Prefixes/Suffixes
Mono- = one
Di- = two
–hybrid = mixed origin
Pheno- = show
Homo- = the same
Hetero- = the different
Our DNA gives us our traits
Example: The ability to roll the tongue
The cell nucleus contains chromosomes which are made of DNA which is made of base pairs.
Heredity – the passing of traits from one generation to another.
Genetics – The study of heredity.
Gregor Mendel – Austrian monk who was the first to predict how traits are passed from one generation to the next. Mendel cross pollinated garden pea plants in controlled experiments for seven different traits.
Alleles – Mendel concluded that each organism has two copies for each of its traits – one from each parent. (ex: 2 alleles for tallness, 2 for shortness, or one of each) Some alleles are expressed while others may be hidden.
1. Dominant – the observed trait – can “see” this trait if there is one copy or two.
2. Recessive – the hidden trait – can only be “seen” if there are two copies.
Phenotype – The way an organism looks and behaves.
Ex: a pea plant may have 1 tall allele and 1 short allele but look tall = phenotype is tall. a pea plant with two tall alleles also looks tall = phenotype is tall.
Genotype – The actual gene combination of an organism.
1. Homozygous – two of the same allele for a trait.
Ex: TT = 2 alleles for tall
2. Heterozygous – two different alleles for a trait.
Ex: Tt = 1 tall, 1 short allele
Punnet Squares – a shorthand way of finding the ratio of genotypes in the offspring.
Monohybrid Crosses – “Mono” means one and “hybrid” mixed origin or genetically different. Monohybrid crosses are when the two parent plants are different for only one trait.
Dihybrid Crosses – When the parents are different for two traits.
Chapters 12-14 Outline
Most of the genetics problems that we have done so far are called Simple Mendelian Inheritance, such as the tall and short pea plants. (TT x tt)
Sickle-cell anemia and cystic fibrosis are determined by simple Mendelian inheritance.
Incomplete dominance is where there is an in between phenotype.
Snap dragon flowers do this!
RR = red
rr = white
Rr = pink
Codominance is where each phenotyp[e is partially represented.
Some breeds of chickens do this!
BB = black
bb = white
Bb = checkered
Multiple alleles is where some traits are controlled by more than two alleles.
Blood types in humans work this way as does hair color in rabbits
Sex Determination in Humans
The 23rd pair of chromosomes in people are called the sex chromosomes. They are also called the X and Y chromosomes.
Males have both an X and Y chromosome and females have two X chromosomes.
Sperm cells contain either an X or a Y chromosome.
Egg cells always contain an X.
Sex-Linked Traits
These traits are controlled by genes found on the sex chromosomes.
Color blindness and blood clotting disorders are sex-linked traits.
Polygenic Inheritance
These traits are controlled by many different genes. Skin color and height in humans are controlled in this way.
Selective breeding
This is a type of breeding that produces offspring with desired traits. We do this with corn, cows, cats, dogs and even snakes!
Pitbulls!! Popcorn!! And Corn Snakes!!
Lysenko and Soviet Agriculture
Lysenko was the head of the Russian Department of Agriculture in the 1930’s.
He thought selective breeding and Mendelian genetics were “Capitalist” ideas and rejected them in favor of an old fashioned idea called “The Inheritance of Acquired Characteristics.”
This ruined Soviet agriculture until 1965.
After Stalin’s death, Lynsenko was replaced and Russian biologists began using more modern biological ideas.
Chromosomes are made of 2 long chains of DNA
DNA = Deoxyribonucleic Acid
DNA is made of three parts:
1. simple sugar = deoxyribose
2. phosphate group
3. nitrogen bases – 4 varieties
adenine (A)
guanine (G)
cytosine (C)
thymine (T)
Structure of DNA
James Watson & Francis Crick were awarded the Nobel Prize in 1962 for their model of DNA.
Structure of DNA is a coiled double helix (like a twisted ladder)
1. Sugar and phosphates are the sides of the ladder.
2. 2 nitrogen bases (base pairs) are the rungs of ladder.
Rosalind Franklin
A scientist that was influential in the discovery of the structure of DNA.
Ms. Franklin was never given the credit she deserved for the X-ray photo that she took of DNA
•Her photo was shown to Watson & Crick by another scientist without her permission.
•As soon as Watson and Crick saw the photo they figured out the structure of DNA.
•She died 4 years before the Nobel Prize was given to the other scientists.
The DNA ladder
Sugar and phosphates are the sides of the ladder.
2 nitrogen bases (base pairs) are the rungs of the ladder.
A pairs with T
C pairs with G
Human Genome Project – international research working to determine the sequence of bases for the human species.
DNA Replication –
1. The double helix unwinds and “unzips”.
2. Each strand is a pattern to form the new strand.
3. An exact copy is made.
4. A copy of the DNA is passed on to clone daughter cells during mitosis.
DNA codes for Proteins:
1. DNA contains the code for making the many proteins your body needs.
2. RNA carries a copy of the code outside the nucleus to the ribosomes, where proteins are made = transcription.
3. Proteins control the chemical reactions in the cell like enzymes needed for digestion.
3 DNA bases ---> 3 RNA bases ---> 1 amino acid ---> protein (many amino acids)
Genetic Mutations:
Mutation – a mistake or change in the DNA sequence.
Mutations are random events that result in cancer or birth defects.
Mutations are caused by exposure to x-rays, ultraviolet light, radioactive substances or certain chemicals.
Point Mutation – a change in a single base pair.
ex: THE DOG BIT THE CAT.
THE DOG BIT THE CAR.
Frameshift Mutation – a single base is added or deleted.
Chromosomal Mutations – parts of chromosomes can be broken off and lost during mitosis.
1. Deletion – part of chromosome left out.
2. Insertion – part breaks off and attaches to the sister chromatid.
3. Inversion – chromosome breaks and reattaches backwards.
4. Translocation – chromosome breaks off and then attaches to a different chromosome.
5. Nondisjuction – chromosomes do not separate during cell division
