Unit 4 The Cell Cycle and Heredity (10-15%)

Reason for divison

as cells increase in volume, the SA decreases an demand for resources increases with limits cells size

Smaller cells have

a more favorable surface area to volume ratio for exchange of materials with the environment (diffusion.) High SA:V ration favorable

Interphase

Has 3 phases: growth (G1), synthesis of DNA (S), and preparation for mitosis (G2)

Mitosis

duplicated chromos line up in center with spindle fibers attached to help them pull them apart. Duplicated chromos are pulled apart by spindle fibers.

Cytokinesis-division of cytoplasm and reformation of cell membrane

Animal cell - pinches in (cleavage) using microfilaments; plant cell - forms cell plate reforms of new cell cell

Cell cycle is directed by

internal control or checkpoints. Internal (enzymes and promoting factors) and external signals (growth factors) provide stop and go signals at the checkpoints (Ex. mitosis - promoting factor MPF)

Cancer result from

disruptions in the cell cycle control (too much division, defective tumor suppressor genes, overactive genes) which are a result of DNA damage to proto-oncogenes (regulatory genes) which make products like cyclins and cyclin-dependent kinases

Cells spend different amount of times in

interphase or division. Nondividing cells may exit the cell cycle; or hold at a particular stage in the cell cycle

Mitosis is used for

growth and repair in animals; plants use mitosis to make gametes and for growth or repair

Mitosis usually begins with 1 cell, makes 2 identical cells or clones; maintains chromosome number; 1n→1n or 2n→2n

1 cell, makes 2 identical cells or clones; maintains chromosome number; 1n→1n or 2n→2n

Meiosis (occurs after interphase) takes

diploid cells and reduces the chromosome number to a haploid; 2n→1n

During meiosis, homologous chromos are

paired (one from mom and one from dad) and line up in the center of the cell randomly. The homologues are pulled apart and separated in meiosis I. A second division occurs in which the duplicated chromos are pulled apart

Variation occurs in gametes during

“crossing over”, and fertilization because of all possible combinations of homologous chromosomes aligning during metaphase I.

Law of Dominance

one allele will be expressed over another (ex: Aa - if big A is purple it will be seen over little a which is white)

Law of Segregation

allele pairs separate from each other during meiosis

Law of Independent Assortment

alleles sort independently during meiosis IF they are on separate chromosomes (ex. AaBb can make gametes AB, Ab, aB, or ab)

Product rule

multiply chance of one event happening by the chance of another to get the chance of both events occurring together

Autosomal vs Sex-linked

Autosomal traits are inherited through non-sex chromosomes, while sex-linked traits are associated with genes located on sex chromosomes

Monohybrid cross

one trait; 3:1 (Aa x Aa); 1:1 (Aa x aa) or 4:1 (AA x __), (aa x aa)

Dihybrid cross

two traits; 9:3:3:1 genotype (AaBb x AaBb) or test cross 1:1:1:1 (AaBb x aabb)

Thomas Hunt Morgan

fruit flies, X-linked traits

Male and Female

heterozygous XY and homozygous XX; single gene mutation of X causes disease such as hemophilia or colorblindness

Sex Limited traits are

dependent on the sex of the individual like milk production or male patterned baldness

Incomplete Dominance

red x white → pink; both protein product are expressed and blended

Codominance

red x white → red and white; both protein products are equally expressed (ex: AB Blood types)

Epistasis

one gene effects expression of another

Linked genes

genes on same chromosome that are inherited together (can be unlinked by crossing over); recombination frequency calculated by recombinants/total; used for chromosome mapping; genes further apart cross over more often

Genes/environment

phenotypes effected by environment; Siamese cat, flower color w/ soil pH, seasonal color in arctic animals, human height and weight

Polygenic

continuous variation, many genes affect one trait - height, color

Karyotype

22 pair autosomes & 1 pair sex chromosomes + 46 total chromosomes

Chromosomal Mutations (occur during gamete formation)

(1) deletion, inversion, addition of genes as a relit of crossing over mistake

(2) chromosomal number abnormalities→ non disjunction is failure of chromosomes to separate at anaphase of meiosis

Anaphase

Stage of mitosis and meiosis where sister chromatids (or homologous chromosomes in meiosis I) separate and move toward opposite poles of the cell.

Autosomal

Refers to chromosomes that are not sex chromosomes; humans have 22 pairs of autosomes.

Cancer

A disorder in which cells lose control over the cell cycle, leading to uncontrolled growth and division.

Cell Cycle

The ordered sequence of events that a cell goes through to grow and divide; includes interphase (G1, S, G2) and mitotic phase (mitosis and cytokinesis).

Cell Division

The process by which a parent cell divides into two or more daughter cells; includes mitosis and meiosis.

Centrioles

Structures in animal cells that help organize spindle fibers during cell division.

Chromosome

A structure made of DNA and protein that carries genetic information.

Crossing Over

The exchange of genetic material between homologous chromosomes during prophase I of meiosis, increasing genetic variation.

Crossover Frequency

The percentage of recombinant offspring resulting from crossing over; used to map genetic loci on chromosomes.

Cyclin-dependent Kinase (CDK)

Enzymes that regulate the cell cycle; activated by cyclins.

Cytokinesis

The division of the cytoplasm to form two separate daughter cells after mitosis or meiosis.

Diploid (2N)

A cell that contains two sets of chromosomes, one from each parent.

Dominant

An allele that masks the effect of a recessive allele when present.

F1/F2 Generation

F1 is the first generation of offspring from a genetic cross; F2 is the offspring of an F1 cross.

Fertilization

The fusion of a sperm and egg cell to form a zygote.

Gamete

A haploid reproductive cell (sperm or egg).

Genotype

The genetic makeup of an organism; the combination of alleles.

Haploid (1N)

A cell with only one complete set of chromosomes.

Heterozygous

Having two different alleles for a trait (e.g., Aa).

Homozygous

Having two identical alleles for a trait (e.g., AA or aa).

Homologous Chromosomes

Chromosome pairs (one from each parent) that are similar in length, gene position, and centromere location.

Interphase

The part of the cell cycle where the cell grows, performs its functions, and replicates DNA; includes G1, S, and G2 phases.

Meiosis

Cell division that produces four genetically unique haploid gametes.

Metaphase

Stage of mitosis and meiosis where chromosomes align at the center (metaphase plate) of the cell

Mitosis

Nuclear division that produces two genetically identical diploid daughter cells.

Nuclear Division

The division of a cell’s nucleus, either by mitosis or meiosis.

Phenotype

The observable traits or characteristics of an organism resulting from its genotype.

Prophase

first stage of mitosis and meiosis where chromosomes condense and spindle fibers form.

Recessive

An allele that is only expressed when two copies are present (homozygous).

Recombination

The formation of new allele combinations through crossing over or independent assortment.

Segregation

The separation of alleles during gamete formation, described by Mendel's first law (Law of Segregation).

Sex Chromosome

Chromosomes that determine an individual's sex (X and Y in humans).

Sex-linked

Traits associated with genes located on sex chromosomes (often X-linked).

Somatic Cell

Any body cell other than a gamete.

Synapsis

The pairing of homologous chromosomes during prophase I of meiosis.

Synthesis (S Phase)

Part of interphase where DNA is replicated.

Telophase

Final stage of mitosis and meiosis where chromosomes decondense, nuclear envelopes re-form, and the cell prepares for cytokinesis.