biology chapter 3

Question 1

genetics

Answer 1

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

Question 2

gene

Answer 2

the basic unit of heredity

Question 3

alleles

Answer 3

when a gene exists in more than one form

Question 4

genotype

Answer 4

the genetic makeup of an individual

Question 5

phenotype

Answer 5

the physical manifestation of the genetic makeup

Question 6

dominant

Answer 6

expressed allele

Question 7

recessive

Answer 7

the silent allele

Question 8

homozygous

Answer 8

organisms that contain two copies of the same allele

Question 9

heterozygous

Answer 9

organisms that carry two different alleles

Question 10

monohybrid cross

Answer 10

only one trait is being studied in this particular mating

Question 11

testcross

Answer 11

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

Question 12

dihybrid cross

Answer 12

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

Question 13

crossing over

Answer 13

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

Question 14

codominance

Answer 14

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

Question 15

sex linked

Answer 15

genes that are located on the X or Y chromosome

Question 16

nondisjunction

Answer 16

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

Question 17

trisomy

Answer 17

three copies of that chromosome

Question 18

monosomy

Answer 18

a single copy of that chromosome

Question 19

mutagenic agents

Answer 19

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

Question 20

colchicine

Answer 20

inhibits spindle formation, thereby causing polyploidy

Question 21

phenylketonuria (PKU)

Answer 21

is a molecular disease caused by the inability to produce the proper enzyme for the metabolism of phenylalanine. A degradation product (phenylpyruvic acid) accumulates

Question 22

sickle cell anemia

Answer 22

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

Question 23

nucleotide

Answer 23

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

Question 24

semiconservative

Answer 24

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

Question 25

RNA

Answer 25

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

Question 26

mRNA

Answer 26

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

Question 27

monocistronic

Answer 27

one mRNA strand codes for one polypeptide

Question 28

tRNA

Answer 28

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

Question 29

rRNA

Answer 29

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

Question 30

transcription

Answer 30

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

Question 31

translation

Answer 31

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

Question 32

anticodon

Answer 32

which is complementary to one of the mRNA codons

Question 33

aminoacyl-tRNA synthetase

Answer 33

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

Question 34

ribosomes

Answer 34

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

Question 35

elongation

Answer 35

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

Question 36

translocation

Answer 36

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

Question 37

episomes

Answer 37

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

Question 38

transformation

Answer 38

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

Question 39

conjugation

Answer 39

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

Question 40

Hfr cells

Answer 40

high frequency of recombination

Question 41

transduction

Answer 41

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.

Question 42

recombination

Answer 42

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

Question 43

promoter

Answer 43

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

Question 44

regulator

Answer 44

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

Question 45

inducible systems

Answer 45

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

Question 46

repressible systems

Answer 46

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

Question 47

inducer-repressor complex

Answer 47

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

Question 48

bacteriophage

Answer 48

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

Question 49

lytic cycle

Answer 49

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

Question 50

lysogenic cycle

Answer 50

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