Genetics Soliman Exam 2

somatic

… tissue, does not give rise to gametes, mutations are only passed through mitosis where cells are replicated

germ-line

mutation existing on the sex cells, are passed down through generations and through meiosis/sexual reproduction. 50% of generation may carry it and other 50% may not.

Base subsitution

most simple, only one nucleotide is altered

Base subsitution: Transition

pyridimidine to pyridimidine (t-c)
purine to purine(A-G)

Base subsitutions : transversions

pyrimidine to purine
T/C becomes A/G
Purine to pyrimidine
A/G to C/T

Insertion and deletion

Addition or deletion of one or more nucleotides, can alter reading frame, usually multiples of 3

Expanding nucleotide repeats

A surplus/increase of repeats that appear in this location of a chromosome. Usuaully a trinulceotide repeat, linked to many as much as 30 disorders
greater repeats, greater instability
the more the repeats the worse the disease and anticipation
trinucleotide repeats can cause strand slippage

anticipation

the chance the next generation displays symptoms of that disease at an earlier age

forward mutation

wild type to mutant type

reverse mutation

mutant to wild type

suppressor mutation

A mutation occurs in another area that silences the first mutation, causing the second mutation to only be seen. (suppresses the first mutation at another site)

Intragenic suppressor mutations

double mutant, normal phenotype
Mutations occur within the same gene coding sequence

Intergenic suppressor mutations

occurs in a secondary gene location, failure of stopping translation
Ribosome reads the stop codon UAG incorrectly, inserting a tyrosine after, full protein is made after

Missense mutation

Single nucleotide error, an amino acid is changed, protein might still work or be partially nonfunctional

Nonsense mutation

A single nucleotide error that creates a stop codon by accident

resulting in truncated/short protein, usually nonfuctional

point mutation: null-loss of function mutation

recessive mutation, you need two copies to see the entire impact of the loss of function

Point mutation: gain of function mutation

Mutation causes the protein or gene to be enhanced and more functional

Conditional mutations

mutations that only occur based on certain mutations
ex: siamese cat pigment gene, black limbs that are cold, but in warm areas gene doesn’t work resulting in white cat

Lethal mutation

results in death

Transposable element

terminal inverted repeat and transposase
when it leaves it will leave behind direct flnaking repeats
can cause a silence of genes and disrupt them,

Transposase

enzyme that helps with cutting dna and pasting the transposon in another section of DNA
makes stagger cuts to let transpoable element insert itself into the DNA

Mutagens

Chemical … that causes a mutation above the spontaneous rate
base analogs, alkylating agents, deamination,

negative supercoil

L=48, down to the left
undercoiled
relaxed = 50

positive supercoils

L=52, down to the right,

overcoiled
relaxed = 50

Topoisomerase

Controls the supercoiling, or coiling in general of any DNA, usually to help relieve strand stress and tension

Plasmid

freefloats in the nucleoid region of a bacteria, replicate independently from the bacteria itself and can use conjugation
small, circular
does not contain genetic information that is essential for life but contains genes that encode for proteins

Conjugation of Plasmids

copies of plasmids transfered from one bacterium to another to share information/DNA
plasmids need a bridge to be established (touching) beofre genetic material can be transfered over

Resistance factor

proteins that protect the bacteria against antibiotics, so it cannot be killed

fertility factors

proteins that enable bacteria to engage in conjugation with other bacteria more effectively

nucleosome

Dna wrapped around 8 histones with the H1 protein

chromosome arms

p; petite arm (top), q: larger arm (bottom)

Metacentric

equal p and q

Subcentric

small p

Acrocentric

very very small p

telocentric

essentially no p at all, too small.

Kinetochore

protein around the centrometere that allows for the spindle fibers to bind to so the homologs or sister chromatids can be separated in anaphase

Euchromatin

Loose region or less condensed region of chromosome, loose enough for gene expression
negatively supercoiled

Heterochromatin

tight region/super condensed region on chromosome, too tight for gene expression to occur
positively supercoiled
if a part of chromosome breaks off and gets near the site the gene may be silenced

Autosomes

chromosome pairs 1-22, non sex cell
1 is the largest, 22 is the smallest

Sex chromosomes

usually chromosome pair 23
sex cells, XX female, XY male

G-banding

-Karyotype (a picture/scan), of chromosomes that are dyed with Giesma (G, name comes from the dye)
-distinct dark and light bands are used to identify chromosomes
cells grown in a culturem special additives used to halt cells from mitosis and metaphase, when chromosomes are most dense, then spilled onto glass slide and spread out (metaphase spread)
A-T bonded regions are darker dyed than T-C regions are
provides system for localizing genes on chromosomes

Euploidy

wild type/ normal number of chromosomes

Aneuploidy

does not have standard number of chromosome
nullisomy - no exact duplicate/copy, can be missing a whole set
monosomy - 1 copy of a specific chromosome
disomy - 2 copies of a specfic chromosome
trisomy, tetrasomy, etc

Polyploidy

one or more extra sets of chromosome, may not be abnormal
haploid - one set of chromosome in one DNA cell
diploid - two sets of chromosome in one DNA cell
triploid, tetraploid, etc

Deletion

segment of dna is deleted, lost in cell division and will not appear in cells
can result in
psuedodominance: recessive phenotype is shown, even without the second copy that it needs
Haploinsufficency: gene only barely makes what is needed

duplication

1.displaced duplication = duplication does not occur near site
Normal = ABCDE, mutated = ABCDEAB

2. Reverse duplication = duplicates an inverted copy
Normal = ABCDE, mutated = ABCDECBA

Insertion

non reciprocal translocation,
piece of chromosome breaks off and inserts itself elsewhere without replacement DNA

Balanced reciprocal

No DNA lost
size does not matter, just if anything at all comes to replace the missing DNA

Unbalanced translocation

nonreciprocal, DNA is lost, with no replacement
size does not matter, just if anything at all comes to replace the missing DNA

Position effect

When a part of a gene moves to a heterochromatic region, resulting in the silence of a gene, chromosome region is too tight and condensed to read or be expressed

Robertsonian translocation // rob t

fusion of two acrocentric chromosomes, two extremely small p arms (acrocentric usually)
can be phenotypcally normal even with 41 chrmosomes
can result in trisomy
these translocations are considered a single chromosome, (two parts of two broken chromsome = 1 chromosome)

Inversion

flips a segment of the chromosome 180 degrees
unbalanced inversions are more likely to cause abnormal phenotype
but balanced inversions can still cause abnormal phenotype because the breakage can occur in the middle of a gene sequence-gene is split into two, will not work without other half

Paracentric breakage

both breakpoints occur on one side of the chromosome, i.e on the same arm

pericentric breakage

breakage occurs on two different arms/sides of chromosome

Chromosome nondisjunction

separation of homologs or sister chromatids does not occur properly during mitosis or meisosis.
can lead to aneusomies/polyploidies
probability of the cells committing nondisjunction increases with age, the ability to recombine/cross over properly decreases
- reason why older mothers are more likely to give birth to a child with down syndrome than younger mothers are

polyspermy

more than one sperm fertilizes one egg

- usually results in a miscarriage
-not like fraternal twins, in which two different eggs and two different sperms

FISH (flouresence in SITU hybridization)

relies on sequences binding to complementary sequences
-dna is labelled with flouresence and grown in culture but halted during metaphase when it is most dense
-chromosomes are examined in a metaphase slide

G1 (gap 1)

first step in cell cycle
stockpiling nucleotides, atp, and enzymes needed to replicate DNA
checked at checkpoint

S phase

second step in cell cycle

DNA synthesis occurs here, replication

G2 (gap 2)

3rd phase of cell cycle
synthesis of microtubules aka spindle fibers, proteins etc needed for cell division occur here
needs MPF (mitosis promoting factor), and once it has enough the cell can activate MPF by phosphorylation to allow m phase
materials again are stockpiled, ATP, enzymes, and nucleotides

M phase

last step in cell cycle
occurs after MPF (mitosis promoting factor) is activated by dephosphorylation
mitosis (mitotic phase)

G0 (Gzero phase)

not a real real phase, but occurs before the first phase in cell cycle
the cell stops replicating and dividing after mitosis due to lack of resources and pauses for the cycle to reset
moves on to G1 after nutrients procured

apoptosis

Cell death
cell kills itself if cell cannot fix itself
-membrane blebbing, bubbles off and dies

Mitosis (IPPMAT)

0. interphase

1. prophase

2. prometaphase

3. metaphase

4. anaphase

5. telophase

prophase (mitosis)

first step of mitosis

chromosomes condense (become their natural X shape)

spindle fibers form
nuclear membrane breaks down

prometaphase (mitosis)

second step in mitosis

nuclear membrane fully broken down
spindle fibers and kinetochore binds on centromere

metaphase (mitosis)

third step in mitosis
homologs or sister chromatids line up in the center to prepare for anaphase

anaphase (mitosis)

fourth step in mitosis
spindle fibers pull apart the homologs or chromatids

Telophase (mitosis)

cleavage
cytokinesis (cell cleavage to create two identical diploid daughter cells)

Meiosis 1 vs Meiosis 2 (PMAT)

meiosis 1 = reduce diploid to haploid (homologs separate)
meiosis 2 = separate sister chromatids and crossing over occurs
1. prophase
- during prophase 1, homologous chromosomes cross over (recombination)

2. metaphase

3. anaphase

4. telophase/cytokinesis

Dyenin motor protein

binds to the centromere of the chromosome, walks along the spindle fibers, towards the spindle poles, and pulls sister chromatids apart from the other

Difference between meiosis and mitosis

Meiosis 1 —→ between homologous chromosomes
Meiosis 2 —→ between sister chromatids
Mitosis —→ between sister chromatids

only spermagoonia and oogonia undergo meiosis
all cells but sex cells undergo mitosis
meiosis produces - 4 unique haploid cells

mitosis produces - two identical daughter diploid cells
recombination only occurs during mitosis (crossing over)

Homologous recombination aka gene conversion

one allele changes its sequence that it codes for originally to copy another allele exactly
one gene now has two alleles that code for the same thing
- heteroduplex DNA, one strand from a homolog is bound to another strand from another homolog and uses each other as a template.

spermatogenesis

produces 4 viable sperm at a time, but only one sperm can donate DNA and centrosome

oogenesis

produces 1 viable egg, two oocytes are produced, all cytoplasm and organelles in this process migrate to one daughter cell, the other becomes a polar body which usually disintegrates, meiosis 1 pauses after 7 months gestation and continues during menstruation, only finishing when finally fertilized.
immediately after fertilized, egg will become a zygote and go through several levels of cleavage and cell division

Autosomal dominant

mutant is on an autosome, you only need one mutant copy to havethe disorder
1. every person affected has at least one affected parent
2. affected daughters and sons w equal frequency, half the children will be affected
3.unaffected parents will have unaffected children

autosomal recessive

mutant gene is on one of its autosomes, you need two copies of the mutant to have the disease
1. an affected person can have affected or unaffected parents
2. two unaffected people can produce affected childreen
3. sons and daughters are affected w the same frequency
4. the disease can skip a generation or a few and reappear later

X linked recessive

mutant gene is on the x chromosome
1. female needs two mutant copies of the gene to be affected
2. males need only copy of the mutant gene since they have one x
3. males often only one affected since they have only one x
4. no male to male transmissoin possible )males only pass down y to sons not x)
5. daughters of an affected male are all carriers if mother does not have disease

x-linked dominant

mutant gene is on the x chromosome
1. female needs one mutant copie of the gene to be affected
2. males need only copy of the mutant gene since they have one x
3. males and females equally affected
4. no male to male transmissoin (males only pass down y to sons not x)
5. daughters of an affected male are all affected even if the mother does not have
6. every affected male has an effected mother

Y-Linked

mutant gene is on Y chromosome
1. only males are affected (women don’t have y chromosome)

2. all sons of affected fathers will be affected

Genetic Heterogeneity

some disorders can exhibit different patterns of inheritance

monoecious

one house
one organism has both sex organs
hermaphrodite

diecious

two houses
each organism of that species posses one genders sex organs

Heterogametic vs homogametic

hetero = XY, ZW, etc
homo = XX, ZZ, etc

SRY Gene

gene only located on Y chromosome next to the TDF 9testis determining factor), on p arm.
Is under the psuedoautosomal region, region in which crossing over occurs, like normal autosomes
can lead to disorder in abnormal recombination situations
-child with xx chromosome develops as a male bc inproper crossing over, in which SRY and TDF gene are accidentally crossed into the second X chromosome
-child with xy chromosomes develop as a female bc of inproper recombination in which SRY and TDF gene are accidentally crossed into the second X instead of staying on Y

Turners Syndrome

(45,X)
female, only one x missing (the second x)
does not go through puberty normall

some develop cognitive disabilities
webbed neck and chubby

Kleinfeller Syndrome

(47,XXY)
male (has y chromosome)
do not go through puberty normally
develops testes and male breasts (gynecomastia)
low sex drive and sterile

alligators

cold- produce females
heat- produce males

crocodiles and turtles

warm- produce females
cold- produce males

and rule

occurs when there is a specific outcome, sequence, requires a specific order
uses words like first and then etc

or rule

no specific outcome, as long as it happens, no order