Lecture 9

_______

• a single parent cell divides, resulting in two daughter cells

  • The daughter cells are ________ to each other (and to the parent cell)

• Unicellular organisms

  • _______ accomplishes ________

• Multicellular organisms

  • _______ accomplishes _________

_______

• a single parent cell divides, resulting in four daughter cells

  • The daughter cells are ________

  • Gametes are _____ from each other (and from the parent cell)

• ______ accomplishes _______

• ____ is the inherited information- containing molecule located in the nucleus of cells

  • Genes are discrete segments of _______ that code for specific proteins ( and therefore for particular traits)

  • ________ exists as very long molecular strands called ________

  • Each ______ consists of thousands of genes

• cells within individuals of the same species have the same number of chromosomes

  • Human cells have ___ chromosomes

When the cell is not dividing:

• chromosomes exist in a diffuse state called ______

  • Spread throughout the nucleus

  • Individual chromosomes cannot be distinguished

As the cell is preparing to divide:

• each chromosome is duplicated

  • Chromosomes now consist of two sister chromatids attached at a _____

• Chromosomes wrap and coil around ______ proteins

  • Chromosomal DNA becomes tightly compacted

    • Chromosomes are no longer in the diffuse _____ state

    • Individual condensed chromosomes can now be distinguished

While the cell is dividing:

• sister chromatids ______ and are ______ to the two daughter cell

  • Each new chromosome is identical to each other (and to the parent chromosome)

  • The daughter cells therefor receive identical genes

The cell cycle is the sequence of stages between when _________ and _________

• 90% of the cell cycle is spent in the ______

  • The cell is not ______ during this time

• _____ is separated into its own three stages

• ______, ______, and ______

Interphase

_____ phase (first gap)

• the cell performs its normal functions

• Cell ______ occurs

  • New ______ (organelles and cytosol) is produced

• Chromosomes are in the diffuse _____ state

  • Chromosomes have not yet duplicated and therefore do not yet consist of sister chromatids

Interphase

____ phase (DNA synthesis)

• chromosomes duplicate

  • Each chromosome now consists of _______ attached at their centromere

Interphase

____ phase (second gap)

• cells continue to perform their usual functions

• Cells continue to grow

• Chromosomes still exist as _______

  • Each chromosome is now two _______, so the amount of DNA has doubles

• 10% of the cell cycle is spent in the _______

  • Cell division occurs during this time

• The _____ consists of mitosis and cytokinesis

• Mitosis = division of the ______

• Cytokinesis = division of the ______

The four continuous stages of mitosis are:

• _____, ______, ______, and _______

• (Cytokinesis occurs simultaneously with ______)

Mitosis

______

• chromosomes (consisting of sister chromatids) coil tightly around histones and become individually distinct

• Two organelles called ______ (each with a pair of centrioles) move toward opposite poles of the cell

  • Centrioles manufacture the miotic spindle

    • Made of ______

  • The miotic spindle extends from each centrosome

Mitosis: Prophase

• the ________ breaks down

• Some of the spindle microtubules attach to the chromosomes at their centromeres

  • At specific centromere proteins called _______

• Other spindle microtubules span across the entire cell

  • From one centrosome to the other, now at opposite poles of the cell

Mitosis

________

• the mitotic spindle aligns the chromosomes (each with two chromatids) at the equator of the cell

  • Called the ________

Mitosis

_______

• the spindle microtubules attached to the chromosomes centromeres shorten

  • Pulling the chromatids apart, toward opposite poles of the cell

  • Once seperated, chromatids are now individual chromosomes

• The _________ extend across the entire cell membrane

  • Pushing the poles farther apart, elongating the cell

Mitosis

________

• chromosomes have now reached opposite poles of the cell

  • A ________ forms around each pole

  • Chromosomes (no laonger consisting of sister chromatids) return to the chromatin state

• The mitotic spindle breaks down

Cytokinesis

• Animal cells

  • A _______ forms

    • A ring of ______ that begins shallow but deepens as it contracts

  • The elongated cell is cleaved down its center

    • Pinching the parent cell into two _______ daughter cells

Cytokinesis: plant cells

• A _______ forms

  • Vesicles with cell wall material are deposited in the center of the elongated cell

  • The vesicles fuse to form a _____

  • The ______ then fuses with the cell wall of the parent cell

    • Separating the parent cell into two _____ daughter cells

Chromosomes occur in pairs called ______

• a gene for a particular trait is found at the same location on both ______

• Called the genes ______

An organisms body cells are called ______ cells

• human ______ cells contain ___ chromosomes

• Human ______ cells therefore contain ___ pairs of homologous chromosomes

• 22 pairs (44 chromosomes) are called ______

  • Genes for traits other than gender are located on these

• 1 pair (2 chromosomes) are called ______

  • These can determine gender

  • They are called X and Y

Meiosis separates chromosomes of a homologous pair, producing cells (gametes) with _____ the number of chromosomes

The human life cycle is the sequence of stages between ________ and ________

• human somatic cells are diploid (2n)

  • Diploid cells have both members of each homologous pair of chromosomes

    • ___ autosomes & ___ sex chromosomes

    • Humans have 2n= _____

• Gametes are haploid (n)

  • Haploid cells have just one member of each homologous pair of chromosomes

    • ___ autosomes & ___ sex chromosome

    • Humans have n= _____

• _______ gametes (egg and sperm) are produced by meiosis only in the gonads (ovaries and testes)

• Fertilization is the fusion of gametes

  • Fertilization produces a single cell called a zygote

    • A zygote receives one member of each homologous pair from the egg and the other member of each homologous pair from the sperm

    • Zygotes are therefore _______

______ (reducing the chromosome number from diploid to haploid) and ______ (reestablishing the diploid chromosome number form the basis of ______

Cell division during which a diploid cell gives rise to four haploid gametes

• Interphase (prior to meiosis)

  • Chromosomes are in the _____ state (They duplicate to form sister chromatids attach at their _____)

• Meiosis I

  • A diploid cell divides producing two _____ cells

• Meiosis II

  • The two _____ cells divide producing four _____ cells (gametes)

Meiosis I: Prophase I

• Chromosomes (consisting of sister chromatids) coil tightly around ______ and become individually distinct

• Homologous chromosomes pair up in ______

  • 2 homologous chromosomes + 2 sister chromatids = ________

• ______ occurs

Meiosis I: Prophase I

• two centrosomes move toward opposite poles of the cell

  • Centrioles manufacture a spindle of ______, which extends from each centrosome

  • The ______ breaks down

Meiosis I: Prophase I

• some spindle microtubules attach to the chromosomes at their centromeres

  • At the ______

  • Each attaches to only one member of each homologous pair

• Others span across the entire cell

Meiosis I: Metaphase I

• homologous pairs of chromosomes (______) are aligned at the equator of the cell (_______)

Meiosis I: Anaphase I

• the spindle microtubules attached to the chromosomes’ _______ shorten

• The spindle microtubules that extend across the entire cell ________

Meiosis I: Telophase I

• homologous chromosomes have reached opposite poles of the cell

• New ________ forms

• Spindle breaks down

• Two daughter cells are haploid with half the number of chromosomes as the parent cell

Meiosis I: Cytokinesis

• animals = _______

• Plants = _______

Meiosis II

• Prophase II, metaphase II, anaphase II, & telophase II

• All same except:

  • In meiosis II, each cell begins and ends with a ____ chromosome number

  • In mitosis, each cell begins and ends with a ____ chromosome number

Genetic variation is essential for ________

• asexual reproduction produces _______ offspring

  • Mitosis

• Sexual reproduction produces _______ offspring

  • Meiosis & fertilization

    • Crossing over

    • Independent assortment of chromosomes

    • Random fertilization

orientation of homologous pairs of chromosomes during metaphase I is random

• number of possible chromosome combinations gamete can receive is 2^n

• N = haploid number

  • Humans = ______

  • 2^23 = ______ million possible combinations

A random egg is fertilized by a random sperm

• resulting c=zygote has ___ x ___ = ___ possible chromosome combinations

Crossing over adds genetic variation

• produces _______ chromosomes with genetic information distinct from the parental chromosomes

• Site of crossing over is called the ______

______ is a failure of chromosomes to separate during meiosis, which results in gametes with an abnormal number of chromosomes (n +/- 1)

• ______ chromosomes fail to separate during anaphase I

• ______ chromatids fail to separate during anaphase II

Nondisjunction

• zygotes will have abnormal chromosome numbers

  • 2n + 1 (______)

  • 2n - 1 (______)

• Abnormality is passed by mitosis to all somatic cells as zygote grows

Nondisjunction

• typically results in _______ early on during pregnancy

• Trisomy 21

  • Extra 21st chromosome

  • Condition: _______

  • Risk increases as mothers age increases

Nondisjunction of sex chromosomes

• XYY _______

Nondisjunction of sex chromosomes

• XXX _______

Nondisjunction of sex chromosomes

• XXY _______

Nondisjunction of sex chromosomes

• XO _______