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Biology

heredity

the passing of characteristics from parent to offspring

genetics

the branch of Biology that focuses on heredity

monohybrid cross

a cross that involves 1 pair of contrasting traits (eg: crossing purple flowers with white flowers)

true-breeding

describes organisms or genotypes that are homozygous for a specific trait and thus always produce offspring that have the same phenotype for that trait

p generation

parent generation; the first two individuals that are crossed in a breeding experiment

F1 generation

the offspring of the P generation; filial generation

F2 generation

the offspring of the F1 generation; the second filial generation

allele

one of the alternative forms of a gene that governs a characteristic (eg: hair color)

dominant

Genetic trait that is expressed when its allele is homozygous or heterozygous

recessive

an allele for a trait that will be masked unless the organism is homozygous for this trait

homozygous

when two alleles of a particular gene present in an individual are the same

heterozygous

when two alleles of a particular gene present in an individual are the different

genotype

an organism's genetic makeup, or allele combinations

phenotype

an organism's physical appearance, or visible traits

law of segregation

Mendel's law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete

law of independent assortment

Mendelian principle stating that genes for different traits are inherited independently of each other

Punnett square

a diagram that predicts the outcome of a genetic cross by considering all possible combinations of gametes

test cross

the crossing of an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype

probability

the likelyhood that a possible future event will occur in any given instance of the event; the mathematical ratio of the number of times one outcome of any event is likely to occur to the number of possible outcomes of the event

pedigree

a diagram that shows the occurance of a genetic trait in several generations of a family

sex-linked gene

a trait that is determined by a gene found on one of the sex chromosomes, such as the X chromosome or the Y chromosome in humans

polygenic inheritance

a characteristic of an organism that is determined by many genes

incomplete dominance

a condition in which a trait in an individual is intermediate between the phenotype of the individual's two parents because the dominant allele is unable to express itself fully

multiple alleles

more than two alleles (versions of the gene) for a genetic trait

codominance

a condition in which both alleles for a gene are fully expressed

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