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68 Cards in this Set
- Front
- Back
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gene
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basic unit of heredity
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allele
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when a gene exists in more than 1 form
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genotype
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genetic makeup of an individual
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phenotype
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phyisical manifestation of genetic makeup
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Mendel's Law of Segregation
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1. genes exist in alternate forms (alleles); gene controls specific trait in an organism
2. organism has 2 alleles for each inherited trait, one inherited from each parent 3. 2 alleles segregate during meiosis, resulting in gametes that carry only 1 allele for any given inherited trait 4. if 2 alleles in an individual organism are different, only 1 will be fully expressed |
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dominant
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expressed allele
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recessive
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silent allele
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homozygous
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organisms that contain 2 copies of the same allele
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heterozygous
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organisms that carry 2 different alleles
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monohybrid cross
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only 1 trait is being studied; parental generations yield filial generations
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1:2:1 genotypic ratio produces...
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3:1 phenotypic ratio
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test cross
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diagnostic tool used to determine the genotype of an organism; genotype can only be predicted with 100% accuracy with a recessive phenotype
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in a test cross, appearance of the recessive phenotype in the progeny indicates...
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that the phenotypically dominant parent is genotypically heterozygous
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typical pattern for Mendelian inheritance in a dihybrid cross between heterozygotes with independently assorting traits
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9:3:3:1
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incomplete dominance
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blended phenotype; phenotype of the heterozygote is an intermediate of the phenotypes of the homozygotes
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codominance
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occurs when multiple alleles exist for a given gene and more than one of them is dominant
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sex-linked genes
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genes that are located on the X or Y chromosome
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when to recessive sex-linked phenotypes occur in men?
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when recessive genes are carried on the x chromosome, they will produce the recessive phenotypes whenever they occur in men because no dominant allele is present to mask them; recessive phenotype is much more frequently found in men
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pattern of inheritance for a sex-linked recessive
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because gene is carried on X chromosome, & men only pass the X chromosome to their daughters, affected men cannot pass the trait to their male offspring; affected men will pass the gene to all of their daughters; unless the daughter receives the gene from her mother, she will be phenotypically normal carrier of the trait; because all of the daughter's male children will receive their only X chromosome from her, half of her sons will receive the recessive sex-linked allele; sex linked recessives generally affect only men
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advantages of working with drosophila melanogaster
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1. reproduces often (short life cycle)
2. reproduces in large numbers 3. chromosomes are large & easily recognizable in size & shape 4. its chromosomes are few (4 pairs) 5. mutations occur relatively frequently |
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DNA
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deoxyribonucleic acid; contains info coded in the sequence of its base pairs, providing the cell with a blueprint for protein synthesis; self-replicating; basis of heredity; mutable
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nucleotide
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basic unit of DNA; composed of deoxyribose bonded to a phosphate group and nitrogenous base (purines or pyrimidines)
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purines
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adenine and guanine
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pyrimidines
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cytosine and thymine
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T always forms...
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2 hydrogen bonds with A
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G forms...
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3 hydrogen bonds with C
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DNA replication
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semi conservative
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leading strand
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continuously synthesized by DNA plymerase in the 5' --> 3' direction
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lagging strand
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synthesized discontinuously in the 5' --> 3' direction as a series of short segments known as okazaki fragments; overall growth of lagging strand occurs in 3' --> 5' direction
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codons
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sequence of three consecutive bases that code for a particular amino acid;
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RNA
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ribonucleic acid; composed of ribose and contains uracil instead of thymine; single stranded; found in nucleus and cytoplasm
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mRNA
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messenger RNA; carries the complement of a DNA sequence and transports it from the nucleus to the ribosomes where protein synthesis occurs; assembled from ribonucleotides that are complementary to the "sense" strand of the DNA; inverted complementary or negative code of original master on DNA
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monocistronic
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1 mRNA strand codes for one polypeptide
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tRNA
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transfer RNA; found in cytoplasm; aids in 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
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ribosomal RNA; structural component of ribosomes and is the most abundant of all RNA; synthesized in nucleolus
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transcription
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process whereby info coded in the base sequence of DNA is transcribed into a strand of mRNA that leaves thenucleus through nuclear pores
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translation
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process whereby mRNA codons are translated into a sequence of amino acids; occurs in cytoplasm & involves tRNA, ribosomes, mRNA, amino acids, enzymes
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anticodon
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3 nucleotide sequence which is complementary to 1 one of the mRNA codons
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P Site
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binds to tRNA attached to growing polypeptide chain
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A site
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binds to incoming aminoacyl-tRNA complex
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E site
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binds existing tRNA
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polypeptide synthesis
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1. initiation
2. elongation 3. termination |
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initiation
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begins when ribosome binds to mRNA near its 5' end; ribosome scan mRNA until it binds to a start codon (AUG); initiator aminoacyl-tRNA complex, methionine-tRNA base pairs with start codon
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elongation
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hydrogen bonds form between mRNA codon in A site and its complementary anticodon on the incoming tRNA; peptide bond forms between amino acid attached to tRNA in A site and aa attached to tRNA in P site; after peptide bond formation, ribosome carries uncharged tRNA in P site and A site
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translocation
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ribosome advances 3 nucleotides along mRNA in 5' --> 3' direction; uncharged tRNA from P site is expelled and A site moves into P site; ribosome has empty A site ready for entry of new corresponding to next codon
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termination
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when 1 of 3 special mRNA termination codons (UAA, UAG, or UGA) arrives in A site
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nondisjunction
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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
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zygote with 3 copies of a chromosome
Down's Syndrome |
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monozsomy
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zygote with 1 copy of chromosome
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mutations
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changes in genetic info of a cell coded in the DNA
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point mutation
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nucleic acid is replaced by another nucleic acid
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silent mutation
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mutation where new codon codes for same amino acid
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missense mutation
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mutation where new codon may code for a different amino acid
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nonsense mutation
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mutation where new codon may be a stop codon
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frameshift mutation
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nucleic acids are deleted or inserted into the genome sequence
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bacterial genome
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consists of a single circular chromosome located in nucleoid region of cell
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plasmids
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small circular rings of DNA in bacteria
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episomes
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plasmids that are capable of integration into bacterial genome
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replicatino of bacterial chromosomes
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begins at unique origin of replication and proceeds in both directions simultaneously
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binary fission
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bacterial cell reproduction
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3 mechanisms for increasing genetic variance of bacteria population
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1. transformation
2. conjugation 3. transduction |
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transformation
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process by which a foreign chromosome fragment (plasmid) is incorporated into bacterial chromosome via recombination
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conjugation
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sexual mating in bacteria' transfer of genetic material between 2 bacteria that are temporarily joined
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transduction
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occurs when fragments of the bacterial chromosome accidentally become packaged into viral progeny produced during a viral infection
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recombination
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occurs when linked genes are separated; occurs by breakage and rearrangement of adjacent regions of DNA when organisms carrying different genes or alleles for the same traits are crossed
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bacteriophage
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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
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phage DNA takes control of bacterium's genetic machinery & manufactures numerous progeny; bacterial cell lyses, releasing new virions, capable of infecting other bacteria; virulent
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lysogenic cycle
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if bacteriophage does not lyse its host cell, it becomes integrated into bacterial genome in provirus form, lying dormant; virus may stay integrated indefinitely replicating along with bacterial genome; could enter lytic cycle spontaneously
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