrosis - genetic disorder caused by a recessive allele. The body produces a lot of thick sticky mucus in the air passages and int the pancreas.

Dominant allele - only one parent needs to be a carrier in order for the child to be able to inherit the condition.

Polydactyly - genetic disorder caused by a dominant allele. A baby is born with extra fingers or toes.

IVF - fertilising and egg with sperm in a lab.

Embryonic screening - a embryo cell is analysed for it's genes before the embryo is implanted after IVF.

Gregor Mendel - an Austrain monk who noted how characteristics in plants where passed on from one generation to the next.


Also see Hormonal coordination, Genetics & Evolution,