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Module 13 in the Syllabus

Mendelian Genetics Images
Image gallery for study with links to larger teaching JPEGs for classroom presentation

Question Drill for Mendelian Genetics
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Conceptual Vocabulary
AlleleAn allele is a viable DNA coding that occupies a given locus on a chromosome.
GenotypeThe genotype describes the genetic constitution of an individual, that is the specific allelic makeup of an individual, usually with reference to a specific character under consideration.
PhenotypeThe phenotype describes the ourward physical appearance or manifestation of a trait in an organism, as opposed to its genotype.
Gregor MendelGregor Mendel (1822 - 1884) was an Austrian Augustinian priest and scientist often called the father of modern genetics for his study of the inheritance of traits in pea plants.
LocusA locus is a fixed position on a chromosome.
Dominance relationshipA dominance relationship refers to how the alleles for a locus interact to produce a phenotype.
Punnett squareThe Punnett square is a diagram used by biologists to determine the probability of an offspring having a particular genotype.
Dihybrid crossA dihybrid cross is a cross between two individuals identically heterozygous at two loci.
Monohybrid crossA monohybrid cross is a cross between individuals who are identically heterozygous at one locus.
Pedigree chartA pedigree chart is a chart which shows the known phenotypes for an organism and its ancestors.
Test crossA test cross crosses a homozygous recessive with an individual with an unknown genotype.
TraitA trait is a distinct phenotypic character of an organism that may be inherited, environmentally determined or somewhere in between.
Wild typeThe wild type is the typical form of an organism, strain, gene, or characteristic as it occurs in nature.
F1 hybridF1 hybrid is a term used in genetics and selective breeding to describe the first filial generation offspring resulting from a cross mating of distinctly different parental types.
Genetic linkageGenetic linkage occurs when particular genetic loci or alleles for genes are inherited jointly because the loci are on the same chromosome and thus tend to segregate together during meiosis.
AutosomeAn autosome is a non-sex chromosome.
Sex linkageSex linkage is the phenotypic expression of an allele that is related to the gender of the individual and is found on the sex chromosomes.
XY sex-determination systemThe XY sex-determination system is the sex-determination system found in humans, most other mammals, and some insects.
HeritabilityHeritability is the proportion of phenotypic variation in a population that is attributable to genetic variation among individuals.
ZygosityZygosity describes the similarity or dissimilarity of DNA between homologous chromosomes at a specific allelic position or gene.
PheneA phene is an individual characteristic or trait which can be possessed by an organism, such as eye colour or height, or any other observable characteristic.
Complete linkageComplete linkage is defined as the state in which two loci are so close together that alleles of these loci are virtually never separated by crossing over.
True breeding organismA true breeding organism is an organism having certain biological traits which are passed on to all subsequent generations when bred with another organism of the same type for the same traits.
Barr bodyA Barr body is the inactive X chromosome in a female cell.
PenetrancePenetrance is a term used in genetics describing the proportion of individuals carrying a particular variation of a gene that also express the particular trait.
Norms of reactionA norm of reaction describes the pattern of phenotypic expression of a single genotype across a range of environments.
PleiotropyPleiotropy occurs when a single gene influences multiple phenotypic traits.
PhenomeA phenome is the set of all phenotypes expressed by a cell, tissue, organ, organism, or species.
ComplementationComplementation refers to a relationship between two different strains of an organism which both have homozygous recessive mutations that produce the same phenotype.
Identity by typeAlleles have identity by type if they have the same phenotypic effect.
X-inactivationX-inactivation (also called lyonization) is a process by which one of the two copies of the X chromosome present in female mammals is inactivated.
Polygenic inheritancePolygenic inheritance, also known as quantitative or multifactorial inheritance refers to inheritance of a phenotypic characteristic that is attributable to two or more genes and their interaction with the environment.
HaplogroupA haplogroup is a large group of haplotypes, which are series of alleles at specific locations on a chromosome.
HaplotypeA haplotype is a combination of alleles at multiple linked loci that are transmitted together.
HeterosisThe term heterosis, also known as hybrid vigor or outbreeding enhancement, describes the increased strength of different characteristics in hybrids.
Advanced terms that may appear in context in MCAT passages
HaploinsufficiencyHaploinsufficiency occurs when a diploid organism only has a single functional copy of a gene and the single functional copy of the gene does not produce enough of a gene product to bring about a wild-type condition.
Null alleleA null allele is a mutant copy of a gene that completely lacks that gene's normal function.
Quantitative trait locusQuantitative trait loci are stretches of DNA that are closely linked to the genes that underlie a trait in question.
CanalizationCanalization is a measure of the ability of a genotype to produce the same phenotype regardless of variability of its environment.
Hypostatic geneA hypostatic gene is one whose phenotype is masked by the expression of an allele at a separate locus, in an epistasis event.
Malecot's method of coancestryMalecot's coancestry coefficient refers to an indirect measure of genetic similarity of two individuals.
OusiotypeOusiotype is a term defined in segregation analysis to describe whether a phenotype is due to common factors, rare or both.
X0 sex-determination systemThe X0 sex-determination system is a system that grasshoppers, crickets, roaches, and some other insects use to determine the sex of their offspring.
ZW sex-determination systemThe ZW sex-determination system is a system that birds, some fish, and some insects (including butterflies and moths) use to determine the sex of their offspring.
Haplodiploid sex-determination systemThe haplodiploid sex-determination system determines the sex of the offspring of many Hymenopterans (bees, ants, and wasps), and coleopterans (bark beetles).

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