Studied by 1 personchromosome theory of inheritance
A basic principle in biology stating that genes are located at specific positions (loci) on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns.
heredity
The transmission of traits from one generation to the next.
wild type
The phenotype most commonly observed in natural populations; also refers to the individual with that phenotype.
variation
Differences between members of the same species.
Mutant phenotype
A trait that is alternative to the wild type due to alleles assumed to have originated as changes, or mutations, in the wild-type allele.
Genetics
The scientific study of heredity and hereditary variation.
sex-linked gene
A gene located on either sex chromosome. Most are on the X chromosome and show distinctive patterns of inheritance; there are very few genes on the Y chromosome.
gene
A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses).
x-linked gene
A gene located on the X chromosome; such genes show a distinctive pattern of inheritance.
gamate
A haploid reproductive cell, such as an egg or sperm. Unite during sexual reproduction to produce a diploid zygote.
somatic cell
Any cell in a multicellular organism except a sperm or egg or their precursors.
locus
A specific place along the length of a chromosome where a given gene is located.
hemophilia
A human genetic disease caused by a sex-linked recessive allele, resulting in the absence of one or more blood-clotting proteins; characterized by excessive bleeding following injury.
barr body
A dense object lying along the inside of the nuclear envelope in cells of female mammals, representing a highly condensed, inactive X chromosome
asexual reproduction
The generation of offspring from a single parent that occurs without the fusion of gametes (by budding, division of a single cell, or division of the entire organism into two or more parts). In most cases, the offspring are genetically identical to the parent.
linked genes
Linked genes are genes located on the same chromosome and tend to be inherited together. They do not assort independently during meiosis
clones
A lineage of genetically identical individual cells.
genetic recombination
General term for the production of offspring with combinations of traits that differ from those found in either parent.
sexual reproduction
A type of reproduction in which two parents give rise to offspring that have unique combinations of genes inherited from both parents via the gametes.
parental type
An offspring with a phenotype that matches on e of the true-breeding parental (P generation) phenotypes; also refers to the phenotype itself.
life cycle
The generation-to-generation sequence of stages in the reproductive history of an organism.
recombinant
The generation-to-generation sequence of stages in the reproductive history of an organism.
karyotype
A display of the chromosome pairs of a cell arranged by size and shape.
crossing over
The reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis.
homoglous chromosome
A pair of chromosomes of the same length, centromere position, and staining pattern that posses genes for the same characters at corresponding loci. One is inherited from each parent.
genetic map
An ordered list of genetic loci (genes or other genetic markers) along a chromosome.
sex chromosome
A chromosome responsible for determining the sex of an individual.
linakge map
A genetic map based on the frequencies of recombination between markers during crossing over of homologous chromosomes.
autocome
A chromosome that is not directly involved in determining sex; not a sec chromosome.
map unit
A unit of measurement of the distance between genes. One unit is equivalent to a 1% recombination frequency.
diploid cell
A cell containing two sets of chromosomes (2n), one ser inherited from each parent.
cytogenic map
A map of a chromosome that locates genes with respect to chromosomal features distinguishable in a microscope.
haploid cell
A cell containing only one set of chromosomes (n)..
nondisjunction
An error in meiosis or mitosis in which members of a pair of homologous chromosomes or sister chromatids fail to separate properly from each other.
fertilization
The union of haploid gametes to produce a diploid zygote.
aneuploidy
A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number.
zygote
The diploid cell produced by the union of haploid gametes during fertilization; a fertilized egg.
meiosis
A modified type of cell division in sexually reproducing organisms consisting of two rounds of cell division but only one round of DNA replication. It results in cells with half the number of chromosome sets as the original cell.
monosomic
Referring to a diploid cell that has only one copy of a particular chromosome instead of the normal two.
trisomic
Referring to a diploid cell that has three copies of a particular chromosome instead of the normal two.
alternation of generation
A life cycle in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants and some algae.
polyploidy
A chromosomal alteration in which the organism possesses more than two complete chromosome sets. It is the result of an accident of cell division.
sporophyte
The multicellular diploid stage of the plant life cycle.
triploidy
3 chromosome sets
spores
Haploid cells produced by meiosis in the sporophyte of plants.
gametoype
The multicellular haploid stage of the plant life cycle.
deletion
A deficiency in a chromosome resulting from the loss of a fragment through breakage.
Meiosis I
The first division of a two-stage process of cell division in sexually reproducing organisms that results in cells with half the number of chromosome sets as the original cell.
duplication
An aberration in chromosome structure due to fusion with a fragment from a homologous chromosome, such that a portion of a chromosome is duplicated.
Meiosis II
The second division of a two-stage process of cell division in sexually reproducing organisms that results in cells with half the number of chromosome sets as the original cell.
inversion
The second division of a two-stage process of cell division in sexually reproducing organisms that results in cells with half the number of chromosome sets as the original cell.
allele
Different versions of a gene.
translocation
An aberration in chromosome structure resulting from attachment of a chromosomal fragment to a nonhomologous chromosome.
synaptonemal complex
A zipper-like protein complex that physically connects paired homologs along their length during prophase I of meiosis.
syndrome
a set of traits
synapsis
The pairing and physical connection of duplicated homologous chromosomes during prophase I of meiosis.
crossing over
The reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis.
character
An observable heritable feature that may vary among individuals.
chiasma
The X-shaped, microscopically visible region where crossing over has occurred earlier in prophase I between homologous nonsister chromatids. Become visible after synapsis ends, with the two homologs remaining associated due to sister chromatid cohesion.
trait
One of two or more detectable variants in a genetic character.
reductional division
A phrase for meiosis I because it halves the number of chromosome sets per cell - a reduction from two sets (the diploid state) to one set (the haploid state).
true-breeding
Referring to organisms that produce offspring of the same variety over many generations of self-pollination.
independent assortment
The arrangement of each pair of homologous chromosomes at the metaphase plate at meiosis I, in which each pair is positioned independently of the other pairs, and thus the first meiotic division results in each pair sorting its maternal and paternal homologs into daughter cells independently of every other pair.
hybridization
In genetics, the mating, or crossing, of two true-breeding varieties.
recombinant chromosome
A chromosome created when crossing over combines DNA from two parents into a single chromosome.
p generation
The true-breeding (homozygous) parent individuals from which F1 hybrid offspring are derived in studies of inheritance.
F1 genertion
The first filial, hybrid (heterozygous) offspring arising from a parental (P generation) cross.
F2 generation
The offspring resulting from interbreeding (or self-pollination) of the hybrid F1 generation.
allele
Any of the alternative versions of a gene that may produce distinguishable phenotypic effects.
dominant allele
An allele that is fully expressed in the phenotype of a heterozygote.
recessive allele
An allele whose phenotypic effect is not observed in a heterozygote.
law of segregation
Mendel's first law, stating that the two alleles in a pair segregate (separate from each other) into different gametes during gamete formation.
Punnett square
A diagram used in the study of inheritance to show the predicted genotypic results of random fertilization in genetic crosses between individuals of known genotype.
homozygous
Having two identical alleles for a given gene.
heterozygous
Having two identical alleles for a given gene.
phenotype
The observable physical and physiological traits of an organism, which are determined by its genetic makeup.
Genotype
The genetic makeup, or set of alleles, of an organism.
Testcross
Breeding an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype. The ratio of phenotypes in the offspring reveals the unknown genotype.
monohybrid
An organism that is heterozygous with respect to a single gene of interest. All the offspring from a cross between parents homozygous for different alleles.
monohybrid cross
A cross between two organisms that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant).
dihybrid
An organism that is heterozygous with respect to two genes of interest. All the offspring from a cross between parents doubly homozygous for different alleles.
dihybrid cross
A cross between two organisms that are each heterozygous for both of the characters being followed (or the self-pollination of a plant that is heterozygous for both characters).
law of independent assortment
Mendel's second law, stating that each pair of alleles segregates, or assorts, independently of each other pair during gamete formation; applies when genes for two characters are located on different pairs of homologous chromosomes or when they are far enough apart on the same chromosome to behave as though they are on different chromosomes.
multiplication rule
A rule of probability stating that the probability of two or more independent events occurring together can be determined by multiplying their individual probabilities.
additional rule
A rule of probability stating that the probability of any one of two or more mutually exclusive events occurring can be determined by adding their individual probabilities.
mutually exclusive
In logic and probability theory, two propositions (or events) cannot both be true (occur). An example are the two outcomes of a single coin toss, which can result in either heads or tails, but not both.
complete dominance
The situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.
incomplete dominance
The situation in which the phenotype of heterozygotes is intermediate between the phenotypes on individuals homozygous for either allele.
codominance
The situation in which the phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways.
Tay-Sachs disease
A human genetic disease caused by a recessive allele for a dysfunctional enzyme, leading to accumulation of certain lipids in the brain.
pleiotropy
The ability of a single gene to have multiple effects.
epistasis
A type of gene interaction in which the phenotypic expression of one gene alters that of another independently inherited gene.
quantitative character
A heritable feature that varies continuously over a range rather than in an either-or fashion.
polygenic inheritance
An additive effect of two or more genes on a single phenotypic character.
multifactorial
Referring to a phenotypic character that is influenced by multiple genes and environmental factors.
carrier
In genetics, an individual who is heterozygous at a given genetic locus for a recessively inherited disorder. The heterozygote is generally phenotypically normal for the disorder but can pass on the recessive allele to offspring.
cystic fibrosis
A human genetic disorder caused by a recessive allele for a chloride channel protein; characterized by an excessive secretion of mucus and consequently vulnerability to infection; fatal if untreated.
sickle-cell disease
A recessively inherited human blood disorder in which a single nucleotide change in the beta-globin gene causes hemoglobin to aggregate, changing red blood cell shape and causing multiple symptoms in afflicted individuals.
Huntington's disease
A human genetic disease caused by a dominant allele; characterized by uncontrollable body movements and degeneration of the nervous system; usually fatal 10 to 20 years after the onset of symptoms.
homozygote
An organism that has a pair of identical alleles for a gene (encoding a character).
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