Genes, Chromosomes and DNA

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Genes, Chromosomes and DNA
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• Mendel and Peas
• simple inheritance patterns
• phenotype/genotype, dominant recessive
• heterozygous/homozygous, Mendels laws
• B. Chromosomal Basis of Inheritance
• Chromosomes
• Cell division mitosis and meiosis
• Gene linkage, crossing over, nondisjunction
• Molecular basis of Inheritance
• DNA structure and replication

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No two individual people are exactly alike, but
most people resemble their parents Heredity was
compared to mixing of fluids blending
inheritance
WHY?
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No two individual people are exactly alike, but
most people resemble their parents
Heredity was compared to mixing of
fluids blending inheritance
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Gregor Mendel (1860s) Lived in a
Monestary Loved to garden Was very
meticulous Pea Plants Reproduce sexually Have
both male and female organs Have distinctive
traits Started with pure-breeding plants
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Gregor Mendel (1860s) Lived in a
Monestary Loved to garden Was very meticulous
Pea Plants Reproduce sexually Have both male and
female organs
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An aside
sex
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adult adult
sperm gametes egg
gametes
fertilized egg
(zygote)
adult
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Another asideex
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Hermes
messenger archer
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Hermes
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Aphrodite
goddess of Love
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Aphrodite
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Hermes
Aphrodite
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Hermes
Aphrodite
sperm
egg
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Hermes
Aphrodite
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Hermaphrodite
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female
male
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Gregor Mendel (1860s) Lived in a
Monestary Loved to garden Was very
meticulous Pea Plants Reproduce sexually Have
both male and female organs Have distinctive
traits (seed, flowers, size, etc)
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Fig 2-1
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Gregor Mendel (1860s) Lived in a
Monestary Loved to garden Was very
meticulous Pea Plants Reproduce sexually Have
both male and female organs Have distinctive
traits Started with pure-breeding plants
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Mendel crossed
tall plants X short plants green
seeds X yellow seeds round seeds X wrinkled
seeds violet flowers X white flowers etc
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Mendel crossed tall plants X short
plants green seeds X yellow seeds round
seeds X wrinkled seeds violet flowers X white
flowers etc An example









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violet flowers X white flowers Parents
(P) violet flowers x white flowers The
offspring (F1) all had red flowers
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violet flowers X white flowers Parents
(P) violet flowers x white flowers The
offspring (F1) all had violet flowers
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Fig 2.3
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violet flowers X white flowers Parents
(P) violet flowers x white flowers The
offspring (F1) all had violet flowers Red is
dominant (it appears) White is recessive (it
doesnt show up)
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violet flowers X white flowers Parents
(P) violet flowers x white flowers The
offspring (F1) all had violet flowers Violet
is dominant (it appears) White is recessive (it
doesnt show up)
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violet flowers X white flowers Parents
(P) violet flowers x white flowers The
offspring (F1) all had violet flowers Violet
is dominant (it appears) White is recessive (it
doesnt show up)
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Fig 2-1
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The physical appearance of the organism
Phenotype The genetic makeup of the
organism Genotype
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Fig 2.3
Are these violet plants the same?
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Fig 2.3
Mendel did a self cross (F1 cross) (F1 X F1)
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F1 cross
F2 3/4 were violet 1/4 were white
fig 2.3
35
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How did Mendel explain these results? see pages
36-37 in text
36
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• Inheritance of traits is controlled by factors
  (genes)
• Everyone has two factors (genes) for each trait
• There can be different forms of genes (alleles)
• e.g. violet vs white
• Homozygous means alleles are identical
• Heterozygous means alleles are different
• Dominant always show up (are expressed)
• Recessive can be masked
• Factors (genes) dont blend
• Gametes (egg or sperm) contain only one factor
  (gene)
• Two factors separate from each other (segregation)

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• How to solve genetics problems
• Define terms
• Parent genotypes
• Gamete genotypes
• Punnett square

38

• Gene for flower color (violet vs white)
• Define terms
• Violet dominant V
• White recessive v

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39

• Gene for flower color (violet vs white)
• Define terms
• 2. Parent genotypes
• Violet dominant V
• White recessive v

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Pure breeding violet plant would be V V Pure
breeding white plant would be v v
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• Gene for flower color (violet vs white)
• Define terms
• 2. Parent genotypes
• Violet dominant V
• White recessive v
• Pure breeding violet plant would be V V
• homozygous dominant
• Pure breeding white plant would be v v
• homozygous recessive

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41

• Gene for flower color (violet vs white)
• Define terms
• Parent genotypes
• Gamete genotypes
• Violet
• White

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adult V V v v
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• Gene for flower color (violet vs white)
• Define terms
• Parent genotypes
• Gamete genotypes
• Violet
• White

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gamete V v
adult V V v v
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• Gene for flower color (violet vs white)
• Define terms
• Parent genotypes
• Gamete genotypes
• Punnett square

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Possible gametes from parent 1
Possible gametes from parent 2
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• Gene for flower color (violet vs white)
• Define terms
• Parent genotypes
• Gamete genotypes
• Punnett square

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V
V
v
V v
V v
V v
V v
v
45
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P V V X v v F1 All are V v (heterozygous) F2
??
F1 cross Do it!
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• Do Punnett square for F1 cross on board
• Mendels first law Law of segregation
• Factors (alleles, genes) separate from each other
  when gametes are produced

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fig 2.3
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• We have just examined one trait (gene)
• Any questions?

• Look now at two traits together
• Seed color
• Seed shape

Yyellow, y green
R round, r wrinkled
49
fig 2.4
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Do the F1 cross (selfcross) YyRr x YyRr ?

• Define terms
• Parent genotypes
• Gamete genotypes
• Punnett square

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Do the F1 cross (selfcross) YyRr x
YyRr Gametes ? (test hypotheses on board)

• Define terms
• Parent genotypes
• Gamete genotypes
• Punnett square

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yellow, round green, round yellow,
wrinkled green, wrinkled
315 108 101 32
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• Mendels first law Law of segregation
• Factors (alleles, genes) separation from each
  other when gametes are produced
• Mendels second law
• Law of independent assortment
• How one pair of factors separate is independent
  of how all other pairs separate.

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Chapter 2
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• Chromosomal basis of inheritance

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Dont know Where are genes located ? Why do
they exist as pairs ? Why do the assort
independently ?
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• Microscopes
• Organisms are made of cells
• Cell has a central nucleus
• surrounded by cytoplasm

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fig 2.5
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Organisms grow because their cells can divide to
make more cells During cell division structures
called chromosomes are visible in the nucleus
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We can now examine the chromosomes individually
and see that they are different
centromere long arm short arm
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Count the chromosomes in gametes N Count
the chromosomes in somatic cells 2N
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Count the chromosomes in gametes N Count
the chromosomes in somatic cells 2N
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Count the chromosomes in gametes N haploid
(single) Count the chromosomes in somatic
cells 2N diploid (double)
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Examine the chromosomes in somatic cell more
closely They are found as pairs
called homologous pairs (think socks)
64
socks
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karyotype
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66

• Sutton noticed
• Eggs cells and sperm cells were very different in
  size, but the nucleus was about the same size.
• Genes are probably in the nucleus
• Chromosomes are in the nucleus
• Therefore genes may be on chromosomes

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67
Chromosomal theory of Inheritance See page 41 of
BT3
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68
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Mitosis (cell division)
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Mitosis (cell division)
gamete vs somatic cell
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Mitosis (cell division)
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Mitosis (cell division)
Fig 2.6
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Mitosis (cell division)
gamete vs somatic cell
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Mitosis (cell division)
gamete vs somatic cell 2N 2N 2N
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Mitosis (cell division)
Before cell division, cell is in
interphase duplicate chromosomes
fig 2.7
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Cell cycle
interphase
Mitosis
prophase
telophase
metaphase
anaphase
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Cell Cycle
Interphase Chromosomes duplicate Prophase Chromo
somes condense Metaphase Chromosome line up at
equator Anaphase Chromosomes separate and
migrate Telophase Chromosomes reach
end cytoplasm splits-cytokinesis
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fig 2-8(1)
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fig 2-8 (2)
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Cell Cycle
Interphase Chromosomes duplicate Prophase Chromo
somes condense Metaphase Chromosome line up at
equator Anaphase Chromosomes separate and
migrate Telophase Chromosomes reach
end cytoplasm splits-cytokinesis
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Draw metaphase (of mitosis)
81
Mitosis vs Meiosis
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Mitosis vs Meiosis
82
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Meiosis sexual reproduction
83
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adult adult sperm gametes
egg fertilized egg (zygote) adult
meiosis
mitosis
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fig. 2-9
85
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86
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Mitosis Meiosis
interphase
interphase
gametes
prophase I
telophase II
telophase
metaphase I
prophase
anaphase II
anaphase I
metaphase II
anaphase
metaphase
telophase I
prophase II
interphase
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fig. 2-10
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Genes are on chromosomes Chromosomes move
during cell division If there are multiple
genes on a chromosome the genes should
travel together
Gene linkage
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fig. 2-11
90
Sex (cell division)
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XX
XY
91
Sex (cell division)
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on Y chromosome
XX
XY
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Chromosomal problems
Diploid cells have 2N chromosomes (46) Gametes
have N chromosomes (23) What if meiosis was
abnormal?
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94
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disjunction
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disjunction
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97
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A B C
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A B C
99
Klinefelters syndrome (XXY)
100
Klinefelters syndrome (XXY)
Characteristics may include Tallness with
extra long arms and legs Abnormal body
proportions (long legs, short trunk)
Enlarged breasts Lack of facial and body
hair Small firm testes Small penis
Lack of ability to produce sperm
Diminished sex drive Sexual dysfunction
Learning disabilities Personality
impairment
101
Turners syndrome (X0)
102
Turners syndrome (X0)
Characteristics may include short
stature lack of ovary development
webbed neck elbows bent out
heart, kidney,thyroid problems bone
problems
103
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104
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105
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Genes are OK have an abnormal of
chromosomes
106
Genes, Chromosomes and DNA
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• Mendel and Peas
• simple inheritance patterns
• phenotype/genotype, dominant recessive
• heterozygous/homozygous, Mendels laws
• B. Chromosomal Basis of Inheritance
• Chromosomes
• Cell division mitosis and meiosis
• Gene linkage, crossing over, nondisjunction
• Molecular basis of Inheritance
• DNA structure and replication

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Molecular basis of inheritance
What molecule(s) is (are) responsible for storing
the genetic information?
108
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Molecular basis of inheritance
Griffith transformation Hershey and
Chase nucleic acid Chargaff nucleotides/ratios
Watson and Crick double helix
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Molecular basis of inheritance

• What molecule(s) is responsible for storing the
  genetic information?
• Carbohydrates
• Nucleic acids (DNA or RNA)
• Lipids
• Proteins

110
The molecule with P (nucleic acid) makes its way
into the infected cells, not the molecule with S
(protein). Is it DNA or RNA ?
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DNA, not RNA (sensitive to DNase)
111
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Digest it Phosphate groups Bases (A, C, G,
T) Sugars (deoxyribose)
DNA
112
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fig 2-20b
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fig 2-20b
114
Cells have constant relative amounts of different
bases 31 A 19 G 31 T 19 C (for humans)
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Cells have constant relative amounts of different
bases 31 A 19 G 31 T 19 C (for humans)
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A T C G
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Watson and Crick Nucleotides(4) P-S-B
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Watson and Crick Nucleotides (4)
P-S-B S-P backbone
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Watson and Crick Nucleotides (4)
P-S-B S-P backbone Linear strands Double helix
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Watson and Crick Nucleotides (4)
P-S-B S-P backbone Linear strands Double helix
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Watson and Crick Nucleotides (4)
P-S-B S-P backbone Linear strands Double
helix Bases are complimentary A and T C and G
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fig 2-21
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With Watson and Cricks double helix model it was
easy to understand how a cell could copy all its
genetic material
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DNA Replication
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fig 2-22
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End of Chapter 2