A&P - Cell Division & Heredity

Divide periodically

In cell division, most cells:

Mitosis & meiosis

What are the two types of cell division?

Somatic (body) cell division - most cells, 2 identical cells from 1 original

Mitosis

Gamete (reproductive) cell division - only to produce eggs + sperm, 4 different cells from 1 original

Meiosis

Somatic Cells (body)

Cell cycle of

Interphase, prophase, metaphase, anaphase, telophase

Steps of the cell cycle include:

One cell divides into two (1-2 hours)

Mitotic Phase

Cell’s normal job, 46 chromosomes

First Gap Phase

Copy DNA, 46 chromosomes in duplicate (6-8 hours)

Synthesis Phase

Synthesizes extra organelles, membrane, enzymes to prepare for mitosis, corrects errors in DNA replication (4-6 hours)

Second gap phase (G2)

G1, S, G2

Interphase includes:

DNA + proteins = form of DNA in nondividing cells

Chromatin

Segments of chromatin condense during prophase

Chromosomes

½ of replicated chromosomes

Chromatid

DNA fits in nucleus & separation without damage

Chromosome structure allows:

23 pairs (46 total) chromosomes = more than 3 billion pairs of nucleotides

The human genome has:

Chromosomes condense, nuclear envelope breaks down. Spindle fibers grow from centrioles, then migrate to opposite poles of cell. (46 chromosomes + 2 chromatids each)

MITOSIS: Prophase includes:

Chromosomes line up along midline of cell. Some spindle fibers attach to kinetochores. Fibers of aster attach to plasma membrane. (Line up in one row of 46)

MITOSIS: Metaphase:

Centromeres divide into two. Spindle fibers pull sister chromatids to opposite poles of cell. Each pole (future daughter cell) now has an identical set of genes (Enzyme cleaves centromere & sister chromatids separate)

MITOSIS: Anaphase includes:

Chromosomes gather at each pole of cell, then decondense. New nuclear envelope appears at each pole. Nucleolus reappears and mitotic spindle vanishes. (Cytokinesis (division) of cytoplasm - 2 identical cells (46 chromosomes each))

MITOSIS: Telophase includes:

2n—>2n - cells are identical

What is the goal of mitosis?

Number of chromosomes

n=

2n=diploid=2sets chromosomes w/ same genes (one each from mom + dad) - 46 chromosomes in 23 pairs

MITOSIS: Parent cell (2n) includes:

Used to produce gametes (eggs/sperm)

Meiosis

Interphase, meiosis I, meiosis II

Phases of meiosis include:

Same (DNA replicates)

MEIOSIS: Interphase

DNA exchange - creates genetic diversity

MEIOSIS: Meiosis I

Reduces number of chromosomes - 2nd round of division

MEIOSIS: Meiosis II

Genetic diversity & reduce number of chromosomes (2n (diploid) —> n (haploid) - reduction division

What is the goal of meiosis?

Pairing of homologous chromosomes - chromatin condenses to form visible chromosomes; each chromosome has 2 chromatids joined by a centromere

MEIOSIS: Synapsis (Prophase I)

Chromosomes exchange segments of DNA & create new combinations of genes (crossing over) - Form tetrads, centrioles produce spindle fibers, and nuclear envelope disintegrates

MEIOSIS: Crossing over (Prophase I)

2 rows of 23 (instead of one row of 46) - Tetrads align on equatorial plane of cell with centromeres attached to spindle fibers

MEIOSIS: Metaphase I

Centromeres do NOT divide (sister chromatids to not separate) - Homologous chromosomes separate and migrate to opposite poles of the cell

MEIOSIS: Anaphase I

New nuclear envelopes form around chromosomes; cell undergoes cytoplasmic division (cytokinesis). Each cell is now haploid (Each daughter cell has 23 chromosomes with 2 chromatids each - haploid (n) after telophase I)

MEIOSIS: Telophase I

Nuclear envelopes disintegrate again; chromosomes still consist of 2 chromatids. New spindle forms (Like mitosis)

MEIOSIS: Prophase II (2nd D)

Chromosomes align on equatorial plane (One row of 23)

MEIOSIS: Metaphase II (2nd D)

Centromeres divide; sister chromatids migrate to opposite pole of cell. Each chromatid now constitutes a single-stranded chromosome (Like mitosis (centromeres divide + sister chromatids separate))

MEIOSIS: Anaphase II (2nd D)

New nuclear envelopes forms; chromosomes uncoil and become less visible; cytoplasm divides (Like mitosis) - each new daughter cell is haploid with 23 chromosomes each

MEIOSIS: Telophase II (2nd D)

4 haploid cells (n) each with 23 chromosomes

Final product of meiosis is:

23/sperm + 23/egg —> 46/fertilized egg (otherwise would have too many chromosomes)

Why does meiosis occur?

Sematic (body) cells

Cell type that uses mitosis:

Games (eggs/sperm)

Cell type that uses meiosis:

1 & 1

Number of cell divisions & number of times DNA replicates in mitosis:

2 & 1

Number of cell divisions & number of times DNA replicates in meiosis:

2

Number of cells produced in mitosis:

4

Number of cells produced in meiosis:

DNA is replicated

S-phase

Autosomes

#1-22 chromosomes are

Sex chromosomes (XX-female, XY-male)

#23: X Y are:

Segment of DNA that codes for RNA/protein

Gene

Different forms of the same gene produce alternative forms of the same trait (Ex. brown eyes vs. blue eyes)

Allele

Trait is expressed (Ex. Brown eyes (B))

Dominant

Trait is only expressed if no dominant allele is present (Ex. blue eyes (b))

Recessive

Having 2 identical alleles (BB or bb)

Homozygous

Having 2 different alleles (Bb - brown eyes b/c brown is dominant)

Heterozygous

Alleles present for a particular trait (Ex. BB or Bb)

Genotype

Observable trait (Ex. brown eyes)

Phenotype

More than one dominant allele, both traits expressed

Co-dominance: ABO blood groups

Traits carried on X chromosome - results in phenotypes present in males more than females

Sex Linkage

A (type A protein), B (type B protein) > dominant; O (no protein) > recessive

Blood Types