Biology Unit 2 Defintions

DNA

The genetic material that carries cellular instructions

Gene

A section of DNA that has a functional purpose, such as coding for a protein that determines a trait

Gene expression

The process of converting the instructions in a gene into a product

Enzyme

Proteins that catalyse (speed up) biochemical reactions

Allele

An alternative form of a gene

Genome

The entire set of genetic information within a cell or organism

Heredity

The passing on of physical characteristics from one generation to another

Somatic Cell

A cell in an organism other than the reproductive cells

Genomics

A branch in genetics that investigates genomes

Histone

The protein that DNA wraps around to form nucleosome

Nucleosome

DNA wrapped around histone proteins

Chromosome

Organised structures that contain DNA

Chromatid

One of the two identical halves of a replicated chromosome; a long, tightly coiled straight of DNA

Centromere

A protein that links sister chromatids to each other

Homologous Chromosomes

A pair of chromosomes that have the same number and position of genes

Locus

The location of a gene on a chromosome

Sex chromosome

A chromosome that determines the sex of an organism

Autosome

A chromosome that is not involved in sex determination

Homogametic

An organism that has two of the same sex chromosomes, e.g. XX

Heterogametic

An organism that has two different sex chromosomes, e.g. XY

Linked Genes

Genes located close together on the same chromosome that are generally inherited together

Diploid

A nucleus or cell that contains two sets of chromosomes, one from each parent (2n)

n

Number of chromosomes

Haploid

A nucleus or a cell (usually an ovum or sperm) that contains one set of chromosomes, so the chromosomes aren’t in pairs (n)

Karyotype

The visual representation of the chromosomes from a cell nuclei of an individual

Aneuploidy

A genetic abnormality in which an individual has an abnormal number of chromosomes

Trisomy

A genetic abnormality in which an individual has an extra copy of a chromosome

Monosomy

A genetic abnormality in which one chromosome of a pair of homologous chromosome is missing

Meiosis

A type of cell division that produces gametes

Germline cell

a diploid cell in ovaries or testes that undergoes meiosis to form gametes

Crossing over

The process during prophase I of meiosis when homologous chromosomes exchange genetic material

Recombinant chromosome

A chromosome formed after the crossing over of genetic material between the homologous chromosomes

Disjunction

The organised separation of chromosomes during meiosis

Law of independent assortment

A law that states that homologous chromosomes orient themselves randomly along the middle of the cell during metaphase I

Ovum

A female gamete

Spermatogenesis

A meiotic process of sperm production in the testes

Oogenesis

The meiotic process of ovum production in the ovaries

Polar body

A small cell that buds off a developing ovum during oogenesis and does not develop into ova

Genotype

A combination of alleles for a gene

Phenotype

The physical expression of the genotype and its environment

Homozygous

A genotype in which the two alleles for the gene are the same

Heterozygous

A genotype in which the two alleles for the gene are different

Dominant trait

The trait that is expressed in the phenotype of a heterozygous individual; trumps over a recessive gene

Recessive trait

The trait that is only expressed in the phenotype of a homozygous individual; trumped by a dominant gene

Carrier

A heterozygous individual with one allele for the recessive trait but who shows the dominant trait

Hemizygous

A genotype in which there is only one copy of the gene

Dominance

Refers to the relationship between the alleles of a gene and the observable phenotype

Complete dominance

A pattern of dominance in which the recessive trait is completely masked by the dominant trait in a heterozygous individual

Dominant phenotype

The phenotype that is seen in a homozygous individual and a heterozygous individual

Recessive phenotype

The phenotype that is observed from a homozygous recessive genotype

Codominance

A pattern of dominance in which two traits are equally dominant and the heterozygous individual displays both traits

Incomplete dominance

A pattern of dominance in which a heterozygous individual displays an intermediate phenotype that is a combination of the two alleles

Polygenic trait

A trait controlled by multiple genes

Epigenetics

The study of changes in gene expression caused by modification of the DNA without changing the sequence

DNA methylation

The process of adding methyl groups to the cytosine bases of DNA, which can change the expression of a gene

Histone modification

The addition of chemical groups to histone proteins, which affects the spacing between nucleosomes and therefore gene expression

Epigenome

The epigenetic modifications to the DNA and histone proteins of an individual

Law of segregation

The law that states that during gametes formation (meiosis) each gamete randomly receives one allele of each gene

Autosomal dominant

A pattern of inheritance where affected individuals have at least on allele for the trait

Autosomal recessive

A pattern of inhertiance where two copies of the same allele on homologous must be present for the trait to show in the phenotype

Sex-linked

Refers to genes that are found on the X or Y chromosome

X-linked recessive

A pattern of inheritance where the gene for a recessive trait for a recessive trait is located on the X chromosome

X-linked dominant

A pattern of inheritance where the gene for a dominant trait is located on the X chromosome

Pedigree

A diagram that shows the inheritance of a trait in a family for at least two generations

True-breeding

Individuals that when crossed together produce offspring with the same genotype and phenotype as the parent for a particular trait

Hybrid

An individual that was produced by phenotypically different parents

Monohybrid test cross

A cross between an individual with the dominant phenotype and an individual with the recessive phenotype to determine the genotype of the dominant individual

Dihybrid cross

A cross between two individuals to observe the inheritance of two different traits

Unlinked genes

Genes on different chromosomes that assort independently from one another

Linked genes

Genes on the same chromosome that are likely to be inherited together

Asexual reproduction

A mode of reproduction in which a single parent reproduces without the fusion of egg or sperm

Fission

A form of asexual reproduction in which a parent cell divides into two or more genetically identical daughter cells

Budding

A form of asexual reproduction in which single-celled and some multicellular organisms develop small growths or buds that develop into new genetically identical organisms

Fragmentation

A form of asexual reproduction in which the body of a multicellular organism divides into many parts containing genetically identical cells

Vegetative reproduction

A form of asexual reproduction in which a plant undergoes fragmentation to form another genetically identical plant

Spore

A reproductive cell produced by bacteria, fungi, mosses and ferns, capable of developing into a new organism without fusing with another reproductive cell

Parthenogenesis

A form of asexual reproduction in which a female animal reproduces without fertilisation of an egg by a male

Clone

A cell or organism that is genetically identical to the parent

Sexual reproduction

A mode of reproduction that involves a haploid female gamete fusing with a haploid male gamete

Enucleate

To remove the nucleus from a cell

Genetic diversity

The variation of genes within a species

Species

A taxonomic group, allocated two names; only members of the same species can produce fertile offspring when mating under natural conditions

Gene pool

All the alleles that exist for all the genes within an interbreeding population

Population

The number of individuals of a species living in a particular place at a particular time

Tolerance range

The range of conditions in which an organism can survive

Optimum range

The range of a conditions in which an organism carry out life processes at an optimal level

Adaptation

A characteristic that enhances an organism’s survival within an environment

Structural adaptation

A physical characteristic of body size and shape that increases an organism’s chances of survival and reproduction

Xerophyte

A plant suited to living in hot, dry environments that is generally drought tolerant

Behavioural adaptation

A behaviour that increases an animal’s chances of survival and reproduction

Plant response

A plant movement that increases its chances of survival

Tropism

A directional movement of a plant towards or away from an environmental factor

Auxin

A hormone responsible for phototropism in plants

Nastic response

A non-directional movement of plants

Physiological adaptation

A function adaptation that increases an organism’s chances of survival

Ecosystem

A community of interacting organisms and the physical factors that surround them

Community

All the species that occupy a specific place at a specific time

Density

The average number of individual organisms living in a population in a given area

Carrying capacity

The total population that can be supported by an environment

Distribution

The way in which members of a population are dispersed in a specific area