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The Living Environment Unit 3
Genetic Continuity
HEREDITY– The passing of genetic information to offspring through reproduction.
GENES – Genetic instructions passed onto offspring that determines traits and characteristics.
ALL living things pass their genetic characteristics to their offspring.
GENES contain instructions to make different types of proteins.
Proteins are the building blocks of all cells and organisms.
Allele – different variations of a specific gene. (ex) Instruction for eye color Blue eyes allele vs. Brown eyes allele.
DNA (Deoxyribo Nucleic acid) – Molecules in sequence that carry genetic information. A—T C---G
CHROMOSOMES – Pairs of tightly wound packets of DNA & Histones (proteins) found in nucleus of cells.
(Ex) Humans - 46 chromosomes (23 pairs)
Fly - 6 chromosomes (3 pairs)
Carp Fish – 104 chromosomes (52 pairs)
METHODS OF REPRODUCTION
Asexual Reproduction – ONE parent produces an identical offspring (Clone).
* CLONE - An exact genetic copy of itself. (ex) Bacteria
Sexual Reproduction – TWO parents (Male and Female) produce sex cells (Sperm and Egg) that carry genetic
information of each parent in creating an offspring.
Genetic Recombination – Sperm & Egg combine to form a unique organism.
(ex) In Humans - Sperm – 23 chromosomes Egg – 23 chromosomes = Offspring 46 chromosomes
Between two parents, there is a possibility of 16,777,216 variations of offspring (
2 23 )
THE GENETIC CODE
The Genetic code of all organisms is chemically held in its DNA.
THE STRUCTURE OF DNA
Pg 46 fig 3-2
Double Helix – Twisted ladder shape.
Rails or sides are a Sugar / Phosphate
Rungs or steps are Bases A - T (Adenine – Thymine)
C - G ( Cytosine – Guanine )
Pg 47 fig 3-3 Subunits – Consists of a Sugar, a Phosphate and a base Pair
Base Sequences – are coded messages for a specific gene trait. (ex) A T
Code for an entire Humans can have 3 billion bases !
G C
PAIRING RULES - A always goes with T
C G
G always goes with C
T A
May determine Eye Color
DNA REPLICATION pg. 47 fig 3 -4
Involves the production of identical copies of DNA to pass genetic information to offspring.
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The bases of DNA are held together by weak chemical bonds
Special enzymes break these bonds (unzipping them apart) into 2 strands
Both strands pair up with free-floating bases following A-T & C-G pairing rules.
Two identical DNA sequence copies are formed.
PROTEINS and CELL FUNCTIONING
Proteins – are formed by 20 kinds of amino acids in a specific sequence.
* The sequence of amino acids determines its shape, which then determines the protein’s function.
(ex) Proteins can be hormones, enzymes, antibodies or different types of organs.
PROTEINS DO MOST OF THE WORK IN CELLS
Pg 48 Fig 3-5
PROTEIN SYNTHESIS (Creation)
Ribosomes – Cell organelles that create different proteins using instructions from DNA.
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Special enzyme molecules read DNA instructions in cell nucleus.
Special enzymes create a “messenger molecule”, RNA, to carry instructions to Ribosome.
The RNA carries the instructions through the cytoplasm to the Ribosome.
Transfer molecules gather up amino acids in cytoplasm and deliver them to Ribosome.
Ribosome assembles the protein molecule using delivered A Acids and following RNA instructions.
Pg 50 Fig 3-6 MUTATIONS – ANY change in the DNA sequence which changes the genetic instructions causing
incorrect protein assembly. MOST mutations are harmful.
* Substitution – Changing the base * Deletion – removing a base
* Addition – adding a base * Inversion – Reversing a base sequence
Mutated cells that don’t die can cause disease or deformities.
Only mutations found in sex cells can be passed onto offspring.
DNA & INDIVIDUALITY - Every cell of an organism has a COMPLETE set of genetic instructions to
make an ENTIRE & EXACT organism. (Clone)
* Cells are different because only SOME of the entire genetic instructions become activated.
Genetic Activation can be Hormonal (ex) Puberty or Environmental (ex) Temperature change (Pg 51 fig 3-8
Genetic Expression - When a genetic trait or characteristic is revealed by hormones or environmental conditions
Genetic Engineering – deliberately altering the genetic instructions in an organism.
Biotechnology – Applying technology to biological sciences. (ex) Bread / Cheese – Adding microbes like yeast.
Selective Breeding – choosing to breed certain plants and animals for desired traits (ex) Chicken / Cattle for less fat
Plants – naturally resistant to disease
GENE MANIPULATION – using genetic engineering to produce better plants and animals
(ex) Plants containing genes that make chemicals harmful to insects but are harmless to humans.
Organisms like Bacteria that eat oil spills or that make insulin for diabetics.
How Genes are manipulated – Special enzymes are used to cut and splice specific DNA gene segments to be attached to
a new organism. Pg 53 Fig 3-9
• Transplanted genes direct organism to make specific desired proteins that were made by original donor organism.
APPLICATIONS OF BIOTECHNOLOGY
By decoding the genes that cause disease, we can alter the sequence mutation and cure the disease.
Medicines can be made more effective.
Creating purer forms of missing chemicals is cheaper and safer than extracting chemicals from other organisms