Alleles |
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The
different forms of a gene. Y and y are different alleles of the gene that
determines seed color. Alleles occupy the same locus, or position, on
chromosomes. |
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Autosomal |
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A
locus on any chromosome but a sex chromosome. Not sex-linked. |
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Co-Dominant Alleles |
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Two
different alleles at a locus are responsible for different phenotypes, and both
alleles affect the phenotype of the heterozygote. |
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Complete Linkage |
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Complete
linkage describes the inheritance patterns for 2 genes on the same chromosome
when the observed frequency for crossover between the loci is zero. |
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Crossing Over |
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Exchange
of genetic material between non-sister chromatids from homologous chromosome
during prophase I of meiosis; results in new allele combinations |
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Dioecious |
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Organisms
produce only one type of gamete; i.e. humans |
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Diploid |
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Cell
with two of each kind of chromosome; is said to contain a diploid, or 2n,
number of chromosomes |
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Dominant Trait |
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cell
with two of each kind of chromosome; is said to contain a diploid, or 2n,
number of chromosomes |
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Egg |
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haploid female sex cell produced by meiosis |
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Epistasis |
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One
gene masks the expression of a different gene for a different trait. |
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F1 Generation |
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Offspring
of a cross between true breeding plants, homozygous for the trait of interest |
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F2 Generation |
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Offspring
of a cross involving the F1 generation. |
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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, sperm and eggs |
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Genetic Recombination |
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major
source of genetic variation among 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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The genetic constitution of an organism with
respect to a trait. |
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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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Hemizygous |
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If
there is only one copy of a gene for a particular trait In a diploid organism,
the organism is hemizygous for the trait, and will display a recessive
phenotype. X-linked genes in fly or human males are hemizygous. |
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Hereditary |
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passing
on of characteristics from parents to offspring |
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Heterozygous |
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Differing
alleles for a trait in an individual, such as Yy. |
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Homologous Chromosomes |
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The
pair of chromosomes in a diploid individual that have the same overall genetic
content. One member of each homologous pair of chromosomes in inherited from
each parent. |
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Homozygous |
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Both
alleles for a trait are the same in an individual. They can be homozygous
dominant (YY), or homozygous recessive (yy). |
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Hybrid |
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heterozygous;
usually referring to the offspring of two true-breeding (homozygous)
individuals differing in the traits of interest. |
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Incomplete Dominance |
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Intermediate phenotype in F1, parental phenotypes reappear in F2. |
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Lethal Alleles |
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Mutated genes that are
capable of causing death. |
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Linkage |
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genes that are inherited
together on the same chromosome. Three inheritance patterns are possible:
non-linkage, Partial linkage, and complete linkage. |
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Meiosis |
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type of cell division where
one body cell produces for gametes, each containing half the number of
chromosomes in a parent’s body. |
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Mendel's Law of Independent Assortment |
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Alleles of different genes
are assorted independently of one another during the formation of gametes. |
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Mendel's Law of Segregation |
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Alleles segregate from one
another during the formation of gametes. |
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Monoecious |
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Organisms produce both male and female gametes; i.e. garden pea. |
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Monohybrid Cross |
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Cross involving parents
differing in only one trait. |
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Mutation |
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Change in the DNA sequence
of a gene to some new, heritable form. Generally, but now always a recessive
allele. |
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Non-Disjunction |
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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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Non-Linkage |
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Non-linkage describes the inheritance patterns for 2 genes on the same
chromosome, when the expected frequency for crossover between the loci is at
least one. |
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Partial Linkage |
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Partial linkage describes one of the inheritance patterns for 2 genes on
the same chromosome, when the expected frequency for crossover between the loci
is greater than zero but less than one. |
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Phenotype |
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The physical appearance of an organism with respect to a trait, i.e.
yellow (Y) or green (y) seeds in garden peas. |
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Pleiotropic |
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A single gene determines
more than one phenotype for an organism. |
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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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The condition in which an organism has
extra sets of chromosomes |
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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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Punnet Square |
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A chart that shows the possible
combinations of alleles that result from a genetic cross. |
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Purebred |
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The offspring of many generations that
have the same traits. |
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Recessive Trait |
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The opposite of dominant. A
trait that is preferentially masked. |
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Reciprocal Cross |
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Using male and female gametes for two different traits, alternating the source of gametes.
|
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Sex Chromosomes |
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Sex determination is based on sex chromosomes |
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Sex-Linked |
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A gene coded on a sex chromosome, such as the X-chromosome linked genes of flies and man.
|
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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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Test Cross |
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Generally a cross involving a homozygous recessive individual.
|
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Trait |
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characteristic that is inherited; can be either dominant or recessive |
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True-Breeding |
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Homozygous for the
true-breeding trait. |
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Wild-Type Allele |
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The non-mutant form of a
gene, encoding the normal genetic function. Generally, but not always a
dominant allele. |
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Zygote |
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diploid cell formed when a
sperm fertilizes an egg. |
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