Variation and Selection

chromosome

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

DNA

a molucule 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 descibe what happens in meiosis, where the number of chromosomes is halved (reduced)

homozygous

having two identical alleles of a particular gene (e.g. GG or gg)

heterozygous

having two different alleles of a particular gene (e.g. Gg)

genotype

the genetice makeup of an organism in terms of the alleles present (e.g. GG)

phenotype

the observable features of an organism

dominant allele

an allele that is expressed if it is present (e.g. G)

recessive allele

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

codominace

alleles that are both expresseed 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 predicitions 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 derermine 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 detemine 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 orther 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 synthesise a protein

expressed

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

Transcription stage

rewrites the base code of DNA into bases of RNA

Translation stage

uses the RNA base sequence to build the amino acid sequence in a protein

stem cells

unspecialised cells that are able to divide by mitosis to produce different types of specialised cell

variation

differences between the individuals of the same species

discontinuous variation

variation in which there are distinct categories of phenotype, with no intermediates

population

a group of organisms of oone species, living in the same area at the same time

continuous variation

variation in which there is a continuous range of phenotypes between two extremes

mutation

a random change in a gene, which can produce new alleles; mutation involves a change in the base sequence in DNA

adaptive feature

an inherited feature that helps an organism to survive and reproduce in its environment

xerophyte

a plant that has adaptive feature that help it to survive in an environment where water is scare

hydrophyte

a plant that has adaptive features that help it to survive in water

natural selection

a process in which individuals with advantageous features are more likely to survive, reproduce and pass on their alleles to the next generation

selevtion pressure

something in the environment that affects the chance that individuals with different features will survive and reporduce

adaptation

the process, resulting from narutal selection, by which populations become more suited to their environment over many generations

drug

any substance thaken into the body that modifies or affects chemical reactions in the body

antibiotic

a substance that is taken into the body, and which kills bacteria but does not affect himan cells or viruses

artificial selevtion / selevtive breeding

choosing particular organisms with desired characteristic to breed together, and continuing this over many generations

restiction enzymes

enzymes (biological catalysts) that cut DNA at specific points, and leave a short length of unpaired bases at each end

sticky ends

lengths of unpaired bases on one strand of a DNA molecule; they are able to form bonds with complementary lengths of unpaired bases on a different DNA molceule

DNA ligase

an enxyme that joins two DNA molecules together

recombinant plasmid

a small circle of DNA, found in bacteria, which contains both the bacterial DNA and DNA from a different organism