Genetics Exam 2 Soliman

DNA structure

-supercoiled to fit in small nucleus
-negative supercoiled by topoisomerase

Bacterium have DNA storage site in form of

-nucleoid
-formed by dna looped domains anchored by DNA BPs
-DNA is supercoiled

Topoisomerase

-supercoils DNA, catalyzes changes in chromatin config.
-NAP (nucleoid assoc. proteins) hold proper config

Bacterium DNA structure

-plasmids (circ. DNA form independently of bact.)
- + or - supercoiled

Plasmid replication process

-replicats independently of bacterium
-copies are transferred to other bact. using conjugation
-plasmids do not contain essential genes for life, contain genes, encoding proteins to help for survival and propogation

Resistance factor

proteins protecting against antibiotics

Fertility factor

proteins enabling them to engage in conjugation w/ other bacteria effectively

Nucleosome

Dna w/ 8 histone proteins

Chromatosome

H1 protein + nucleosome

H1 protein

anchors histones together

Euk DNA form

-supercoiled to fit inside nucleus

Linker DNA

DNA segments separating histones

Gene expression in chroms

Chromatin relaxes to allow gene expression
-histones loosening grip on DNA

Euk chrom. structures

Metacentric (centromere in center), submetacentric (centromere closer to end of arms), acrocentric (centromere on top of arms)

Polycentric

Centromeres distributed along chrom
-spindle fibers attach along chrom

Centromeres have

-repeated seqs
-all orgs. have diff repeated seqs on centromeres
-variant form of h3 histone & adopt chromatin config.- allows for function

Centromere

region in middle of chrom.

Kinetochore

protein that allows for attachment of spindle fibers & pull apart homologs

Telomere stabilization

-telomeric end of long strand binds to itself at compl. seq to form t-loop

Shelterin

binds to telomeres & keeps them from being repaired

Euchromatin

less condensed/greater gene express.

Heterochromatin

More condensed/ less gene express.

Chrom. 1

largest autosome

chrom. 2

smallest autosome

Karyotype

used to refer individ's chrom status
-ex. how many/which sex chroms/abnormalities
-ex. refer to pic of indiv's chroms

Karyotype Phrase

-total # chroms, sex chroms, abnormalities

Trisomy 21 (down syndrome)

extra chrom. 21= 47, XY, +21

Turner syndrome

missing X 45, X

G-banding

-chrom band colors on arms
-gives unique comb of black, white and grey bands
-provides system for localizing genes on their chroms
-knowing banding pattern makes it easy to see if there is missing material or recomb.
-AT regions stain darker than GC regions
-Giemsa dye and protease in chromatin in process

Aneuploidy

not having standard # of chroms for your spp., Wild type (euploidy)

Nullisomy

no copies of spec. chrom

Monosomy

1 copy of spec. chrom.

Disomy

2 copies of spec. chrom.

Trisomy

3 copies of spec. chrom.

Tetrasomy

4 copies of spec. chrom.

Polyploidy

Having 1 or more extra full sets of chroms.

Haploid

1 set of chroms

Diploid

2 sets of chroms

Triploid

3 sets of chroms

Tetraploid

4 sets of chroms

Mutations on indiv. chroms

-deletions

-duplications

-insertions

-reciprocal translocations

-inversions

Deletions

-results in loss of function gene copies

-depends on how many genes are in deleted regions

-if centromere is deleted, chrom will be lost during next division

Pseudo dominance

if individual loses dominant allele, whatever phenotype characteristics are influenced by that gene will reflect presence of recessive allele as only one allele

Phenotype abnormality depends on

ratio of several proteins needed for optimal function

Haploinsufficiency

in some proteins, two working copies of the gene only make enough of protein to barely fulfill body’s need for the protein (missing one copy of gene causes abnormal phenotype)

Duplication

-copy of chrom segment inserted to another piece of chrom.

Tandem Duplication

copied segment sits right next to parent segment

Displaced Duplication

not side by side duplication

Reverse duplication

inverted repeat/duplication

Insertions

Nonreciprocal translocations

-piece of one chrom is broken and inserted into another chrom.

balanced translocation results in

No DNA lost

Unbalanced translocation results in

DNA lost

Which mutation are most likely to produce abnormal phenotype?

Nonreciprocal translocation

balanced reciprocal translocations

-can result in normal phenotypes

-1 + genes are moved, entire conding seq & regul. seq moved and remain together

unbalanced reciprocal translocations

• 1 or more portions of 1+ genes lost

• less likely to express normal phenotypes

Breaks in middle of gene can cause

break points can fall inside gene’s seq and breaking it into two separated main parts

Position Effect

translocation moving normally active gene close to heterochromatic region, silencing the gene

Gametes of balanced reciprocal translocations

• if contain 2 normal chroms/derivatives, it is balanced

• if contains 1 normal chrom and 1 deriv, unbalanced

Robertsonian translocations

-result in fusion of two acrocentric chroms (chroms 13, 14, 15, 21, 22)

-2 fully functioning chroms, 1 centromere (cell recognizes as 1 chrom)

short arm of 1 chrom is exchanged w/ long arm of another

creation of large metacentric chrom & frag that fails to segregate and is lost

Inversion

seg of chrom turned 180 deg

Pericentric invers.

inversion breakpoints lie on either side of centromere

Paracentric invers.

both breakpoints lie within some chrom arm

Unbalanced invers.

when the chrom breaks, some DNA may/may not be lost at one or both breakpoints

Balanced inversion

-1 or both break points can fall inside a gene’s seq. splitting a gene in half

Nondisjunction

-can occur during mitosis and be somatic

-lead to aneusomies

-likelihood increases with age

-trisomy 21 is only nondisj. with viable offspring

-during anaphase when a chrom failed to pull apart

Autopolyploidy

type of polyplopidy- all chroms are from same spp

-wholesale nondisj. of all chroms (all chrom pairs get pulled to one daughter cell)

-result in twice # of chroms than normal

Allopolyploidy

indiv. inherits chroms from two diff. spp.

Polyspermy

-more than 1 sperm penetrate one oocyte

-result of miscarriages

Fluorescent In Situ Hybridization

• complementary breaks bind to each other

• uses ssDNA molecules labeled w/ fluorescent molecule

• metaphase spread of chroms

Cell cycle stages

M (mitosis

G1

interphase

G2

G1

Stockpile nucleotides, ATP, enzymes to replicate DNA

checkpoint after G1 to make sure it has all enzymes before going into s phase

S (interphase)

DNA replication

G2

synth. microtubules & other proteins needed for division, ATP stockpile

cell accumulates mitosis promoting factors activated by dephosphorylation before entering M phase

End of G2- cell checks for DNA damage, DNA damage keeps MPF inactive, halts cell and checks telomere length

M phase

Mitosis/divison

checkpoint- checks every chrom is aligned properly at eq. plane, every centromere has spindle fibe contact

G0 (sometimes)

Cell will halt cycle at G0 if it doesn’t have all needed materials for replication/division

Apoptosis

programmed cell death

when cell fails to correct problems detected at checkpoints- turns on genes that induce self-destruction

Separase

degrades cohesin to allow separation of sister chromatids

Cohesin

holds sister chromatids together at centromere until separase degrades cohesin- chromatids separate

Dynein

motor protein that sits on two spindle fibers- pulls on spindle fibers connected to chroms

number of chroms=

centromeres

each chromatid is

separate DNA molecule

Only spermatogonia and oogonia undergo meiosis during which phase

M phase of meiosis, other cells undergo mitosis

Meiosis produces

4 haploid daughter cells, 1 set chroms per cell

mitosis produces

2 identical diploid daughter cells

Recombination occurs b/t

homologous chroms during meiosis

child inherits some chroms that contain a combb of alleles coming down from the gradnfather & grandmother

Prophase 1

chromosomes condense and engage in close synapsis producing bivalents/tetrads, then crossing over occurs/swapping of arms

Leptotene stage

• chromatin condenses appears as two threads

Zygotene stage

• chromatin consenses, homolog. chroms pair up in synapsis

Pachytene stage

chromatin condenses, synaptonemal complex develops b/t homologous chroms

Diplotene stage

two chroms in each bivalent begin to separate, but remain joined at chiasma (place of crossing over)

Diakenesis

chromatin condenses further, two chroms in bivalent separate farther apart, chroms only joined at ends

Metaphase 1

bivalents aligned in tetrads along eq. plane

spindle fibers connect to chroms by kinetochores at centromeres

Anaphase 1

Separase degrades cohesin that holds homologs together

leaves cohesin that is holding sister chromatids together at centromere intact

Shugoshin protein

protects cohesin at centromeres- only from degration by separase

holds chromatids together at centrosomes during anaphase 1 so no separation until anaphase II

Interkenesis

nuclear membrane reforms, spindle fibers degenerate, chromatin decondenses

First cell div known as

reduction division (reduces # of chroms in cell by half)

Second div. known as

equational div.- no change in chrom. # per cell

DNA repair proteins

cut out bubbles/mismatch bases, use remaining strand as template

Cytoplasm packaging in oogenesis

all cytoplasm & organelles migrate into one daughter cell (becomes egg), other cell becomes polar body & dies off

Male spermatogenesis time course

• infancy- errections begin

• 11-14- secondary sex characterists. appear

• 13-16 sperm produced in adult amounts