Chapters: 12-15

1
Cell Division and Genetics

• Chapters 12-15

2
Why do we need cell division?

• 2 REASONS
• Growth and maintenance
• Reproduction

3
Cell Cycle Overview
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4
The Cell Cycle Control System

• A cyclically operating set of molecules in the
  cell that both triggers and coordinates key
  events in the cell cycle
• regulated at certain checkpoints by both internal
  and external signals

5
The Checkpoints

• A control point where stop and go-ahead signals
  can regulate the cycle
• animal cells have built-in stop signals that halt
  the cell cycle at checkpoints until overridden by
  go ahead signals
• signals come from cellular surveillance
  mechanisms inside the cell
• determine if the major processes of the cell
  cycle have been completed
• Three major check points G1, G2, M

6
G1 Checkpoint

• Restriction Point"
• if a cell receives the go ahead at G1 checkpoint,
  then the cell will continue with the cell cycle.
• If the cell DOES NOT get the go ahead it will
  enter G0
• the nondividing state of a cell
• most cells in body are in G0 (nerves and muscle
  cells)
• liver cells can be taken out of G0 phase if
  necessary (growth factors released during injury)

7
The Cell Cycle Clock

• The cell cycle is controlled by fluctuations of
  cycle control molecules that occur in intervals
• these rhythmic abundances pace the events of the
  cell cycle
• Regulatory molecules are two proteins
• cyclins
• protein kinase
• enzymes that will activate or inactivate other
  proteins by phosphorylating them
• give the go ahead signal at the G1 and G2
  checkpoints

8
Cell Division in Prokaryotes

• Called Binary Fission
• means "division in half" (asexual reproduction)
• starts at the origin of replication where the
  circular DNA begins replicating
• once the DNA is fully replicated, the cell begins
  to stretch toward the poles of the cell
• the membrane begins pinching off in the middle
• you now have two new daughter cells

9
Interphase

• the longest phase of the cell cycle
• accounts for 90 of the cell's life
• the cell is producing proteins and cytoplasmic
  organelles
• The chromatin is not condensed during interphase
  because it is needed for protein synthesis
• Divided into 3 subphases
• G1 Phase gt first gap
• S Phase gt synthesis (chromosome duplication)
• G2 Phase gt second gap

10
Mitosis

• The part of the cell cycle where the cell is
  actually undergoing cell division
• Consists of 5 stages
• prophase
• metaphase
• anaphase
• telophase
• Timing and rate of cell division are crucial to
  normal growth, development and maitenance
• varies with type of cell
• Cytokinesis is part of the Mitotic (M) phase, but
  not apart of mitosis itself.
• Different in plants and animals

11
Prophase

• 1st stage of mitosis
• the chromatin condenses into two identical
  chromosomes and the nuclear envelope begins to
  disappear

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12
Metaphase

• 2nd stage of mitosis
• the chromosomes line up on the equatorial plate
• spindle fibers are attached to the kinetochore of
  each chromosome pair
• "tug of war"

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13
Anaphase

• 4th stage of mitosis
• shortest
• cohesion proteins are cut and the sister
  chromatids are now separated
• the cell beings elongating

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14
Telophase

• Final stage of mitosis
• daughter cells begin to form
• nuclear envelope is visible again
• nucleoli reappear
• spindle fibers disappear

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15
Comparing Cytokinesis
Animals
Plants

• There is NO cleavage furrow
• because plant cells have cell walls in addition
  to cell membranes, they need to build a new cell
  wall
• vesicles will form in the middle of the original
  parent cell from the golgi apparatus (starts
  during telophase)
• merge and become the cell plate
• enlarges until the membranes fuse

• In animals
• occurs by cleavage
• a cleavage furrow will form in what was the
  middle of the parent cell
• the furrow is a contractile ring of actin
  filaments that contract
• eventually splits the cell into two daughter
  cells

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16
Cyclins and Protein Kinases

• Timing of the cell cycle is initiated by growth
  factors and controlled by two kinds of molecules
  cyclins and protein kinases
• protein kinases (cell signal transduction)
  catalyze the phosphorylation of target proteins
  that regulate the cell cycle
• Cyclin-dependent kinases (CDKs)

17
Cyclin-dependent Kinase

• Activated by binding to the protein cyclin
• exposes the active site to the CDK and activates
  the molecule
• allosteric regulation
• Several CDKs regulate the cell cycle at specific
  stages called cell cycle checkpoints
• each cyclin is manufactured at a precise time
  during the cell cycle and therefore each CDK is
  activated at a precise time
• The activity of CDKs rises and falls with changes
  in the concentration of its cyclin partner MPF

18
The Chain Reaction that Controls the Cell Cycle
Cell Cycle events
CDK activation
growth factor
cyclin synthesis
19
Meiosis

• this video made us laugh, if you get the gist
  of it, move on
• http//www.youtube.com/watch?viCL6d0OwKt8

20
Meiosis Different than Mitosis

• Meiosis generates the genetic diversity taht is
  the raw material for natural selection and
  evolution
• produces gametes (egg and sperm) or sex cells
• that are haploid the chromosome number (n) of the
  parent cell
• the chromosome number will return to diploid (2n)
  during sexual fusion
• NOT MITOSIS TWICE

21
Meiosis I The Source of Genetic Variation

• Known as reduction division
• Meiosis I is characterized by
• homologous chromosomes pairing up
• crossing over genetic information
• the nonsister chromatids exchange genetic
  information
• results in recombination of genetic material
• CROSSING OVER ENSURES GREATER VARIATION AMONG
  GAMETES

22
Meiosis Prophase I

• Synapsis the pairing of homologous chromosomes
  occur
• crossing over occurs
• Chiasmata the point where the crossing over
  occurs

23
Prophase vs. Prophase I
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chiasmata

• Prophase Mitosis
• the chromosomes condense and sister chromatids
  meet at the kinetochore

• Prophase I Meiosis
• homologous chromosomes pair up
• non-sister chromatids exchange genetic
  information (crossing over) at the chiasmata

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24
Meiosis I Overview
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25
Meiosis II

• Meiosis II is exactly like mitosis in the sense
  that the sister chromatids are separating and
  forming two new cells
• remember that after Meiosis I, there are two
  haploid cells (half of the number of chromosomes)
  that are genetically different
• meiosis II continues as cell division, separating
  the sister chromatids
• In the end, each gamete should have half the
  chromosomes of the parent cell and no sister
  chromatids

26
Egg sex cells vs. Sperm cells

• Male sex cells (sperm)
• undergo meiosis where each sperm is equal
• like you think a normal cell would undergo
  meiosis
• quantity over quality
• Female sex cells (eggs)
• specialized meiosis
• an egg will undergo meiosis to "get rid of" half
  of genetic material, but will keep the rest of
  the cells resources
• leftover cells are called polar bodies
• quality over quantity

27
Egg cells vs sperm cells
http//veterinary-online.blogspot.com/2012/12/deve
lopment-of-animals-formation-of.html.UX86879qpNY
28
Ch. 14 Mendel and the Gene Idea
29
Law of Dominance

• Mendels first law is the law of dominance
• Law of dominance states that when two organisms,
  each homozygous (pure) for two opposing traits
  are crossed, the offspring will be hybrid (carry
  two different alleles) but will exhibit only the
  dominant trait
• The trait that remains hidden is known as the
  recessive trait

Parent (P) TT X tt
(pure tall) (pure
dwarf) Offspring (F1) Tt
All hybrid
T
T
Tt Tt
Tt Tt
t
t
Law of dominance
All offspring are tall
30
Law of Segregation

• The law of segregation states that during the
  formation of gametes, the two traits carried by
  each parent separate
• 
  Gametes
• The cross that best exemplifies this law the
  monohybrid cross, Tt X Tt. In the monohybrid
  cross, a trait that was not evident in either
  parent appears in the F1 generation

Tt
T
t
31
Law of Independent Assortment

• The only factor that determines how these alleles
  segregate or assort is how the homologous pairs
  line up in metaphase of meiosis I, which is
  random.

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32
Law of Independent Assortment

• The law of independent assortment applies when a
  cross is carried out between two individuals
  hybrids for two or more traits that are not on
  the same chromosome.
• This cross is called the dihybrid cross.
• This law states that during gamete formation, the
  alleles of a gene for one trait segregate
  independently from the allele of a gene for
  another trait.

33
Multiplication Rule

• Multiply the chance of one happening by the
  chance that the other will happen
• For example
• The chance of a couple having two boys depends on
  two independent events. The chance of the first
  child being a boy is ½ and the chance of the
  next child being a boy is ½
• Therefore, the chance that the couple will have
  two boy is ½ x ½ ¼
• The chance of having three boys is ½ x ½ x ½
  1/8

34
Addition Rule

• When more than one arrangement of events
  producing the specified outcome is possible, the
  probabilities for each outcome are added
  together.
• For example if a couple is planning on having
  two children, what is the chance that they will
  have one boy and one girl
• The probability of having a girl and then a boy
  is ½ x ½ ½
• The probability of having one boy and one girl is
  ¼ ¼ ½

35
Monohybrid cross

• The monohybrid cross (Tt XTt) is a cross between
  two organisms that are each hybrid for one trait.
  
• The phenotype (appearance) ration from this cross
  is 3 tall to 1 dwarf plant.
• The genotype (type of genes) ratio, 1 to 2 to 1,
  given as percentages 25 homozygous dominant,
  50 heterozygous, and 25 homozygous recessive.
  These results are always the same for any
  monohybrid cross.

T
t
TT Tt
Tt tt
T
F1 Tt X Tt F2 TT, Tt, or tt
t
Monohybrid cross
36
Testcross

• The testcross is way to determine the genotype of
  an individual plant or animal showing only the
  dominant trait.
• If the parent of unknown genotype is BB, there
  can be no white offspring
• B black
• b white
• If the parent of the unknown genotype is hybrid,
  there is a 50 chance that any offspring will be
  white.

B
B
Bb Bb
Bb Bb
b
b
B
b
Bb bb
Bb bb
b
b
37
The Dihybrid Cross

• A dihybrid cross is a cross between two F1 plants
  because it is a cross between individual that are
  hybrid fro two different traits
• This cross can produce 4 different types of
  gametes, such as TY, Ty, tY, and ty.

tY
ty
TY
Ty
TTYY TTYy TtYy TtYy
TtYy TTyy TtYy Ttyy
TtYY TtYy ttYY ttYy
TtYy Ttyy ttYY ttyy
TY
Ty
tY
Phenotype ratio 9331
ty
38
Incomplete dominance

• Incomplete dominance is characterized by
  blending.
• For example A red flower (RR) crossed with a
  white flower (WW) produces all pink offspring
  (RW)

R
R
RW RW
RW RW
W
W
R
W

• If 2 pink flowers are crossed, there is a 25
  chance that the offspring will be red, a 25
  chance the offspring will be white, and a 50
  chance the offspring will be pink

RR RW
RW WW
R
W
39
Codominance

• In codominance, both traits show.
• For example Different blood groups M, N, and MN

MM
NN
MN
40
Multiple alleles

• Occurs when there are are more than two allelic
  forms of a gene
• For example Human blood types- A, B, AB and O
• The 3 alleles A, B, and O
• determine 4 different blood types

Human Blood Types Genotypes
Blood Type Genotype
A Homozygous A AA
A Hybrid A Ai
B Homozygous B BB
B Hybrid B Bi
AB AB
O ii
41
Gene InteractionsPleiotropy

• Pleiotropy is the ability of one single gene to
  affect an organism in several or many ways.
• For example autosomal recessive disease cystic
  fibrosis? abnormal thickening to mucus that coats
  certain cells
• ? thick mucus builds up in the pancreas, lungs,
  digestive tract and other organs
• leads to multiple pleiotropic effects including
  poor absorption of nutrients in the intestine and
  chronic bronchitis

42
Gene Interactions Epistasis

• Where two separate genes control one trait, but
  one gene masks the expression of the other gene
• The gene that masks the expression of the other
  gene is epistatic to the gene it masks
• For example agouti coat color in mice?
• 2 genes control different enzymes in 2 different
  pathways that both contribute to coat color
• Both genes A and B must be present in order to
  produce that agouti color

AB aB Ab ab
AB A/A B/ B Agouti A/a B/B Agouti A/A B/b Agouti A/a B/b Agouti
aB A/ a B/ B Agouti a/a B/B Black A/a B/b Agouti a/a B/b Black
Ab A/A B/b Agouti A/a B/B Agouti A/A b/b Albino A/a b/b Abino
ab A/a B/b Agouti a/a B/b Black A/a b/b Albino a/a b/b Albino
AaBb X AaBb
?In the absence of B, even if A is present, the
coat is colorless (albino) ?Therefore gene B is
epistasis to gene A
43
Polygenic Inheritance

• Polygenic traits many characteristics such as
  skin color, hair color, and height result from
  blending of several separate genes that vary
  along a continuum
• The wide variation in genotypes always results in
  a bell-shaped curve in an entire population

http//photos1.blogger.com/blogger/4252/2243/400/S
kin_Pigmentation.jpg
44
The Pedigree

• A pedigree is a family tree that indicates the
  phenotype of one trait being studied for every
  member of a family
• It can determine how a particular trait is
  inherited
• Females are represented by a and males
  by a
• A shape is completely shaded
  in if a person exhibits the trait

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45
Ch. 15The Chromosomal Basis of Inheritance
46
The Chromosomal Basis of Inheritance

• Chromosome theory of inheritance
• Genes have specific loci along chromosomes
• Chromosomes undergo segregation and independent
  assortment

47
Thomas Hunt Morgan's Experiment

• Fruit fly (drosophila melanogaster)
• Bred flies for 2 years with no conclusion
• Finally, 1 male had white eyes instead of the
  usual red (red is the wild type-- characteristic
  most commonly observed)
• White eyes were a mutant phenotype
• Continued mating females with white-eyed male
• Discovered the gene for eye color is gender
  related and on the X chromosome
• Supported chromosome theory of inheritance that a
  specific gene is on a specific chromosome

http//en.wikipedia.org/wiki/FileSexlinked_inheri
tance_white.jpg
48
Sex-linked genes

• X and Y chromosomes
• XX-- female XY-- male (sex determination is
  50-50 chance)
• Sex-linked gene- gene located on either X
  chromosome
• Very few Y-linked genes, passed from father to
  son
• About 1,100 X-linked genes
• Males more likely to have disorders from X-linked
  gene (have disease if either recessive or
  dominant because only one X chromosome)
• ex. color blindness, Duchenne muscular dystrophy,
  hemophilia

49
Sex-linked Genes

• X inactivation in Females
• Most of one X chromosome becomes inactivated when
  embryo is developing
• If did not become inactivated, chromosomes would
  make 2x the amount of proteins for X-linked genes
  as males
• Inactive X condenses into compact object called a
  Barr Body
• Selection for which X chromosome is inactivated
  occurs randomly

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Linked Genes

• Linked genes- genes located near each other on
  the same chromosome tend to be inherited together
  in a genetic cross
• Genetic recombination- the production of
  offspring with combinations of traits that differ
  from those found in either parent
• Parental type- the half of the offspring that
  inherit a phenotype that matches either parent's
  phenotype
• Recombinant types (recombinants)- offspring that
  have non parental phenotypes

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Gene Recombination and Linkage

• The physical basis of recombination between
  unlinked genes is the random orientation of
  homologous chromosomes
• Happens in metaphase I of meiosis
• Leads to independent assortment of the 2 unlinked
  genes
• Crossing over- reciprocal exchange of genes
  between one paternal and one maternal chromatid.
• accounts for the recombination of linked genes

52
Gene Recombination and Linkage
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Alterations of Chromosomes

• Large-scale chromosomal changes can affect an
  organism's phenotype
• physical/ chemical disturbances or error during
  meiosis
• results in developmental disorders
• Nondisjunction- members of a pair of homologous
  chromosomes don't move apart properly during
  meiosis I or sister chromatids fail to separate
  during meiosis II

http//www.nature.com/scitable/content/32851/10.10
38_nrm1526-f1_large_2.jpg
54
Nondisjunction

• Aneuploidy- a condition where a normal gamete
  unites with an abnormal one, resulting in a
  zygote with an irregular amount of chromosomes
• Monosomic- missing a chromosome (2n-1)
• Trisomic- chromosome tripled (2n1)
• If organism survives, has a set of traits that
  result from abnormal amount or missing chromosome
• ex. Down Syndrome (trisomy)
• Nondisjunction can occur during mitosis as well
• If happens during embryonic development, mitosis
  will pass aneuploid condition to large number of
  cells

55
Nondisjunction

• Polyploidy-general term for chromosomal
  alteration where organism has two complete
  chromosome sets
• triploidy (3n) tetraploidy (4n)
• More common in plants
• Have less effect than aneuploids because is a
  full set of chromosomes and one missing
  chromosome disrupts genetic balance more

56
Alterations in Chromosome Structure

• Error in meiosis or damaging agents can in 4
  types of changes in chromosome structure
• Deletion- when a chromosome fragment is lost
• Results in chromosome missing certain genes
• Duplication- the "deleted" fragment becomes
  attached as an extra segment to a sister
  chromatid
• Inversion- chromosome fragment reattaches to the
  original chromosome, but in the reverse
  orientation
• Translocation- fragment joins a nonhomologous
  chromosome
• Deletions and duplications are likely to occur
  during meiosis (in crossing over)

57
Alterations of Chromosome Structure

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58
Genomic Imprinting

• Genomic Imprinting- Idea that the expression of
  an allele in offspring depends on whether the
  allele is inherited from the mother or father
• Genes are autosomal (not sex-linked)
• Zygote only expresses one allele of an imprinted
  gene, from mother or father
• Occurs during gamete formation and results in the
  silencing of particular alleles
• Only affects a small fraction of gene in
  mammalian genomes, but are usually genes critical
  for development

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Organelle genes

• Extranuclear/cytoplasmic
• genes
• Genes located outside the nucleus
• Can be in mitochondria, chloroplast
• Are not distributed to offspring like with
  nuclear chromosomes
• Extranuclear genes first noticed by Karl Correns
  (1909)
• Noticed inheritance of yellow and white patches
  on the leaves of a green plant
• Coloration only determined by the maternal plant
• Research showed that coloration patterns are due
  to mutations in genes that control pigmentation

http//s3.amazonaws.com/picable/2009/07/23/1195661
_Lovely-green-Plant_620.jpg
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Sources

• Goldberg, Deborah M.S. Barron's AP Biology. 3rd
  ed. New York Baron's Educational Series, 2013.
  Print.
• Reece, Jane B., and Neil A. Campbell. Campbell
  Biology. 9th ed. Boston Benjamin Cummings /
  Pearson Education, 2011. Print.