Genetic Variation and Change

Flash Cards

Genetics

The study of genes, inheritance and variation and organisms

DNA

A molecule that stored genetic information and instructions needed for an organism and their development

Gene

A section of DNA that contains instructions for producing a functional product such as protein

Allele

An alternative version of a gene

Chromosome

A long, organised DNA molecule containing many genes

Locus

The specific position of a gene on a chromosome

Genotype

The combination of alleles on an organisms possesses for particular gene or genes

Phenotype

The observable characteristics of an organism resulting from its genotype and environmental influences.

Homozygous

Having two identical alleles for a particular gene

Heterozygous

Having two different alleles for a particular gene

Dominant allele

An allele that is expressed in the phenotype when at least one copy is present in complete dominance

Recessive allele

An all that is expressed in the phenotype when two copies are present in complete dominance

Genetic variation

Differences in genetic information between individuals within a population.

Gene pool

All the alleles present in a population.

Allele frequency

How common a particular allele is within a population.

Population

A group of organisms of the same species living in the same area and capable of reproducing with each other.

Gamete

A haploid reproductive cell, such as a sperm or egg, that contains half the normal chromosome number.

Zygote

The diploid cell formed when a sperm and egg join during fertilisation.

Haploid

A cell containing one set of chromosomes.

Diploid

A cell containing two sets of chromosomes, one inherited from each parent.

Mutation

A permanent change in the DNA nucleotide sequence that can create a new allele.

Mutagen

An agent that increases the likelihood of mutations occurring in DNA.

Somatic mutation

A mutation that occurs in a body cell and is generally not passed on to offspring.

Gametic mutation

A mutation that occurs in a cell involved in producing gametes and can be inherited by offspring.

Crossing over

The exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I of meiosis.

Homologous chromosomes

A pair of chromosomes containing the same genes at the same loci, with one inherited from each parent.

Non-sister chromatids

Chromatids belonging to different homologous chromosomes.

Chiasmata

The points where non-sister chromatids overlap and exchange genetic material during crossing over.

Independent assortment

The random arrangement of homologous chromosome pairs during metaphase I of meiosis, resulting in different combinations of maternal and paternal chromosomes in gametes.

Random fertilisation

The chance joining of any genetically different sperm and egg, producing a genetically unique zygote.

Genetic recombination

The rearrangement of genetic material that creates new combinations of alleles.

Meiosis

A type of cell division that produces four genetically different haploid cells, each containing half the original chromosome number.

Meiosis I

The first division of meiosis, where homologous chromosomes separate into two cells.

Meiosis II

The second division of meiosis, where sister chromatids separate to produce four haploid cells.

Prophase I

The first stage of meiosis I, where homologous chromosomes pair up and crossing over occurs between non-sister chromatids.

Metaphase I

The stage where homologous chromosome pairs line up randomly along the equator of the cell.

Anaphase I

The stage where homologous chromosomes separate and move to opposite poles of the cell.

Telophase I

The stage where chromosomes reach opposite poles and two haploid cells form, each containing duplicated chromosomes.

Prophase II

The stage where spindle fibres form in each of the two cells before the second meiotic division.

Metaphase II

The stage where chromosomes line up individually along the equator of each cell.

Anaphase II

The stage where sister chromatids separate and move to opposite poles.

Telophase II

The final stage where nuclei reform and four genetically different haploid cells are produced.

Inheritance

The passing of genetic information from parents to offspring.

Monohybrid inheritance

The inheritance of one gene with two alleles.

Dihybrid inheritance

The inheritance of two different genes at the same time.

Punnett square

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

Genotype ratio

The ratio of the different allele combinations expected in offspring.

Phenotype ratio

The ratio of the different observable characteristics expected in offspring.

Co-dominance

An inheritance pattern where both alleles are fully expressed in the phenotype of a heterozygous individual.

Incomplete dominance

An inheritance pattern where neither allele is completely dominant, resulting in an intermediate phenotype in a heterozygous individual.

Multiple alleles

A situation where a gene has more than two possible alleles within a population, although each individual can only have two.

Lethal allele

An allele that causes death when a particular genotype is present.

Linked genes

Genes located on the same chromosome that tend to be inherited together.

Recombination

The formation of new combinations of alleles, often through crossing over.

Sex-linked inheritance

The inheritance of characteristics controlled by genes located on sex chromosomes, usually the X chromosome.

Sex chromosomes

Chromosomes that determine biological sex in many organisms; in humans these are X and Y.

Carrier

An individual who carries a recessive allele but does not express the associated characteristic under complete dominance.

Complete dominance

An inheritance pattern where the dominant allele completely masks the effect of the recessive allele in a heterozygous individual.

Evolution

A change in the inherited characteristics or allele frequencies of a population over generations.

Natural selection

The process where individuals with advantageous inherited characteristics have greater reproductive success, causing those alleles to become more common over generations.

Selection pressure

An environmental factor that affects the survival and reproductive success of individuals in a population.

Adaptation

An inherited characteristic that improves an organism's ability to survive and reproduce in a particular environment.

Fitness

An organism's ability to survive and successfully reproduce, passing its alleles to the next generation.

Genetic drift

A random change in allele frequencies within a population due to chance rather than natural selection.

Bottleneck effect

A type of genetic drift where a population is suddenly reduced in size, leaving a small group of survivors with potentially different allele frequencies.

Founder effect

A type of genetic drift that occurs when a small group separates from a larger population and establishes a new population with only a sample of the original alleles.

Gene flow

The movement of alleles between populations when individuals migrate and reproduce.

Migration

The movement of individuals into or out of a population.

Reproductive success

The ability of an organism to produce surviving, fertile offspring that pass on its alleles.

Selection

The process where certain inherited characteristics become more or less common because of differences in reproductive success.