BSC1005 Exam 4 Study guide Section 12

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Sister chromatids

Two identical copies of a single replicated chromosome connected by a centromere.

Centromere

The centralized region where two sister chromatids are joined together tightly.

Cell cycle

An ordered sequence of events extending from a cell's origin until its own division.

Interphase

The continuous growth and DNA replication phase, taking up roughly 90% of the cell cycle.

Mitosis

The process of nuclear division that allocates identical genetic material to two new daughter nuclei.

Prophase

The first mitotic stage where chromatin condenses into chromosomes and the mitotic spindle forms.

Metaphase

The stage where fully condensed chromosomes align perfectly along the center midline of the cell.

Anaphase

The phase where sister chromatids separate at their centromeres and move toward opposite poles.

Telophase

The final stage where two nuclear envelopes reform around the separated sets of chromosomes.

Mitotic spindle

A football-shaped structure of microtubule fibers that guides the separation of daughter chromosomes.

Cleavage furrow

A shallow groove in the cell surface near the old metaphase plate in animal cells.

Cell plate

A double membrane across the midline of a dividing plant cell, forming a new cell wall.

Cell cycle checkpoints

Critical regulatory integration points where stop and go-ahead signals regulate the entire cycle.

Cancer

A disease of severe cell cycle regulation failure causing uncontrolled cellular division and growth.

Homologous chromosomes

A pair of matching chromosomes carrying genes controlling the same inherited characteristics.

Haploid

Containing only a single set of chromosomes (\(n\)); standard characteristic of reproductive cells.

Gametes

A sex cell; a haploid egg or sperm cell that unites during fertilization

Fertilization

The physical union of haploid gametes to form a new diploid zygote.

Meiosis

Cell division producing haploid daughter cells from diploid cells for sexual reproduction.

Karyotype

A stylized photographic display of an individual's condensed chromosomes arranged in matching pairs.

Nondisjunction

An error where homologous chromosomes or sister chromatids fail to separate during division

What are all of the phases of the cell cycle?

G1 (Gap 1) – Cell grows and performs normal functions.

S (Synthesis) – DNA is copied.

G2 (Gap 2) – Cell grows more and prepares for mitosis.

Mitosis (M) – Nucleus divides.

Cytokinesis – Cytoplasm divides, forming two daughter cells.

What occurs during each phase?

G1: Cell grows; organelles are made.

S: DNA replication.

G2: Cell checks DNA and prepares to divide.

Mitosis: Chromosomes separate into two nuclei.

Cytokinesis: Cell splits into two cells.

How is cytokinesis different in animals vs. plants?

Animal cells:

A cleavage furrow pinches the cell in half.

Plant cells:

A cell plate forms and becomes a new cell wall.

What factors tell a cell to stop growing?

Cell becomes too crowded (contact inhibition)

Lack of nutrients

DNA damage

Growth factors are absent

What factors promote cell growth?

Growth factors

Nutrients

Enough space

Healthy DNA

Describe the checkpoints that keep the cell cycle under control.

G1 checkpoint: Checks cell size, nutrients, and DNA damage.

G2 checkpoint: Ensures DNA was copied correctly.

M checkpoint (Spindle checkpoint): Makes sure chromosomes are attached properly before separating.

What are the two types of gametes?

Sperm (male)

Egg/Ovum (female)

How do they differ from somatic (body) cells?

Gametes

Haploid (n)

23 chromosomes in humans

Produced by meiosis

Somatic cells

Diploid (2n)

46 chromosomes in humans

Produced by mitosis

Explain what happens in the phases of Meiosis I.

Prophase I

Chromosomes pair with homologous chromosomes.

Crossing over occurs.

Metaphase I

Homologous pairs line up in the middle.

Anaphase I

Homologous chromosomes separate.

Sister chromatids stay together.

Telophase I

Two haploid cells form.

. Explain what happens in the phases of Meiosis II.

Prophase II

Chromosomes prepare for division.

Metaphase II

Chromosomes line up individually.

Anaphase II

Sister chromatids separate.

Telophase II

Four genetically unique haploid cells form.

What ways does Meiosis contribute to genetic variability?

Crossing over

Independent assortment (random arrangement of chromosomes)

Random fertilization

Explain the process of crossing over.

Crossing over occurs during Prophase I.

Homologous chromosomes exchange pieces of DNA, creating new combinations of genes.

d. How does it lead to genetic diversity?

It creates new allele combinations, making each gamete genetically unique.

Explain how a person could get Down Syndrome.

Down syndrome is caused by nondisjunction during meiosis.

A gamete receives an extra copy of chromosome 21. After fertilization, the person has three copies of chromosome 21 (Trisomy 21) instead of two.

What are some abnormal combinations of sex chromosomes?

XO = Turner syndrome (female)

XXY = Klinefelter syndrome (male)

XXX = Triple X syndrome (female)

XYY = Jacob syndrome (male)