B5 genes, inheritance and selection

Gamete

An organism's reproductive cell (egg in female and sperm in males), which has half the number of chromosomes (23).

Chromosome

A structure found in the nucleus which is made up of a long strand of DNA.

Gene

A short section of DNA that codes for a protein, and therefore contribute to a characteristic.

Allele/variant

The different forms of the gene - humans have two alleles for each gene as they inherit one from each parent.

Dominant allele

Only one (out of the two alleles) is needed for it to be expressed and for the corresponding phenotype to be observed.

Recessive allele

Two copies are needed for it to be expressed and for the corresponding phenotype to be observed.

Homozygous

When both inherited alleles are the same (i.e. two dominant alleles or two recessive alleles).

Heterozygous

When one of the inherited alleles is dominant and the other is recessive.

Genotype

The combination of alleles an individual has, e.g. Aa.

Phenotype

The physical characteristics that are observed in the individual, e.g. eye colour.

Genome

The genome describes all the genetic information of that organism.

Genetic variance

All variants (alleles) are caused by mutation.

Coding DNA

If the mutation occurs in a coding region of DNA then it can alter the activity of the protein that the altered area of DNA is meant to code for.

Non-coding DNA

If the mutation is in a non-coding region of DNA it can still affect how genes are expressed by stopping transcription of mRNA in the protein synthesis process.

mRNA nucleotides

Messenger RNA: a different type of nucleotide that matches to their complementary base on the strand.

Protein synthesis

The process where DNA contains the genetic code for making a protein, but it cannot move out of the nucleus as it is too big.

Ribosomes

Structures in the cytoplasm where mRNA moves to after leaving the nucleus.

mRNA

The molecule that carries genetic information from DNA to the ribosomes for protein synthesis.

Amino Acid

The building blocks of proteins, coded for by sequences of three bases on the mRNA.

Carrier Molecules

Molecules that transport amino acids to the ribosomes during protein synthesis.

Protein Folding

The process by which a protein assumes its unique 3D structure after being synthesized.

Asexual Reproduction

A mode of reproduction that involves only one parent and produces genetically identical offspring.

Sexual Reproduction

A mode of reproduction that involves two parents and produces offspring with genetic variation.

Variation

Differences in characteristics among individuals in a population that can provide survival advantages.

Survival Advantage

A characteristic that increases the likelihood of survival in changing environments.

Selective Breeding

The process of breeding organisms with desirable traits to produce offspring with those traits.

Natural Selection

The process through which organisms better adapted to their environment tend to survive and produce more offspring.

Meiosis

The process of cell division that results in four non-identical gametes, each with half the normal number of chromosomes.

Gametes

Reproductive cells that carry one copy of each chromosome, produced through meiosis.

Diploid

A cell that contains two complete sets of chromosomes, one from each parent.

Haploid

A cell that contains only one set of chromosomes, half the normal amount.

Genetically Different

Describes cells that have unique combinations of chromosomes due to the shuffling during meiosis.

Punnett Square

A diagram used to predict the genotypes and phenotypes of offspring from a genetic cross.

Dominant Characteristics

Traits that are expressed in the phenotype even when only one allele is present.

Recessive Characteristics

Traits that are expressed in the phenotype only when two copies of the allele are present.

Sex Determining Genes

Genes located on the 23rd pair of chromosomes that determine an individual's sex.

X Chromosomes

One of the two sex chromosomes, females have two X chromosomes.

Y Chromosomes

The smaller sex chromosome that, when paired with an X chromosome, determines male sex.

Chromosomes

Structures within cells that contain DNA and genetic information.

X chromosome

A sex chromosome that males have one of, allowing them to pass on either X or Y chromosomes in their sperm.

Y chromosome

A sex chromosome that males have one of, allowing them to pass on either X or Y chromosomes in their sperm.

Gregor Mendel

A scientist who observed characteristics passed on to the next generations in plants through breeding experiments on pea plants.

Hereditary units

Units that offspring inherit from their parents, which can be dominant or recessive.

Dominant

A type of hereditary unit that can mask the presence of a recessive unit.

Recessive

A type of hereditary unit that is masked by a dominant unit.

DNA

The molecule whose structure was determined in 1953, allowing for an understanding of how genes work.

Evolution

A change in the inherited characteristics of a population over time through natural selection, potentially resulting in a new species.

Mutations

Changes in the genetic material that provide variation between organisms.

Speciation

The process by which one population of a species becomes so different that they can no longer interbreed to produce fertile offspring.

Artificial classification

A classification system based purely on observations, invented by Carl Linnaeus.

The Linnaean system

A classification system that divides living things into kingdoms, phylum, class, order, family, genus, species.

Natural classification

A classification system developed based on advances in biology, including improvements in microscopes and studies of biochemistry.

Phylogenetics

The study of how closely related two organisms are, helping to trace species origins.

Molecular techniques

Methods used in natural classification to see similarities between species, such as DNA sequencing.

DNA sequencing

A method used to compare protein structures and similarities between species in natural classification.

Domains

Three large groups added by Carl Woese above kingdoms: Archaea, Bacteria, and Eukaryota.

Archaea

Primitive bacteria which live in extreme environments such as hot springs.

Bacteria

True bacteria that have similar features to archaea.

Eukaryota

Organisms that have a nucleus enclosed in membranes, including kingdoms protists, fungi, plants, and animals.

Binomial system

A naming system for organisms that includes a genus and a species, used worldwide.

Example of binomial naming

The ladybug is named Harmonia axyridis, where Harmonia is the genus and axyridis is the species.

Fossils

Remains of organisms from many years ago, found in rocks, used to show how anatomy has changed over time.

Formation of fossils

Fossils are formed by parts of organisms that have not decayed, parts being replaced by minerals, or preserved traces.

Selection pressure

A condition that creates a survival advantage for organisms with certain traits, such as antibiotic resistance.

Antibiotic resistance

A trait in bacteria that allows them to survive exposure to antibiotics, leading to increased population of resistant bacteria.

MRSA

A 'superbug' that is resistant to many types of antibiotics and spreads in hospitals.

Survival of the fittest

The concept that organisms with characteristics best suited to the environment are more likely to survive and reproduce.

Darwin's theory

Variation exists within species due to mutations, and beneficial characteristics are passed on to the next generation.

Controversy of Darwin's ideas

Darwin's ideas contradicted the belief in God as the creator, lacked evidence, and the mechanisms of inheritance were unknown.

Wallace

Worked alongside Darwin, focusing on the theory of speciation.

Speciation process

Involves variation, selection of advantageous alleles, population isolation, and eventually the formation of a new species.

Genetic mutations

Changes in DNA that create variation within a population.

Isolation in speciation

Occurs when populations are prevented from breeding together, often due to physical barriers.

Genetic variation

The diversity of alleles within a population, which can increase due to selection of different alleles.

Fertile offspring

Offspring that can reproduce and create viable progeny, important for defining species.