Genetics Part 1. By the end of this class you should understand: The purpose of mitosis and the consequences of failure to control mitosis The purpose.

Genetics Part 1

By the end of this class you should understand:

• The purpose of mitosis and the consequences of failure to control mitosis

• The purpose and mechanism of increasing genetic diversity

• The relationship between mutations and alleles

• The importance of genes to a living organism

Understanding Mitosis/Meiosis

• WHY do mitosis and meiosis matter?– What cells in

our bodies are performing mitosis?

– What cells in our bodies are performing meiosis?

Where Does Mitosis Occur? Stem cells in our bodies that grow new tissue

Bone marrow (blood) Skin (epidermis, hair & nails) Tissues (injury repair)

Development of a fetus Remember we all started as just one cell!

Amitotic cells

Many cells in our body are amitotic, which means they cannot produce more cells like themselves

Of course, some people seem to not have this problem.....

Mitosis = Tissue Growth

• Mitosis is how our cells make new cells– This is also why you get

bigger over time

• If this process gets out of control, we’re in trouble– Fortunately it rarely gets

out of control!

Failure of Mitosis Control Cancer is the result of

a single cell that is undesirably and constantly reproducing

Any cell in the body can become cancerous But some are more

likely candidates than others!

Cell Replication There are molecular

mechanisms (checkpoints) that prevent a cell from constantly undergoing mitosis Occur at G1/S and G2/M Cells also cannot

replicate without an external signal

Cancer Checklist To become cancerous, a

cell must: Have its control genes fail

via mutation (fresh or inherited)

Have its go-ahead signal stuck in the “on” position

Develop expression of telomerase if it was not already a stem cell

This is a long list! Typically, to

facilitate the checklist being met, cancer cells also have a failure of mutation repair This begins to

prompt many, many mutations

Tumors A cell that has begun to

undergo mitosis until it has exhausted all its blood supply forms a tumor A lump, sometimes hard,

sometimes just an outgrowth of flesh

If no further mutation takes place, it is typically benign (not harmful)

Dangerous Cancer For cancer to

become malignant, two additional steps must be met: Angiogenesis

(ability to create new blood vessels to feed the tumor)

Metastasis (ability to spread through tissues and blood)

Cancer Treatments Two standard treatments

today are radiation therapy and chemotherapy

Both work by poisoning cells during mitosis– Since cancer cells are

constantly undergoing mitosis they are affected the most

– This is why you also lose your hair

Lethal Cancer• If the cancer is not caught early

enough or develops too rapidly, risk of death is high

• Once cancer cells spread through the body, they hog all the resources and block blood flow to vital organs

• Deaths from severe cancer often involve liver and kidney failure, brain failure, and internal bleeding

Where Does Meiosis Occur?

The 'nads The technical term, gonads, refers to the testes of

men and ovaries of women The formation of gametes is triggered by

puberty In men it continues the entire life In women, the oogonia (precursor eggs) have

already formed as a fetus, but one cell completes meiosis per month

The Purpose of Meiosis

Meiosis is the cellular mechanism for sex Not all organisms engage in sex Bacteria and some plants and animals reproduce

asexually (purely through mitosis) Sex increases the available variation in

individuals If an organism has a mutation that gives them an

advantage, they will spread that genetic advantage around faster

Increased Variation During Metaphase I, the chromosomes engage in

crossing over before being separated This mixes the chromosomes inherited from each

parent together

Random Assortment = Increased Variation

Net Result

• Mitosis creates two identical cells– Cells may take on different

functions if they express different genes

• Meiosis creates haploid cells that can combine to form a brand new diploid cell– This individual has 50% of the

DNA from each parent

Quick check: why does it matter what’s in DNA?

DNA Information

• Genes code for proteins!– Enzymes– Structural fibers– Transport proteins

• If the DNA sequence is different, amino acid sequence is different– Protein has different shape!– Different versions of the same genes are called

alleles

Example:

• Hair color!– The proteins that make up your hair may be

different colors if the structures are different

Allele Origin

• Alleles originate from mutations– Accidental alterations to DNA– Caused by mutagens

• Most new alleles are problematic and the cell or organism dies– Imagine changing one word in an essay: unless it’s

just the right word, it probably makes no sense now…

• Occasionally beneficial!

Mutagens There are many different

mutagens Radiation– Energy from radioactive

materials– High-energy light from the

sun or tanning booths DNA-binding chemicals– Many are used in labs

Mutation Types Categorized by what has

happened to the DNA sequence– Point mutation/Substitution– Insertion– Deletion– Inversion

Results of Mutation

• Mutations alter the functionality of proteins• Usually harmful• Occasionally beneficial!

• Some proteins become defective (sickle cell anemia is a mutation of hemoglobin)

• Some proteins fail to be produced (albinism is a failure to produce melanin)

Enzymes and Mutation• Recall that enzymes are

proteins• Ergo they are each made from a

gene in your DNA• If the enzyme gene should

mutate the enzyme will be shaped slightly differently because its amino acid chain is different• Genetics result in different

metabolisms because of different enzyme functions!

Gene Expression Each cell has the entire

genome so why only express certain proteins? Some genes control other

genes (Homeotic genes) Many genes are permanently

inactivated in adult cells Much like bookmarks,

transcription factors must attach to genes to activate them

Homeotic Genes

• Genes that determine which cells will develop where are called homeotic genes• All animals have the same set

of homeotic genes• Mutations in homeotic genes

result in different body plans

• These genes control other genes by signaling cells to activate or block genes

Homeotic Genes in Animals• The development of

homeotic genes was a revolution in genetics

• In chapter 15 we will cover animal evolution, these genes will be discussed again!• Just like ribosomes are

part of the core operating system of life, homeotic genes are part of the core operating system of animals

That’s all for today!

• Next week: more genetics!