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Genetics
genes and alleles chapters 12-14
29
Biology
9th Grade
02/07/2012

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Term
codominance
Definition
when alleles are neither dominant nor recessive to one another, and both traits of the allels are expressed, but not in a blending pattern
Term
continuous variation
Definition
when a gene that codes for a certain trait is modified by other genes, this results in the phenotypes that are expressed falling within a continuous range between two extremes
Term
dihybrid cross
Definition
examines the effects of crossing two genes with two alleles each
Term
epistasis
Definition
the condition where one or more genes which do not code for a trait affect the expression of the trait
Term
incomplete dominance
Definition
inheritance patterns that occur when there are no forms if the gene that are dominant. The resulting phenotype is a blend of the allele phenotypes
Term
modifier genes
Definition
genes that modify the way a trait is expressed and are responsible for epistasis
Term
monohybrid cross
Definition
crossing organisims that differ in only one allele that has two different forms
Term
multiple alleles
Definition
three or more alleles that code for the some trait within a population 
Term
sex-linked
Definition
genetic traits the are transmitted from parent to offspring by the sex chromosomes
Term
allele
Definition
an alternate form of the same gene that codes for a slightly different trait than another allele.
Term
characteristics
Definition
inheritable features such as skin color, height, flower color, etc.
Term
cross pollination
Definition
taking pollen from one flower and pollinating another plant with it
Term
dominant allele
Definition
a form of a gene whose trait is always expressed
Term
gene segregation
Definition
the fact that when gametes are formed, the two alleles that code for the same trait separate from one another
Term
genome
Definition
the entire sequence or content of DNA in an organism
Term
heterozygous
Definition
the condition where and organism has two different alleles for the same trait
Term
homozygous
Definition
the condition where an organism has the same two alleles for a trait
Term
homozygous dominant
Definition
where both the alleles for a given trait are dominant
Term
homozygous recessive
Definition
where both the alleles for a given trait are recessive. This is the only way a recesive trait can be expressed
Term
phenotype
Definition
the expression of the genotype
Term
genotype
Definition
the DNA makeup in an organism
Term
albinism
Definition
a type of mutation that makes an animal unable to produce pigments of the skin, hair, and eyes
Term
Down's Syndrome
Definition
DNA mutation caused ny nondisjunction of chromosome 21 during meiosis I.
Term
Duplication Mutation
Definition
when  a piece of broken-off chromosome inserts into the homologous chromosome. This results in two copies or the same segment within the same chromosome
Term
Frame-shift mutation
Definition
a change in DNA sequence resulting in the DNA polymerase reading codons incorrectly
Term
inversion mutation
Definition
when a broken off segment of DNA reattaches at the end of the chromosome, or within the chromosome, but in reverse order
Term
missense mutation 
Definition
the term used when a substitute  mutation causes an incorrect amino acid to be inserted into the protien
Term
mutagens
Definition
environmental conditions which can cause changes in the normal DNA structure
Term
nondisjunction
Definition
when homologous chromosomes do not separate during metaphase I of meiosis
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