Transcript Chromosomes come in pairs

Types of Cell Division
Mitosis - Body cell replication
Meiosis - Sex cell replication
Meiosis - Sex cell replication
What is sex?
Sexual reproduction:
The production of offspring whose genetic
constitution is a mixture of that of two
potentially genetically different gametes.
-Futuyma, p. 771
Sexual reproduction in
diploid organisms:
-Chromosomes come in pairs
Sexual reproduction in
diploid organisms:
-Chromosomes come in pairs
-One member of each pair comes from each parent
Sexual reproduction in
diploid organisms:
-Chromosomes come in pairs
-One member of each pair comes from each parent
- Cells that will turn into gametes are sequestered early in
development - minimizing replication.
Sexual reproduction in
diploid organisms:
-Chromosomes come in pairs
-One member of each pair comes from each parent
- Cells that will turn into gametes are sequestered early in
development - minimizing replication.
-At sexual maturity, gamete production begins.
Sexual reproduction in
diploid organisms:
-Chromosomes come in pairs
-One member of each pair comes from each parent
- Cells that will turn into gametes are sequestered early in
development - minimizing replication.
-At sexual maturity, gamete production begins.
-Gametes are haploid. Their union produces a new diploid
organism.
Sexual reproduction in
diploid organisms:
-Chromosomes come in pairs
-One member of each pair comes from each parent
- Cells that will turn into gametes are sequestered early in
development - minimizing replication.
-At sexual maturity, gamete production begins.
-Gametes are haploid. Their union produces a new diploid
organism.
-Non-chromosomal cell matter comes from the mother.
Barbara
McClintock
Barbara
McClintock
Nobel Prize: 1983
Discoverer of
transposition &
recombination
Meiosis
Sex cell division, aka
gametogenesis
During meiosis,
chromosome pairs
double, then the center
two chromatids
recombine, or
“cross-over”
Meiosis - Sex cell division, aka
gametogenesis
Sampling error
3 chromosomes = 64 combinations
but only 1 to 4 gametes
MutationAn error in replication of a nucleotide
sequence, or any other alteration of the
genome that is not manifested as
reciprocal recombination.
Mutation is the ultimate source
of all hereditary variation
Basic types of mutationsPoint mutation
Insertion/Duplication
Deletion
Translocation
Inversion
Fission/Fusion
Horizontal transfer
Point mutation -An error in
replication of a nucleotide sequence.
G
For example, a
daughter cell
might end up
with a guanine
molecule where
the parent cell
had a adenine
molecule at that
same position in
its DNA
sequence.
Point mutation -An error in
replication of a nucleotide sequence.
Many point
mutations have
no effect
whatsoever on
phenotype.
This is very
often the case
when the
mutation
occurs in the
third position
of a nucleotide
triplet
G
For example, a
daughter cell
might end up
with a guanine
molecule where
the parent cell
had a adenine
molecule at that
same position in
its DNA
sequence.
Point mutation -An error in
replication of a nucleotide sequence.
Many point
mutations have
no effect
whatsoever on
phenotype.
This is very
often the case
when the
mutation
occurs in the
third position
of a nucleotide
triplet
Why would the
position matter?
G
Point mutation -An error in
replication of a nucleotide sequence.
Many point
mutations have
no effect
whatsoever on
phenotype.
This is very
often the case
when the
mutation
occurs in the
third position
of a nucleotide
triplet
Why would the
position matter?
Because the DNA code
is redundant.
G
Point mutation -An error in
replication of a nucleotide sequence.
Many point
mutations have
no effect
whatsoever on
phenotype.
This is very
often the case
when the
mutation
occurs in the
third position
of a nucleotide
triplet
Why would the
position matter?
Because the DNA code
is redundant.
G
DNA
nucleotide
triplets code
for amino
acids.
Point mutation -An error in
replication of a nucleotide sequence.
But there are
64 possible
triplet
combinations
(“codons”) yet
only 20 amino
acids.
Why would the
position matter?
Because the DNA code
is redundant.
G
DNA
nucleotide
triplets code
for amino
acids.
Point mutation -An error in
replication of a nucleotide sequence.
But there are
64 possible
triplet
combinations
(“codons”) yet
only 20 amino
acids.
Some
combinations
are
synonymous.
Why would the
position matter?
Because the DNA code
is redundant.
G
DNA
nucleotide
triplets code
for amino
acids.
Point mutation -An error in
replication of a nucleotide sequence.
But there are
64 possible
triplet
combinations
(“codons”) yet
only 20 amino
acids.
Some
combinations
are
synonymous.
For example
CCC codes for
the amino
acid proline.
G
But so do
CCA, CCT, and
CCG
fmi see
Futuyma,
p. 45
Insertions &
Deletions
During meiosis,
chromosome pairs
double, then the center
two chromatids
recombine, or
“cross-over”
Insertions &
Deletions
Sometimes, the
recombination is not
perfectly reciprocal,
producing “unequal
crossing-over”
Deletion
Insertion
From Futuyma
Translocation
Equal crossing over
Unequal
crossing
over
Deletion
Duplication
or
Equal crossing over
with
Translocation
Sometimes, chromosomal
material is exchanged among
non-homologous chromosomes.
Also, copies of certain nucleotide
sequences can be transposed -inserted on other chromosomes.
Transposition events sometimes
occur in plants, eg flax, during
times of ecological stress. It is a
quick way to disrupt the
phenotype, giving rise to new
morphologies and physiologies in
one generation, thus allowing
rapid evolution of new
adaptations.
Inversion
Sometimes, a bit of
chromosomal material is
excised during recombination
and ends up back in place, but
upside down.
Doublets Game
post from Carl Zimmer’s blog: www.corante.com/loom/
The challenge of a doublet is to turn one word into another.
You are allowed to change one letter at a time, but each
change must produce a real word. Here's a doublet that
suits a post on evolution: Change APE to MAN.
APE
APT
OPT
OAT
MAT
MAN
Doublets Game
post from Carl Zimmer’s blog: www.corante.com/loom
Now imagine that having solved the APE-to-MAN puzzle, you tell a
friend about your triumph.
Your friend scoffs. "That's ridiculous," he says. "I don't believe
you've found a missing link between APE and MAN. It doesn't
exist."
You furrow your brow. "Wait," you say. "No, I think maybe you
didn't hear how the puzzle works--"
"I mean, what comes in between?"
"Well, there's APT, and then--."
"APT? Please! That's nothing like MAN. They don't have a single
letter in common. It's just a completely separate word on its own."
"But then there's OPT--"
"OPT? Are you kidding me? That's just as irrelevant. You can't just
go from APE to MAN through OPT."
"But what about MAT? That's a lot like MAN."
"Sure," your friend says, rolling his eyes. "But what on Earth does
it have to do with APE?"
Doublets Game
MAN
RAN
RAM
RIM
RIB
ROB
> translocation adds MAN
ROB MAN
> deletion takes away the B & the space
ROMAN
WOMAN
Structure of the genome
Structure of the genome
-integrated system of modules of various kinds
Structure of the genome
-integrated system of modules of various kinds
-10,000-100,000 genes in most metazoans
Structure of the genome
-integrated system of modules of various kinds
-10,000-100,000 genes in most metazoans
-90% or more is non-genic & “junk DNA”
Structure of the genome
-integrated system of modules of various kinds
-10,000-100,000 genes in most metazoans
-90% or more is non-genic & “junk DNA”
-repetitive sequence
Structure of the genome
-integrated system of modules of various kinds
-10,000-100,000 genes in most metazoans
-90% or more is non-genic & “junk DNA”
-repetitive sequence
-highly repetitive satellite DNA
eg. alu repeats have been inserted all
over the genome of Drosophila
Structure of the genome
-integrated system of modules of various kinds
-10,000-100,000 genes in most metazoans
-90% or more is non-genic & “junk DNA”
-repetitive sequence
-highly repetitive satellite DNA
eg. alu repeats have been inserted all
over the genome of Drosophila
-introns
DNA that codes for protein is arranged within the
gene in a series of exons. The non-coding introns are
spliced out during transcription and translation.
A gene generally forms part of a gene family, a
group of genes descended from an ancestral gene.
Gene families evolve primarily via insertions.
When a second copy of a functional gene is inserted
downstream (or sometimes on another
chromosome), the second copy (and often the
original as well) is free to accumulate additional
mutations without compromising gene product
volume or quality.
Gene families often have numerous member genes
which specialise in producing subtly different forms
of the gene product at different stages of organismal
development (eg. fetal hemoglobin)
Complex additive loci model
-Most traits arise from many genes working together
Locus
Alleles (versions)
equals
any Combination
1
2
3
4
5
Locus
1
2
3
4
5
Alleles (versions)
nearly translucent skin
Virtually no one would have all 10 of the same allele
Locus
Alleles (versions)
nearly black skin
1
2
3
4
5
So, in our hypothetical example:
Locus
1
2
3
Alleles (versions)
So these two very different
gene combinations
both produce
the same skin tone, but share no alleles
4
5
Locus
1
2
3
4
Alleles (versions)
nearly translucent skin
Person 1
1
2
3
4
5
Person 2
medium tone skin
Each shares more alleles with the translucent
person than with each other
5