genetics final

heredity

study of transgenerational inheritance of phenotype traits

genetics

study of transgenerational gene transmission

genetic variation from

meiosis and de novo germline mutations

germline mutations

mutation in sperm and eggs that can be inherited

meiosis

the two nuclear divisions that accompany sexual cell division that creates four genetically diverse gametes from one diploid cell.

meiosis consists of

two stages: meiosis I and meiosis II, which include processes like crossing over and independent assortment.

prophase

I is the first stage of meiosis, where chromosomes condense, homologous chromosomes pair, and crossing over occurs.

metaphase

I is the second stage of meiosis, during which homologous pairs of chromosomes line up at the equatorial plate of the cell, preparing for separation.

telophase

I is the final stage of meiosis, where the chromosomes arrive at opposite poles, begin to de-condense, and the nuclear envelope reforms around each set of chromosomes.

leptotene

I is the first substage of prophase I in meiosis, where chromosomes begin to condense and become visible as thin threads.

zygotene

I is the second substage of prophase I in meiosis, where homologous chromosomes start to pair and undergo synapsis, forming tetrads.

pachytene

I is the third substage of prophase I in meiosis, characterized by the complete pairing of homologous chromosomes and the exchange of genetic material through crossing over.

diplotene

I is the fourth substage of prophase I in meiosis, where homologous chromosomes begin to separate but remain attached at chiasmata, and further condense.

in meiotic prophase 1 the exchange of chromosomal material between homologous chromatids due to crossing over has a recombination frequency of

50% or less between two selected markers on the same chromosome arm

the frequency of recombinants is used to

estimate genetic distance between genes. 1% RF = 1 map unit = 1 centimorgan

a typical human chromosome may have a genetic map length of

about 200 centimorgans

three pairs of homologous chromosomes creates

8 haploid gametes

maximum RF between 2 markers is 50%

because sister chromatids do not undergo recombination

crossing over

a strand from one sister chromatid breaks, unwinds, and invades a non sister chromatid

Holiday Junction: horizontal

breakage and reunion of the inner two strands results in a non crossover conformation

holiday Junction: vertical

breakage and reunion of the outer two strands resulting in a crossover conformation.

recombination tends to occur at

promotors/euchromatin not at centromeres

double strand brekas appear at the same time the

axial elements of synaptonemal complex form

synaptonemal complex

consequence of recombination, that inhibits/ supresses further recombination

types of DNA recombination

include homologous recombination, transposition, and site-specific recombination.

homologous recombination

a type of genetic recombination that occurs at two of the four strands between similar or identical DNA sequences, facilitating the exchange of genetic information during meiosis in euraryotes

site specific recombination

a mechanism of genetic recombination where DNA segments are inserted, deleted, or rearranged at specific sequences in the genome, used by prokaryotes

transpostition

a process where DNA segments move from one location to another within the genome, involves breakage and reuinion of DNA strands

genetic disease

a condition in which there is no observable/detectable genetic component

chromosomes are classified by

position of the centromere - arm length ratio, and secondary constrictions - nucleolar organizers

classification of chromosomes

telocentric, acrocentric, metacentric

telocentric

only one arm because the centromere is located at the end

acrocentric

two uneven arms because the centromere is close to one of the ends

metacentric

two even arms because the centromere is located right tin the middle

human karyotype has

46 chromosomes

each parent contributes

23 chromosomes

sex is determined by

X and Y chromosome

males chromosomes

XY

female chromosomes

XX

the sex of an offspring is determined by the sex chromosome carried in the

sperm

human chromosomes are divided into

7 groups plus the sex chromosomes

satellites

long runs of repeats that give chromosome arm structure or staining pattern

chromosomes are laid out from

longest to shortest, then sex chromosomes

end of chromosome called

pseudoautosomal region (PAR)

pseudoautosomal region (PAR)

a region at the ends of sex chromosomes where they share homology, allowing for pairing during meiosis.

FISH

(Fluorescence In Situ Hybridization) is a molecular cytogenetic technique that uses fluorescent probes to bind to specific parts of the chromosome, allowing for visualization of chromosome structure and abnormalities.

nomenclature of crhomosomes

total number of chomrosomes, sex chromosomes constitution, description of abnormality

ie. 46,XX Normal Female

chromosomal abnormalaties

loss or gain of whole chromosomes or sub chromosomal segmentsthat may lead to various genetic disorders.

numerical chromosome abnormalities

change in number with no chromosome breakage

polyploidy

abnormailty of an entire chromosome set

ie. triploidy & tetraploidy

triploidy

due to double fertilization

tetraploidy

due to failure to complete first zygotic division

natually polyploid cells

regenerating liver, and magakaryocyte

aneuploidy

abnormal number of a specific chromosome

ie. monosomy, trisomy, & nullisomy

monosomy

loss of one copy of a homologous chromosome pair - lethal in embryo

trisomy

additional copy viable

nullisomy

loss of both homologous - lethal before implantaion

cells that often show extreme aneuploidy

cancer cells

aneuploid cells arise by

nondisjunction and anaphase lag

nondisjunction

failure of paure chromosomes to separate at meiosis 1

anaphase lag

failure to incorporate a chromosome into a daugher call at cell division ( this chromosome is lost)

type of numerical chromosome abnormalities

polyploidy, aneuploidy, and mixoploidy

mixoploidy

an individual has cells different chromosomal compositons

mixoploidy occurs due to

mosaicism and chimera

mosaicism

individual has two or more genetically difference cell lines derived from a single zygote

chimera

mosaicism but cells derived from different zygotes, very rare

aneuploidy mosaics

are common

ie. normal/trisomic mixture due to nondisjunction in cell of early embryo

polyploidy mosaics

rare

diploid/triploid mixture due to fusion of second polar body with nucleaus of early embryo cell

types of structural abnormalities due to chromosome breakage

single break, two or more breaks, chromosomal inversion, interstitial deletion, ring chromosome

single break

occurs when one chromosome undergoes a fracture, leading to loss or alteration of genetic material. often repaired!

two or more breaks

results in more complex chromosome changes, including deletions or recombinations of genetic material.

chromosomal inversion

a structural alteration where a chromosome segment breaks at two points, flips around, and reinserts, potentially altering gene expression.

interstitial deletion

a type of chromosomal deletion where a segment of the chromosome is lost between two break points.

ring crhomosome

a chromosome that forms a ring structure due to the fusion of its ends, often leading to genetic abnormalities.

breaks on different chromosomes can cause

chromosomal translocations

types of chromosomal translocation

reciprocal translocation ballanced, roberstonian (centric) fusion, insertional translocation

reciprocal translocation balanced

is a type of chromosomal translocation where segments from two different chromosomes are exchanged without any loss of genetic material, maintaining genetic balance.

roberstonian centric fusion

is a type of chromosomal translocation that occurs when two acrocentric chromosomes fuse at their centromeres, resulting in a single chromosome and often leading to a reduction in chromosome number.

insertional translocation

is a type of chromosomal translocation where a segment of one chromosome is inserted into another chromosome, which can disrupt genes and lead to genetic disorders.

uniparental diploidy & uniparental disomy

imbalance between maternal and parental contributions to the karyotype

looks normal

causes abnormalities if affected region is subject to genomic imprinting

uniparental diploidy

all chromosomes are derived from the same parent, genetic markers on these chromosomes are homozygous

androgenetic mole

is a type of gestational trophoblastic disease in which the embryo contains only paternal genetic material, often resulting in abnormal placental development.

ovarian teratromas

are tumors that arise from germ cells and can contain a variety of tissue types, including hair, muscle, and nerve tissue. They are often benign but can be malignant.

uniparental disomy

is a genetic condition where an individual inherits both copies of a chromosome from one parent, could by casued by loss from an embryo with trisomy

uniparental isodisomy

is a specific form of uniparental disomy where two identical copies of a chromosome are inherited from one parent, and could be caused by a monosomic embryo duplicating a monosomic chromosome

triploidy

leads to individaul having 3 sex chromosomes ie 69, xxx or 69,xxy

trisomy

an extra chromosome 21 leading to down syndrome, 47,xx+21

monosomy

is the presence of only one copy of a chromosome, fatal in all cased except for turner syndrome, 45,X

p

the short chromosome arm

q

the long chromosome arm

examples of diseases caused by chromosomal abnormalities

down syndrome, trisomies, turner syndrome, Prader-Willi syndrome, burkitts lymphoma, chronic myelogenous leukemia

down syndrome is more likey

in older women - can be due to social, legal and other societal aspects

down syndrome is mostly caused by..

most cases have extra ..

21st chromosome material, resulting in trisomy 21

maternal 21

both usually due to nondisjunction at meiosis.

down syndrome can also be (rarely) caused by

unbalanced translocation between long arm 21 and long arm 14

probably de novo events or inherited

down syndrome usually also results in the individual having an extra copy of this protein

amyloid precurser protien - protein that is jey in dementia and alzheimers

meiosis for an individual with down syndrome didnt

align correctly, resulting in no polar body so both chromosomes were equal size

down syndrome can be prevented by

correction mechanisms during puberty, but these mechanisms degrade as mother ages

patau syndrome

trisomy 13, 47,+13, has a very rare survival rate

edwards syndrome

trisomy 18, 47,+18, almost all die in the eutero or die after. age 1

turner syndrome

45, X (O) only viable monosomy