Gametes are ____ due to the process of meiosis. Sequence of events is identical for both sexes. ____ of events is dramatically diff
diploid germ cells –> ____gametes and occurs via 2 succesive meiotic div’s without intervening ____ phase. Germ cells are called oogenia or spermatogenia, but as they enter meiosis 1 they are called primary ____ and primary _____
haploid; S; oocyte; spermatocyte
What are the genetic consequences of meiosis
- Reduction of chromosome number (46 diploid to 23 haploid)
- Segregation of alleles
- Random assortment of homologs
- Inc in genetic variation via recombination
What is ploidy
origin of an ind chromsomes DNA
single parent = \_\_\_\_ both parents = \_\_\_\_ anything else = \_\_\_\_ euploid =\_\_\_\_\_\_ aneuploid = \_\_\_\_\_\_
extra full set of chromosomes due to polyspermy
extra single chromosome due to non disjunction
N is the total # of DS ___ copies of each chromosome
Interphase somatic cell is _____ and ____ N. Somatic cell after S phase is ____ and ____N which is an intermediate phase. Gamete prior to meiosis II is ____ and ___N which is also an intermediate phase. Our final gamete is ____ and ___N
What are homologues
identical chromosomes originating from different parents
what are sister chromatids
duplicated copy of each chromosome following S phase; conn at centromere
What are bivalents/tetrads
pair of duplicated homologues…2 pairs of sister chromatids
what is chiasmata
regions where bivalents/tetrads crossover and recombine during prophase 1 of meiosis
Female oocytes never complete ____ unless they are fertilized and at that point they are called a ______.
meiosis II (locked in metaphase II); zygote
an immature male gamete is called a _____. A mature male gamete is called a _____
Males begin meiosis at _____ and generate ____ haploid gametes from one PGC. Female meoisis begins before ______. Meiosis arrests twice, in prophase 1 and metaphase II. We only get ____ haploid from PGC
puberty until death; 4
we are born (in utero); 1
The first meiotic division is called ____division and is going from diploid to haploid. While entering meiosis I, cells are diploid & ___N after S phase. Centromeres do not split at ___I. Daughter cells have 1 copy of sister chromatid chromosomes from _____ parent.
reductive; 4; metaphase; single.
In mitosis, When sister chromatids line up they go to sep cells so you remain diploid (copies coming from 2 diff parents) so you are ____ and ____N
The diff bet meiosis and mitosis is that:
in meiosis sister chromatids stay together to give you a haploid 2N and then eventually 1N, but in mitosis, sister chromatids sep to give you diploid, 2N
What is the longest phase of meiosis?
prophase; where recombination occurs between tetrads.
What are the stages of prophase1 in meiosis?
- Leptotene: chromosomes begin to condense. chromomeres are evident
- Zygotene: tetrads form bet homologs; this unique to meiosis!
- Pachytene: homologus recombination occurs; bivalents are evident.
- Diplotene: bivalents “repel,” chiasmata evident.
- diakinesis: chromosomes are maximally condensed.
Oocytes are arrested at ____stage until ovulation. The prolonged diplotene stage is called _____
what is chiasmata impt for
Patients with trisomy’s dont have enough chiasmata forming in their gametes compared to normal people. Chiasmata are impt in keeping tetrads aligned until the right time and rep places where homologous recombination is occuring.
crossing over occurs during _____
What makes up the synaptonemal complex
- lateral element
2. central element
What is the recombination nodule
huge protein complex. Placement corresponds to regions of chiasmata formation.
what happens during metaphase I
- nuclear membrane disappears
- spindle forms
- paired chromosmes align at equatorial plane.
- centromeres orient toward opp poles.
Why don’t sister chromatids sep in meosis 1? *** ask about this slide (18)
Securin is not sep or being ubiquinated and separase does not become active. Not breaking the cohesin thats holding the sister chromatids together in meosis 1. Not being ubiquinated by APC.
What happens during anaphase
Where disjunction occurs: tetrads disjoin and sister chromatid pairs are drawn to opp poles of the cell; thus chromosome # is halved. You get indep assort of chromosomes from maternal vs paternal origin. Each chromatid contains segments derived from each parental chromosome pair due to crossing over.
What is the most error prone step of meiosis
when does nondisjunction occur
when homologous chromsomes fail to sep during meiosis. Results in some gametes with 24 or 22 chromosomes. Can occur at meiosis I or II. If abormal gametes involved in fertilization you get: monosomy, trisomy or uniparental disomy.
how does telophase I or cytokinesis work?
- Decondensation of chromosomes
- Reformation of nuclear membrane
- 2 haploid daughter cells (2N)
- cells enter a brief interphase
* cells do not enter S phase prior to next div*
Spermatocytes divide their cytoplasm approx equally to yield ____ secondary spermatocytes. Oocytes div. very unevenly to yield ____ secondary oocyte which yields to ___ polar body
2; 1; 1
What has all the genetic info that the female egg has?
Meiosis II refers to ____division bc its going from ___N to ___N. Sister chromatids are now separated. The end result is ____haploid secondary spermatocytes, ____ haploid secondary occyte + ____only if egg is fertilized
equational; 2; 1;
4; 1; polar body