Genetics definitions

Genetic variation

The differences in organisms within a population - can be continuous or discontinuous.

Chromosome

Made up of a long strand of DNA, it carries genetic information in the form of many genes.

Nucleus

The part of the cell that contains chromosomes

Genotype

the particular set of alleles of an organism

Karyotype

The photograph of an individual’s chromosomes cut out and arranged according to their size

Asexual reproduction

Reproduction involving only one parent. Offspring genetically identical to parent and each other (NO variation)

Gene

short length of DNA that carries the genetic code for a particular feature or trait

Gametes

reproductive cells (sperm / egg) that contain a half set of  chromosomes

Mitosis

The cell division of body cells for growth and repair. 2 genetically  identical new cells to each other and parent cell

Meiosis

cell division in reproductive organs producing 4 new haploid cells, gametes. Genetically different to each other

Zygote

A fertilised ovum/egg that contains the full set of chromosomes

Alleles

Different (Alternative) forms of the same gene. They can be dominant or recessive

Sexual reproduction

Reproduction involving 2 parents. Offspring different to parents and to each other (Variation due to random segregation of alleles into gametes AND random combination of gametes during fertilization)

Mutation

a permanent change in the base sequence of DNA. Only passed onto offspring if in a gamete and forming new alleles

Fertilisation

joining of male and female gametes

Diploid

full set of chromosomes - in homologous pairs

Phenotype

The observable characteristics of an individual resulting from its genotype

Pure breeding

being homozygous eg. aa, GG - pure breeding parents always produce pure breeding offspring when bred together

Homozygous

having two of the same allele for a particular trait

Heterozygous

Two different alleles for a particular trait

Dominant

allele which is always expressed (phenotype) when present.

Sex chromosomes

X and Y chromosomes that determine the sex of an offspring

Haploid

having a single set of chromosomes (has half the number of chromosomes than in a normal body cell)

Recessive

allele which is only expressed (phenotype) when 2 present (and the dominant is not present

Deoxyribonucleic acid (DNA)

A long, twisted (double helix) strand of material that makes up chromosomes. It is the carrier of genetic information.

Inbreeding depression

The reduced survival and fertility of offspring of closely related individuals

Crossing over

exchange of genetic material between homologous chromosomes during meiosis (a source of variation)

Independent assortment

The process where homologous chromosome pairs are randomly line up before splitting to go into sex cells (Main source of variation)

Homologous chromosomes

Chromosome pairs (one from each parent) that are similar in length, gene position, and location.

Gene flow

The introduction of new genes into a population (immigration)

Continuous variation

Variations are distributed on a continuum (I.e. not just a few options but a wide range of options (e.g. height))

Discontinuous variation

Variations are placed into discrete, individual categories. (i.e. Only a few (often 2) options)

Natural selection

The process over time where individuals that are most “fit” for an environment (have advantageous alleles) survive and reproduce

Segregation

The random process where each homologous chromosome splits up to go into a particular daughter cell (A source of variation)