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64 terms

Genetics Chapter 2

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allele
one of the different forms of a gene that can exist at a single locus
ascus
in a fungus, a sac that encloses a tetrad or an octad of ascospores
bivalent
homologous chromosomes paired at meiosis
character
an attribute of individual members of a species for which various heritable differences can be defined
chromatid
one of the two side-by-side replicas produced by chromosome division
cross
the deliberate mating of two parental types of organisms in genetic analysis
dimorphism
a polymorphism with only two forms
dioecious species
a plant species in which male and famale organs are on separate plants
dominant
the phenotype shown by a heterozygote
dyad
a pair of sister chromatids joined at the centromere, as in the first division of meiosis
first filial generation
produced by crossing two parental lines
forward genetics
the classical approach to genetic analysis, in which genes are first identified by mutant alleles and mutant phenotypes and later cloned and subjected to molecular analysis
gene
the fundamental physical and functional unit of heredity, which carries information from one generation to the next; a segment of DNA composed of a transcribed region and a regulatory sequence that makes transcription possible
gene discovery
the process whereby geneticists find a set of genes affecting some biological process of interest by the single-gene inheritance patterns of their mutant alleles or by genomic analysis
genetic dissection
the use of recombination and mutation to piece together the various components of a given biological function
genotype
the allelic composition of an individual or of a cell-either of the entire genome or, more commonly, of a certain gene or let of genes
haploid number
the number of chromosomes in the basic genomic set of a species
haploinsufficient
describes a gene in which a null mutant allele will be dominant because, in a heterozygote, the single wild-type allele cannot provide enough product from normal function
haplosufficient
describes a gene that, in a diploid cell, can promote wild-type function in only one copy (dose)
hemizygous
a gene present in only one copy in a diploid organism- for example, an X-linked gene in a male mammal
heterogametic sex
the sex that has heteromorphic sex chromosomes (e.g. XY) and hence produces two different kinds of gametes with respect to the sex chromosomes
heterozygote
an individual organism having a heterozygous gene pair
homogametic sex
the sex with homologous sex chromosomes (e.g. XX)
homozygote
an individual organism that is homozygous
homozygous dominant
refers to a genotype such as A/A
homozygous recessive
refers to a genotype such as a/a
law of equal segregation (Mandel's first law)
the production of equal numbers (50%) of each allele in the meiotic products (e.g. gametes) of a heterozygous meiocyte
leaky mutation
a mutation that confers a mutant phenotype but still retains a low but detectable level of wild-type function
meiocyte
a cell in which meiosis takes place
meiosis
two successive nuclear divisions (with corresponding cell divisions) that produce gametes (in animals) or sexual spores (in plants and fungi) that have one-half of the genetic material of the original cell
mitosis
a type of nuclear division (occurring at cell division) that produces two daughter nuclei identical with the parent nucleus
molecular markers
a site of DNA heterozygosity, not necessarily associated with phenotypic variation, used as a tag for a particular chromosomal locus
monohybrid
a single-locus heterozygote of the type A/a
monohybrid cross
a cross between two individuals identically heterozygous at one gene pair- for example, A/a x A/a
morph
one form of a genetic polymorphism; the morph can be either a phenotype or a molecular sequence
mutant
an organism or cell carrying a mutation
mutation
the process that produces a gene or a chromosome set differing from that of the wild type. or. the gene or chromosome set that results from such a process
null allele
an allele whose effect is the absence either of normal gene product at the molecular level or of normal function at the phenotypic level
parental generation
the two strands or individual organisms that constitute the start of a genetic breeding experiment; their progeny constitute the F1 generation
pedigree analysis
deducing single-gene inheritance of human phenotypes by a study of the progeny of matings within a family, often stretching back several generations
phenotype
the form taken by some character (or group of characters) in a specific individual. or. the detectable outward manifestations of a specific genotype
polymorphism
the occurrence in a population (or among populations) of several phenotypic forms associated with alleles of one gene or homologs of one chromosome
product of meiosis
one of the (usually four) cells formed by the two meiotic divisions
product rule
the probability of two independent events both occurring is the product of their individual probabilities
property
a characteristic feature of an organism, such as size, color, shape, or enzyme activity
propositus
in a human pedigree, the person who first came to the attention of the geneticist
pseudoautosomal regions 1 and 2
small regions at the ends of the X and Y sex chromosomes; they are homologous and undergo pairing and crossing over at meiosis
pure line
a population of individuals all bearing the identical fully homozygous genotype
reverse genetics
an experimental procedure that begins with a cloned segment of DNA or a protein sequence and uses it (through directed mutagenesis) to introduce programmed mutations back into the genome to investigate function
second filial generation
the progeny of a cross between two individuals from the F1 generation
self
to fertilize eggs with sperms from the same individual
sex chromosome
a chromosome whose presence or absence is correlated with the sex of the bearer; a chromosome that plays a role in sex determination
sex linkage
the location of a gene on a sex chromosome
SRY gene
the maleness gene, residing on the Y chromosome
testcross
a cross of an individual organism of unknown genotype or a heterozygote (or a multiple heterozygote) with a tester
tester
an individual organism homozygous for one or more recessive alleles; used in a testcross
tetrad
four homologous chromatids in a bundle in the first meiotic prophase and metaphase. or. the four haploid product cells from a single meiosis
trait
more or less synonymous with phenotype
wild type
the genotype or phenotype that is found in nature or in the standard laboratory stock for a given organism
X chromosome
one of a pair of sex chromosomes, distinguished from the Y chromosome
X linkage
the inheritance pattern of genes found on the Y chromosome but not on the X chromosome (rare)
Y chromosome
one of a pair of sex chromosomes, distinguished from the X chromosome
Y linkage
the inheritance pattern of genes found on the Y chromosome but not on the X chromosome (rare)
zygote
a cell formed by the fusion of an egg and a sperm; the unique diploid cell that will divide mitotically to create a differentiated diploid organism