Biology Terms

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DNA

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DNA is a double helix molecule made up of a large number of nucleotides and contains the genetic instructions used in the development proteins.

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Chromosomes

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Chromosomes are thread like structures found in the nucleus of a cell and are composed of DNA and protein.

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Gene

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A gene is a length of DNA that codes for a specific protein which determines particular traits. (e.g eye color)

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Allele

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An allele is an alternative form of a gene that has a slightly different sequence of bases so produces a slightly different protein. This results in a different trait for a characteristic

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Genotype

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A genotype is the genetic information on the two alleles present.

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Phenotype

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The phenotype is the physical observable expression of the two alleles

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Dominant

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The dominant allele is always expressed in the phenotype if it occurs in the genotype. It masks the presence of the recessive allele

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Recessive

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The recessive allele is only expressed in the phenotype if both recessive alleles are present in the genotype.

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Meiosis

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Meiosis is a type of cell division for the production of gametes. It produces 4 new gametes that are genetically different to each other and to the parent cell. They contain half the number of chromosomes that are in the parent cell.

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Independent Assrotment

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When homologous pairs of chromosomes line up during meiosis, they do so randomly. This means it is completely random which combinations of alleles end up in which particular gamete.

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Crossing over

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This occurs when homologous pairs of chromosomes line up at the cell equator and swap sections of genetic material. Because of crossing over, each gamete will contain different combinations of alleles.

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Variation in fertilistaion

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When the male and female gametes come together and the egg is fertilized, there is 50% probability of each gender. The sex of the child is determined by whether it is the X or Y chromosome that fertilizes the egg.

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Genetic Varation

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Is the variety within a population because different alleles are possible for each gene that controls a particular characteristic. Variation within a population allows some individuals to survive when the environment changes. Those with favorable alleles will be able to survive.

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Mutation

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A change in the base sequence in the DNA. They can change an allele or create a new one. Somatic cells are not passed on to offspring as they are not inherited. Gametes can.