SCIENCE - Genetics

Adenine

The base that combines with thymine to form a base pair

Adenine is one of the four letter that make up the genetic code in humans and other living things

Allele

A version of a gene

An organism gets two alleles of each gene - one from its mother and one from its father

Amino acid

A small molecule that joins with others to form proteins

Amino acids are the building blocks of proteins, which are the building blocks of cells

Anaphase

A stage of cell division in which the chromosomes separate

Anaphase is when the chromosomes separate and are pulled away from each other to opposite sides of the cell.

Base

Part of a DNA molecule that comes in four types: A, C, G and T

Bases join together in pairs to form the 'rungs' of the DNA molecule.

Base pair

Two bases joined together

Base pairs form in only two combinations: A-T or G-C. These are the letters that make up the genetic code.

Cell cycle

The repeated process of cell growth and division

During most of the cell cycle, a cell grows and performs its function. This ends when the cell divides by mitosis.

Cell division

The splitting of a cell to form new cells

Cell division allows organisms to grow, repair damage and reproduce. There are two types: mitosis and meiosis.

Chromosome

A DNA molecule that condenses during cell division

Most human cells contain 46 chromosomes but sex cells only contain 23 chromosomes.

crossing over

The swapping of genes between chromosomes in a homologous pair

Crossing over only occurs in meiosis, during prophase I. It increases the genetic variety of the sex cells produced.

Cytosine

The base that combines with guanine to form a base pair

Cytosine is one of the four letters that make up the genetic code in humans and other living things.

Daughter cell

Any new cell formed by cell division

Each daughter cell has its own nucleus and set of DNA.

DNA

A molecule that contains genetic information

DNA, or deoxyribonucleic acid, is a very large molecule that contains instructions for building proteins.

dominant allele

A version of a gene that is expressed even when only one copy is present

A dominant allele is represented by an uppercase letter. Yy or YY will result in the appearance of the Y trait.

dominant trait

A feature that appears when at least one allele is present

Dominant traits include freckles, dimples and the ability to roll your tongue.

Double helix

A structure consisting of two chains twisted around each other

The DNA molecule has a double helix structure. The 'rungs' connecting the two chains are base pairs.

fertilisation

The joining of an egg and a sperm to form a new organism

Fertilization combines DNA from the mother and father so the child gets half of its chromosomes from each parent.

Gene

A unit of genetic information

A gene is a section of a DNA molecule that provides instructions for building a specific protein.

generation

A unit of genetic information

A gene is a section of a DNA molecule that provides instructions for building a specific protein.

Genotype

A pair of alleles that influence the appearance of a particular trait

A genotype is represented by two letters. An organism's genotype determines which traits it acquires – its phenotype.

Guanine1

The base that combines with cytosine to form a base pair

Guanine is one of the four letters that make up the genetic code in humans and other living things.

Heterozygous

A genotype in which the two alleles are different

A heterozygous genotype consists of one dominant allele and one recessive allele – Yy.

Homologous pair

Two chromosomes that contain versions of the same genes

One chromosome in a homologous pair is inherited from the mother and the other from the father.

homozygous

A genotype in which the two alleles are the same

A homozygous genotype consists of either two dominant alleles – YY – or two recessive alleles – yy.

inheritance

The passing down of traits via genes from one generation to the next

The inheritance of traits via sexual reproduction explains family resemblances.

Interphase

The stage of the cell cycle in which a cell grows and copies its DNA

Interphase covers most of a cell's life span, while it is growing and performing its normal function in the body.

meiosis

A type of cell division that produces sex cells for reproduction

Meiosis produces egg and sperm cells. One cell divides into four sex cells by two cycles of cell division.

Metaphase

A stage of cell division in which the chromosomes line up

Metaphase is when the chromosomes line up in the middle of the cell.

mitosis

A type of cell division that produces cells for growth and repair
Mitosis continues from birth to death, producing new cells to allow an organism to grow and stay healthy.

mutation

A permanent change in the sequence of bases that make up a gene

Some mutations are harmless while others cause disease. Mutations can be inherited by offspring.

Parent cell

Any cell that divides to form new cells

A parent cell needs to copy its DNA before dividing so that it can be passed down to its daughter cells.

pedigree

A family tree that shows how a trait is passed down through generations

In a pedigree, filled symbols show the presence of a trait and open symbols show its absence.

phenotype

The collection of traits observable in an organism

A phenotype includes traits such as tall, purple flowers and yellow seeds. It is determined by the organism's genotype.

prophase

A stage of cell division in which the chromosomes condense

Prophase is when the cell prepares to divide. The chromosomes condense and the nucleus starts to break down.

Protein

A large molecule made up of amino acids

Proteins form structures and perform functions in an organism. DNA contains instructions for building proteins.

recessive allele

A version of a gene that is only expressed when two copies are present

A recessive allele is represented by a lowercase letter. Only yy will result in the appearance of the y trait.

recessive trait

A feature that only appears when two alleles are present

Recessive traits include cleft chins, attached earlobes and hitchhiker's thumbs.

sex chromosome

A chromosome that helps determine an organism's gender

Sex chromosomes come in two types: X or Y. Most females have two X chromosomes while most males have an X and a Y.

simple inheritance

When the appearance of a trait is controlled by a single gene

Many traits are influenced by lots of genes but some, like albinism, are controlled by single genes.

telophase

A stage of cell division in which two nuclei form

Telophase is when two new nuclei form, each with its own set of DNA.

thymine

The base that combines with adenine to form a base pair

Thymine is one of the four letters that make up the genetic code in humans and other living things

Trait

A feature of an organism

Traits include height, hair colour, skin colour and freckles.