Genetics

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chromosome

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a structure that transfers hereditary information to the next generation.

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gene

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the basic unit of heredity carried by the chromosomes; code for features of organisms.

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allele

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variations of genes that determine traits in organisms; the two corresponding alleles on two
paired chromosomes constitute a gene.

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genotype

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an organism’s particular combination of paired alleles.

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phenotype

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the traits produced by the genotype; the expression of the genes.

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heterozygous

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a gene composed of two different alleles ( a dominant and a recessive).

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homozygous

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a gene composed of two identical alleles (e.g., both dominant or both
recessive).

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Punnett square

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the square is a grid, with alleles of one parent on top and the other parent’s
alleles on the side. A simple and useful technique for prediction the characteristics of
offspring when the dominant and recessive traits of the parents are known.

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dominant allele

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a form of a gene that is expressed as the trait when a dominant allele is present.

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recessive allele

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a form of the gene that is expressed as the trait only when a dominant allele is
not present.

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homozygous dominant

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identical dominant alleles are paired together example AA

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homozygous recessive

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identical recessive alleles are paired together example aa

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heterozygous

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one dominant and one recessive allele are paired together example Aa

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meiosis

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the process that occurs in the formation of sex cells (sperm and egg) by which the number of chromosomes is reduced by half

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gamete

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a sex cell (sperm or egg) that contains half the chromosome number of a normal cell.

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fertilization

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the joining of a sperm cell and an egg cell

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zygote

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the cell formed when a sperm cell and an egg cell join together during fertilization, it contains the full number of chromosomes

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DNA

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a complex molecule that contains the genetic information that codes for a particular trait or protein.

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structure of DNA

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DNA is made of phosphates, sugars and nitrogen bases. Phosphates and sugars make the rail of the ladder and the nitrogen bases make up the rungs of the ladder.

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4 nitrogen bases

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adenine, thymine, guanine, and cytosine. They always pair up A with T and C with G

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probability

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a number that describes how likely it is that an event will occur

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hybrid

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an organism that has two different alleles for a trait; an organism that is heterozygous for a particular trait

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purebred

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the offspring of many generations that have the same traits

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trait

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a characteristic that an organism can pass on to its offspring through its genes

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heredity

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the passing of traits from parents to offspring

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genetics

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the scientific study of heredity

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codominance

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a condition in which neither of two alleles of a gene is dominant or recessive

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messenger RNA

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RNA that copies the doded message from DNA in the nucleus and carries the message into the cytoplasm

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transfer RNA

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RNA in the cytoplasm that carries an amino acid to the ribosome and adds it to the growing protein chain

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multiple alleles

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three or more forms of a gene that code for a single trait

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sex chromosomes

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a pair of chromosomes carrying genes that determine whether a person is male or female

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sex-linked gene

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a gene that is carried on the X or Y chromosome

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carrier

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a person who has one recessive allele for a trait, but does not have the trait

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selective breeding

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the process of selecting a few organisms with desired traits to serve as parents of the next generation

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inbreeding

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a selective breeding method in which two individuals or similar sets of alleles are crossed

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hybridization

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a selective breeding method in which two genetically different individuals are crossed

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clone

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an organism that is genetically identical to the organism from which it was produced

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genetic engineering

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the transfer of a gene from the DNA of one organism into another, in order to produce an organism with desired traits

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gene therapy

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the insertion of working copies of a gene into the cells of a person with a genetic disorder in an attempt to correct the disorder

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genome

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all of the DNA in one cell of an organism

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adaptation

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a trait that helps an organism survive and reproduce

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evolution

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the gradual change in a species over time

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natural selection

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the process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species

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variation

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any difference between individuals of the same species