unit 3: chromosomes, mitosis, and meiosis

explain how mitosis fits into the human life cycle and some reasons that cells divide by mitosis in multicellular organisms

mitosis is a type of cell division that takes place throughout the life cycle of humans and all multicellular organisms. the way a human zygote (fertilized egg) begins to develop into a multicellular embryo is by going through many forms of mitosis. the embryo develops into a fetus, child, and eventually adult by going through the cell division process over many years. mitosis is used to regenerate cells that are lost from tissues on a continuous bases. mitosis can also replace cells that are lost due to injury (cut in your mouth, cells will be replaced using mitosis)

list examples of animal tissues whose cells are “in the cell cycle” as well as examples of animal tissues whose cells have pulled out of the cell cycle

in some of the tissues of your body, cells are in the cell cycle meaning they are capable of dividing by mitosis.

cells in any epithelial tissues (tissue exposed to the outside environment and cells lining body parts) are in the cell cycle. these include cells in your epidermis, cells lining the digestive, respiratory, and reproductive tracts . cells in your bone marrow and lining your blood vessels are in the cell cycle too.

by contrast some cells in the body have pulled out of the cell cycle. this means they are no longer able to divide. these include specialized neurons and some types of muscle fibers

explain how DNA molecules are packaged in both dividing and non dividing cells

in cells that are non dividing, the DNA fibers are loosely coiled around organizing proteins in the nucleus. when the DNA fibers and their organizing proteins are in this state we call them chromatin fibers.

in dividing cells, the DNA fibers are tightly coiled around their organizing proteins. when the DNA fibers and their organizing proteins are in this highly condensed state they’re called chromosomes

name all the stages in the cell cycle in the order in which they occur. Describe the major events that occur in each stage

the cycle has two major phases. interphase and the cell division phase.

interphase refers to the time between cell divisions and can be subdivided into 3 stages: G1, S, and G2. A small newly formed cell begins its life in G1. During G1 it takes up nutrients and gets bigger. During S phase, all of the cell DNA is replicated. During the last phase, G2, enzymes and other proteins are produced that help guide the cell through mitosis

the cell division phase has two major events

1. mitosis (division of the nucleus)

2. cytokinesis (division of the cytoplasm)

Mitosis

mitosis has 4 phases

1. prophase

   1. during prophase, chromatin fibers condense into chromoses, the nuclear envelope breaks down, and the spindle fibers begin to form

2. metaphase

   1. during metaphase, the chromosomes are lined up along the center of the cell

3. anaphase

   1. during anaphase, sister chromatids within a chromosome separate and migrate towards opposite poles

4. telophase

   1. telophase begins when the unreplicated chromosomes reach their respective poles. as telophase progresses each set of chromosomes uncoils back into chromatin fibers and a nuclear envelope forms around each set of fibers

draw a chromosome as it appears in a cell that is just beginning mitosis. Label the sister chromatids, centromeres, and kinetochore. Then define sister chromatids, centromeres, and kinetochore.

sister chromatids are identical copies of the same genetic information. the centromere is a region where the two sister chromatids are held together. kinetochores are structures loacted on both sister chromatids at the centromeres location. their function is to attach the sister chromatids to spindle fibers and help them move toward oppostite poles

be able to recognize various stages of the cell cycle and identify which stage each one is in. know the structures: chromatin, chromosomes, sister chromatids, spindle fibers

what purpose do spindle fibers serve during mitosis?

spindle fibers align the replicated chromosomes up along the equator of the cell at metaphase. during anaphase the spindle fibers help guide the chromosomes towards opposite poles.

what is the purpose of meiosis? where in a person’s body does it occur?

the sole purpose of meiosis is to produce gametes (reproductive cells) these include sperm cells for males and ova (unfertilized eggs) for females. meiosis occurs in the testes for males and the ovaries for females.

what does haploid and diploid mean ?

a diploid cell always contains two of each type of chromosome meaning there are two full sets of chromosomes.

haploid cells contain only one of each type of chromosome meaning they only have one set of chromosomes.

give different examples of animal cell types that are diploid and haploid

in animals pretty much every cell is diploid (skin cells, muscle cells, nerve cells, liver cells, etc). the only cells that are haploid are gametes (sperm and ova)

how many chromosomes are found in the diploid cells and haploid cells of healthy humans?

healthy human diploid cells have 46 chromosomes, whereas haploid has 23 cells

what are homologous chromosomes and how do we explain the fact that people (and other animals) have their chromosomes in homologous pairs?

in a diploid cell any 2 chromosomes that are the same shape and size and carry genes that influence the same traits. a healthy human has 23 pairs of homologous chromosomes in almost every body cell. for each pair of homologous chromosomes a person has, one chromosomes was inherited from the mother and the other from the father

if we examine a pair of homologous chromosomes within an individual person, should we expect those chromosomes to be identical? explain.

homologous chromosomes within a pair are NOT identical. this is because genes come in different versions. for example, a person might inherit one version of gene influencing eye color from mom and a different version of that eye color gene from dad

list the stages of meiosis in order. what events are seen during meiosis that distinguish it from mitosis?

meiosis has two different rounds of cell division called:

MEIOSIS 1 & MEIOSIS 2

Meiosis 1 consists of prophase 1, metaphase 1, anaphase 1, and telophase 1.

Meiosis 2 consists of prophase 1, metaphase 2, anaphase 2, and telophase 2

mitosis has just one round of cell division. meiosis has 2 rounds of cell division. during prophase 1 of meiosis, unique events include: homologous chromosomes become joined at their lengths (synapsis). each pair of synapsed homologous chromosomes is referred to as a tetrad because it contains a total of 4 chromatids. while synapsed,

explain how events that occur during meiosis and fertilization contribute to the genetic diversity of humans and other sexually reproducing organisms

crossing over which happens during prophase 1 of meiosis 1. crossing over creates unique gene combos along chromosomes

the random nature of fertilization also contributes to the number of genetically different sperm cells and and woman can produce a number of genetically different ova

compare mitosis and meiosis using these guidelines below

purpose of cell division?, when it occurs in the human life cycle?, where in a person’s body the process occurs, products of cell division (in terms of number of cells produced, chromosome status of those cells, and genetic variety seen amongst those cells)

mitosis

purpose: growth and development, replace lost cells, repair tissues due to injury

when in life cycle: entire life beginning with zygote

where in the body: any tissue where cells are capable of dividing

number of cells it produces as a result: two

diploid or haploid: diploid

are cells produced genetically different or identical?: identical

meiosis

purpose: produce reproductive sells (sperm and ova)

when in life cycle: during the years a person is forming reproductive cells

where in body: only in reproductive organs, testes and ovaries

number of cells produced: up to 4

are cells diploid or haploid: haploid

are cells different or identical? different

explain what oogenesis and spermatogenesis are

spermatogenesis is the process of making sperm in a male. it occurs in the testes and involves meiosis. oogenesis is the process of producing ova in a female. it occurs in the ovaries and involves meiosis

list the importance similarities and differences between these two processes (oogenesis and spermatogenesis)

both processes involve meiosis and result in the production of haploid cells. in spermatogenesis cytokinesis occurs equally during meiosis 1 and meiosis 2. this results in 4 sperm cells.

in oogenesis, cytokinesis is very unequal during meiosis 1 and meiosis 2. this results in the production of one large ovum and a few tiny cells known as polar bodies. the polar bodies end up disintegrating

what does nondisjunction mean during meiosis and what the result of this phenomenon can be. name and describe a syndrome observed in humans that is caused by non-disjunction

nondisjunction means the chromosomes do not separate properly during meiosis. this error can happen during anaphase 1 or anaphase 2. the end result of nondisjunction is the production of reproductive cells with too many or too few chromosomes. (down syndrome, extra copy of chromosome 21)