Genes, Chromosomes and DNA
A. 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
C. Molecular basis of Inheritance
DNA structure and replication
No two individual people are exactly alike,
but most people resemble their parents
Heredity was compared to mixing of fluids:
WHY?
“blending inheritance”
No two individual people are exactly alike,
but most people resemble their parents
Heredity was compared to mixing of fluids:
“blending inheritance”
Gregor Mendel (1860’s)
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
Gregor Mendel (1860’s)
Lived in a Monestary
Loved to garden
Was very meticulous
Pea Plants
Reproduce sexually
Have both male and female organs
adult
sperm
adult
gametes
gametes
fertilized egg
(zygote)
adult
egg
Hermes
messenger
archer
Hermes
Aphrodite
goddess of Love
Aphrodite
Hermes
Aphrodite
Hermes
sperm
Aphrodite
egg
Hermes
Aphrodite
Hermaphrodite
female
male
Gregor Mendel (1860’s)
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)
Fig 2-1
Gregor Mendel (1860’s)
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
Mendel crossed:
tall plants X
green seeds X
round seeds X
violet flowers
etc…
short plants
yellow seeds
wrinkled seeds
X
white flowers
Mendel crossed:
tall plants X
green seeds X
round seeds X
violet flowers
etc…
An example:
short plants
yellow seeds
wrinkled seeds
X
white flowers
violet flowers X
Parents (P)violet flowers x
white flowers
white flowers
The offspring (F1) all had red flowers
violet flowers X
Parents (P)violet flowers x
white flowers
white flowers
The offspring (F1) all had violet flowers
Fig 2.3
violet flowers X
Parents (P)violet flowers x
white flowers
white flowers
The offspring (F1) all had violet flowers
Red is dominant (it appears)
White is recessive (it doesn’t show up)
violet flowers X
Parents (P)violet flowers x
white flowers
white flowers
The offspring (F1) all had violet flowers
Violet is dominant (it appears)
White is recessive (it doesn’t show up)
violet flowers X
Parents (P)violet flowers x
white flowers
white flowers
The offspring (F1) all had violet flowers
Violet is dominant (it appears)
White is recessive (it doesn’t show up)
Fig 2-1
The physical “appearance” of the organism
Phenotype
The genetic makeup of the organism
Genotype
Are these violet plants the same?
Fig 2.3
Mendel did a self cross (F1 cross)
(F1 X F1)
Fig 2.3
F1 cross
F2
3/4 were violet
fig 2.3
1/4 were white
How did Mendel explain these results?
see pages 36-37 in text
•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) don’t “blend”
•Gametes (egg or sperm) contain only one factor (gene)
•Two factors separate from each other (segregation)
• How to solve genetics problems:
– Define terms
– Parent genotypes
– Gamete genotypes
– Punnett square
Gene for flower color (violet vs white):
1. Define terms
Violet
White
dominant
recessive
V
v
Gene for flower color (violet vs white):
1. Define terms
2. Parent genotypes
Violet
White
dominant
recessive
V
v
Pure breeding violet plant would be V V
Pure breeding white plant would be v v
Gene for flower color (violet vs white):
1. Define terms
2. Parent genotypes
Violet
White
dominant
recessive
V
v
Pure breeding violet plant would be V V
homozygous dominant
Pure breeding white plant would be v v
homozygous recessive
Gene for flower color (violet vs white):
1. Define terms
2. Parent genotypes
3. Gamete genotypes
Violet
White
adult
VV
vv
Gene for flower color (violet vs white):
1. Define terms
2. Parent genotypes
3. Gamete genotypes
Violet
White
adult
VV
vv
gamete
V
v
Gene for flower color (violet vs white):
1.
2.
3.
4.
Define terms
Parent genotypes
Gamete genotypes
Punnett square
Possible gametes from parent 1
Possible
gametes
from
parent 2
Gene for flower color (violet vs white):
1.
2.
3.
4.
Define terms
Parent genotypes
Gamete genotypes
Punnett square
V
V
v
Vv
Vv
v
Vv
Vv
P
F1
F2
VV
X
vv
All are V v (heterozygous)
??
F1 cross
Do it!
• Do Punnett square for F1 cross on board
• Mendel’s first law: Law of segregation
Factors (alleles, genes) separate from each other
when gametes are produced
fig 2.3
• We have just examined one trait (gene)
Any questions?
• Look now at two traits together:
–Seed color
–Seed shape
Y=yellow, y = green
R =round, r = wrinkled
fig 2.4
Do the F1 cross (selfcross):
YyRr
x
?
1.
2.
3.
4.
Define terms
Parent genotypes
Gamete genotypes
Punnett square
YyRr
Do the F1 cross (selfcross):
YyRr
x
Gametes ?
(test hypotheses on board)
1.
2.
3.
4.
Define terms
Parent genotypes
Gamete genotypes
Punnett square
YyRr
yellow, round
green, round
yellow, wrinkled
green, wrinkled
315
108
101
32
• Mendel’s first law: Law of segregation
Factors (alleles, genes) separation from each other
when gametes are produced
• Mendel’s second law:
Law of independent assortment
How one pair of factors separate is independent of
how all other pairs separate.
Chapter 2
Chromosomal basis of inheritance
Don’t know:
Where are genes located ?
Why do they exist as pairs ?
Why do the assort independently ?
Microscopes:
•Organisms are made of cells
•Cell has a central nucleus
surrounded by cytoplasm
fig 2.5
Organisms grow because their cells can
divide to make more cells
During cell division structures called
chromosomes are visible in the “nucleus”
We can now examine the chromosomes
individually and see that they are different:
centromere
long arm
short arm
Count the chromosomes in gametes
N
Count the chromosomes in somatic cells
2N
Count the chromosomes in gametes
N
Count the chromosomes in somatic cells
2N
Count the chromosomes in gametes
N
haploid (single)
Count the chromosomes in somatic cells
2N diploid (double)
Examine the chromosomes in somatic cell more
closely:
They are found as pairs called
homologous pairs
(think socks)
“socks”
karyotype
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
Chromosomal theory of Inheritance
See page 41 of BT3
Mitosis
(cell division)
Mitosis
(cell division)
gamete
vs
somatic cell
Mitosis
(cell division)
Mitosis
(cell division)
Fig 2.6
Mitosis
(cell division)
gamete
vs
somatic cell
Mitosis
(cell division)
gamete
vs
somatic cell
2N
2N
2N
Mitosis
(cell division)
Before cell division, cell is in interphase
duplicate chromosomes
fig 2.7
Cell cycle
interphase
telophase
anaphase
prophase
metaphase
M
i
t
o
s
i
s
Cell Cycle
Interphase
Chromosomes duplicate
Prophase
Chromosomes condense
Metaphase
Chromosome line up at equator
Anaphase
Chromosomes separate and migrate
Telophase
Chromosomes reach “end”
cytoplasm splits-cytokinesis
fig 2-8(1)
fig 2-8 (2)
Cell Cycle
Interphase
Chromosomes duplicate
Prophase
Chromosomes condense
Metaphase
Chromosome line up at equator
Anaphase
Chromosomes separate and migrate
Telophase
Chromosomes reach “end”
cytoplasm splits-cytokinesis
Draw metaphase (of mitosis)
Mitosis vs Meiosis
Meiosis
sexual reproduction
adult
adult
meiosis
sperm
gametes
fertilized egg
(zygote)
mitosis
adult
egg
fig. 2-9
Mitosis
Meiosis
interphase
interphase
gametes
telophase II
telophase
metaphase I
prophase
anaphase II
anaphase
prophase I
anaphase I
metaphase II
metaphase
telophase I
prophase II
interphase
fig. 2-10
Gene linkage
Genes are on chromosomes
Chromosomes move during cell division
If there are multiple genes
on a chromosome……
…the genes should travel together
fig. 2-11
Sex
(cell division)
XX
XY
Sex
(cell division)
XX
on Y
chromosome
XY
Chromosomal problems
Diploid cells have 2N chromosomes (46)
Gametes have N chromosomes (23)
What if meiosis was abnormal?
disjunction
disjunction
A
B
C
A
B
C
Klinefelter’s syndrome (XXY)
Klinefelter’s 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
Turner’s syndrome (X0)
Turner’s syndrome (X0)
Characteristics may include:
*
*
*
*
*
*
short stature
lack of ovary development
webbed neck
elbows bent “out”
heart, kidney,thyroid problems
bone problems
Genes are OK…
… have an abnormal # of chromosomes
Genes, Chromosomes and DNA
A. Mendel and Peas
B.
C.
simple inheritance patterns
phenotype/genotype, dominant recessive
heterozygous/homozygous, Mendels “laws”
Chromosomal Basis of Inheritance
Chromosomes
Cell division: mitosis and meiosis
Gene linkage, crossing over, nondisjunction
Molecular basis of Inheritance
DNA structure and replication
Molecular basis of inheritance
What molecule(s) is (are) responsible for storing
the genetic information?
Molecular basis of inheritance
Griffith
transformation
Hershey and Chase
nucleic acid
Chargaff
nucleotides/ratios
Watson and Crick
double helix
Molecular basis of inheritance
What molecule(s) is responsible for storing the
genetic information?
•Carbohydrates
•Nucleic acids (DNA or RNA)
•Lipids
•Proteins
The molecule with P (nucleic acid) makes its way
into the infected cells, not the molecule with S
(protein).
Is it DNA or RNA ?
DNA, not RNA (sensitive to DNase)
DNA
Digest it
Phosphate groups
Bases (A, C, G, T)
Sugars (deoxyribose)
fig 2-20b
fig 2-20b
Cells have constant relative amounts of
different bases:
31%
A
19%
G
31%
T
19%
C
(for humans)
Cells have constant relative amounts of
different bases:
31%
A
19%
G
[A] = [T]
31%
T
[C] = [G]
19%
C
(for humans)
Watson and Crick
Nucleotides(4)
P-S-B
Watson and Crick
Nucleotides (4)
S-P backbone
P-S-B
Watson and Crick
Nucleotides (4)
S-P backbone
Linear strands
Double helix
P-S-B
Watson and Crick
Nucleotides (4)
S-P backbone
Linear strands
Double helix
P-S-B
Watson and Crick
Nucleotides (4)
P-S-B
S-P backbone
Linear strands
Double helix
Bases are complimentary
A and T
C and G
fig 2-21
With Watson and Crick’s double helix model
it was easy to understand how a cell could
copy all its genetic material
DNA Replication
fig 2-22
End of Chapter 2