meiosis

Question 1

total chromosomes in each somatic cell?

Answer 1

somatic cells (not egg or sperm) have 46 chromosomes = 23 pairs (22 autosomes and 1 pair of sex chromosomes)

Question 2

aneuploidy

Answer 2

abnormal chromosome number

Question 3

monosomy

Answer 3

missing a chromosome (single copy of 1)

Question 4

triploidy

Answer 4

complete duplication of whole set

Question 5

abnormal chromosome rearrangement is called

Answer 5

translocation -balanced = switch but not loss

Question 6

chromosome anatomy p arm q arm centromere dark bands light bands

Answer 6

p arm is the small arm centromere is the central super coiled portion dark bands are rich in G and C = gene poor light bands are rich in A and T = gene RICH!

Question 7

mitosis abnormality

Answer 7

if it doesnt lead to death in that cell, it is perpetuated in lineage of that cell how cancer starts

Question 8

meiosis

Answer 8

reduction cell division isolated to germ cells to generate egg and sperm with 23 chromosomes 2 parts = meiosis 1 and 2

Question 9

meiosis 1 vs meiosis 2

Answer 9

o Meiosis 1: reductional division that reduces the chromosome number from diploid to haploid  PAIRS pull apart in anaphase 1 o Meiosis 2: equational division that begins with haploid number but processes like mitosis with that number  Chromatids pull apart

Question 10

two unique meiosis events

Answer 10

pairing crossing over/chiasmata formation

Question 11

pairing

Answer 11

Homologous chromosomes, after duplicating themselves into two chromatids held together by a single chromosome, are matched by homologue alignment  formation of a synaptonemal complex of protein which holds the pair together in synapsis  X and Y pair end to end; all others pair longitudinally

Question 12

crossing over/chiasmata formation

Answer 12

Homologue pairs are locked together through recombination of chromosome  Why parents genetic information combine!  Crossing over is preceded by double stranded DNA breaks  Followed by adherence of the arm from one homologous pair to the site of the break on the other pair  pieces then cross over

Question 13

exchange events are…

Answer 13

• Only occur in euchromatin (stretched out material); not in heterochromatin (condensed) • Exchanges are lowest near the telomere • Highest in the medial regions of the euchromatin arms • Usually one exchange per chromosome arm

Question 14

translocations

Answer 14

If pairing occurs between non-homologous chromosomes, then exchange can place pieces of one chromosome inside another  not a problem if there is no loss of chromosome material (balanced)  if material is lost, then it is an unbalanced translocation – usually severe!!

Question 15

sperm meiosis

Answer 15

initiates at puberty and continues throughout male lifetime o spermatogonium –> primary spermatocyte –> meiosis 1 makes a secondary spermatocyte –> meiosis 2 makes a spermatid  Yields 50% 23X/50% 23Y sperm  Minimal cytoplasm and mitochondria maintained

Question 16

egg meiosis

Answer 16

o Process initiates in embryonic life o Primordial germ cells originate from yolk sac at 4 weeks embryonic age o Migrate to gonadal ridges and undergo mitosis to create 7 million oogonia by 20 weeks gestational age o Cells then lose ability to undergo mitosis and enter meiosis 1 follicular atresia decreases egg count

Question 17

o Follicular atresia

Answer 17

Majority of developing oogonia complete varying stages of maturation and die • 2 million left at birth, 400,000 left at puberty, and about 400 are ovulated in a lifetime – usually a few are fertilized by 51.3 (average) down to 0!

Question 18

egg meiosis

Question 19

initial arrest in egg meiosis

Answer 19

Initial arrest in egg development at Meiosis 1, prior to metaphase

At point of chiasmata formation and crossing over –> Called dictyotene

Dictyotene = first arrest

May last from 12-50 years

Question 20

when does meiosis 1 complete in egg?

Answer 20

• Completion of meiosis 1 triggered by LH surge in menstrual cycle
  
  • Unequal cytokinesis, extruding only nuclear marker material as the first polar body

Question 21

2nd arrest in egg meiosis

Answer 21

• 2^nd Arrest at ovulation - occurs at beginning of meiosis 2 –> not completed until fertilization, after sperm penetrates oocyte

Question 22

completion of meiosis 2

due to what? net result?

Answer 22

• With fertilization, nuclear completes meiosis 2
  
  • Unequal cytokinesis again à nuclear material extruded as second polar body
  • First polar body might also complete meiosis 2
• Results in one large ovum and 3 polar bodies

Question 23

fertilization: pronuclei to zygote?

Answer 23

• Remaining nuclear material in the oocyte forms the female pronucleus
• Sperm after entry to egg sheds its tail and forms the male pronucleus
• Two pronuclei fuse to form the zygote!

Question 24

do male and female meiosis have checks and balances?

Answer 24

male does!

• Can detect misalignment of chromosomes à errors in recombination or synapsis trigger an arrest at pachytene leading to apoptosis
• No similar processes identified in the female meiosis

Question 25

maternal age effect on meiosis

Answer 25

• Maternal Age can impair chromosome segregation machinery, protein assembly in spindle apparatus (mitochondrial energy process impairment), and chromosome exchange process
  
  • Overall reduction in number of exchanges
  • Position of exchanges alters towards the telomeres
  • With reduced number of exchanges, chromatid are less likely to separate
• The longer the egg remains in meiosis 1 (aka the older the mother) à the greater the likelihood it will divide unevenly (greater potential for error)

Question 26

Question 27

trisomy 21

Answer 27

downs syndrome

• Most common live-born aneuploidy (1/700)
• Usually a straight extra chromosome and related to maternal meiosis 1 abnormalities
• Flattened facial profile, small ears, protruding tongue, transverse common crease, small mouth; friendly and outgoing; risk for many issues: cardiac, leukemia, thyroid, developmental Delay, alzheimers early onset

Question 28

trisomy 18

Answer 28

edwards

• 1/3000 LB
• Clenched, overlapping digits, small babies, windswept ears, hammertoe, narrow/delicate

Question 29

trisomy 13

Answer 29

rarest of the three

Many die early (1st week-1st year)

Question 30

turner syndrome

Answer 30

45,X

missing an x

Question 31

5p deletion

Answer 31

cri du chat

distinct cat like cry

Question 32

williams syndrome

Answer 32

deletion 7q

elastin gene issue; small upslanting eyes, large full lips, mild developmentally delays; outgoing personality

Question 33

deletion 15q11, maternal

vs

deletion 15q11, paternal

Answer 33

• Angelman syndrome (deletion 15q11, maternal) – small, wide mouth, nonverbal, seizures, paroxysmal laughter
• Prader Willi Syndrome (deletion 15q11, paternal) – fair skin (tyrosinase), small extremities and genitals, obese tendency/will eat everything; paroxysmal anger

Question 34

deletion 22q11

Answer 34

Velocardiofacial syndrome (deletion 22q11 – long nose/face, tetraology of fallot

Question 35

kleinfelter genome

Answer 35

47, xxy

• most go unrecognized until trying to conceive, infertile, neck webbing, tall!

Question 36

two ways to diagnose chromosomal abnormality before birth

Answer 36

• Amniocentesis – obtain a sample of fetal amniotic fluid (fetal urine) at 15-18 weeks
• CVS (chorionic villus sampling) – obtain a sample of placenta (same chromosomal origin as the fetus) at 11-13 weeks

Question 37

how much of the cell free DNA in maternal plasma is of fetal origin?

Answer 37

5% is ffDNA (free fetal DNA)

Question 38

ffDNA is 100% specific test for what?

Answer 38

fetal Rh and sex (XY)

trisomy 21