NotesNotes

DNADNA

Chapter 9Chapter 9

WHAT IS DNA?WHAT IS DNA?

DNADNA= = DDeoxyriboeoxyribonnucleic ucleic AAcidcidDNADNA’’s job is to s job is to hold the entire genetic code for hold the entire genetic code for

the organismthe organism. .

Human, tree, bacteria, mushroom, paramecium, Human, tree, bacteria, mushroom, paramecium, etc! ALL HAVE DNA!etc! ALL HAVE DNA!

DNA is DNA is held on chromosomesheld on chromosomes (genes) in the (genes) in the NUCLEUSNUCLEUS of every cell. of every cell.

DNA DNA ““codescodes”” for all your traits. for all your traits.

Each organism has a different strand of DNA Each organism has a different strand of DNA that makes it different from all other that makes it different from all other organisms!organisms!

QUESTIONQUESTION

How tall would a stack of books be that How tall would a stack of books be that stores all of the genetic information in stores all of the genetic information in the DNA of the DNA of ONE CELLONE CELL? ?

GUESS:GUESS:

ANSWERANSWER

As tall as a 19 story As tall as a 19 story building!building!

We have We have over 3 billionover 3 billion nitrogen bases put nitrogen bases put

together in a specific waytogether in a specific way

IS DNA AN ORGANIC IS DNA AN ORGANIC MOLECULE?MOLECULE?

Yes!Yes!

Remember Nucleic Acids?Remember Nucleic Acids?

(Carbohydrates, Proteins, Lipids, (Carbohydrates, Proteins, Lipids, Nucleic Acids)Nucleic Acids)

Deoxyribonucleic Acid is a Nucleic Acid!Deoxyribonucleic Acid is a Nucleic Acid!

The structure of DNAThe structure of DNADNA is in the form of a DNA is in the form of a ““twisted laddertwisted ladder””. .

This means that it looks like two This means that it looks like two ribbons twisted together.ribbons twisted together.

The scientific The scientific

name for this is: name for this is:

DOUBLE HELIXDOUBLE HELIX

WATSON & CRICKWATSON & CRICK

In 1953, two men were credited with the In 1953, two men were credited with the discovery of the double helix. (They did discovery of the double helix. (They did notnot discover DNA, but they figured out what discover DNA, but they figured out what DNA DNA looked likelooked like.).)

Their names were James Watson & Francis Their names were James Watson & Francis Crick.Crick.

DNA Notes Part 2DNA Notes Part 2

DNA StructureDNA Structure

NUCLEOTIDESNUCLEOTIDESDNA is made of repeating DNA subunits DNA is made of repeating DNA subunits

called nucleotides that make up the called nucleotides that make up the entire DNA molecule.entire DNA molecule.

They contain the nitrogen bases, a They contain the nitrogen bases, a sugar and a phosphate group.sugar and a phosphate group.

Nucleotides join together to make the Nucleotides join together to make the long strand of DNA.long strand of DNA.

The bases are the The bases are the ““rungsrungs”” of the of the ladderladder

There are four DNA bases:There are four DNA bases:

1.1. Adenine (A)Adenine (A)

2.2. Thymine (T)Thymine (T)

3.3. Guanine (G)Guanine (G)

4.4. Cytosine (C)Cytosine (C)

The sides of the ladderThe sides of the ladderThe sides of the ladder are made up of The sides of the ladder are made up of

alternating sugars (alternating sugars (deoxyribosedeoxyribose) and ) and phosphate groups.phosphate groups.

DNA BASE PAIRINGSDNA BASE PAIRINGSThe DNA bases will The DNA bases will alwaysalways be paired in a be paired in a

specific way.specific way.

A will A will alwaysalways be paired with T be paired with T

T will T will alwaysalways be paired with A be paired with A

C will C will alwaysalways be paired with G be paired with G

G will G will alwaysalways be paired with C be paired with C

SO……………………SO……………………Because your DNA is two strands Because your DNA is two strands

intertwined….intertwined….

It will look something like this: It will look something like this: AATGGCACCGAATCGGTCATCAATGGCACCGAATCGGTCATC

TTACCGTGGCTTAGCCAGTAGTTACCGTGGCTTAGCCAGTAG

These two strandsThese two strands

are calledare called

““COMPLIMENTARYCOMPLIMENTARY

SEQUENCESSEQUENCES””

DIFFERENT DNA = DIFFERENT DNA = DIFFERENT ORGANISMDIFFERENT ORGANISM

Will an elm tree, a deer and a bacteria Will an elm tree, a deer and a bacteria have the same DNA sequence?have the same DNA sequence?

Of course not!Of course not!

How about you & the person you are How about you & the person you are sitting next to?sitting next to?

NO!NO!

Each organism, even of the same Each organism, even of the same species has a different DNA sequence!species has a different DNA sequence!

SIMILAR ORGANISM = SIMILAR SIMILAR ORGANISM = SIMILAR DNADNA

Which pair has DNA sequences closest to Which pair has DNA sequences closest to the other?the other?

1. Elm Tree & Deer1. Elm Tree & Deer

2. Elm Tree & You2. Elm Tree & You

3. Deer & You3. Deer & You

4. You & The Person Next To You4. You & The Person Next To You

ANSWERSANSWERS1. A deer would have a closer DNA 1. A deer would have a closer DNA

sequence to you than an elm tree sequence to you than an elm tree (because a deer is an animal, just like (because a deer is an animal, just like you!)you!)

2. But, the person next to you will have 2. But, the person next to you will have an even closer DNA sequence to you an even closer DNA sequence to you than either the elm tree or the deer than either the elm tree or the deer (because you are of the same (because you are of the same species!)species!)

3. But—NO ONE (unless you have an 3. But—NO ONE (unless you have an identical twin) has the SAME DNA!!!!!!identical twin) has the SAME DNA!!!!!!

WHAT MAKES DNA SEQUENCES WHAT MAKES DNA SEQUENCES DIFFERENT?DIFFERENT?

The species that you belong to will The species that you belong to will determine about 99% of your gene determine about 99% of your gene combinations. (THESE ARE SHARED combinations. (THESE ARE SHARED CHARACTERISTICS)CHARACTERISTICS)

It is passed along from generation to It is passed along from generation to generation in the species.generation in the species.

YOUR SPECIFIC PARENTS WILL YOUR SPECIFIC PARENTS WILL DETERMINE THE OTHER <1% OF DETERMINE THE OTHER <1% OF YOUR DNA SEQUENCE.YOUR DNA SEQUENCE.

THE ORDER OF DNA THE ORDER OF DNA BASES MAKES YOU- BASES MAKES YOU- YOUYOU!!

Even though there are only 4 nitrogen Even though there are only 4 nitrogen bases IN ALL THE ORGANISMS OF bases IN ALL THE ORGANISMS OF THE WORLD….itTHE WORLD….it’’s the SEQUENCE of s the SEQUENCE of those bases that makes the those bases that makes the differences!differences!

The sequence ATATGACCG codes for The sequence ATATGACCG codes for different traits than CGGATCTAA.different traits than CGGATCTAA.

DNA Notes 3DNA Notes 3

DNA Replication and Protein Synthesis introDNA Replication and Protein Synthesis intro

WHY DO WE NEED DNA?WHY DO WE NEED DNA?

Besides Besides coding for all your traitscoding for all your traits, DNA , DNA helps in the process of making amino helps in the process of making amino acidsacids (which link together to form (which link together to form proteins).proteins).

Remember…proteins are important to Remember…proteins are important to you because they make up the you because they make up the structure of your body (organs, structure of your body (organs, muscles, eye balls, skin, hair, etc)muscles, eye balls, skin, hair, etc)

THREE STEPS IN PROTEIN THREE STEPS IN PROTEIN SYNTHESISSYNTHESIS

Synthesis = Making somethingSynthesis = Making something

Gene expressionGene expression is the process by which is the process by which inheritable information from a inheritable information from a gene, such , such as the as the DNA sequence, is made into a , is made into a functional functional gene product, such as , such as protein or or RNA..

Protein synthesis = making proteinsProtein synthesis = making proteins

1.1. DNA replicationDNA replication

2.2. RNA transcriptionRNA transcription

3.3. Amino acid (protein) translationAmino acid (protein) translation

1. DNA REPLICATION1. DNA REPLICATION

Replication = copyingReplication = copying

DNA ReplicationDNA Replication means that the existing means that the existing strand of strand of DNADNA COPIESCOPIES itself to make itself to make an exact replica.an exact replica.

This new strand then goes to new cells This new strand then goes to new cells (during cell division)(during cell division)

HOW DOES REPLICATION HOW DOES REPLICATION HAPPEN?HAPPEN?

1.1. DNA is made of 2 strands (double helix).DNA is made of 2 strands (double helix).

2.2. The bases are paired up A-T, T-A, C-G, G-C.The bases are paired up A-T, T-A, C-G, G-C.

3.3. An An enzymeenzyme called a DNA helic called a DNA helicasease starts to starts to break apart the break apart the hydrogen bondshydrogen bonds that hold the that hold the bases together.bases together.

4.4. As the DNA As the DNA ‘‘unzipsunzips’’, new , new ““free-floatingfree-floating”” nucleotides nucleotides attach themselves to each side of the DNA.attach themselves to each side of the DNA.

5.5. Two exact copies of the DNA strand now exist.Two exact copies of the DNA strand now exist.

REPLICATION EXAMPLEREPLICATION EXAMPLEORIGINAL STRAND OF DNAORIGINAL STRAND OF DNA::ACTACAGCATCGAGTACGCATGACTACAGCATCGAGTACGCATGTGATGTCGTAGCTCATGCGTACTGATGTCGTAGCTCATGCGTAC

The original strand The original strand ““unzipsunzips””::ACTACAGCATCGAGTACGCATGACTACAGCATCGAGTACGCATG

TGATGTCGTAGCTCATGCGTACTGATGTCGTAGCTCATGCGTAC

New bases attach themselves to the New bases attach themselves to the unzipped strand:unzipped strand:

NEW BASES ATTACH NEW BASES ATTACH

ACTACAGCATCGAGTACGCATGACTACAGCATCGAGTACGCATG

TGATGTCGTAGCTCATGCGTACTGATGTCGTAGCTCATGCGTAC

TGATGTCGTAGCTCATGCGTACTGATGTCGTAGCTCATGCGTAC

ACTACAGCATCGAGTACGCATGACTACAGCATCGAGTACGCATG

NOW YOU HAVE 2 COPIES OF THE NOW YOU HAVE 2 COPIES OF THE ORIGINAL STRAND!ORIGINAL STRAND!

Final Check!Final Check!

There is an enzyme called a DNA There is an enzyme called a DNA polymerase that checks to make sure that polymerase that checks to make sure that there are no errors in the newly made DNA.there are no errors in the newly made DNA.

WHY REPLICATION?WHY REPLICATION?

Why do you need Why do you need EXACT COPIESEXACT COPIES of of DNA whenever you create a new cell?DNA whenever you create a new cell?

Because if your DNA did not copy Because if your DNA did not copy EXACTLYEXACTLY, you would CHANGE! What , you would CHANGE! What kind of changes might happen?kind of changes might happen?

With exact DNA, you remain the same With exact DNA, you remain the same organism.organism.

DNA Notes 4DNA Notes 4

Transcription and TranslationTranscription and Translation

Review from Last Class on Protein Review from Last Class on Protein SynthesisSynthesis

THREE STEPS IN PROTEIN SYNTHESISTHREE STEPS IN PROTEIN SYNTHESISSynthesis = Making somethingSynthesis = Making something

Protein synthesis = making proteinsProtein synthesis = making proteins

1.1. DNA replicationDNA replication

2.2. RNA transcriptionRNA transcription

3.3. Amino acid (protein) translationAmino acid (protein) translation

2. RNA TRANSCRIPTION2. RNA TRANSCRIPTIONTo continue our process of making proteins for To continue our process of making proteins for

your body, we need to your body, we need to

make make RNARNA in a process called in a process called TRANSCRIPTIONTRANSCRIPTION..

RNA=RNA=RRiboibonnucleic ucleic AAcid (NUCLEIC ACID)cid (NUCLEIC ACID)

RNA contains the sugar ribose. Not RNA contains the sugar ribose. Not deoxyribosedeoxyribose

RNA is a SINGLE STRAND (ribbon) that has 4 RNA is a SINGLE STRAND (ribbon) that has 4 bases. bases.

THE RNA BASESTHE RNA BASESIn RNA, the nitrogen bases are attached In RNA, the nitrogen bases are attached

to a phosphate group & a sugar to a phosphate group & a sugar (ribose).(ribose).

Now, the bases are: A, C, G, U (uracil).Now, the bases are: A, C, G, U (uracil).

How would the bases match up now?How would the bases match up now?

A – U, C – G, U – A, G - CA – U, C – G, U – A, G - C

TRANSCRIPTIONTRANSCRIPTION

The DNA strand again The DNA strand again ““unzipsunzips”” and free and free floating RNA bases match up with the floating RNA bases match up with the unwound DNA strand.unwound DNA strand.

DNA strand: DNA strand: TGATGTCGTAGCTCATGCGTACTGATGTCGTAGCTCATGCGTAC

NEW RNA strand:NEW RNA strand:

ACUACAGCAUCGAGUACGCAUGACUACAGCAUCGAGUACGCAUG

TYPES OF RNATYPES OF RNA

There are 2 types of RNA that each have a There are 2 types of RNA that each have a different job in the process of making different job in the process of making proteins.proteins.

1.1. mRNA= RNA on the strandmRNA= RNA on the strand

2.2. tRNA= Transports amino acids to tRNA= Transports amino acids to ribosomes to be assembled into proteinsribosomes to be assembled into proteins

3. PROTEIN (AMINO ACID) 3. PROTEIN (AMINO ACID) TRANSLATIONTRANSLATION

After we have RNA, we can now make After we have RNA, we can now make amino acids (which link together to amino acids (which link together to form proteins.)form proteins.)

How does this happen?How does this happen?

1.1. The RNA strand gets split into The RNA strand gets split into CODONS (3 RNA bases). CODONS (3 RNA bases).

Example: ACUExample: ACU

TranslationTranslation2.2. Once the RNA is split into codons, Once the RNA is split into codons,

your body matches them up to a your body matches them up to a code to form the amino acid.code to form the amino acid.

There is a chart There is a chart

that has all 20 of that has all 20 of

the amino acid the amino acid

codes on it, alongcodes on it, along

with a start & stop: with a start & stop:

To use the chart:To use the chart:EXAMPLE mRNA CODON: ACUEXAMPLE mRNA CODON: ACU

Look on the left side of the chart to find Look on the left side of the chart to find the first base (A).the first base (A).

Look on the top of the chart to find the Look on the top of the chart to find the second base (C).second base (C).

Look on the right side of the chart to find Look on the right side of the chart to find the third base (U).the third base (U).

THE AMINO ACID IS: ThreonineTHE AMINO ACID IS: Threonine

Abbreviating the Abbreviating the amino acidsamino acids

Instead of writing out the entire name of Instead of writing out the entire name of each amino acid, you can abbreviate.each amino acid, you can abbreviate.

The rule is: The rule is: use the first 3 lettersuse the first 3 letters of the of the amino acid as the abbreviation.amino acid as the abbreviation.

ExceptExcept when the amino acid ends in the when the amino acid ends in the word word ““acidacid””, in which case you use the , in which case you use the first 2 letters and a capital A.first 2 letters and a capital A.

The role of tRNA:The role of tRNA:

Transfer RNA (tRNA) moves the mRNA Transfer RNA (tRNA) moves the mRNA codons codons to the ribosomes from the to the ribosomes from the cytoplasmcytoplasm so they can be translated so they can be translated into proteins.into proteins.

Each tRNA molecule only fits onto ONE Each tRNA molecule only fits onto ONE mRNA codon. Its ANTICODON fits mRNA codon. Its ANTICODON fits onto the mRNA codon like a puzzle onto the mRNA codon like a puzzle piece and carries it away.piece and carries it away.

THE END OF THE END OF TRANSLATIONTRANSLATION

Once the protein chain has been made, Once the protein chain has been made, the body codes the body codes ““stopstop””..

The protein strand is cut and it goes off The protein strand is cut and it goes off to do a job (like be a hair or skin to do a job (like be a hair or skin protein.)protein.)

So…the ORDER of amino acids So…the ORDER of amino acids determines the protein & how we are determines the protein & how we are put together!put together!

WHAT HAPPENS IF THE WHAT HAPPENS IF THE AMINO ACID ORDER AMINO ACID ORDER

CHANGES?CHANGES?

THE PROTEIN CHANGES!THE PROTEIN CHANGES!

And…if the protein changes…And…if the protein changes…YOU CHANGE!YOU CHANGE!

DNA Notes 5DNA Notes 5

MutationsMutations

GENETIC MUTATIONSGENETIC MUTATIONSA mutation is any permanent change in A mutation is any permanent change in

the DNA sequence.the DNA sequence.

Mutations are caused by MUTAGENS Mutations are caused by MUTAGENS like UV radiation, X-rays, toxins, etc.like UV radiation, X-rays, toxins, etc.

Some mutations are Some mutations are ““silentsilent”” (do not have (do not have any effect).any effect).

Some mutations have major effects like Some mutations have major effects like DownDown’’s Syndrome or cancer.s Syndrome or cancer.

TYPES OF MUTATIONSTYPES OF MUTATIONS

1.1. Point mutationsPoint mutations

2.2. Frameshift mutationsFrameshift mutations

3.3. Chromosomal mutationsChromosomal mutations

POINT MUTATIONSPOINT MUTATIONS

Point mutations are when Point mutations are when ONEONE DNA DNA BASE is BASE is CHANGEDCHANGED..

THE DOG BIT THE CATTHE DOG BIT THE CATTHE DOG BIT THE CARTHE DOG BIT THE CAR

What happened in the DNA strand?What happened in the DNA strand?

What probably happened in the body?What probably happened in the body?

FRAMESHIFT MUTATIONSFRAMESHIFT MUTATIONS

Frameshift mutations are when Frameshift mutations are when ONEONE DNA BASE is DNA BASE is ADDED or DELETEDADDED or DELETED..

THE DOG BIT THE CATTHE DOG BIT THE CATTHE DOG BIT HEC ATTHE DOG BIT HEC AT

What happened in the DNA strand?What happened in the DNA strand?

What probably happened in the body? What probably happened in the body?

CHROMOSOMAL CHROMOSOMAL MUTATIONSMUTATIONS

A chromosomal mutation is when A chromosomal mutation is when MANYMANY DNA BASES are DNA BASES are CHANGED, ADDED CHANGED, ADDED or DELETEDor DELETED..

THE DOG BIT THE CATTHE DOG BIT THE CATTHE DGB ITE HAT CTHE DGB ITE HAT C

What happened in the DNA strand?What happened in the DNA strand?What most likely happened in the body?What most likely happened in the body?

CAN MUTATIONS BE CAN MUTATIONS BE PASSED ON TO PASSED ON TO

OFFSPRING (progeny)?OFFSPRING (progeny)?Some can!Some can!

If the mutation occurs in a BODY cell, If the mutation occurs in a BODY cell, they are called NON-INHERITED they are called NON-INHERITED mutations.mutations.

If the mutation occurs in a SEX cell If the mutation occurs in a SEX cell (gamete) they are called INHERITED (gamete) they are called INHERITED mutations & can be passed on.mutations & can be passed on.

Are all mutations bad?Are all mutations bad?NO!NO!

Some mutations, like the ones that can be Some mutations, like the ones that can be passed on to offspring, can create passed on to offspring, can create GENETIC VARIATION, or changes for the GENETIC VARIATION, or changes for the species.species.

Sex Cell DivisionSex Cell Division

MEIOSISMEIOSIS

AFTER DNA REPLICATION, AFTER DNA REPLICATION, WHERE DOES THE NEW DNA WHERE DOES THE NEW DNA

STRAND GO?STRAND GO?The new DNA strand goes into a new The new DNA strand goes into a new

cell.cell.

If it is a body cell, it goes to a new cell If it is a body cell, it goes to a new cell by MITOSIS.by MITOSIS.

If it is a sex cell (sperm or egg) it goes If it is a sex cell (sperm or egg) it goes there by MEIOSIS.there by MEIOSIS.

HOW DO WE PASS DNA HOW DO WE PASS DNA ON TO OUR PROGENY ON TO OUR PROGENY

(OFFSPRING)?(OFFSPRING)?We, as humans, along with many other We, as humans, along with many other

types of organisms, pass on our DNA types of organisms, pass on our DNA through sexual reproduction.through sexual reproduction.

This simply means that 2 gametes (1 This simply means that 2 gametes (1 sperm & 1 egg) fuse to form a zygote, sperm & 1 egg) fuse to form a zygote, exchange DNA, and create new gene exchange DNA, and create new gene combinations.combinations.

MeiosisMeiosis

This process is done by the process This process is done by the process called MEIOSIS.called MEIOSIS.

Remember…the reproduction of body Remember…the reproduction of body cells (known as somatic cells) is called cells (known as somatic cells) is called MITOSIS.MITOSIS.

MEIOSIS is the reproduction of sex cells.MEIOSIS is the reproduction of sex cells.

THE STEPS OF MEIOSISTHE STEPS OF MEIOSIS

Meiosis is divided into 2 parts: Meiosis is divided into 2 parts:

MEIOSIS IMEIOSIS I MEIOSIS IIMEIOSIS II1. Interphase1. Interphase 6. Prophase 26. Prophase 22. Prophase 12. Prophase 1 7. Metaphase 27. Metaphase 23. Metaphase 13. Metaphase 1 8. Anaphase 28. Anaphase 24. Anaphase 14. Anaphase 1 9. Telophase 29. Telophase 25. Telophase 15. Telophase 1 10. Cytokinesis10. Cytokinesis

During each of these phases, During each of these phases, certain things happen:certain things happen:

The steps in Meiosis I are VERY similar The steps in Meiosis I are VERY similar to mitosisto mitosis

And remember…the point of meiosis is And remember…the point of meiosis is to create 4 cells from the original 1 to create 4 cells from the original 1 cell.cell.

MEIOSIS 1 –MEIOSIS 1 –1.1. Interphase: The cell grows & Interphase: The cell grows &

chromosomes double (46 to 92)chromosomes double (46 to 92)2.2. Prophase 1: The nucleus goes away Prophase 1: The nucleus goes away

& chromosomes (92) become visible& chromosomes (92) become visible3.3. Metaphase 1: The chromosomes Metaphase 1: The chromosomes

(92) line up in the middle of the cell(92) line up in the middle of the cell4.4. Anaphase 1: The chromosomes Anaphase 1: The chromosomes

begin to travel to the ends of the cell begin to travel to the ends of the cell (46 on one end & 46 on the other)(46 on one end & 46 on the other)

5.5. Telophase 1: The nuclei comes back Telophase 1: The nuclei comes back & the cell starts to split into 2 cells& the cell starts to split into 2 cells

This is where it gets a little This is where it gets a little different….different….

Instead of splitting into 2 cells & thatInstead of splitting into 2 cells & that’’s the end s the end of the process….the 2 new cells undergo of the process….the 2 new cells undergo another division.another division.

At the end we want 4 cells, right?At the end we want 4 cells, right?

MEIOSIS 2-occurs in both MEIOSIS 2-occurs in both new cellsnew cells

6.6. Prophase 2: Prophase 2: chromosomes (46 in each chromosomes (46 in each

cell) are visible & nuclei disappearcell) are visible & nuclei disappear

7.7. Metaphase 2Metaphase 2: chromosomes (46 in : chromosomes (46 in each) line up in the middle of each celleach) line up in the middle of each cell

8.8. Anaphase 2: Anaphase 2: chromosomes (23 now in chromosomes (23 now in each end) start to move to the ends of each end) start to move to the ends of each celleach cell

9.9. Telophase 2: the 2 cells start to split Telophase 2: the 2 cells start to split into 4 cells (each with 23 into 4 cells (each with 23 chromosomes) chromosomes)

10.10. Cytokinesis: 4 new cells are formedCytokinesis: 4 new cells are formed

Putting it all togetherPutting it all together

At the end of mitosis our chromosomes are At the end of mitosis our chromosomes are arranged in homologous pairs. arranged in homologous pairs.

Each cell contains 23 pairs of chromosomes Each cell contains 23 pairs of chromosomes (46 total)(46 total)

Since they are in pairs, we also refer to the Since they are in pairs, we also refer to the total number of doubled chromosomes as total number of doubled chromosomes as the diploid number. (46 in humans)the diploid number. (46 in humans)

Homologous chromosomes Homologous chromosomes in meiosisin meiosis

When our cells are undergoing meiosis, When our cells are undergoing meiosis, each homologous pair divides & they each homologous pair divides & they become single chromosomes- or become single chromosomes- or HAPLOID (n).HAPLOID (n).

In which phases of mitosis & meiosis are In which phases of mitosis & meiosis are there haploid chromosomes present?there haploid chromosomes present?(HINT: are there ANY in mitosis)?(HINT: are there ANY in mitosis)?

CROSSING OVERCROSSING OVERCrossing over is another way to create Crossing over is another way to create

genetic variation.genetic variation.

During prophase, the chromosomes are During prophase, the chromosomes are so tightly wound together, that some of so tightly wound together, that some of the genes, called the genes, called ““jumping genesjumping genes”” leave their chromosome & go (cross leave their chromosome & go (cross over) to another.over) to another.

This results in recombination of genes & This results in recombination of genes & genetic material, which creates all new genetic material, which creates all new possibilities in offspring!possibilities in offspring!

WHY MEIOSIS?WHY MEIOSIS?

To make sperm and egg (gametes or sex To make sperm and egg (gametes or sex cells) and eventually produce offspring!cells) and eventually produce offspring!

Meiosis creates HAPLOID CELLS (23 Meiosis creates HAPLOID CELLS (23 chromosomes in each) (sperm & egg) that chromosomes in each) (sperm & egg) that can join together to create a DIPLOID can join together to create a DIPLOID CELL (46 chromosomes in each).CELL (46 chromosomes in each).

Meiosis creates new possibilities for Meiosis creates new possibilities for offspringoffspring’’s DNA…they are NOT exactly s DNA…they are NOT exactly like their parents!like their parents!

When do these processes take When do these processes take place?place?

MitosisMitosis: :

Takes place any time we need to Takes place any time we need to replace a cellreplace a cell

MeiosisMeiosis::

Males: Males are creating sperm all Males: Males are creating sperm all the time!the time!

Females: All eggs are created before Females: All eggs are created before the female is born!the female is born!

MITOSIS vs. MEISOISMITOSIS vs. MEISOISYour assignment is to compare mitosis with Your assignment is to compare mitosis with

meiosis.meiosis.

These 2 processes are very similar, but they These 2 processes are very similar, but they have some major differences too.have some major differences too.

ExampleExample::A horse and a donkey can mate to A horse and a donkey can mate to

produce a mule, but the mule is produce a mule, but the mule is almost always sterile.almost always sterile.

Horses have a diploid # of 60.Horses have a diploid # of 60.

Donkeys have a diploid # of 66.Donkeys have a diploid # of 66.

1.1. How many chromosomes would the How many chromosomes would the mule receive from each parent?mule receive from each parent?

2.2. What is the diploid number of the What is the diploid number of the mule?mule?

3.3. Why do you think mules are sterile?Why do you think mules are sterile?