Genetics (BIO 352) Final Exam URI

Centromeres, chromosomes, chromatids, tetrads

# of centromeres = # of chromosomes, 1 chromosome = 2 sister chromatids, 1 tetrad = 2 homologous chromosomes

Inversion loop

(KNOW HOW TO DRAW) loop used by chromosomes to pair up when one has variations, including inversions or deletions

Mendelian Conditions

1. Single gene controlled 2. 2 allelic alternatives (dominant/recessive) 3. Non-independent assortment

Rho dependent transcription termination

rho binds to transcript at rho loading site, persuing RNA polymerase to form hair pine, pausing RNA polymerase activity and allowing rho to catch up and release the transcript

Independent assortment

segregating genes for 2 different traits assort independently of one another and are not linked; for meiotic recombination, AaBb independently assortment would yield 1:1:1:1 AB:Ab:aB:ab

Promoters

similar to a promoter, initiate transcription

Locus

site on chromosome where particular genes reside

rRNA

structural component of ribosomes

Phosphodiester backbone

sugar-phosphate backbone, linkages that make up the backbone of ½ of DNA's shape

Transcription

synthesis of RNA directed by DNA; produces mRNA, rRNA, tRNA; making an RNA copy of a single gene

Translation

synthesis of polypeptide directed by mRNA; involves rRNA, tRNA, occurs on ribosomes

Primase

synthesizes primers that are necessary for initiation of the replication process

karyotype

the number and visual appearance of the chromosomes in the cell nuclei of an organism or species; 2n = 46 for humans

ZW system of sex determination

females are ZW, males are ZZ; birds, reptiles

Role of DNA

replicate, store information, express information, and allow variation by mutation

Nondisjunction

autosome OR sex chromosome, 1 chromosome or entire genome; the failure of chromosomes to separate and segregate into daughter cells at division

Prophase I stages

1) Leptonema → chromosomes begin to condense 2) zygonema → bivalents form (spaced out tetrads) 3) pachynema → tetrads 4) diplonema → crossing over occurs at chaismata (RECOMBINATION) 5) diakinesis → spindle fibers attach

Limitations of 2-point linkage analysis

1) limited data generated per cross 2) maximum recombination frequency detectable is 50% 3) double crossovers not detectable (0% recombination frequency)

Conservative model

1 daughter cell inherits all parental strands while the other has all newly synthesized strands

Dominant epistasis

12:3:1

Double Dominant epistasis

15:1

Bacterial termination

2 replication forks approach each other at the terminus region; leaves 2 daughter cells entangled to separate, or else no cell division can occur

Deoxyribose

5 carbon sugar, has one less oxygen than ribose; 5 and 3 end significant in DNA's structure

DNA polymerase III

5' → 3' polymerase activity and 3' → 5' exonuclease activity, very high processivity (30,000 base pairs/minute) and the enzyme responsible for replication

Recessive epistasis

9:3:4

Double recessive epistasis

9:7

Sex determination is drosophila

= # X chromosomes / # autosome sets; >= 1 - female, >.5 <1 - intersex, <= .5 - male

Recombination frequency

= # recombinant progeny / total progeny; same as x; 1 mU = 1 cm = 1% frequency of recombination

Chi-Squared (x^2)

= the sum of [(observed-expected)^2 / expected] degrees of freedom = n-1, n=# of phenotypic classes PROBABILITY: >= .05 - fails to reject null, < .05 - rejects null

Chargaff's rule

A = T, C = G, A+G/C+T = 1

Lethal Alleles

AA:Aa kill → dominant lethal, aa kill → recessive lethal

Sex determination

AB - heterogametic, AA - homogametic

Central dogma

DNA (returns to itself by replication, mutation) → through transcription → mRNA, rRNA, tRNA } on ribosome → through translation → PROTEIN

Kornberg Enzyme

DNA polymerase I

Rho independent transcription termination

G-C rich inverted repeat form hairpin loop, pausing RNA polymerase and giving DNA time to renature and kick off the RNA polymerase

DNA denaturing processes

Gradient centrifugation procedures or heat, although they can renature when cooled

Eukaryotic forms of RNA polymerase

I (rRNA), II (mRNA), III (tRNA)

Protenor system of sex determination

females are XX (hermaphrodites), males are X; grasshoppers, roaches, C. elegans

Pedigree

O - female - XX; □ - male - XY; empty symbol - unaffected; filled in symbol - affected; dot in center of symbol - carrier; a line between a O and □ - union; lines and symbols stemming from a union - children

Processing

OCCURS ONLY IN EUKARYOTES: 1. Transcription yields pre-mRNA 2. 5' guanine cap is added 3. 3' cleavage for poly A 3' tail 4. Splicing removes introns, ligates exons together

Neurospora

an organism's whose system is the model for centromere mapping because it is uniquely compromised of haploid cells; able to reproduce sexually as well as asexually

Lygaeus system of sex determination

females are XX, males are XY; mammals

Turner's syndrome

XO chromosomes, no barr bodies; scientifically classified as male

Klinefelter's syndrome

XXY chromosomes, 1 barr body; scientifically classified as a male

Eukaryotic DNA polymerase

a (alpha): essential to replication, has low processivity and functions in synthesizing primers during initiation; δ (delta): 3' → 5' exonuclease activity, switches with alpha for elongation

Colchicine

a chemical that can stimulate the production of polyploids

Robertsonian translocation

aka centric fusion; involves breaks at extreme ends of short arms of 2 non-homologous arocentric chromosomes

Dispersive model

all completely random strands made up of parental as well as newly synthesized material

Sex-linked (X-linked) dominant

all females from affected males have trait, not all males from affected females have trait; more females affected than males; NO carriers or skipping of generations

Pseudoautosomal region

allows X and Y chromosomes to pair up like homologs despite being different sizes

Autosomal dominant

almost always appear in every generation, regardless of sex; affect individuals have affected parent

Allele

alternate forms of gene that can exist at a single locus

Barr bodies

an X chromosome inactivated in mammals; if an X chromosome is inactivated, it is retained in that form even after mitosis; barr bodies = total X's - 1

polyploids

autopolyploids - same genome; allopolyploids - closely related, can result from interspecific matings

Lagging strand

because DNA polymerase III can only synthesize in the 5' → 3' direction and DNA is antiparallel, the lagging strand is synthesized in pieces and then sealed together

Female chromosomal determination

can be XX, XXX, XXXX, ... as long as no Y

Male chromosomal determination

can be XY, XXY, XXX...Y as long as there is a Y

mRNA

carries DNA sequence info to the ribosomes

Linkage with recombination

cis: ½-x/2 AB: x/2 Ab : x/2 aB : ½-x/2 ab; trans: ½-x/2 Ab : x/2 AB : x/2 ab : ½-x/2 aB; for both, x = recombination frequency

Leading strand

continuous replication by DNA polymerase III in the 5' → 3' direction

Types of linkage (repulsed/coupled)

coupled/cis = AB and ab linked; repulsed/trans = Ab and aB linked

Autosomal recessive

cross of 2 carriers can produce affected (homozygous) offspring, regardless of sex; if both parents are affected, all children all

Semi-conservative model

daughter cells inherit 1 parental strand and 1 newly synthesized strand each, the actual model of inheritance

Hyperchromic effect

denatured DNA absorbs light more than helical DNA because base-stacking in DNA helix prevents purines and pyrimidines from fully absorbing light

Arthur Kornberg

discovered the four necessary compounds for replication: dNTPs (A, T, G, C), DNA polymerase, a DNA template, and MG^2+

Telomeres

ends of linear chromosomes consist of long stretches of short repeating sequences that preserve the integrity and stability of chromosomes

Haploid-diploid system of sex determination

females are 2n, males are n; ants, bees, wasps

Okazaki fragments

fragments of DNA that each begin with a primer and then are "glued" together on the lagging strand

Pseudoautosomal mode of inheritance

gene that shows autosomal-like inheritance but are known to be on the X/Y chromosome

Meiosis

genetically interphase, prophase I, metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II, telophase II; due to variation, daughter cells are genetically different; produces haploid (n) gametes; centromeres duplicate M2

Euploid

haploid - n, diploid - 2n, polyploid - 3n, 4n, ... (only even #'s are fertile)

Y chromosome

has SRY gene, codes for testis-determining factor (TDF) protein that might code for male genitalia

Incomplete inheritance

heterozygous genotype has blended phenotype (RR - red, rr - white, Rr - pink)

Codominance

heterozygous possess both dominant and recessive phenotype (I^a I^a,o - A blood type, I^b I^b,o - B blood type, I^a I^b - AB blood type, I^o I^o - O blood type)

Hydrogen bonds

hold together the base pairs that give DNA its helical shape

Testcross

homozygous recessive individual (tester) x suspected heterozygote to determine genotype

telomerase

insert telomeres into the gap where RNA primers are removed

Mitosis

interphase, prophase, metaphase, anaphase, telophase; daughter cells genetically the same, produces diploid (2n) cells, centromeres duplicate M1

Ligase

joins together gaps that are formed during the replication process, especially the fragments of the lagging strand, needs ATP to function

DNA polymerase I

requires template and primer; synthesis (finding and inserting appropriate base pairs) in the 5' → 3' direction; exonuclease activity (error correcting, proofreading) in 3' → 5' AND 5' → 3' direction

Major groove

largest space between two strands of DNA, where the DNA-binding proteins can interact with DNA

Linkage

linked genes are genes too close to one another so crossing over occurs more rarely

RNA polymerase

main enzyme of transcription, still in 5' → 3' direction

Protein or DNA

major question of early experiments for discovering the genetic material

Dosage compensation

males with one X have on functional copy of genes, whereas females with XX have one X randomly inactivated (inactivated X becomes a barr body); this occurs only in mammals, in drosophila, X chromosomes are up-regulated in males (work 2x), in C. elegans, C chromosomes are down-regulated in hermaphrodites (½)

Classification of chromosomes

metacentric = centromere in middle, submetacentric = centromere near middle but not exact, arocentric = near end, telocentric = at end; p arm is the shorter arm, q arm is the longer arm

Eukaryotic mRNA

monocistronic - codes for only 1 polypeptide

DNA absorbance values

more C-G rich DNA molecules will have higher absorbance, higher melting points because of the more H-bonds

Helix

most DNA exists as a double-stranded _____, but some can be triple stranded while others can be single stranded (Chargaff's rule would no longer apply)

B-DNA

most biologically significant form of DNA, less compact than A-DNA (both are right handed) but more compact that C, D, E-DNA

Mitochondrial/maternal inheritance

mother's phenotype is inherited by ALL offspring

Eukaryotic termination

multiple origins of replication allow genomes to be replicated over hours; individual Dna subunits for replication called replicons are clusters that replicate synchronously

Consensus sequence

not all promoters are identical but similar, make up these sequences

Nucleotide

nucleoside + phosphate group

DNA structure

nucleotides are linked by phosphodiester bonds between the C4 phosphate and the C3 OH group

First division nondisjunction

occurs during segregation during meiotic anaphase I, results in 2 trisomic, 2 monosomic gametes

Second division nondisjunction

occurs during segregation during meiotic anaphase II, results in 2 normal, 1 trisomic, and 1 monosomic gametes

TATA box

one type of promoter, a region of repeating TATAA sequence

Types of inversion

paracentric: arm ratio is unchanged, excludes the centromere; pericentric: arm ratio changed, includes the centromere

Nucleoside

pentose sugar (deoxyribose or ribose) + nitrogen base (A,C,G,U/T)

Gene

physical and functional unit of heredity

Prokaryotic mRNA

polycistronic - codes for more than 1 polypeptide

Product law

probability 2 independent events occurring simultaneously = the product of their individual probabilities, ex. AaBb x AaBb = AABb → ¼ x 2/4 = 2/16

tRNA

provides linkage between mRNA and amino acids; transfers amino acids to ribosomes

Nitrogen bases

pyrimidines = 1 ring = C, U/T; purines = 2 rings = A, G; C-G is a triple bond while A-U/T is only a double bond

Y-linked or holandric

rarer due to fewer genes being on the Y chromosome, father always passes to son, females unaffected

ATP, CTP, GTP, UTP

raw materials for transcription

Gyrase

reduces the coiling that increases during the unwinding process

Minor groove

the smaller space between the two strands of DNA

2-point linkage analysis

to determine genetic proportions of frequencies using testcross

Sex-linked (X-linked) recessive

trait never passed from father to son; females can be carriers; sons of affected mothers affected, daughters of affected fathers are carriers

Transcription: eukaryotes v prokaryotes

transcription and translation are coupled and occur simultaneously in bacteria, whereas only transcription occurs in the nucleus of eukaryotic cells and translation occurs in the mitochondria

Aneuploids

trisomy = 2n + 1, monosomy = 2n - 1, tetrasomy = 2n + 2, nullsomy = 2n - 2

Helicase

unwinds the DNA helix so that other enzymes can get in to replicate the strands

RNA vs DNA

uracil (U) not thymine (T), ribose not deoxyribose

Nonreciprocal Translocation

variation in structural arrangement; ABCDEFG + HIJKLM → CDEFG + ABHIJKLM (non-homologous chromosomes)

Reciprocal Translocation

variation in structural arrangement; ABCDEFG + HIJKLM → HIJCDEFG + ABKLM (non-homologous chromosomes)

Duplication

variation in structural arrangement; ABCDEFG → ABCBCDEFG

Deletion

variation in structural arrangement; ABCDEFG → ABCEFG

Inversion

variation in structural arrangement; ABCDEFG → ADCBEFG

Recombination

when genes gross over in meiosis, leads to genetic variation and creates recombinant types (as opposed to parental types)

Epistasis

where one gene hides or masks another

Absolute linkage

yields 1:1 of cis or trans linkage type (AB/ab would yield 1:1 AB:ab, etc.)

Centromere mapping

½ x [(#asci with second division segregation)/total # of asci] x 100