Genetics

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allele

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alternate forms of a gene for each variation of a trait of an organism

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chromosome

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threadlike structure in a cell that contains the genetic information

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codominance

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condition in which both alleles of a gene are expressed (results in both showing up)

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crossing over

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exchange of genetic material between non-sister chromatids from homologous chromosomes during prophase one of meiosis; results in new allele combinations

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diploid

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cell with two of each kind of chromosome; said to contain a diploid, or 2n, number of chromosomes

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dominant

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observed trait of an organism that mask the recessive form of a trait

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dihybrid cross

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a cross involving two different traits

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DNA

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a self-replicating material that serves as the main constituent of chromosomes, it is the carrier of genetic information

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egg

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haploid female sex cell produced by meiosis

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fertilization

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fusion of male and female gametes

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gamete

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male and female sex cells (eggs and sperm)

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gene

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segment of DNA that codes for a particular protein

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genetic recombination

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major sours of genetic variation amount organisms caused by re-assortment or crossing over during meiosis

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genetics

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branch of biology that studies heredity

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genotype

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combination of genes in an organism

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haploid

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cell with one of each kind of chromosome; is said to contain a haploid or 'n' number of chromosomes

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heredity

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passing on of characteristics from parents to offspring

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heterozygous

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when there are two different alleles for a trait

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homologous chromosome

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paired chromosomes with genes from the same traits arranged in the same order

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homozygous

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when there are two identical alleles for a trait

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hybrid

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offspring formed by parents having different forms of a specific trait

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incomplete dominance

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inheritance in which neither allele is dominant over the other and a blending of traits occurs

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law of independent assortment

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

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law of segregation

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mendelian principle explaining that because each plant has two different alleles, it can produce two different types of gametes; during fertilization, male and female gametes randomly pair to produce four combinations of alleles

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meiosis

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type of a cell division where one body cell produces foor gametes, each containing half the number of chromosomes in a parents body

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monohybrid cross

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a cross involving only one trait

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nondisjunction

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failure of homologous chromosomes to separate properly during meiosis; results in gametes with too many or too few chromosomes

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phenotype

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outward or physical appearance of an organism, regardless of its genes

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pollination

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transfer of male pollen grains to the pistil of a flower

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polyploidy

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a condition in which an organism has extra sets of chromosomes (more common in plants than animals)

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recessive

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trait of an organism that can be masked by the dominant form of a trait

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sexual reproduction

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pattern of reproduction that involves the production of subsequent fusion of haploid cells

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sperm

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haploid male sex cells produced by meiosis

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trait

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characteristic that is inherited; can be either dominant or recessive

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zygote

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diploid cell formed when a sperm fertilizes an egg