Chromosomes, genes and proteins

Chromosomes

A length of DNA, found in the nucleus of a cell; it contains genetic information in the form of many different genes.

DNA

A molecule that contains genetic information, in the form of genes, that controls the proteins that are made in the cell.

Gene

A length of DNA that codes for one protein.

Alleles

Alternative forms of a gene.

Reduction division

A term used to describe what happens in meiosis, where the number of chromosomes is halved (reduced).

Homozygous

Having two identical alleles for a particular gene (GG or gg)

Heterozygous

Having two different alleles for a particular gene (Gg)

Genotype

genetic makeup of an organism in terms of the alleles present (GG)

Phenotype

The observable features of an organism

Dominant allele

An allele that is expressed if it is present (G)

recessive allele

An allele that is only expressed when there is no dominant allele of the gene present (g)

Codominance

Alleles that are both expressed in the phenotype when they are both present

Inheritance

the transmission of genetic information from generation to generation

Genetic diagram

a standard way of showing all the steps in making predictions about the probable genotypes and phenotypes of the offspring from two parents

monohybrid cross

A cross where we consider the inheritance of only one gene

Punnett Square

The part of a genetic diagram that shows the predicted genotypes and phenotypes that can result from the random fusion of the male and female gametes

Test cross

A cross used to try to determine the genotype of an organism showing the characteristic produced by a dominant allele; the unknown organism is crossed with one showing the recessive characteristic

Sex chromosomes

Chromosomes that determine sex

X chromosome

the larger of the two sex chromosomes in mammals

Y chromosome

The smaller of the two sex chromosomes in mammals

Sex-linked genes

Genes that are found on a part of one of the sex chromosomes (usually the X chromosome) and not on the other sex chromosome; they therefore produce characteristics that are more common in one sex than in the other

Messenger RNA (mRNA)

A molecule that carries a copy of the information on DNA to a ribosome, to be used to synthesize a protein

Expressed

Used to make a protein; a gene is expressed when the protein that it codes for is synthesized in a cell

Stem cells

unspecialized cells that are able to divide by mitosis to produce different types of specialized cell