Lecture 9 - Mitosis and Meiosis Flashcards
What are the main phases of the cell cycle?
Interphase (G1, S, G2): Preparation for replication.
M phase: Mitosis and cytokinesis.
G0 phase: Resting phase, non-dividing cells.
What is the role of condensin proteins in mitosis?
Condensin proteins organize chromatin into structured chromosomes by:
Binding to two chromatin locations and folding DNA.
Forming DNA loops for compaction.
What is a karyotype, and what does it show?
A karyotype displays the full set of chromosomes arranged in homologous pairs.
Includes autosomes and sex chromosomes.
Male: XY; Female: XX (or ZW system in birds).
What are the chromosomal regions and their roles in mitosis?
Centromeres: Bind kinetochores for spindle attachment.
Telomeres: Protect chromosome ends from degradation.
What are the stages of mitosis?
Interphase: DNA replication.
Prophase: Chromatin condenses.
Metaphase: Chromosomes align at the center.
Anaphase: Sister chromatids separate.
Telophase: Chromosomes decondense, cytokinesis occurs.
What is the role of cohesion proteins in mitosis?
Cohesion proteins:
Hold sister chromatids together after DNA replication.
Are gradually removed during mitosis for separation.
What are 3 main features of meiosis?
Occurs in germ cells (for sexual reproduction).
Reduces chromosome number by half (diploid to haploid).
Two divisions: Meiosis I (homolog separation) and Meiosis II (sister chromatid separation).
What are 3 roles of the synaptonemal complex in meiosis?
Stabilizes homologous chromosomes during Prophase I.
Facilitates recombination through DNA repair.
Disassembles after DNA repair is complete.
What are the evolutionary benefits of recombination?
Creates genetic diversity.
Prevents the accumulation of harmful mutations.
Restores mutation-free chromosomes.
What are pseudo-autosomal regions, and why are they important?
Pseudo-autosomal regions:
Allow pairing and segregation of X and Y chromosomes during meiosis.
Ensure proper segregation in males.
How do gametogenesis processes differ between sexes?
Spermatogenesis: Continuous, produces 4 sperm cells.
Oogenesis: Produces 1 ovum and polar bodies (non-functional).
How does paternal age affect mutation rates in offspring?
Older fathers contribute more mutations due to higher cell divisions in sperm precursors.
Maternal age increases the risk of chromosomal segregation errors.
What is bacterial parasexuality?
Bacterial processes for genetic exchange:
Transduction: DNA transfer by viruses.
Conjugation: DNA transfer via physical contact.
Transformation: DNA uptake from the environment.
Why is correct chromosome segregation important?
Prevents gene dosage imbalances.
Maintains proper cellular function and prevents diseases.
Drives evolution through balanced expression.
How do epigenetic mechanisms compensate for sex chromosome imbalances?
X-inactivation (in females) balances gene dosage between XX and XY individuals.
Involves DNA methylation and histone modifications.
What happens during the G0 phase of the cell cycle?
Cells enter a reversible, non-dividing state where they are metabolically active but not proliferating.
What role do cohesion proteins play in mitosis?
Cohesion proteins hold sister chromatids together until their gradual removal allows separation during anaphase.
What happens during Meiosis I and Meiosis II?
Meiosis I: Homologous chromosomes separate, reducing the chromosome number by half.
Meiosis II: Sister chromatids separate, producing four haploid cells.
What is the synaptonemal complex, and why is it important?
The synaptonemal complex stabilizes homologous chromosomes, enabling crossover events and proper segregation in meiosis.
Why is recombination important in evolution?
Recombination:
Creates genetic diversity.
Prevents harmful mutations from accumulating.
Restores beneficial mutations while removing deleterious ones.
What is the impact of paternal age on mutation rates?
Older fathers contribute more mutations due to higher numbers of cell divisions in sperm production, increasing the likelihood of errors.
Why is correct chromosome segregation critical?
Prevents gene dosage imbalances.
Maintains cellular function.
Reduces the risk of genetic disorders.
How is X chromosome dosage compensated in females?
By X-inactivation, where one X chromosome is silenced through epigenetic mechanisms (e.g., DNA methylation).
What chromosomal anomaly is found in most tumors?
Aneuploidy (abnormal number of chromosomes).
What are two conditions caused by chromosomal miss-segregation?
Cancer and Down’s syndrome.
Why is Down’s syndrome unique among autosomal aneuploidies?
It is the only autosomal aneuploidy compatible with a lifespan longer than a few weeks.
How is gene dosage related to chromosomal segregation errors?
Imbalances in gene dosage from extra or missing chromosomes can lead to pathological conditions or evolutionary adaptations.
What is “one-sided” inheritance?
It refers to inheritance limited to specific lines, such as mitochondrial DNA (maternal) or Y chromosomes (paternal).
How does cancer relate to chromosomal instability?
Aneuploidy leads to higher mutation rates and extensive dosage changes.
Structural chromosomal alterations contribute to tumor progression and therapeutic resistance.
What gene is overexpressed in Down’s syndrome and linked to heart defects?
COL6A.
How is genetic testing related to chromosomal aneuploidy?
Pre-implantation genetic testing can screen for aneuploidies.
Ethical concerns arise around decisions to terminate pregnancies or use embryos.
What causes aneuploidy in mitosis?
Miss-segregation of sister chromatids.
Cohesion defects or spindle attachment issues.
Why are plants more tolerant of aneuploidy?
Plants display dosage compensation mechanisms for some chromosomes.
Seed pod shapes vary depending on trisomic chromosome identity, showing better adaptability.
How does aneuploidy in meiosis affect offspring?
Miss-segregation in Meiosis I: All gametes affected.
Miss-segregation in Meiosis II: 50% of gametes affected.
Trisomies are more compatible with life than monosomies in humans.
How does chromosomal segregation impact gene dosage?
Loss of a chromosome = 0.5× normal expression.
Extra chromosome = 1.5× normal expression, potentially causing imbalances.
