Heredity and the Origin of Life

Genes and Cell Division

• Genes – the cell’s “blueprints”; contain the information needed to build cells and cell products.

• Genes are stored in the chromosome (just like blueprints would be stored in a filing cabinet in a factory).

• Chromosomes (like filing cabinets), which are found in the nucleus (like in the file room).

• Each cell contains a complete set of all the organism’s genes.

Genes and Cell Division

• Cell Division – aka “binary fission”, occurs when one cell (parent cell) divides to produce two new cells (daughter cells).

• Can be compared to building a new factory exactly like the old one.

• In order to build, you have to have a plan and an order of steps.

• A cell goes through THREE stages to prepare and finally divide into two new cells

Genes and Cell Division

• Three stages of cell division• Interphase

• Stage where genes are copied• Genes are on long, thin

chromosomes• Sister chromatids – two identical

strands

Genes and Cell Division• Mitosis

• The equal distribution of the parent cell’s genes

• Prophase

• Membrane around nucelus disappears

• Sister chromatids attached and spindle fibers form

• Metaphase

• All chromosomes line up in middle

• Anaphase

• Each pair separates and move to opposing ends

• Telophase

• Reach each end and begin to uncoil; form two new nuclei

Genes and Cell Division• Cytokinesis

• Final stage of cell division• Divides each daughter cell with some

cytoplasm and organelles• The parent cell pinches in between the two

nuclei until cytoplasm divides

The purpose of mitotic cell division is to insure that each new daughter cell has genes identical to those in the parent cell.

Asexual Reproduction: A result of mitotic cell division

• Asexual reproduction – reproduction by mitotic cell divisions.

• Budding – a method of asexual reproduction illustrated by yeast• The bulge is called a “bud”

• Regeneration – process of regrowing missing parts. Examples: planarians, lizard tail, starfish arms.

• Spores – a cell surrounded by a protective coating Example: Bread mold

Sexual Reproduction

• Occurs when two organisms each give a complete copy of their genes to form a new organism.

• Meiosis – when copies of genetic information during sexual reproduction are produced

• During meiosis, the genetic material is doubled just as in mitosis, but there is an additional step, where the daughter cells divide, making 4 total instead of 2.

Onion Root Tip Mitosis

Onion Root Tip Mitosis

Animal Mitosis

Review: Cell Division

• List the three stages of cell division in proper order

• List the four phases of mitosis in proper order

• Name the process in which the cell’s cytoplasm is divided

• Does regeneration always result in the formation of a new organism?

• Define spore. Give an example of an organism that forms spores

We will complete the class investigation 6E p. SA65.

• In your group of 3 or 4, you will look for all 4 stages of mitosis yourselves.

• Once you find one, you need to get approved before you move on to the next.

• You will draw what you see on p. SA66 at the bottom.

Warm-up

• Go to the next two pages and label the following:

• Left page: “Functions of Genes, what?” and date

• Right page: “How Genes function” and date

How Genes Function

• There is a specific “language” of genes. • In this language, four symbols are called

nucleotides.• Adenine, Thymine, Guanine, Cytosine – A, T,

C, G – in DNA• Adenine, Uracil, Guanine, Cytosine – A, U, C,

G – in RNA• Letters are made out of 3 nucleotides and are

called codons• Words made from the codons are called genes. • These “words” can even be translated into another

language – the language of protein.

How Genes Function

• Symbols A,T,G,C (nucleotides)• Letters (codons)• Words (genes)• Four main points to keep in mind:

• Nucleotides (symbols) are arranged into codons (words)

• Codons are arranged into genes (words)• Genes are instructions for making proteins• During reproduction, a complete copy is made of

all genes and is given to each new organism

DNA is coded messages

• 1953 Watson and Crick – discovered and worked out the model for DNA (deoxyribonucleic acid)

• DNA – looks like a twisted ladder and it is made up of units called nucleotides

• There are four different nucleotides and each contains a sugar, phosphate, and base• Adenine• Thymine• Cytosine• Guanine

DNA is coded messages

• In DNA, nucleotides are arranged so that the sugars and phosphates form the sides of the ladder while the bases make up the rungs of the ladder

• A always pairs up with T• C always pairs up with G• Genes – they are specific sections of DNA• Replication – the process by which one DNA

molecule forms two DNA molecules• This occurs before a cell divides• See p. 87 for process (and handout)

RNA is coded messages

• DNA contains genetic information in a code

• The code is an arrangement of bases in the DNA molecule

• When a cell needs a certain protein, the section of DNA (gene) for that protein makes ribonucleic acid (RNA)

• It differs from DNA in its bases; Thymine is replaced by Uracil

• mRNA – messenger RNA; because the RNA contains a copy of the DNA’s coded message

• Transcription – process of making mRNA molecule

The Decoded messages are Proteins

• After mRNA is made in the nucleus, it carries a working copy of DNA’s coded message to a ribosome in the cytoplasm

• Ribosome reads the code to make a protein

• Protein synthesis – the manufacturing of proteins inside a cell

• tRNA – transfer RNA – involved in protein synthesis

• Within one cell, there are over 20 different kinds of tRNA molecules

• Various tRNA molecules carry amino acids to the ribosome and mRNA

The Decoded messages are Proteins

• During protein synthesis, the nucleotide sequence of the mRNA determines which amino acids to use.

• Codon – group of three bases; codes for a specific amino acid

• A protein contains at least one chain of amino acids

• tRNA molecules bring amino acids to the mRNA and line them up according to the RNA’s sequence

Answer the following question

• Name the four bases that make up DNA molecules

• Name the process in which DNA is duplicated• What organelle helps read the code for making

proteins• Name two types of RNA

Warm up

• Label the next two pages “The origin of modern genetics, what?” and date

• Right page – “The origin of modern genetics”• Complete “What is the difference” box on page

96 AND “What do you think?” box on p. 97

The origin of modern genetics

• Genetics – the study of inheritance (passing from parents to offspring) of traits

• Gregor Mendel – Roman catholic monk, highly educated; experimented with pea plants

• He observed traits (height and pod color) of pea plants.

• Purebred – organism in which the traits remain the same for many generations• Example: TT or tt (both alleles the same)

• Hybrid – when the ancestors are not alike• Example: Tt (both alleles not the same; a “carrier”)

The origin of modern genetics

• Cross – mating specific organisms to see how the traits are inherited

• Mendel’s Theories:• Traits are controlled by factors; each offspring has

two factors for each trait, one from each parent)• The same factors (alleles) purebred; different –

hybrid• Each factor in the set of two is either dominant or

recessive• Dominant – has more influence on a trait• Recessive – the “hidden” or masked factor

The origin of modern genetics• Mendel discovered that when both factors were dominant

(TT) the plant showed the dominant trait. • When both factors were recessive (tt), the plant showed the

recessive trait• When had one dominant and one recessive trait, showed

the dominant trait (Tt)• Purebred – TT or tt• Hybrid – Tt• Phenotype – the physical characteristics of an organism• Genotype – specific factors (or alleles) an organism

possess

The origin of modern genetics• Zygote – when pollen and eggs united; when two

gametes form a union• Later Discoveries:

• Mendel published a paper describing his experiments and stating his theories

• His paper sat unnoticed for 35 years, in which scientists discovered mitosis and meiosis.

• Then scientists began to make connections as they further studied genetics.

Answer the following questions• ____________ is the study of inheritance• What kind of plants did Mendel use in his experiments?• How did Mendel represent factors for dominant traits?

Complete Ideas 7A

Warm up

• Label the next two pages• LEFT: “Genes, Chromosomes, and Heredity,

what?” and date• Right page – “Genes, chromosomes, and

Heredity”• Finish Ideas 7A

Genes, Chromosomes, and Heredity• Not all chromosomes have the same number of genes• Chromosome number is different for different organisms,

but in humans = 46.• Chromosomes occur in pairs; thus, humans have 23 pairs

of chromosomes• Each member of a pair of chromosomes has the same type

of genes (ex. eye color and eye color)• Each type of gene comes from each parent – one from

mother and one from father• Today, Mendel’s “factors” are called “Genes” which are

made of DNA

Punnett Squares• Punnett squares are a visual way to understanding how

Mendel’s theories work. • Use symbols to represent genes (factors)• Symbols represent two genes because genes are normally

paired• However, when they form gametes, they will have one gene

from each pair• To illustrate Mendel’s cross, you can use a Punnett Square

• Practice the Punnett Square under “What do you think?” on page 99

Variations in Mendel’s Theories• If all were either dominant or recessive, it would be easy;

however, not all traits are either dominant or recessive• Incomplete dominance – two traits combine or blend

together to produce a different Trait• Example: RR x WW (crossing red and white flowers)• Because both are dominant – when they cross they will

produce PINK flowers• Codominance – Dominant AND recessive traits are both

expressed. • Example: BB x WW (crossing black and white chickens)

will produce chickens with both black AND white traits.

Variations in Mendel’s Theories• Codominance – Dominant AND recessive traits are

both expressed. • Example: BB x WW (crossing black and white

chickens) will produce chickens with both black AND white traits.

• Multiple gene inheritance – more than two genes are responsible for producing a single trait• Example: scientists believe that hair color may be

controlled by as many as 12 different genes (which explains why all hair is different from another!)

Inheritance of Sex Chromosomes• Normal humans have 23 pairs of chromosomes• The 23rd pair determines the sex of the individual• In females, the pair is XX• In males, the pair is XY• The Y chromosome is smaller than the X chromosome

and has very few genes• It is the father who determines the sex of the child.

Sex-linked traits• Sex-linked trait – an inherited trait that has a gene on

the X chromosome but no corresponding gene on the Y chromosome.

• In this case, an unpaired gene of the X chromosome of the male will automatically express the trait.

• With females, only the dominant trait will express itself• Example: red-green color blindness• Carrier – people who have the gene for that trait but do

not express the trait themselves

Inherited Disorders• These are abnormal traits that are passed on through

genes• Why does God allow a person to be born with an

inherited disorder?• God has a purpose; it is NOT punishment

WARM – UP (ON YOUR OWN)Write the ?’s and answer these on the left hand side of your notes from yesterday

1. How many chromosomes does a normal human cell have?

2. What are Mendel’s factors called today?

3. What do the letters that are placed along the top and side of a Punnett square represent?

4. Explain the difference between incomplete dominance and codominance

5. TURN IN Ideas 7B-C

Warm up

• Label the next two pages “Genetic changes, what?” and date

• Right page – “Genetic changes”

Mutations

• Mutation – any change in an organism’s genetic material

• Can occur in a single base pair, a whole chromosome, or a whole set of chromosomes

• Most are almost always harmful (i.e. lethal mutations – mutations that cause death)

• Types of mutations: gene and chromosomal

Gene Mutations

• Gene mutation – due to the change in the sequence of bases of a segment of DNA that makes up a gene.

• When mRNA comes to translate the mutated section of DNA, it gets the wrong message!

• Some gene mutations affect the entire organism; other do not affect the organism at all.

What is the harmful nature of gene base-pair mutations?

“THE SHY BOY SAW THE MAD DOG EAT THE FAT HAM TOO”

Somatic and Germ Mutations

• Somatic mutations (body cells – do not make gametes) – are not passed on to future generations

• Germ mutations – mutations that occur in the gametes or cells that form gametes – can be passed on to future generations

• It may not affect the organism in which it occurs, but can affect the offspring

Chromosomal Changes

• Chromosomal Change – involving the number of chromosomes or the number or location of genes on a chromosome

• Can be somatic or affect the gametes• Does not involve the formation of proteins, unlike gene

mutations• Chromosomes normally occur in sets• Most people have two sets and are called diploid –

humans have 23 sets (pairs)• Ploidy – an unusual number of chromosomes (number of

sets of chromosomes)• Example: down syndrome (3 of the twenty-first pair

instead of 2)

Applied Genetics

• Mankind has used genetics principles for thousands of years.

• Selective breeding – choosing organisms with desirable traits and breeding them in hopes of offspring having those traits

• Inbreeding – a form of selective breeding; mating of an organism with its close relatives, in hopes of getting purebred organisms

• Breed – a group of organisms

Applied Genetics

• Crossbreeding – another method used to produce animals and plants with desirable traits; breeding individuals from different varieties to produce offspring with traits from both parents

• Biotechnology – uses living organisms to make new, more desirable organism or products

• Genetic engineering – using special techniques to control the genetic makeup of an organism• cloning