Meiosis Flashcards
(54 cards)
1
Q
Three characteristics used to determine chromosome:
A
- size
- centromere index
- G-bright
2
Q
Centromere Index:
A
= P-arm length/(total chromosome length X 100)
3
Q
G-bright areas:
A
- bright regions are euchromatic, early-replicating and GC rich
- rich in SINE and Alu sequences
- contain “house-keeping” genes
4
Q
What is the goal of meiosis?
A
- to reduce the number of chromosomes in the parent cell (23 pairs; n = 46) by half and produce gamete cells (each with n = 23).
- which two homologs go into a single gamete and that an offspring inherits is completely random
5
Q
Fertilization of an oocyte with a spermatocyte (each with 23 chromosomes) reconstitutes:
A
- a diploid zygote
- a cell with 23 pairs (46 individual) chromosomes
- these chromosomes will make up all of the descendant cells in the offspring via mitosis
6
Q
Meiosis I separates:
A
homologue chromosomes
(sister chromatids remain attached at centromere)
7
Q
Meiosis II separates:
A
sister chromatids
(sister chromatids separated at centromere)
8
Q
The four stages of Meiosis I:
A
- Prophase I
- Metaphase I
- Anaphase I
- Interkinesis I
9
Q
Prophase I:
A
- pairing of homologous chromosomes
- leptotene and zygotene (synapsis)
- chromosome condensation
- pachytene
- formation of sister chromatids
- diplotene
10
Q
Metaphase I:
A
- homologous chromosomes lined up in middle of cell
11
Q
Anaphase I:
A
- Chiasmata at the chromosome ends.
- Paired chromosomes migrate to opposite poles of the cell.
12
Q
Interkinesis I:
A
- formation of nuclei and 2 daughter cells
13
Q
Meiosis II:
A
Similar to mitosis:
- Prophase II (no DNA synthesis)
- Metaphase II
- Anaphase II
Final result = 4 haploid cells (in males)
14
Q
Meiosis in males:
A
STARTS AT PUBERTY
- Meiosis I followed by meiosis II at puberty
- final result = 4 haploid spermatids
15
Q
Meiosis in females:
A
- Meiosis I begins in utero.
- Primary oocytes arrested in prophase I until puberty.
- Meiosis I completed at time of ovulation. First polar body ejected.
- Meiosis II completed at fertilization. Second polar body ejected.
FINAL RESULT:
1 MATURE OOCYTE; 2 LOST POLAR BODIES
16
Q
What stage of meiosis I are primary oocytes arrested in?
A
- dictyotene of prophase I before birth
- complete meiosis I at ovulation
17
Q
The first polar body created by meiosis in females contains:
A
- one pair of sister chromatids
- ejected at time of ovulation when meiosis I is completed
18
Q
The second polar body created by meiosis in females contains:
A
- a single chromatid
- ejected at time of fertilization when meiosis II is completed
19
Q
Nondisjunction in meiosis I:
A
- failure of homologous chromosomes to separate
- will lead to abnormal gametes and aneuploidy in zygote
20
Q
Nondisjunction in meiosis II:
A
- failure of sister chromatids to separate
- will lead to abnormal gametes and aneuploidy in zygotes
21
Q
Klinefelter Syndrome:
A
47, XXY
- trisomy
- tall, hypogonadism, gynecomastia (breasts)
- more X, greater risk for mental retardation
22
Q
Edward’s Syndrome:
A
47, XX, +18
- trisomy
- CNS, heart, renal, clenched hands
23
Q
Turner Syndrome:
A
45, X
- monosomy, cystic hygroma, short stature, infertile
- 4% survive; 96% die in utero
24
Q
Down Syndrome:
A
47, XX, +21
- trisomy
25
Patau Syndrome:
**47, XY, +13**
* trisomy
* CNS, renal, heart
26
How do you answer the question did the nondisjunction event occur in meiosis I or meiosis II?
1. Studying polymorphic DNA markers (CA repeats) can help determine parental origin.
2. Studying polymorphic DNA markers near the centromere will help determine whether meiosis I or meiosis II.
27
How do you know if a nondisjunction event occurred in meiosis I?
* heterozygosity for both alleles from one parent near the centromere
28
How do you know if a nondisjunction event occurred in meiosis II?
* homozygosity for one parental allele near centromere
29
Nullisomic gametes yield:
* monosomic zygotes
* lethal except for X chromosome
* "Turner's Syndrome"
30
Disomic gametes yield:
* trisomic zygotes
* lethal except for X, Y, a few small autosomes (13, 18, 21)
31
Balanced translocations in a parent raise the risk of:
* partial trisomy/monosomy syndromes.
* increases the risk of extra/less genetic material being inherited.
* synapsis is driven by DNA homology, and translocations can lead to quadri-radial synapsis that does not separate properly.
32
Quadri-radial synapsis due to balanced translocations in a parent can lead to how many possible segregations?
16
* only 2/16 (12%) are balanced and will give rise to normal gametes
33
Reciprocal translocations:
* two non-homologous chromosomes break and exchange fragments.
* Individuals carrying such abnormalities still have a balanced complement of chromosomes and generally have a normal phenotype, but with varying degrees of subnormal fertility.
* quadri-radial synapsis must now form during meiosis, which leads to genetically unbalanced gametes 14/16 of the time
34
Recombination of homologous chromosomes when one has an inversion leads to:
1. Formation of an inversion loop to maximize pairing.
2. Recombination within the inversion loop that leads to abnormal chromatids.
* acentric/dicentric chromosomes with duplications/deficiencies of genetic material
35
Pericentric inversions:
* Inversions in which the rotated segment includes the centromere:
* A**BC - cen - D**EFGH
* A**D - cen - C**BEFGH
* recombinant gametes will have altered gene dosage (a duplicated region and a deleted region)
36
Paracentric inversions:
* Inversions in which the rotated segment is located completely on one chromosomal arm and do not include the centromere:
* cen - A**BCD**EFGH
* cen - A**DCB**EFGH
* recombinant gametes have altered gene dosage and centromere number (one acentric and one dicentric).
37
The two reasons why a couple may be having miscarriages:
* inversions
* balanced translocations
38
Barr bodies in 46, XY:
0
39
Barr bodies in 46, XX
one Barr body in each nucleus
40
Barr bodies in 47, XXX
2 Barr bodies in each nucleus
41
Barr bodies in 48, XXXX
3 Barr bodies in each nucleus
42
Lyon Hypothesis:
* states that during early development (blastocyst stage) one of the X chromosomes in a female gets turned off
* this is maintained in all descendant cells of the clone
43
A "darkly staining" Barr body is:
* the condensed, inactive X chromosome in females
44
During the blastocyst stage (roughly 100 cells), all females inactivate a X-chromosome in each of the 100 cells. Which X-chromosome is deactivated is completely random.
This means that:
* under normal conditions a female is a genetic mosaic in each tissue derived from somatic cells.
* some tissues will express the allele from the father and some will express the allel from the mother
45
If there is a translocation between an X-chromosome and an autosome, which X-chromosome in the nucleus is preferentially inactivated?
* the normal X-chromosome is inactivated.
* **X-AUTOSOME TRANSLOCATIONS ARE PROTECTED/EXPRESSED.**
46
If there is a deletion/insertion in an X-chromosome, which X-chromosome in the nucleus is preferentially inactivated?
* X-chromosomes with deletions/insertions are preferentially inactivated.
* Normal X-chromosomes expressed.
47
The three genes involved in X-inactivation in females:
Xic, Xist, and Tsix
48
Xic:
* X Inactivation Center
* contains genes for Xist and Tsix that control inactivation of X-chromosomes in females
49
Xist:
* a gene that encodes a large non-coding RNA that is responsible for mediating the specific silencing of the X chromosome from which it is transcribed.
* The inactive X chromosome is coated by Xist RNA.
50
Tsix:
* Antisense RNA strand to Xist
* inactivates Xist, activating X-chromosome expression
51
Uniparental disomy can occur via:
* a random event during the formation of egg or sperm cells.
* during trisomic rescue.
52
Epigenetic:
* changes in gene expression in response to the environment
53
Prader-Willis Syndrome is due to a deletion on what chromosome and where?
paternal chromosome 15q11-13
* Maternal disomy and Paternal deletion.
54
Angelmann Syndrome is due to a deletion on what chromosome and where?
maternal chromosome 15q11-13
* Paternal disomy and Maternal deletion
