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