CSU Life 102, Exam 3.

Why do cells divide?

To grow, repair, and reproduce.

What is the difference between asexual and sexual reproduction?

Asexual = one parent, identical offspring; Sexual = two parents, genetically unique offspring.

In which organisms does asexual reproduction occur?

Bacteria, some plants, some animals.

In which organisms does sexual reproduction occur?

Most animals and plants.

What are the main stages of eukaryotic cell division?

Interphase, Mitosis, Cytokinesis.

How is DNA organized in a eukaryotic cell?

Into chromosomes made of chromatin (DNA + proteins).

What is the genome?

All DNA in a cell.

What is chromatin?

Uncoiled form of DNA and proteins.

What are sister chromatids?

Identical DNA copies joined at a centromere.

What are the stages of the cell cycle?

G1 (growth), S (DNA replication), G2 (prep), M (mitosis + cytokinesis), G0 (resting).

When does a cell commit to dividing?

At the end of G1 phase.

What happens in non-dividing cells?

They enter G0 phase.

What happens in Prophase?

Chromosomes condense, spindle fibers form.

What happens in Metaphase?

Chromosomes line up in the middle of the cell.

What happens in Anaphase?

Sister chromatids separate and move to opposite poles.

What happens in Telophase?

New nuclei form around separated chromosomes.

What is the role of the mitotic spindle?

Moves chromosomes during division.

What is the function of centrosomes?

Organize the spindle fibers.

What is the function of centromeres?

Join sister chromatids together.

What is the function of kinetochores?

Attach spindle fibers to chromosomes.

What happens during cytokinesis?

Cytoplasm divides, forming two new cells.

How does cytokinesis differ in plant and animal cells?

Animal = cleavage furrow; Plant = cell plate.

What is density-dependent inhibition?

Cells stop dividing when too crowded.

What is a gene?

A DNA segment that codes for a trait.

What are gametes?

Sex cells (egg and sperm).

What is asexual reproduction?

One parent produces identical offspring.

What is sexual reproduction?

Two parents produce genetically different offspring.

What are somatic cells?

Body cells that are diploid (2n).

What does diploid mean?

Two sets of chromosomes (2n).

What does haploid mean?

One set of chromosomes (n).

What happens during meiosis?

Cells divide twice to make four haploid gametes.

What happens during fertilization?

Two gametes fuse to form a diploid zygote.

What are homologous chromosomes?

Chromosomes with the same genes but possibly different alleles.

What are nonhomologous chromosomes?

Chromosomes with different sets of genes.

What separates during meiosis I?

Homologous chromosomes.

What separates during meiosis II?

Sister chromatids.

What happens in Prophase I?

Homologs pair up and crossing over occurs.

What happens in Metaphase I?

Homologous pairs line up in the middle.

What happens in Anaphase I?

Homologous chromosomes separate.

What happens in Telophase I?

Two haploid cells form.

What happens in Meiosis II?

Chromatids separate, forming four unique haploid cells.

How does mitosis differ from meiosis?

Mitosis = 2 identical cells; Meiosis = 4 unique gametes.

Sources of genetic diversity

Independent assortment, crossing over, and random fertilization.

Independent assortment

Random distribution of chromosomes into gametes.

Crossing over

Exchange of DNA between homologous chromosomes.

Synapsis

Pairing of homologous chromosomes during Prophase I.

Stage of meiosis for crossing over

Prophase I.

Gene

A DNA sequence that codes for a trait.

Alleles

Different versions of the same gene.

Locus

The physical location of a gene on a chromosome.

Gregor Mendel

The scientist who studied inheritance using pea plants.

Generations in Mendelian genetics

P = parents, F1 = first offspring, F2 = second generation.

Law of segregation

Alleles separate during gamete formation.

Law of independent assortment

Genes on different chromosomes sort independently.

Dominant alleles

Alleles that mask recessive ones in heterozygotes.

Recessive alleles

Alleles expressed only when homozygous.

Homozygote

An individual with two identical alleles (AA or aa).

Heterozygote

An individual with two different alleles (Aa).

Genotype

Genetic makeup of an organism.

Phenotype

Physical traits of an organism.

Linked inheritance

Genes close together on a chromosome inherited together.

Punnett square

A tool used to predict offspring genotypes and phenotypes.

Complete dominance

One allele completely masks another.

Incomplete dominance

Blending of traits (red + white = pink).

Codominance

Both alleles are expressed equally (AB blood type).

Polygenic traits

Traits controlled by multiple genes (like skin color).

Epistasis

One gene affects the expression of another (coat color in mice).

Pedigree

Chart showing family inheritance of a trait.

Carrier

Someone with a recessive allele but no symptoms.

Meiosis and Mendel's law of segregation

Homologous chromosomes separate in meiosis I.

Meiosis and independent assortment

Nonhomologous chromosomes assort randomly.

Wild-type alleles

Normal, most common forms of a gene.

Mutant alleles

Altered or changed versions of a gene.

Sex determination in mammals

Females = XX; Males = XY.

Sex-linked gene

A gene located on a sex chromosome (X or Y).

X-linked disorders in males

They have only one X chromosome.

X-inactivation

One X chromosome in females becomes inactive (Barr body).

Linked genes

Genes on the same chromosome.

Why linked genes don't always stay together

Crossing over can separate them.

Genetic recombination

Exchange of DNA between homologous chromosomes.

Recombination frequency calculation

% of recombinant offspring out of total.

Nondisjunction

Chromosomes fail to separate properly.

Aneuploidy

An abnormal number of chromosomes.

Polyploidy

Extra sets of chromosomes.

Deletion

Missing part of a chromosome.

Duplication

Repeated chromosome segment.

Inversion

Chromosome piece flips direction.

Translocation

A piece of one chromosome moves to another chromosome.