midterm 2 genetics

Genotype

Homozygous dominant AA

Heterozygous Bb

Homozygous recessive cc

Interphase

The phase of the cell cycle where the cell spends most of its life, preparing for division by replicating its DNA and organelles.

G1

S phase

G2

G1 Phase

• cell grows and prepares to divide

• procedures proteins and builds resources

• if condtions are right, passes restrciton points, continues onto division

S phase ( DNA replication)

• chromosomes are replicated

• each chromosome becomes 2 sister chromatids

• during this phase, DNA is synthesized, leading to the duplication of genetic material, ensuring that each daughter cell receives an identical set of chromosomes.

kinetochore

A protein structure on the chromosome that is essential for the separation of sister chromatids during cell division, as it serves as the attachment point for spindle fibers.

G2 phase

The G2 phase is the final stage of the interphase where the cell continues to grow, produces additional proteins, and quickly prepares for mitosis, ensuring all cellular components are ready for division.

Mitosis

The process of cell division that results in two identical daughter cells, involving several stages: prophase, metaphase, anaphase, and telophase. During mitosis, the chromosomes are equally divided between the two new nuclei.

Mitosis vs meiosis 1 vs meiosis 2

Mitosis is the type of cell division that produces two identical diploid daughter cells, while meiosis consists of two rounds of division (meiosis I and meiosis II) that lead to four genetically diverse haploid gametes, essential for sexual reproduction.

Purpose of meiosis

The purpose of meiosis is to produce gametes for sexual reproduction, reducing the chromosome number by half to create genetic diversity through recombination and independent assortment.

Purpose of recombination

The purpose of recombination is to increase genetic diversity during meiosis by exchanging genetic material between homologous chromosomes, leading to new combinations of alleles in gametes.

astral MT

position of spindle apparatus within a cell

polar MT

seperation of two poles, push each other away

kinetochore MT

Attachement to kinetochore protein

prophase ( condense)

is the first stage of mitosis and meiosis during which chromosomes condense and become visible, the nuclear envelope breaks down, and spindle fibers begin to form.

• chromosomes already replicated

• chromatin condenses

• nuclear membrane breaks down

• ctresomes move apart

• spindle fibers geing to form

prometaphase ( attach to fibers)

During prometaphase, the nuclear membrane fully fragments, allowing spindle fibers to attach to the kinetochores, and microtubules capture chromatids for alignment during cell division.

metaphase ( lineup)

is the stage of cell division where chromosomes align at the metaphase plate, ensuring equal separation during anaphase. Spindle fibers are fully attached to the kinetochores of each chromosome.

anaphase ( pull apart)

• sister chromatids sperate → now individual chromosomes

• chromosomes pulled to opposite poles

• kinetochore spindle fibers shorten, pulling apart sister chromatids to opposite ends of the cell.

telophase ( reform)

• chormosomes reach poles and decondense

• nuclear membrane reform

• nucleoli appear

• cytokinesis begins, dividing the cytoplasm of the parent cell into two daughter cells.

cytokinesis

is the process that follows mitosis or meiosis, resulting in the division of the cytoplasm, forming two separate daughter cells.

meiosis

is a specialized form of cell division that reduces the chromosome number by half, producing four genetically diverse gametes from one original cell.

meiosis 1

is the first stage of meiosis, where homologous chromosomes are separated and reduced by half, resulting in two haploid cells.

prophase of meiosis 1 ( synapsis, chiasma form)

• synapsis ( pairing)

  • is the stage in meiosis 1 where homologous chromosomes pair up, forming tetrads, and crossing over occurs at chiasmata, facilitating genetic recombination.

  • The associated chromatids form a bivalent

• Chiasma ( crossing over)

  • physical exchange of chromosome pieces

  • at a chiasma, the DNA within a chromatid form each homolog

Prommetaphase of meiosis 1

spindle apparatus is complete

chromosome attached via Kinetochore microtubulin

Metaphase of meiosis 1

• bivalents organized along metaphase plate

• double row

• ordered by homologous chromosomes, ensuring proper segregation during anaphase.

bivalent

A structure formed during meiosis consisting of a pair of homologous chromosomes that are physically joined together. Bivalents play a crucial role in ensuring accurate segregation of chromosomes during meiosis.

Anaphase

cohesin along arms of sisters are released

• sister chromatids within a bivalent seperate

• two dyads within a tetrad seperate from each other and migrate to opposite poles

telophase

sister chromatids reach their poles

nuclear membrane reform

Meiosis 2

Same as mitosis but starts with haploid cells instead of diploid

already went through meiosis 1

have half chromosome

5 key principles of the theory inheritance

1. chromosomes carry genetic material

2. chromosomes replicatetd and passed on from parent to offspring

3. chromosomes exist in homologous pairs

4. different chromosomes pair seperate independently

5. at fertilization each parent contributes one set of chromosomes