Meiosis Flashcards
What is another word for haploid cell?
Gamete
What kind of gamete is associated with birth defect and infertility in humans?
Aneuploid Gamets
What are the meiotic contributors to genetic diversity in populations?
Recombination and redistribution of homologous chromosomes
Are the daughter cells haploid or diploid after meiosis 1?
Haploid (2)
What happens in Meiosis 2?
Sister chromatids segregate, leading to the formation of four non-identical haploid gametes.
What is the difference between a homologue and sister chromatids?
Homologues - Starting diploid cell involving two different chromosomes
Sister Chromatids - an identical pair of chromosomes made by replication
Why is the fact that meiosis is reductive necessary?
It halves the number of chromosome sets that originally are doubled by fertilization
Are the diploid cells that remain after Meiosis 1 homologous or sister chromatids?
Homologous
What is the order of segregation in terms of the type of chromatids?
Homologous chromosomes segregate first, and sister chromatids segregate after
How do some protists and fungi fit into the cell cycle?
They live as haploid cells, and only undergo mitosis in the upper part of the cycle, skipping the diploid generation
How do humans fit into the cell cycle?
They live as diploid cell, and only undergo mitosis in the lower part of the cell cycle, skipping the haploid generation
How do plants fit into the cell cycle?
They have two distinct multicellular generations (alternation of generations), they undergo mitosis in both sides of the cell cycle
How are haploid ESCs (embryonic stem cells) different than diploid ones?
Haploids have smaller volume, they only have one expressed X chromosome, and can differentiate
In yeast, what phase triggers mitosis and which regulators trigger it?
In the G1 phase IME (inducer of mitosis) 1 and 2 promote entry into the mitotic S phase
What are the roles of IME 1 and 2?
IME 2 encodes a CDK-like protein in G1 phase which regulates IME 1 transcription, which transcribes the meiotic program
What is the difference in CDK levels in mitosis and meiosis?
There is a second peak of levels (of IME2 and therefore CDK) in meiosis
Why do meiotic CDK levels drop between Meiosis 1 and 2?
It prevents further DNA replication
What is the difference in the amount of time it takes for male vs female mice to undergo the first meiotic prophase?
10 days for males, roughly 4 days for females ( but the oocytes arrest for months)
What triggers the transition from a mitotic to meiotic cell cycle?
Endogenous programmed events
What substance is the key inducer of meiosis?
Retinoic Acid (RA)
What two key targets does RA hit after diffusing into the germ cell?
It transcribes the target genes (Stra8 is critical) and transcribes meiosin, a gene essential for mitosis - meiosis transition
What do epigenetic modifiers in chromatin coordinate with to activate downstream targets?
Stra8 and meiosin
How was meiotic gene regulation studied 1980-2000?
Genetic screening was done on mutants with meiotic defects
How was meiotic gene regulation studied 2000-2020?
Transcriptome profiling is the use of RNA to understand gene expression and links to physical differences
Briefly explain the modern genomic assays findings?
They detail regulatory mechanisms that govern gene expression
Name and briefly explain the 5 steps of meiotic prophase
Leptotene - Condensation of chromosomes
Zygotene - pairing of homologues into tetrads
Pachytene - Thickening of chromosomes and crossing over
Diplotene - Separation of chromosomes
Diakinesis - Chromosomes condense, nuclear envelope breaks down
What is the general mechanism for Homologous recombination (HR)?
It is the DNA response to genetically programmed double strand breaks
What model do we follow for meiotic recombination?
The Early Crossover Decision (ECD) model
What are the two options for the ECD model?
It can go the NCO (non crossover) or CO (crossover) pathway
What direction of resection does the DNA follow in crossing over?
the 5 to 3 direction
What are the differences in the NCO and CO pathways?
It depends where the Holliday Junctions are cut
How can we get a good estimate of chromosome length?
The frequency of recombination is a fair estimate of gene length, they are proportional to each other
Define recombination
The process that results in gametes with different alleles than the parental generation
What is the frequency of recombination?
The number of crossover events in the section of the genome per meiosis (0-1)
What is a recombination hotspot?
Regions with a higher frequency of recombination than elsewhere
What are 4 features of human hotspots?
- They have rates hundreds of times higher than surrounding
- They are found near telomeres and in certain gene rich areas
- More than 30,000 have been identified in the human genome
- It is where cancer and other diseases are located due to genetic instability
What enzyme removes coheisins from sister chromatids during the onset of anaphase?
protease separase
What complex activates separase?
APC (anaphase promoting complex)
Why do centromeric rings of coheisins persist through meiosis 1?
So sister chromatids can co-segregate
What allows for the separation of sister chromatids in anaphase 2?
Separase dissociates the coheisins around sister chromatids
What are the study results in terms of cells affected by poor meiosis?
1 in 4 sperm cells and 1 in 12 eggs have mutations
What are the complications an aneuploidy?
Infertility, miscarriages, and birth defects
What is the leading cause of mental developmental issues?
Aneuploidy
What are the three ways meiosis can affect human health adversely?
- Re-expression of remnant miotic proteins can have oncogenic consequences
- Aneuploid cancer cells are very prevalent
- Genetic recombination can change pathogen properties, factoring into treatment and vaccination equations
