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Genetics and Evolution > Lecture 9 - Mitosis and Meiosis > Flashcards

Lecture 9 - Mitosis and Meiosis Flashcards

1
Q

What are the main phases of the cell cycle?

A

Interphase (G1, S, G2): Preparation for replication.
M phase: Mitosis and cytokinesis.
G0 phase: Resting phase, non-dividing cells.

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2
Q

What is the role of condensin proteins in mitosis?

A

Condensin proteins organize chromatin into structured chromosomes by:

Binding to two chromatin locations and folding DNA.
Forming DNA loops for compaction.

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3
Q

What is a karyotype, and what does it show?

A

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).

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4
Q

What are the chromosomal regions and their roles in mitosis?

A

Centromeres: Bind kinetochores for spindle attachment.

Telomeres: Protect chromosome ends from degradation.

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5
Q

What are the stages of mitosis?

A

Interphase: DNA replication.

Prophase: Chromatin condenses.

Metaphase: Chromosomes align at the center.

Anaphase: Sister chromatids separate.

Telophase: Chromosomes decondense, cytokinesis occurs.

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6
Q

What is the role of cohesion proteins in mitosis?

A

Cohesion proteins:

Hold sister chromatids together after DNA replication.
Are gradually removed during mitosis for separation.

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7
Q

What are 3 main features of meiosis?

A

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).

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8
Q

What are 3 roles of the synaptonemal complex in meiosis?

A

Stabilizes homologous chromosomes during Prophase I.
Facilitates recombination through DNA repair.
Disassembles after DNA repair is complete.

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9
Q

What are the evolutionary benefits of recombination?

A

Creates genetic diversity.
Prevents the accumulation of harmful mutations.
Restores mutation-free chromosomes.

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10
Q

What are pseudo-autosomal regions, and why are they important?

A

Pseudo-autosomal regions:

Allow pairing and segregation of X and Y chromosomes during meiosis.
Ensure proper segregation in males.

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11
Q

How do gametogenesis processes differ between sexes?

A

Spermatogenesis: Continuous, produces 4 sperm cells.

Oogenesis: Produces 1 ovum and polar bodies (non-functional).

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12
Q

How does paternal age affect mutation rates in offspring?

A

Older fathers contribute more mutations due to higher cell divisions in sperm precursors.
Maternal age increases the risk of chromosomal segregation errors.

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13
Q

What is bacterial parasexuality?

A

Bacterial processes for genetic exchange:

Transduction: DNA transfer by viruses.
Conjugation: DNA transfer via physical contact.
Transformation: DNA uptake from the environment.

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14
Q

Why is correct chromosome segregation important?

A

Prevents gene dosage imbalances.
Maintains proper cellular function and prevents diseases.
Drives evolution through balanced expression.

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15
Q

How do epigenetic mechanisms compensate for sex chromosome imbalances?

A

X-inactivation (in females) balances gene dosage between XX and XY individuals.
Involves DNA methylation and histone modifications.

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16
Q

What happens during the G0 phase of the cell cycle?

A

Cells enter a reversible, non-dividing state where they are metabolically active but not proliferating.

17
Q

What role do cohesion proteins play in mitosis?

A

Cohesion proteins hold sister chromatids together until their gradual removal allows separation during anaphase.

18
Q

What happens during Meiosis I and Meiosis II?

A

Meiosis I: Homologous chromosomes separate, reducing the chromosome number by half.
Meiosis II: Sister chromatids separate, producing four haploid cells.

19
Q

What is the synaptonemal complex, and why is it important?

A

The synaptonemal complex stabilizes homologous chromosomes, enabling crossover events and proper segregation in meiosis.

20
Q

Why is recombination important in evolution?

A

Recombination:

Creates genetic diversity.
Prevents harmful mutations from accumulating.
Restores beneficial mutations while removing deleterious ones.

21
Q

What is the impact of paternal age on mutation rates?

A

Older fathers contribute more mutations due to higher numbers of cell divisions in sperm production, increasing the likelihood of errors.

22
Q

Why is correct chromosome segregation critical?

A

Prevents gene dosage imbalances.
Maintains cellular function.
Reduces the risk of genetic disorders.

23
Q

How is X chromosome dosage compensated in females?

A

By X-inactivation, where one X chromosome is silenced through epigenetic mechanisms (e.g., DNA methylation).

24
Q

What chromosomal anomaly is found in most tumors?

A

Aneuploidy (abnormal number of chromosomes).

25
Q

What are two conditions caused by chromosomal miss-segregation?

A

Cancer and Down’s syndrome.

26
Q

Why is Down’s syndrome unique among autosomal aneuploidies?

A

It is the only autosomal aneuploidy compatible with a lifespan longer than a few weeks.

27
Q

How is gene dosage related to chromosomal segregation errors?

A

Imbalances in gene dosage from extra or missing chromosomes can lead to pathological conditions or evolutionary adaptations.

28
Q

What is “one-sided” inheritance?

A

It refers to inheritance limited to specific lines, such as mitochondrial DNA (maternal) or Y chromosomes (paternal).

29
Q

How does cancer relate to chromosomal instability?

A

Aneuploidy leads to higher mutation rates and extensive dosage changes.
Structural chromosomal alterations contribute to tumor progression and therapeutic resistance.

30
Q

What gene is overexpressed in Down’s syndrome and linked to heart defects?

A

COL6A.

31
Q

How is genetic testing related to chromosomal aneuploidy?

A

Pre-implantation genetic testing can screen for aneuploidies.
Ethical concerns arise around decisions to terminate pregnancies or use embryos.

32
Q

What causes aneuploidy in mitosis?

A

Miss-segregation of sister chromatids.
Cohesion defects or spindle attachment issues.

33
Q

Why are plants more tolerant of aneuploidy?

A

Plants display dosage compensation mechanisms for some chromosomes.
Seed pod shapes vary depending on trisomic chromosome identity, showing better adaptability.

34
Q

How does aneuploidy in meiosis affect offspring?

A

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.

35
Q

How does chromosomal segregation impact gene dosage?

A

Loss of a chromosome = 0.5× normal expression.
Extra chromosome = 1.5× normal expression, potentially causing imbalances.

Genetics and Evolution (30 decks)

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