Meiosis Flashcards
What is gametogenesis?
Making of oocytes and sperm
Are gametes haploid or diploid?
Haploid due to meiosis
What are sex cells called when they enter meiosis I?
Primary oocyte or primary spermatocyte
Define ploidy.
Origin of an individual chromosome’s DNA
What is euploid?
An extra full set of chromosomes usually due to polyspermy (triploidy)
What is aneuploid?
Extra single chromosome due to nondisjunction (trisomy)
What is “N”?
Total # of DS DNA copies of each chromosome
What kind of ploidy and N does a gamete have?
Haploid and 1N
Define homologues.
Identical chromosomes originating from different parents
Define sister chromatids.
Duplicated copy of each chromosome following S phase; connected centromere
Define bivalents or tetrads.
Pair of duplicated homologues… 2 pairs of sister chromatids
Define chiasmata.
Regions where bivalents crossover and recombine during prophase I of meiosis
What are the male and female versions of the primordial germ cell?
Spermatogonium
Oogonium
What are the male and female versions of cells committed to Meiosis I?
Primary Spermatocyte
Primary Oocyte
What are the male and female versions of Completed meiosis I/Committed to Meiosis II cells?
Second Spermatocyte
Secondary Oocyte
What are the male and female versions of completed meiosis I/Immature gamete cells?
Spermatid
No female version
What are the female and male versions of a mature gamete cell?
Spermatozoa
No female version (fertilized egg or zygote)
When do males and females begin begin meiosis?
Males begin at puberty
Females begin in utero
Is meiosis continuous or arresting in males and females?
Continuous in males
Arrests twice in females
How many haploid gametes are produced in males and females?
4 haploid gametes in males
1 haploid gamete in females
What is another name for the 1st meiotic division?
Reduction division or diploid to haploid
In meiosis I do sister chromatids stay together or separate?
Stay together
What happens in Meiosis I: Prophase I?
Oocytes are arrested at diplotene stage until ovulation; this prolonged female diplotene is called dictyotene
What occurs during Prophase I?
Crossing over
What happens in Meiosis I: Metaphase I?
Nuclear membrane disappears
Spindle forms
Paired chromosomes align at equatorial plane
Centromeres orient toward opposite poles
How do sister chromatid kinetochores behave in Metaphase I?
They behave as one and orient toward a single pole
What is the most error prone step of meiosis?
Meiosis I: Anaphase I
What happens in Meiosis I: Anaphase I?
Bivalents disjoin and sister chromatid pairs are drawn to opposite poles of the cell; thus, chromosome number is halved.
When does nondisjunction occur?
When homologous chromosomes fail to separate during meiosis.
What does nondisjunction result in and when may it occur?
Results in some gametes with 24 chromosomes, some with 22
May occur at meiosis I or meiosis II
In Meiosis I: Telophase I and Cytokinesis what happens?
Decondensation of chromosomes
Reformation of nuclear membrane
2 Haploid daughter cells made
Cells enter a brief interphase
Do cells going through Meiosis enter S phase before going on to the next division?
Nope they do not
What happens in cytokinesis in the spermatocyte?
Spermatocytes divide their cytoplasm approximately equally to yield two secondary spermatocytes
What happens in cytokinesis in the primary oocyte?
Oocytes divide very unevenly to yield one secondary oocyte and the first polar body
What has oocyte biopsy been found to help with?
Oocyte biopsy of a polar body could possibly be used to determine which eggs have the best chance to produce a viable embryo.
What is another name for 2nd meiotic division?
Equational division or 2N to 1N
Are sister chromatids separated or together in Meiosis 2?
Separated
What is the end result of the 2nd meiotic division?
4 haploid secondary (1N) spermatocytes
1 secondary oocyte + 2nd polar body
When does an oocyte complete meiosis 2?
Only if the egg is fertilized.
