cell division and genetics

Question 1

What occurs in the cell during metaphase of mitosis?

Answer 1

centromeres of chromosomes line up at the metaphase plate
- mitotic spindles start to form

Question 2

Name two things that make mitosis and meiosis different.

Answer 2

1. number of cell divisions

mitosis: involves one cell division, resulting in two identical daughter cells
Meiosis: involves two cell divisions, resulting in four non-identical daughter cells

2. genetic variation
   mitosis: produces genetically identical cells, maintaining the same number of chromosomes as the parent cell (2n)

meiosis: produces genetically diverse cells with half the number of chromosomes as the parent cell (haploid) due to processes like crossing over and independent assortment

Question 3

What are the 5 phases of mitosis?

Answer 3

PMAT

PROPHASE: the chromatin condenses into visible chromosomes, and each consists of two sister chromatids joined at the centromere
- the mitotic spindle begins to form, and the nuclear membrane starts to break down

prometaphase: the nuclear envelope completely dissolves, allowing spindle fibers to attach to the kinetochores of the chromosomes
chromosomes begin to move toward the center of the cell

metaphase: chromosomes align at the metaphase plate, ensuring that each sister chromatid will be separated into the two daughter cells

anaphase: the sister chromatids are pulled apart by the spindle fibers, moving towards opposite poles of the cell. this ensures that each daughter cell will receive an identical set of chromosomes

telophase: the chromosomes reach the cell poles and begin to de-condense back into chromatin
- the nuclear membrane re-form around each chromosomes

cytokinesis dividing the cytoplasm into two daughter cells
new cells enter interphase

Question 4

What occurs during Prophase I in meiosis?

Answer 4

chromosomes condense - become visible
2. homologous chromosomes pair up (synapsis) and form tetrads
3. crossing over occurs, where genetic material is exchanged between homologous chromosomes, increasing genetic diversity
4. nuclear envelope breaks down, and the spindle apparatus forms

Question 5

What occurs during anaphase I of meiosis?

Answer 5

Homologous chromosomes separate: The paired homologous chromosomes (each consisting of two sister chromatids) are pulled apart by the spindle fibers.
Move to opposite poles: Each chromosome, still composed of sister chromatids, moves toward opposite ends of the cell.

Question 7

How many daughter cells are produced in meiosis and mitosis?

Answer 7

Mitosis produces two daughter cells, each identical to the parent cell and with the same number of chromosomes (diploid).

Meiosis produces four daughter cells, each genetically different from the parent cell and with half the number of chromosomes (haploid).

Question 8

What is crossing over and why is crossing over important?

Answer 8

Increases Genetic Diversity:

Crossing over results in new combinations of alleles on each chromosome, which leads to genetically unique gametes (sperm and egg cells). This genetic variation is crucial for evolution and adaptation in populations.
Ensures Proper Chromosome Segregation:

It helps hold homologous chromosomes together until they are ready to be separated during Anaphase I, ensuring they segregate correctly into daughter cells.

Question 9

What occurs in the G1 phase? S phase? G2 phase? or also known as interphase

Answer 9

G1 Phase:
Cell growth: The cell increases in size.
Protein and organelle synthesis: Prepares for DNA replication.
S Phase:
DNA replication: The cell duplicates its DNA, resulting in two identical sets of chromosomes.
G2 Phase:
Final growth and preparation for mitosis: The cell continues to grow and produces proteins needed for cell division.
Checks for DNA errors: Ensures the DNA has been accurately replicated.

Question 10

What is significant about the G0 phase?

Answer 10

The G0 phase is a resting or non-dividing stage where cells exit the cell cycle.

Cells in the G0 phase are not actively preparing to divide. They may enter this phase temporarily or permanently.
-Specialized Function: Some cells, like neurons and muscle cells, remain in G0 permanently because they are fully differentiated and perform specific functions without dividing.

Question 11

what are the two checkpoints?

Answer 11

G1: passed if nutrients sufficient, cell size big enough, DNA undamaged

G2 checkpoint: before mitosis
-checks for DNA damage after replication and ensures all DNA has been accurately replicated

Question 12

what are the two regulatory proteins involved in cell cycle control?

Answer 12

cyclins are proteins that regulate the progression of the cell cycle by activating cyclin-dependent kinases CDKs.

CDKS: are enzymes that, when activated by binding to cyclins phosphorylate target proteins to drive the cell cycle forward.

Question 13

what are some external factors that control the cell cycle?

Answer 13

density dependent inhibition: when cells become too crowded, they stop dividing, this mechanism ensures that cells grow in a controlled manner and maintain proper tissue organization

anchorage dependence: means that many cells need to be attached to something solid, like the surrounding tissue to be able to divide.

Question 14

What error causes Down’s syndrome?

Answer 14

Down’s syndrome is caused by an error called nondisjunction during cell division (meiosis). This error leads to an extra copy of chromosome 21, resulting in a condition known as trisomy 21.

Question 15

What are some division errors in meiosis?

Answer 15

Nondisjunction: Failure of chromosomes to separate, leading to an extra chromosome (trisomy) or a missing chromosome (monosomy).
Translocation: A chromosome piece attaches to a different chromosome, causing genetic imbalance.
Deletion: Loss of a chromosome segment, resulting in missing genetic information.
Duplication: Extra copies of a chromosome segment, causing gene imbalances.
Inversion: A chromosome segment flips and reattaches in reverse, potentially disrupting genes.

Question 16

Give an example of a sex-linked disease and state which parent is more likely to pass this disease on to their child?

Answer 16

An example of a sex-linked disease is hemophilia, a disorder where blood does not clot properly. It is an X-linked recessive condition, meaning the defective gene is located on the X chromosome.

Which Parent is More Likely to Pass it On?
Mothers are more likely to pass X-linked recessive diseases to their children because they have two X chromosomes. If a mother is a carrier (one normal and one affected X), she can pass the affected X chromosome to her children.
Sons are more likely to express the disease because they only have one X chromosome (inherited from their mother). If they inherit the affected X, they will have the disease since they lack a second X chromosome to compensate.

Question 17

What is codominance and incomplete dominance?

Answer 17

In codominance, both alleles are fully expressed in the phenotype when they are present together. Neither allele is dominant over the other, so the traits from both alleles appear side by side.
Example: In blood types, a person with IAIB genotype has AB blood type, where both A and B antigens are equally expressed.
Incomplete Dominance:
In incomplete dominance, the phenotype is a blend of the two alleles. Neither allele is completely dominant, resulting in a mixed or intermediate trait.
Example: In snapdragon flowers, a cross between a red flower (RR) and a white flower (WW) produces pink flowers (RW), showing a blend of red and white.

Question 18

what is pleiotropy?

Answer 18

one gene, many effects