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Attendance
Test Information
Review powerpoints
Time to work on owed work.
Division of Sex Cells
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
A process of reduction division in which the
number of chromosomes per cell is cut in half
through the separation of homologous
chromosomes in a diploid cell.
Diploid – 2 sets of chromosomes
Haploid – 1 set of chromosomes
Homologous – chromosomes that each have a
corresponding chromosome from the opposite
sex parent

Meiosis usually involves 2 distinct stages


Meiosis I
Meiosis II
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Each chromosome pairs with its corresponding
homologous chromosome to form a tetrad.
There are 4 chromosomes in a tetrad.
The pairing of homologous chromosomes is the
key to understanding meiosis.
Crossing-over may occur here
Crossing-over is when chromosomes overlap
and exchange portions of their chromatids.

Spindle fibers attach to the chromosomes

The fibers pull the homologous chromosomes
toward opposite ends of the cell.


Nuclear membranes form.
The cell separates into 2 cells.


Meiosis I results in two haploid (N) cells.
Each cell has half the number of chromosomes
as the original cell.

The chromosomes line up similar to metaphase
in mitosis.

Sister chromatids separate and move to
opposite ends of the cell.

Meiosis II results in 4 haploid cells.


In males, meiosis results in 4 sperm cells
In females, meiosis results in 1 egg cell and
three polar bodies, which are not used in
reproduction.
Results in
Cells are
Occurs in
Mitosis
2 Diploid Cells
(2N)
Genetically
Identical
Somatic (Body)
Cells
Meiosis
4 Haploid Cells
(N)
Genetically
Different
Sex Cells
Name That Whatzitdoing!
Getting ready to
divide
Lining up on the
equator
Separating to the
poles
Mitosis!
Now
there
are 2
cells!
Meiosis! Of course! End up with 4
cells, not 2 as in mitosis
Humans
have 46
chromosome
s, so
gametes
have HALF
that number 23
4 functional (all 4 work) sperm
Right!
Only
one!
Mitosis
Cell division for
All cells
what kind of cells? EXCEPT for
Meiosis
ONLY gametes
gametes
Ends up with this
many chromosomes
compared to the
species number of
chromosomes
Identical number
as the species
number (46 for
humans)
1/2 the number as
the species
number
(23 for humans)
Ends up with this
many cells
2
4
Ends up with this
many
FUNCTIONAL
2
4 for sperm
but only

Skin color comes from the pigment melanin


Produced by melanocytes in skin cells
More than 100 genes directly or indirectly influence
amount of melanin in an individual’s skin
 Lead to many variations in skin color


Genes provide the instructions for all human traits,
including physical features and how body parts
function
Each person inherits a particular mix of maternal
and paternal genes

Genes





Humans have ~21,500
Chemical instructions for building proteins
Locus: specific location on a chromosome
Diploid cells contain two copies of each gene
on pairs of homologous chromosomes
Allele: each version of a gene

Homozygous condition: identical alleles

Heterozygous condition: different alleles

Dominant allele

Effect masks recessive allele paired with it

Genetic representations




Genotype


Homozygous dominant (AA)
Homozygous recessive (aa)
Heterozygous (Aa)
Inherited alleles
Phenotype

Observable functional or physical traits



DNA consists of two molecules that are arranged
into a ladder-like structure called a Double Helix.
A molecule of DNA is made up of millions of tiny
subunits called Nucleotides.
Each nucleotide consists of:
1.
2.
3.
Phosphate group
Pentose sugar
Nitrogenous base
Phosphate
Nitrogenous
Base
Pentose
Sugar


The phosphate and sugar form the backbone of
the DNA molecule, whereas the bases form the
“rungs”.
There are four types of nitrogenous bases.
A
Adenine
C
Cytosine
T
Thymine
G
Guanine

Each base will only bond with one other specific
base.




Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Form a base pair.
Form a base pair.

Because of this complementary base pairing, the
order of the bases in one strand determines the
order of the bases in the other strand.
A
T
C
G
T
A
C
G
A
T
G
C
T
A


To crack the genetic code found in DNA we need
to look at the sequence of bases.
The bases are arranged in triplets called codons.
AGG-CTC-AAG-TCC-TAG
TCC-GAG-TTC-AGG-ATC
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


A gene is a section of DNA that codes for a
protein.
Each unique gene has a unique sequence of bases.
This unique sequence of bases will code for the
production of a unique protein.
It is these proteins and combination of proteins
that give us a unique phenotype.
DNA
Gene
Protein
Trait
DNA and RNA
Unified Science
DNA: Deoxyribonucleic Acid
• Made up of nucleotides
• Building block of DNA
• Contains:
– Phosphate
– Sugar
– Nitrogen Base
DNA: Deoxyribonucleic Acid
•Adenine
•Thymine
•Guanine
•Cytosine
Deoxyribose
Base Pairing RULE
• Adenine pairs with Thymine
A
T
• Guanine pairs with Cytosine
G
C
Each base
pair is
connected
by a
hydrogen
bond
Backbone
has covalent
bonds
DNA Founders
• James Watson
• Francis Crick
• Rosalind Franklin
• Maurice Wilkins
1962 Noble Prize
Double Helix
There is
approximately
6.5 feet of DNA
in one single
human cell and
10 – 20 billion
miles of DNA in
the whole body!!!
RNA: Ribonucleic Acid
•Adenine
•URACIL
•Guanine
•Cytosine
RIBOSE
DNA vs. RNA
DNA
RNA
Sugar
Deoxyribose
Ribose
Nitrogen
Base
Structure
Thymine
Uracil
Double
Stranded
Single
Stranded
DNA  RNA  Protein
3 Types of RNA:
• Messenger RNA (mRNA) – carries
genetic information from nucleus
to cytoplasm
• Transfer RNA (tRNA) – carries
amino acids from cytoplasm to
ribosomes
• Ribosomal RNA (rRNA) – consists
of RNA nucleotides in globular
form
Transcription
• Process of genetic
information being copied
from DNA to RNA
Translation
• Process of genetic information
being changed from RNA into
amino acids
• Codon - 3 mRNA nucleotides that
code for amino acids
• Anticodon - 3 tRNA nucleotides
that complement mRNA codon
Translation & Transcription
RNA
Ribonucleic Acid
Structure of RNA





Single stranded
Ribose Sugar
5 carbon sugar
Phosphate group
Adenine, Uracil, Cytosine, Guanine
Types of RNA
 Three main types
 Messenger RNA (mRNA) – transfers
DNA code to ribosomes for translation.
 Transfer RNA (tRNA) – brings amino
acids to ribosomes for protein synthesis.
 Ribosomal RNA (rRNA) – Ribosomes are
made of rRNA and protein.
Transcription
 RNA molecules are produced by copying part
of the nucleotide sequence of DNA into
complementary sequence in RNA, a process
called transcription.
 During transcription, RNA polymerase binds to
DNA and separates the DNA strands. RNA
polymerase then uses one strand of DNA as a
template from which nucleotides are
assembled into a strand of mRNA.
mRNA
How Does it Work?
 RNA Polymerase looks for a region on
the DNA known as a promoter, where it
binds and begins transcription.
 RNA strands are then edited. Some
parts are removed (introns) - which are
not expressed – and other that are left
are called exons or expressed genes.
The Genetic Code
 This is the language of mRNA.
 Based on the 4 bases of mRNA.
 “Words” are 3 RNA sequences called
codons.
 The strand aaacguucgccc would be
separated as aaa-cgu-ucg-ccc the amino
acids would then be Lysine – Arginine –
Serine - Proline
Genetic Codes
Translation
 During translation, the cell uses information
from messenger RNA to produce proteins.
 A – Transcription occurs in nucleus.
 B – mRNA moves to the cytoplasm then to the
ribosomes. tRNA “read” the mRNA and obtain
the amino acid coded for.
 C – Ribosomes attach amino acids together
forming a polypeptide chain.
 D – Polypeptide chain keeps growing until a
stop codon is reached.
Mutations
 Gene mutations result from changes in a
single gene. Chromosomal mutations
involve changes whole chromosomes.
Gene Mutation
 Point Mutation – Affect one nucleotide
thus occurring at a single point on the
gene. Usually one nucleotide is
substituted for another nucleotide.
 Frameshift Mutation – Inserting an extra
nucleotide or deleting a nucleotide
causes the entire code to “shift”.
Gene Mutation
Chromosomal Mutations
 Deletion – Part of a chromosome is deleted
 Duplication – part of a chromosome is
duplicated
 Inversion – chromosome twists and inverts the
code.
 Translocation – Genetic information is traded
between nonhomologous chromosomes.
Chromosomal Mutations
Gene Regulation
 In simple cells (prokaryotic) lac genes
which are controlled by stimuli, turn
genes on and off.
 In complex cells (eukaryotic) this process
is not as simple. Promoter sequences
regulate gene operation.