Types of Cell Division Mitosis - Body cell replication Meiosis - Sex cell replication.

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



-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.






-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

3 chromosomes = 64 combinations but

only 1 to 4 gametes

Sampling error

Mutation-An 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 mutations-

Point mutation

Insertion/Duplication

Deletion

Translocation

Inversion

Fis

Horizontal transfer

/Fusionsion

G

Point mutation -An error in replication of a nucleotide sequence.

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.

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.

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


Why would the position matter?


G



Because the DNA code is redundant.


G





DNA nucleotide

triplets code for amino

acids.

G




But there are 64 possible triplet combinations (“codons”) yet only 20 amino acids. DNA

nucleotide triplets code

for amino acids.

G




But there are 64 possible triplet combinations (“codons”) yet only 20 amino acids.

Some combinations are synonymous.

DNA nucleotide

triplets code for amino

acids.

G


For exampleBut there are 64 possible triplet combinations (“codons”) yet only 20 amino acids.

Some combinations are synonymous.

CCC codes for the

amino acid proline.

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”

InsertionDeletion

From Futuyma

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.

Duplication

Deletion

Translocation

Equal crossing over

or

Equal crossing over

with

Unequal

crossing

over

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.

APEAPTOPTOATMATMAN

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


-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






-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)

Locus 1 2 3 4 5

Alleles (versions)

equals

any Combination

Complex additive loci model

-Most traits arise from many genes working together

Complex additive loci model

-Most traits arise from many genes working together

Locus 1 2 3 4 5

Alleles (versions)

nearly black skin

Locus 1 2 3 4 5

Alleles (versions)

nearly translucent skin

Virtually no one would have all 10 of the same allele

Locus 1 2 3 4 5

Alleles (versions)

So these two very different

gene combinations both produce

the same skin tone, but share no alleles

So, in our hypothetical example:So, in our hypothetical example:

Person 1 1 2 3 4 5

Person 2

medium tone skin

Locus 1 2 3 4 5

Alleles (versions)

nearly translucent skin

Each shares more alleles with the translucent person than with each other

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Types of Cell Division Mitosis - Body cell replication Meiosis - Sex cell replication.

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