Biology - Chapter 8: Mitosis and Meiosis

cell division

preexisting cells make new cells

asexual reproduction

offspring has same genetic copies as the parent

• (identical to each other)

• ex: bacteria, fungi, various plants, some animals

sexual reproduction

creates a variety of offspring

• uses gametes (eggs and sperm)

• ex: humans, flowering plants, mammals, various fish, insects

binary fission

parent organisms divide into two genetically identical daughter cells

• prokaryotes divide through this (asexual reproduction)

eukaryotic cell

• has more genes than prokaryotic cells

• genes grouped into multiple chromosomes in the nucleus

  • each chromosome contains one long DNA molecule

chromatin

complex of thin and loosely packed fibers of DNA containing up to 1000s of genes together with proteins

chromosomes

structure made of DNA and proteins (chromatin), carrying genes, number of chromosomes (2n) vary by organism (eukaryotes)

sister chromatids

identical copies of a chromosome joined at the centromere

the cell cycle

ordered sequence of events that extends from the time a cell is first formed from a dividing parent cell until its own division (two phases: interphase and mitotic)

interphase

• longest stage of the cell cycle

• split into three phases:

  • G1 = cell grows

  • DNA synthesis = DNA is replicated

  • G2 = cell grows and prepares for cell division

mitotic phase

• consists of five phases:

  • prophase, prometaphase, metaphase, anaphase, and telophase involving chromosome alignment and separation

mitosis

• division of a eukaryotic cell to form two identical daughter cells

1.) duplicated chromosomes move into two identical daughter nuceli —> chromosome coil up

2.) mitotic spindle forms and moves the chromosomes to the middle of the cell

3.) sister chromatids separate and move to opposite poles of the cell, to nuclei form

mitotic spindle

made up of microtubules

cytokinesis

when the cell divides into two, overlaps the end of mitosis

• in animals: occurs when a cell constricts, forming a cleavage furrow

• in plants: a membraneous cell plate forms and then splits the cell in two

creates two genetically identical cells

how do cells know when to divide?

• the rate of cell division is affected by environmental factors

• most animal cells divide when stimulated by growth factors, and some don’t divide at all

growth factors

regulate the cell cycle by initiating various signaling pathway

How is the cell cycle controlled?

• growth factors signal the cell cycle control system

• a set of proteins within the cell controls the cell cycle

  • signals affecting critical checkpoints in the cell cycle determine whether a cell will go through the complete cycle and divide

  • the binding of growth factors to specific receptors on the plasma membrane is usually necessary for cell division

cancer

cells can divide excessively to form massive cells called tumors

malignant tumor

can invade other tissues

similarities between mitosis and meiosis

• both begin with diploid parent cells that have chromosomes duplicated during the previous interphase

differences between mitosis and meiosis

• mitosis produces two genetically identical diploid somatic daughter cells

• meiosis produces four genetically unique haploid gametes

diploid cells

• cells that contains two sets of chromosomes (2n)

• in humans: n = 46, 23 from each parent

• all somatic cells

haploid cells

• cells that contain a single set of chromosomes (n)

• in humans: n = 23

• only gametes (egg cells and sperm)

somatic (body) cells

any cells of a living organisms other than the reproductive cell

homologous chromosomes

two chromosomes in a matching pair

locus

place a gene is found on a chromosome

meiosis I

starts with the pairing of homologous chromosomes

crossing over

homologous chromosomes exchange corresponding segments

• creates genetic recombination

random fertilization

nondisjunction

an abnormal chromosome count

karyotype

an individual’s complete set of chromosomes

trisomy 21

chromosome number alteration resulting in a condition called down syndrome

reciprocal translocations

occur when part of one chromosome is exchanged with another