Midterm I Important Terms and Concepts

Question 1

purpose of mitosis

Answer 1

prokaryotes/unicellular eukaryotes:
-asexual reproduction (replicating the nucleus to produce two new identical cells)
multicellular eukaryotes: generate new somatic cells for growth and repair

Question 2

purpose of meiosis

Answer 2

make haploid cells (gametes) from a single diploid cell called a meiocyte

Question 3

ori

Answer 3

• in e coli, a region of the DNA rich in AT sequences (easier to melt bc less H bonds), with binding sites for proteins
• each eukaryotic chromosome will have multiple, while the circular chromosomes of prokaryotes only have one

Question 4

auxotrophic

Answer 4

has a block in a biosynthetic pathway and is unable to grow on minimal media if not supplemented with the appropriate compound

Question 5

prototrophic

Answer 5

wildtype; all genes are intact and the organism is able to synthesize everything necessary for growth from the simple compounds in MM

Question 6

allelic mutations

Answer 6

when two mutant diploid cells are mated and the mutations fail to complement, it means the mutants are in the same gene, and the strains couldn’t be rescued

Question 7

non-allelic muations

Answer 7

mutations that complement, because the parental haploids were mutant in different genes, meaning the functional gene from one parent makes up for the dysfunction in the other

Question 8

complementation group

Answer 8

a number of strains that, by complementation testing, have been found to be allelic mutants, meaning they are all mutant in the same gene, and any one would fail to complement all the others in the group

Question 9

complementation rules

Answer 9

• can only be performed in diploids
• mutations must be recessive (the presence of one WT copy must mask a mutant copy)
• mutations don’t need to be in the same pathway (so long at the mutant gene isn’t used across both pathways)
• mutations do not need to be growth/no growth (could be purple vs white flower for ex)

Question 10

gene

Answer 10

• occupies specific location in the genome and can be mapped
• has at least one specific effect on the phenotype of an organism
• can mutate to various forms (alleles)
• is a unit of inheritance
• can recombine with similar units (other genes)

Question 11

types of genes

Answer 11

1. DNA acting directly (ori, centromeres, telomeres)
2. DNA whose RNA transcripts have direct function (ex tRNA, rRNA, various smaller RNAs involved in splicing and gene regulation)
3. Protein coding genes (contain a regulatory region and a transcribed sequence which is translated to a peptide for use in enzyme activity, structure, and gene regulation)

Question 12

levels of control for gene regulation

Answer 12

transcriptional:
-structural changes such as histone modifications (condensed DNA is transcriptionally inaccessible) or DNA methylation
-inhibition via differential recruitment of transcriptional factors (the only real control for prokaryotes)
post transcriptional:
-RNA processing in the nucleus (splicing and alternate splicing)
-transport to cytoplasm
-cytoplasmic degradation
protein processing:
-protein modification
-transport to cellular location of action
transcriptional regulation is the most energy efficient

Question 13

elements in an mRNA transcript of a prokaryotic gene

Answer 13

5'UTR
RBS (ribosomal binding site)
translation start codon (AUG) and open reading frame 
(which codes the polypeptide)
translation stop codon
3'UTR

Question 14

lac genes

Answer 14

lac I - codes for the repressor protein which can bind to the operator, blocking the promoter and therefore transcription
lac Z - codes B-galactosidase, which breaks down lactose in to glucose and galactose
lac Y - codes for the permease which allows for uptake of lactose into the cell
lac A - codes for a transacetylase whose function is unclear

Question 15

cis acting loci

Answer 15

• a control element that only affects genes on the same DNA strand (meaning it produces no diffusible product)
• this is usually a DNA element on the same strand as affected gene (such as an operator or promotor)

Question 16

trans acting loci

Answer 16

• control element that affects genes on both its own strand and on different ones (meaning it codes for a diffusible product)
• this is usually a protein that can act at genes on other strands (such as a repressor protein)

Question 17

intergenetic DNA

Answer 17

• variable number tandem repeats (ex. microsatellites, minisatellites and satellite DNA)
• transposons (jumping genes)

Question 18

eukaryotic RNA modification

Answer 18

• 5’ cap (7-methyl guanosine) and 3’ poly A tail prevent degradation of the transcript by exonucleases (that chew from one end in)
• removal of introns by splicing

Question 19

changes in chromatin and DNA modification

Answer 19

euchromatin (true chromatin): loosely packaged and accessible by transcription enzymes, making gene expression possible; histones are acetylated

heterochromatic: DNA tightly packed around deacylated histones, preventing gene expression
- methylation of cytosine in CpG sites is associated with transcriptionally inactive DNA

Question 20

mutation

Answer 20

• heritable change in DNA sequence, and the process by which it occurs
• usually reserved for events that cause changes negatively affecting the organism, an abnormal phenotype

Question 21

mutant

Answer 21

cell or organism possessing a mutation

Question 22

polymorphism

Answer 22

a new/changed for in DNA sequence that causes naturally occurring variation (no direct negative impact on phenotype)

Question 23

small scale mutations

Answer 23

• base substitutions

- single nucleotide insertions/deletions

Question 24

large scale (chromosomal) mutations

Answer 24

• large scale insertions or deletions
• inversions
• duplications
• translocations

Question 25

types of point mutations within genes

Answer 25

silent (no change to AA sequence)
missense (change to AA sequence; can be conservative or non-conservative, depending on how similar the new AA is to the original)
nonsense (change from the intended AA to a stop codon, usually resulting in a truncated, non-functional protein)

Question 26

alelle

Answer 26

form or variant of a gene; may result in a different observable trait

Question 27

genotype

Answer 27

the complete set of all alleles at all genes in and individual (though usually only the genes of interest are listed)

Question 28

phenotype

Answer 28

complete set of observable traits in and individual (morphology, behaviour, biochemical activity, etc)

Question 29

naming genes

Answer 29

• genes are named by their mutant phenotype or by the protein they encode
• ex the white gene in drosophilia is named after the mutation producing white eyes, and the Pfrx gene is names after the enzyme it encodes, phosphofructokinase

Question 30

naming alleles

Answer 30

alleles are named by their discovery or the phenotype they cause

Question 31

homozygous

Answer 31

the individual has the same two alleles at each of the two copies of the gene present in the genome

Question 32

heterozygous

Answer 32

the individual has two different alleles at each of the two copies for that gene in the genome

Question 33

hemizygous

Answer 33

the individual only has one copy of the gene

Question 34

complete dominance

Answer 34

• one allele masks the phenotype of another

- can only be determined by observing the phenotype of the heterozygote

Question 35

haplo-sufficent

Answer 35

in a hemizygous organism, 50% of the gene activity generated by the functional protein is enough to give the full phenotypical outcome associated with that gene

Question 36

incomplete dominance

Answer 36

the alleles affect a trait additively, and a heterozygote will display an intermediate phenotype (meaning that the gene is haplo-insufficient)

Question 37

haplo-insufficient

Answer 37

in a heterozygous individual with one non-functional gene, the 50% percent of normal gene activity maintained by the WT isn’t enough for the full phenotypical expression)

Question 38

codominance

Answer 38

-heterozygous individuals express both alleles as two distinct traits (ex ABO blood relationships; indvs homozygous for A will only produce A, for B will only produce B, but an AB heterozygote will produce both antigens; only those homozygous for O completely lack the antigen)

Question 39

amorph

Answer 39

• allele causing a complete loss of function (implies a dominant/recessive relationship)
  ex. drosophilia white1 allele, Lac I-

Question 40

hypomorph

Answer 40

• allele resulting in a partial loss of function

ex. Lac Oc mutation (change in DNA sequence didn’t obliterate the binding function, rather just reduced it)

Question 41

hypermorph

Answer 41

causing an increase in function

ex. arguably the LCTp allele (allowing for lactose metabolism whll after the gene should be inactivated)

Question 42

neomorph

Answer 42

alleles resulting in novel function

ex. expression of a gene in a new cell type

Question 43

antimorph

Answer 43

allele imparting an antagonistic function; works against the WT function
ex. BRCA1 mutations (work against the normal function of the BRCA1 DNA repair enzyme, causing accumulation of mutations)

Question 44

morphological mutants

Answer 44

change the physical appearance of an organism (ex. flower or eye colour)
-many different forms of the same gene can exist

Question 45

allelic series

Answer 45

alleles of a single gene that have different types of dominance relationships with each other
ex. in drosophilia, W1 is hypomorphic and W+ is WT, but there are several hypomorphs between them creating a spectrum of expression)

Question 46

pleiotrophy

Answer 46

in which one gene is responsible for more than one phenotypical trait
ex. sickle cell disease can be advantageous in parts of the world where malaria is common, as it helps to protect, but deleterious in others

Question 47

epistasis

Answer 47

expression of one gene is dependent on the expression of other genes
ex. labrador retriever coat colour: the deposition of black pigment into the coat is dependent upon two enzymes, one that makes the pigment and another that transfers it to the fur

Question 48

polygenic

Answer 48

in which many genes additively affect a phenotypic trait

ex. human height depends on growth hormone, ability to process food, the environment