Genetics Flashcards
(136 cards)
1
Q
chromosome theory of inheritance
A
A basic principle in biology stating that genes are located at specific positions (loci)
on chromosomes and that the behaviour of chromosomes during meiosis accounts
for inheritance patterns.
2
Q
wild type
A
The phenotype most commonly observed in natural populations; also refers to the individual with that phenotype
3
Q
sex-linked gene
A
A gene located on either sex chromosome. Most sex-linked genes are on the X chromosome and show distinctive patterns of inheritance; there are very few genes on the Y chromosome.
4
Q
X-linked gene
A
A gene located on the X chromosome; such genes show a distinctive pattern of inheritance.
5
Q
hemophilia
A
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.
6
Q
Barr body
A
A dense object lying along the inside of the nuclear envelope in cells of female mammals, representing a highly condensed, inactivated X chromosome
7
Q
linked genes
A
Genes located close enough together on a chromosome that they tend to be inherited together.
8
Q
genetic recombination
A
General term for the production of offspring with combinations of traits that differ from those found in either parent
9
Q
parental type
A
An offspring with a phenotype that matches one of the true-breeding parental (P generation) phenotypes; also refers to the phenotype itself.
10
Q
recombinant types (recombinants)
A
An offspring whose phenotype differs from that of the true-breeding P generation parents; also refers to the phenotype itself.
11
Q
crossing over
A
The reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis.
12
Q
genetic map
A
An ordered list of genetic loci (genes or other genetic markers) along a chromosome.
13
Q
linkage map
A
A genetic map based on the frequencies of recombination between markers during crossing over of homologous chromosomes.
14
Q
map unit
A
A unit of measurement of the distance between genes. One map unit is equivalent to a 1% recombination frequency.
15
Q
nondisjunction
A
An error in meiosis or mitosis in which members of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from each other.
16
Q
aneuploidy
A
A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number.
17
Q
monosomic
A
Referring to a diploid cell that has only one copy of a particular chromosome instead of the normal two
18
Q
trisomic
A
Referring to a diploid cell that has three copies of a particular chromosome instead of the normal two.
19
Q
polyploidy
A
A chromosomal alteration in which the organism possesses more than two complete chromosome sets. It is the result of an accident of cell division
20
Q
deletion
A
A deficiency in a chromosome resulting from the loss of a fragment through breakage. (2) A mutational loss of one or more nucleotide pairs from a gene.
21
Q
duplication
A
An aberration in chromosome structure due to fusion with a fragment from a homologous chromosome, such that a portion of a chromosome is duplicated.
22
Q
inversion
A
An aberration in chromosome structure resulting from reattachment of a chromosomal fragment in a reverse orientation to the chromosome from which it originated.
23
Q
translocation
A
(1) An aberration in chromosome structure resulting from attachment of a chromosomal fragment to a nonhomologous chromosome. (2) During protein synthesis, the third stage in the elongation cycle, when the RNA carrying the growing polypeptide moves from the A site to the P site on the ribosome. (3) The transport of organic nutrients in the phloem of vascular plants.
24
Q
Down syndrome
A
A human genetic disease usually caused by the presence of an extra chromosome 21; characterized by developmental delays and heart and other defects that are generally treatable or non-life-threatening.
25
genomic imprinting
A phenomenon in which expression of an allele in offspring depends on whether the allele is inherited from the male or female parent.
26
DNA replication
The process by which a DNA molecule is copied; also called DNA synthesis.
27
transformation
(1) The conversion of a normal animal cell to a cancerous cell. (2) A change in genotype and phenotype due to the assimilation of external DNA by a cell. When the external DNA is from a member of a different species, transformation results in horizontal gene transfer.
28
double helix
The form of native DNA, referring to its two adjacent antiparallel polynucleotide strands wound around an imaginary axis into a spiral shape.
29
antiparallel
Referring to the arrangement of the sugar-phosphate backbones in a DNA double helix (they run in opposite 5′ → 3′ directions).
30
semiconservative model
Type of DNA replication in which the replicated double helix consists of one old strand, derived from the parental molecule, and one newly made strand.
31
origins of replication
Site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides.
32
replication fork
A Y-shaped region on a replicating DNA molecule where the parental strands are being unwound and new strands are being synthesized.
33
helicase
An enzyme that untwists the double helix of DNA at replication forks, separating the two strands and making them available as template strands.
34
single-strand binding protein
A protein that binds to the unpaired DNA strands during DNA replication, stabilizing them and holding them apart while they serve as templates for the synthesis of complementary strands of DNA.
35
topoisomerase
A protein that breaks, swivels, and rejoins DNA strands. During DNA replication, topoisomerase helps to relieve strain in the double helix ahead of the replication fork.
36
primer
A short stretch of RNA with a free 3′ end, bound by complementary base pairing to the template strand and elongated with DNA nucleotides during DNA replication.
37
primase
An enzyme that joins RNA nucleotides to make a primer during DNA replication, using the parental DNA strand as a template.
38
DNA polymerase
An enzyme that catalyzes the elongation of new DNA (for example, at a replication fork) by the addition of nucleotides to the 3′ end of an existing chain. There are several different DNA polymerases; DNA polymerase III and DNA polymerase I play major roles in DNA replication in E. coli.
39
leading strand
The new complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory 5′ → 3′ direction.
40
lagging strand
A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5′ → 3′ direction away from the replication fork.
41
Okazaki fragment
A short segment of DNA synthesized away from the replication fork on a template strand during DNA replication. Many such segments are joined together to make up the lagging strand of newly synthesized DNA.
42
DNA ligase
A linking enzyme essential for DNA replication; catalyzes the covalent bonding of the 3′ end of one DNA fragment (such as an Okazaki fragment) to the 5′ end of another DNA fragment (such as a growing DNA chain).
43
mismatch repair
The cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides.
44
nuclease
An enzyme that cuts DNA or RNA, either removing one or a few bases or hydrolyzing the DNA or RNA completely into its component nucleotides.
45
nucleotide excision repair
A repair system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide.
46
telomere
The tandemly repetitive DNA at the end of a eukaryotic chromosome’s DNA molecule. Telomeres protect the organism’s genes from being eroded during successive rounds of replication. See also repetitive DNA.
47
telomerase
An enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells.
48
nucleoid
A non-membrane-bounded region in a prokaryotic cell where the DNA is concentrated.
49
histone
A small protein with a high proportion of positively charged amino acids that binds to the negatively charged DNA and plays a key role in chromatin structure.
50
nucleosome
The basic, bead-like unit of DNA packing in eukaryotes, consisting of a segment of DNA wound around a protein core composed of two copies of each of four types of histone.
51
chromatin
The complex of DNA and proteins that makes up eukaryotic chromosomes. When the cell is not dividing, chromatin exists in its dispersed form, as a mass of very long, thin fibres that are not visible with a light microscope.
52
heterochromatin
Eukaryotic chromatin that remains highly compacted during interphase and is generally not transcribed.
53
euchromatin
The less condensed form of eukaryotic chromatin that is available for transcription
54
gene expression
The process by which information encoded in DNA directs the synthesis of proteins or, in some cases, RNAs that are not translated into proteins and instead function as RNAs
55
transcription
The synthesis of RNA using a DNA template
56
messenger RNA (mRNA)
A type of RNA, synthesized using a DNA template, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein. (In eukaryotes, the primary RNA transcript must undergo RNA processing to become mRNA.)
57
translation
The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule. There is a change of “language” from nucleotides to amino acids.
58
ribosome
A complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and a small subunit. In eukaryotic cells, each subunit is assembled in the nucleolus. See also nucleolus.
59
primary transcript
An initial RNA transcript from any gene; also called pre-mRNA when transcribed from a protein-coding gene.
60
triplet code
A genetic information system in which a set of three-nucleotide-long words specify the amino acids for polypeptide chains.
61
template strand
The DNA strand that provides the pattern, or template, for ordering, by complementary base pairing, the sequence of nucleotides in an RNA transcript
62
codon
A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code.
63
reading frame
On an mRNA, the triplet grouping of ribonucleotides used by the translation machinery during polypeptide synthesis.
64
RNA polymerase
An enzyme that links ribonucleotides into a growing RNA chain during transcription, based on complementary binding to nucleotides on a DNA template strand.
65
promoter
A specific nucleotide sequence in the DNA of a gene that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place.
66
terminator
In bacteria, a sequence of nucleotides in DNA that marks the end of a gene and signals RNA polymerase to release the newly made RNA molecule and detach from the DNA.
67
transcription unit
A region of DNA that is transcribed into an RNA molecule.
68
start point
In transcription, the nucleotide position on the promoter where RNA polymerase begins synthesis of RNA.
69
transcription factor
A regulatory protein that binds to DNA and affects transcription of specific genes.
70
transcription initiation complex
The completed assembly of transcription factors and RNA polymerase bound to a promoter.
71
TATA box
A DNA sequence in eukaryotic promoters crucial in forming the transcription initiation complex.
72
RNA processing
Modification of RNA primary transcripts, including splicing out of introns, joining together of exons, and alteration of the 5′ and 3′ ends.
73
5′ cap
A modified form of guanine nucleotide added onto the 5′ end of a pre-mRNA molecule.
74
poly-A tail
A sequence of 50–250 adenine nucleotides added onto the 3′ end of a pre-mRNA molecule.
75
RNA splicing
After synthesis of a eukaryotic primary RNA transcript, the removal of portions of the transcript (introns) that will not be included in the mRNA and the joining together of the remaining portions (exons).
76
intron
A noncoding, intervening sequence within a primary transcript that is removed from the transcript during RNA processing; also refers to the region of DNA from which this sequence was transcribed.
77
exon
A sequence within a primary transcript that remains in the RNA after RNA processing; also refers to the region of DNA from which this sequence was transcribed.
78
spliceosome
A large complex made up of proteins and RNA molecules that splices RNA by interacting with the ends of an RNA intron, releasing the intron and joining the two adjacent exons.
79
ribozyme
An RNA molecule that functions as an enzyme, such as an intron that catalyzes its own removal during RNA splicing.
80
alternative RNA splicing
A type of eukaryotic gene regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns
81
domain
(1) A taxonomic category above the kingdom level. The three domains are Archaea, Bacteria, and Eukarya. (2) A discrete structural and functional region of a protein.
82
transfer RNA (tRNA)
An RNA molecule that functions as a translator between nucleic acid and protein languages by carrying specific amino acids to the ribosome, where they recognize the appropriate codons in the mRNA.
83
anticodon
A nucleotide triplet at one end of a tRNA molecule that base-pairs with a particular complementary codon on an mRNA molecule.
84
aminoacyl-tRNA synthetase
An enzyme that joins each amino acid to the appropriate tRNA.
85
wobble
Flexibility in the base-pairing rules in which the nucleotide at the 5′ end of a tRNA anticodon can form hydrogen bonds with more than one kind of base in the third position (3′ end) of a codon.
86
ribosomal RNA (rRNA)
RNA molecules that, together with proteins, make up ribosomes; the most abundant type of RNA.
87
P site
One of a ribosome’s three binding sites for tRNA during translation. The P site holds the tRNA carrying the growing polypeptide chain. (P stands for peptidyl tRNA.)
88
A site
One of a ribosome’s three binding sites for tRNA during translation. The A site holds the tRNA carrying the next amino acid to be added to the polypeptide chain. (A stands for aminoacyl tRNA.)
89
E site
One of a ribosome’s three binding sites for tRNA during translation. The E site is the place where discharged tRNAs leave the ribosome. (E stands for exit.)
90
signal peptide
A sequence of about 20 amino acids at or near the leading (amino) end of a polypeptide that targets it to the endoplasmic reticulum or other organelles in a eukaryotic cell.
91
signal-recognition particle (SRP)
A protein-RNA complex that recognizes a signal peptide as it emerges from a ribosome and helps direct the ribosome to the endoplasmic reticulum (ER) by binding to a receptor protein on the ER.
92
polyribosomes (polysome)
A group of several ribosomes attached to, and translating, the same messenger RNA molecule.
93
mutation
A change in the nucleotide sequence of an organism’s DNA or in the DNA or RNA of a virus.
94
point mutation
A change in a single nucleotide pair of a gene.
95
nucleotide-pair substitution
A type of point mutation in which one nucleotide in a DNA strand and its partner in the complementary strand are replaced by another pair of nucleotides.
96
silent mutation
A nucleotide-pair substitution that has no observable effect on the phenotype; for example, within a gene, a mutation that results in a codon that codes for the same amino acid.
97
missense mutation
A nucleotide-pair substitution that results in a codon that codes for a different amino acid.
98
nonsense mutation
A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein.
99
insertion
A mutation involving the addition of one or more nucleotide pairs to a gene.
100
deletion
(1) A deficiency in a chromosome resulting from the loss of a fragment through breakage. (2) A mutational loss of one or more nucleotide pairs from a gene.
101
frameshift mutation
A mutation occurring when nucleotides are inserted in or deleted from a gene and the number inserted or deleted is not a multiple of three, resulting in the improper grouping of the subsequent nucleotides into codons.
102
mutagen
A chemical or physical agent that interacts with DNA and can cause a mutation.
103
character
An observable heritable feature that may vary among individuals.
104
trait
One of two or more detectable variants in a genetic character.
105
true-breeding
Referring to organisms that produce offspring of the same variety over many generations of self-pollination.
106
hybridization
In genetics, the mating, or crossing, of two true-breeding varieties.
107
P generation
The true-breeding (homozygous) parent individuals from which F1 hybrid offspring are derived in studies of inheritance; P stands for “parental.”
108
F1 generation
The first filial, hybrid (heterozygous) offspring arising from a parental (P generation) cross.
109
F2 generation
The offspring resulting from interbreeding (or self-pollination) of the hybrid F1 generation.
110
allele
Any of the alternative versions of a gene that may produce distinguishable phenotypic effects.
111
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.
112
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.
113
homozygous
Having two identical alleles for a given gene
114
heterozygous
Having two different alleles for a given gene.
115
phenotype
The observable physical and physiological traits of an organism, which are determined by its genetic makeup.
116
genotype
The genetic makeup, or set of alleles, of an organism.
117
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.
118
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 are monohybrids. For example, parents of genotypes AA and aa produce a monohybrid of genotype Aa.
119
monohybrid cross
A cross between two organisms that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant).
120
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 are dihybrids. For example, parents of genotypes AABB and aabb produce a dihybrid of genotype AaBb.
121
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).
122
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.
123
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.
124
addition 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.
125
complete dominance
The situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.
126
incomplete dominance
The situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele.
127
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.
128
pleiotropy
The ability of a single gene to have multiple effects
129
epistasis
A type of gene interaction in which the phenotypic expression of one gene alters that of another independently inherited gene.
130
quantitative character
A heritable feature that varies continuously over a range rather than in an either-or fashion.
131
polygenic inheritance
An additive effect of two or more genes on a single phenotypic character.
132
multifactorial
Referring to a phenotypic character that is influenced by multiple genes and environmental factors.
133
pedigree
A diagram of a family tree with conventional symbols, showing the occurrence of heritable characters in parents and offspring over multiple generations.
134
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.
135
amniocentesis
A technique associated with prenatal diagnosis in which amniotic fluid is obtained by aspiration from a needle inserted into the uterus. The fluid and the fetal cells it contains are analyzed to detect certain genetic and congenital defects in the fetus.
136
chorionic villus sampling (CVS)
A technique associated with prenatal diagnosis in which a small sample of the fetal portion of the placenta is removed for analysis to detect certain genetic and congenital defects in the fetus.
