biology chapter 3 Flashcards
genetics
is the study of how traits are inherited from one generation to the next
gene
the basic unit of heredity
alleles
when a gene exists in more than one form
genotype
the genetic makeup of an individual
phenotype
the physical manifestation of the genetic makeup
dominant
expressed allele
recessive
the silent allele
homozygous
organisms that contain two copies of the same allele
heterozygous
organisms that carry two different alleles
monohybrid cross
only one trait is being studied in this particular mating
testcross
an organism with a dominant phenotype of unknown genotype (Ax) is crossed with a phenotypically recessive organism (genotype aa)
dihybrid cross
parents differ in two traits, as long as the genes are on separate chromosomes and assort independently during meiosis
crossing over
exchanges information between chromosomes and may break the linkage of certain patterns
codominance
occurs when multiple alleles exist for a given gene and more than one of them is dominant
sex linked
genes that are located on the X or Y chromosome
nondisjunction
is either the failure of homologous chromosomes to separate properly during meiosis I, or the failure of sister chromatids to separate properly during meiosis II
trisomy
three copies of that chromosome
monosomy
a single copy of that chromosome
mutagenic agents
include cosmic rays, x-rays, ultraviolet rays, and radioactivity as well as chemical compounds such as colchicine or mustard gas
colchicine
inhibits spindle formation, thereby causing polyploidy
phenylketonuria (PKU)
is a molecular disease caused by the inability to produce the proper enzyme for the metabolism of phenylalanine. A degradation product (phenylpyruvic acid) accumulates
sickle cell anemia
is a disease in which red blood cells become crescent shaped because they contain defective hemoglobin. The sickle cell hemoglobin carries less oxygen. Caused by a substitution of valine for glutamic acid because of a single base pair substitution in the gene coding for hemoglobin
nucleotide
which is composed of deoxyribose ( a sugar) bonded to both a phosphate group and a nitrogenous base
semiconservative
each new daughter helix contains an intact strand from the parent helix and a newly synthesized strand
RNA
ribonucleic acid, is a polynucleotide structurally similar to DNA except that its sugar is ribose, it contains uracil (U) instead of thymine, and it is usually single stranded
mRNA
carries the complement of a DNA sequence and transports it from the nucleus to the ribosomes, where protein synthesis occurs
monocistronic
one mRNA strand codes for one polypeptide
tRNA
is a small RNA found in the cytoplasm which aids in the translation of mRNA’s nucleotide code into a sequence of amino acids. Brings amino acids to the ribosomes during protein synthesis
rRNA
is a structural component of ribosomes and is the most abundant of all RNA types. rRNA is synthesiszed in the nucleolus
transcription
is the process whereby information coded in the base sequence of DNA is transcribed into a strand of mRNA which leaves the nucleus through nuclear pores. The remaining events of protein synthesis occur in the cytoplasm
translation
is the process whereby mRNA codons are translated into a sequence of amino acids. Translation occurs in the cytoplasm and involves tRNA, ribosomes, amino acids, enzymes, and other proteins
anticodon
which is complementary to one of the mRNA codons
aminoacyl-tRNA synthetase
which has an active site that binds to both the amino acid and its corresponding tRNA, catalyzing their attachment to form an aminoacyl-tRNA complex
ribosomes
are composed of two subunits (consisting of proteins and rRNA), one large and one small, that bind together only during protein synthesis
elongation
hydrogen bonds form between the mRNA codon I the A site and its complementary anticodon on the incoming aminoacyl-tRNA complex
translocation
in which the ribosome advances 3 nucleotides along the mRNA in the 5’ to 3’ direction
episomes
DNA sequences sometimes found in plasmids, are capable of integration into the bacterial genome
transformation
is the process by which a non-chromosomal fragment (plasmid) is incorporated into the bacterial chromosome via recombination, creating new inheritable genetic combination
conjugation
can be described as sexual mating in bacteria; it is the transfer of genetic material between two bacteria that are temporarily joined
Hfr cells
high frequency of recombination
transduction
occurs when fragments of the bacterial chromosome accidentally become packaged into viral progeny produced during a viral infection. These virions may infect other bacteria and introduce new genetic arrangements through recombination with the new host cell’s DNA. the closer two genes are to one another on a chromosome are more likely they will be to transduce together.
recombination
occurs when linked genes are separated. It occurs by breakage and rearrangements of adjacent regions of DNA when organisms carrying different genes or alleles for the same traits are crossed
promoter
is the noncoding sequence of DNA that serves as the initial binding site for RNA polymerase
regulator
which codes for the synthesis of a repressor molecule that binds to the operator and blocks RNA polymerase from transcribing the structural genes
inducible systems
are those that require the presence of a substance, called an inducer, for transcription to occur
repressible systems
are in a constant state of transcription unless a corepressor is present to inhibit transcription
inducer-repressor complex
for transcription to occur, an inducer must bind to the repressor. This complex cannot bind to the operator, thus permitting transription
bacteriophage
is a virus that infects its host bacterium by attaching to it, boring a hole through the bacterial cell wall, and injecting its DNA, while its protein coat remains attached to the cell wall
lytic cycle
the phage DNA takes control of the bacterium’s genetic machinery and manufactures numerous progeny
lysogenic cycle
if the bacteriophage does not lyse its host cell, it becomes integrated into the bacterial genome in a harmeless form (provirus), lying dormant for one or more generations
