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Flashcards in biology chapter 3 Deck (50):
1

genetics

is the study of how traits are inherited from one generation to the next

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gene

the basic unit of heredity

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alleles

when a gene exists in more than one form

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genotype

the genetic makeup of an individual

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phenotype

the physical manifestation of the genetic makeup

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dominant

expressed allele

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recessive

the silent allele

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homozygous

organisms that contain two copies of the same allele

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heterozygous

organisms that carry two different alleles

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monohybrid cross

only one trait is being studied in this particular mating

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testcross

an organism with a dominant phenotype of unknown genotype (Ax) is crossed with a phenotypically recessive organism (genotype aa)

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dihybrid cross

parents differ in two traits, as long as the genes are on separate chromosomes and assort independently during meiosis

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crossing over

exchanges information between chromosomes and may break the linkage of certain patterns

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codominance

occurs when multiple alleles exist for a given gene and more than one of them is dominant

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sex linked

genes that are located on the X or Y chromosome

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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

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trisomy

three copies of that chromosome

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monosomy

a single copy of that chromosome

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mutagenic agents

include cosmic rays, x-rays, ultraviolet rays, and radioactivity as well as chemical compounds such as colchicine or mustard gas

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colchicine

inhibits spindle formation, thereby causing polyploidy

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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

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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

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nucleotide

which is composed of deoxyribose ( a sugar) bonded to both a phosphate group and a nitrogenous base

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semiconservative

each new daughter helix contains an intact strand from the parent helix and a newly synthesized strand

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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

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mRNA

carries the complement of a DNA sequence and transports it from the nucleus to the ribosomes, where protein synthesis occurs

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monocistronic

one mRNA strand codes for one polypeptide

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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

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rRNA

is a structural component of ribosomes and is the most abundant of all RNA types. rRNA is synthesiszed in the nucleolus

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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

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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

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anticodon

which is complementary to one of the mRNA codons

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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

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ribosomes

are composed of two subunits (consisting of proteins and rRNA), one large and one small, that bind together only during protein synthesis

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elongation

hydrogen bonds form between the mRNA codon I the A site and its complementary anticodon on the incoming aminoacyl-tRNA complex

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translocation

in which the ribosome advances 3 nucleotides along the mRNA in the 5' to 3' direction

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episomes

DNA sequences sometimes found in plasmids, are capable of integration into the bacterial genome

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transformation

is the process by which a non-chromosomal fragment (plasmid) is incorporated into the bacterial chromosome via recombination, creating new inheritable genetic combination

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conjugation

can be described as sexual mating in bacteria; it is the transfer of genetic material between two bacteria that are temporarily joined

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Hfr cells

high frequency of recombination

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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.

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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

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promoter

is the noncoding sequence of DNA that serves as the initial binding site for RNA polymerase

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regulator

which codes for the synthesis of a repressor molecule that binds to the operator and blocks RNA polymerase from transcribing the structural genes

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inducible systems

are those that require the presence of a substance, called an inducer, for transcription to occur

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repressible systems

are in a constant state of transcription unless a corepressor is present to inhibit transcription

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inducer-repressor complex

for transcription to occur, an inducer must bind to the repressor. This complex cannot bind to the operator, thus permitting transription

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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

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lytic cycle

the phage DNA takes control of the bacterium's genetic machinery and manufactures numerous progeny

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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