Book C
Chapter 3
Genetics
Section 1, Mendel's Work
Heredity -- the passing of traits from parents to offspring
It was first studied by Gregor Mendel (1822-1884).
Chapter 3
Genetics
Section 1, Mendel's Work
Heredity -- the passing of traits from parents to offspring
It was first studied by Gregor Mendel (1822-1884).
Gregor Mendel was born in 1822 in what is now Czechoslovakia. His parents were very poor, but he faced poverty with courage, tending fruit trees for the lord of the manor. He developed a love for plants that can be see in his later work.
As he grew up, he had to struggle to get an education. He helped to support himself by tutoring other students. He entered an Augustinian monastery when he was 21 years old. They sent him to the University of Vienna to be trained to be a math and science teacher.
Mendel combined his interest in math and botany with research. He investigated how traits are inherited by growing pea plants which grow fast and reproduce by self-pollination. He grew them in the monastery garden. He self-pollinated plants and wrapped them carefully to keep insects from pollinating them by accident. That way he was sure that the seeds would inherit characteristics from only one parent.
He studied the traits of many plants. He discovered that short plants always produced short plants but tall plants were different. About 1/4 of their offspring where short and 3/4 were tall. He realized that there were two types of tall plants: true-breeders (pure) and non-true-breeders. The non-true-breeders contained both tall and short traits.
He then did more experiments. He crossbreed pure short and pure tall plants. Surprisingly he found that all the offspring were tall. However, when these first generation offspring were self-pollinated about 1/4 of the next generation were pure tall, 1/2 were non-true-breeding tall (today we call them hybrid) and 1/4 were pure short. This was his historic discovery!
Like any good scientist Mendel kept careful records of his work on thousands of plants. However, when he reported his results to the local natural history society, they paid little attention. He tried other ways to get people to recognize his work but failed. Finally he published his findings in a small scientific magazine but no one paid attention.
After 12 years of research Mendel was made abbot of the monastery. His new duties and his increasing weight made it impossible for him to continue to work in his gardens.
His work remained unnoticed during his lifetime and he died in 1884 without knowing that he would be famous as the discoverer of the Mendelian laws of inheritance.
In 1900 three other scientists simultaneously found the same results as Mendel. They were very surprised when the checked the literature and found that Mendel had made these same discoveries 30 years earlier!
Mendel did many experiments using different plant traits. Some of them are shown below:
Mendel's plant height experiment:
1. He bred pea plants so they always produced offspring with heights like the parents.
(tall parent ---------> tall offspring
and short parent ----------> short offspring)
2. Then he bred a tall pea plant and a short pea plant
together. He found that their offspring were all tall.
3. Then he bred two of these tall offspring together. This time there were some tall and some short offspring.
This lead him to say that the plants had traits for tallness and shortness.
He called them dominant and recessive traits.
A dominant trait is one that prevents another trait from appearing or showing in the offspring.
A recessive trait is one that will not appear
when a dominant trait is present.
An organism with a pure trait has all dominant
or all recessive traits.
A pure breed is an organism that always produces offspring with the same form of a trait as the parent.
Examples:
1. He bred pea plants so they always produced offspring with heights like the parents.
(tall parent ---------> tall offspring
and short parent ----------> short offspring)
2. Then he bred a tall pea plant and a short pea plant
together. He found that their offspring were all tall.
3. Then he bred two of these tall offspring together. This time there were some tall and some short offspring.
This lead him to say that the plants had traits for tallness and shortness.
He called them dominant and recessive traits.
A dominant trait is one that prevents another trait from appearing or showing in the offspring.
A recessive trait is one that will not appear
when a dominant trait is present.
An organism with a pure trait has all dominant
or all recessive traits.
A pure breed is an organism that always produces offspring with the same form of a trait as the parent.
Examples:
Today we know that Mendel's "traits" are genes
A dominant gene (represented by a capital letter)
covers up (or hides) a recessive gene
(represented by a lower case letter.)
Genes are inherited in pairs -- one gene comes from each parent
Different forms of a gene are called alleles.
For example: The gene for height in some plants has two forms (tall or short)
-one allele is for short stems
-the other allele is for tall stems
Examples:
Let the dominant gene for height = H
Let the recessive gene for height = h
A dominant gene (represented by a capital letter)
covers up (or hides) a recessive gene
(represented by a lower case letter.)
Genes are inherited in pairs -- one gene comes from each parent
Different forms of a gene are called alleles.
For example: The gene for height in some plants has two forms (tall or short)
-one allele is for short stems
-the other allele is for tall stems
Examples:
Let the dominant gene for height = H
Let the recessive gene for height = h
all tall offspring
also called hybrids
Hybrid trait -- made of a combination of dominant and recessive traits (mixed)
pure tall + pure short ------------> hybrid offspring
Example:
also called hybrids
Hybrid trait -- made of a combination of dominant and recessive traits (mixed)
pure tall + pure short ------------> hybrid offspring
Example:
Principles of Genetics
1. Traits pass from parents to offspring
2. Gene pairs determine traits
3. One gene of a pair comes from the gamete of each parent
( A gamete is the sex cell of the parent -- either the
sperm or egg)
4. Gene pairs are inherited separately for each trait
Section 2 Probability and Genetices
Probability is the likelihood that a specific event will happen.
Suppose you were to toss a coin 20 times. Predict how many times the coin would land "heads up"__________ and how many times it would land "heads down" _____________
Now test your prediction by tossing a coin 20 times. Record the number of times the coin lands heads up ________ and heads down _________
Combine the data from the entire class
class data -- heads up __________ heads down _______
The class found that the probability of heads up was _______ out of ______ tries.
This can also be shown as a fraction or a percent. For example one out of two times is 1/2or 50 percent.
Four out of five times is 4/5 or 80%
These are all probabilities.
Punnett Squares -- show all possible combinations of a genetic cross
-- determine the genes of a particular
set of offspring
Genotype -- the gene combination in the chromosomes
Phenotype -- the outside physical trait that shows (what
it looks like)
When the genotype is :
-2 dominant genes it is pure dominant
(two capital letters)
-2 recessive genes it is pure recessive
(two lower case letters)
- 1 dominant and 1 recessive gene it is hybrid
(one capital and one lower case letter)
Examples:
H = dominant (tall plant) h= recessive (short plant)
breed (cross) one pure dominant (HH) with one pure recessive (hh)
1. Traits pass from parents to offspring
2. Gene pairs determine traits
3. One gene of a pair comes from the gamete of each parent
( A gamete is the sex cell of the parent -- either the
sperm or egg)
4. Gene pairs are inherited separately for each trait
Section 2 Probability and Genetices
Probability is the likelihood that a specific event will happen.
Suppose you were to toss a coin 20 times. Predict how many times the coin would land "heads up"__________ and how many times it would land "heads down" _____________
Now test your prediction by tossing a coin 20 times. Record the number of times the coin lands heads up ________ and heads down _________
Combine the data from the entire class
class data -- heads up __________ heads down _______
The class found that the probability of heads up was _______ out of ______ tries.
This can also be shown as a fraction or a percent. For example one out of two times is 1/2or 50 percent.
Four out of five times is 4/5 or 80%
These are all probabilities.
Punnett Squares -- show all possible combinations of a genetic cross
-- determine the genes of a particular
set of offspring
Genotype -- the gene combination in the chromosomes
Phenotype -- the outside physical trait that shows (what
it looks like)
When the genotype is :
-2 dominant genes it is pure dominant
(two capital letters)
-2 recessive genes it is pure recessive
(two lower case letters)
- 1 dominant and 1 recessive gene it is hybrid
(one capital and one lower case letter)
Examples:
H = dominant (tall plant) h= recessive (short plant)
breed (cross) one pure dominant (HH) with one pure recessive (hh)
Phenotypes:
tall - 100 %
short - 0 %
Genotypes
hybrid - 100%
pure dominant - 0%
pure recessive - 0%
example:
cross a hybrid (Hh) with another hybrid (Hh)
tall - 100 %
short - 0 %
Genotypes
hybrid - 100%
pure dominant - 0%
pure recessive - 0%
example:
cross a hybrid (Hh) with another hybrid (Hh)
Phenotypes:
tall - 75 %
short - 25%
Genotypes
hybrid - 50%
pure dominant - 25%
pure recessive - 25%
example:
cross a pure dominant (AA) with a hybrid (Aa)
do Punnett square on your own and find genotypes and phenotypes
tall - 75 %
short - 25%
Genotypes
hybrid - 50%
pure dominant - 25%
pure recessive - 25%
example:
cross a pure dominant (AA) with a hybrid (Aa)
do Punnett square on your own and find genotypes and phenotypes
example:
cross a pure recessive (bb) with a hybrid (Bb)
do Punnett square like the one below and find genotypes and phenotypes on your own
cross a pure recessive (bb) with a hybrid (Bb)
do Punnett square like the one below and find genotypes and phenotypes on your own
NOTE to students who have missed class and are copying these notes at home: If you find the above examples confusing or difficult be sure to come for help.
Other types of inheritance: (besides dominant and recessive)
Codominance- neither allele is masked (neither dominant
nor recessive)
-offspring show characteristics of both parents
example: p. 93 in text
Incomplete dominance- each allele is equally dominant
-results in a blended or intermediate phenotype
example:
R= red W = white
RR = red
WW = white
RW = pink (blended red and white)
WW = white
RW = pink (blended red and white)
Section 3, The Cell and Inheritance
Chromosomes
- found in nucleus of the cell
- contain genes
- each type of organism has a different
number of chromosomes
-humans have 23 pairs or 46 total
chromosomes in body cells.
- each chromosome has a specific number of genes
- a human chromosome contains hundreds of genes
Meiosis -- cell division which forms gametes
number of chromosomes
-humans have 23 pairs or 46 total
chromosomes in body cells.
- each chromosome has a specific number of genes
- a human chromosome contains hundreds of genes
Meiosis -- cell division which forms gametes
(see p. 99 in text)
In sexual reproduction - half of genes come from each parent
- sexually reproduced offspring are not identical to either parent
Section 4, The DNA Conncetion
Remember that chromosomes are made of DNA
DNA is made of of four different nitrogen bases
(adenine(A), thymine(T), guanine(G), cytosine(C)
These bases form the rungs of the DNA ladder. A single gene on a chromosome may contain a few hundred to more than a million of these bases. The order of the nitrogen bases determines what type of proteins the cell makes.
Mutations are changes in the DNA. They can be harmful, helpful, or neither.
Book C, Chapter 4, Modern Genetics
Section 1, Human Inheritance
Multiple alleles
Some traits are controlled by a single gene that has more than two alleles. Such a gene is said to have multiple alleles (three or more forms of a gene that control a single trait.)
Because genes are inherited in pairs, a person can only inherit two forms of any allele.
A good example is blood types.
There are four main human blood types: A,B,AB,O
Three alleles control their inheritance. The allele for blood type A and the allele for blood type B are codominant
In sexual reproduction - half of genes come from each parent
- sexually reproduced offspring are not identical to either parent
Section 4, The DNA Conncetion
Remember that chromosomes are made of DNA
DNA is made of of four different nitrogen bases
(adenine(A), thymine(T), guanine(G), cytosine(C)
These bases form the rungs of the DNA ladder. A single gene on a chromosome may contain a few hundred to more than a million of these bases. The order of the nitrogen bases determines what type of proteins the cell makes.
Mutations are changes in the DNA. They can be harmful, helpful, or neither.
Book C, Chapter 4, Modern Genetics
Section 1, Human Inheritance
Multiple alleles
Some traits are controlled by a single gene that has more than two alleles. Such a gene is said to have multiple alleles (three or more forms of a gene that control a single trait.)
Because genes are inherited in pairs, a person can only inherit two forms of any allele.
A good example is blood types.
There are four main human blood types: A,B,AB,O
Three alleles control their inheritance. The allele for blood type A and the allele for blood type B are codominant
is the allele for blood type A
is the allele for blood type B
The allele for blood type O is recessive. It is written i
Blood type Combination of alleles
Blood type Combination of alleles
Blood types are not evenly distributed throughout the human population. O+ is the most common, AB- is the rarest. There are also variations in blood-type distribution within human subpopulations. According to wikipedia.org, the approximate distribution of blood types in the United States are as follows:
Blood type is important when a person receives blood. The chart below shows what types of blood people can receive.
Rh factor is inherited separately from blood type.
Rh positive (Rh+) is dominant over Rh negative (Rh-).
Rh+ people can receive blood type compatible blood that is either Rh+ or Rh-.
Rh- people can only receive blood type compatible blood that is Rh-.
For example:
O+ can donate to A+, B+,AB+, and O+ but receive blood from both O- and O+ while
O- can donate to A+, B+,AB+, and O+ and A-, B-,AB-, and O- but receive blood only from another O-.
Which blood type would be the true universal donor?
O-
Which blood type would be the true universal receiver?
AB+
Sex determination
- females have two X chromosomes
- males have one X chromosome
and one Y chromosome.
- Unlike individual genes, whole chromosomes are
NOT dominant or recessive
Karyotype - a picture of the chromosomes of a species. Humans have 23 pairs of chromosomes. The picture below is a karyotype of a female human.
The image below is a karyotype of a human male.
Pedigrees
-a chart or "family tree" that shows which members
of a family have a particular trait
If you are doing this from home be sure to see your teacher for the more detailed notes on pedigrees.
Sex linked genes
--genes found on the X and Y chromosomes
--(sex-linked traits are controlled by sex-linked genes)
A = no disease gene
a =disease gene
--genes found on the X and Y chromosomes
--(sex-linked traits are controlled by sex-linked genes)
A = no disease gene
a =disease gene
-- dominant allele on the X chromosome
--recessive allele on the X chromosome
-- dominant allele on the Y chromosome
-- recessive allele on the Y chromosome
Section 2 Human Genetic Disorders
A genetic disorder is an abnormal condition that a person inherits through genes or chromosomes. They are caused by mutations or changes in a person's DNA.
examples:
1. Cystic fibrosis
- a genetic disorder in which the body produces abnormally thick mucus in the lungs and intestines. This makes in hard for the person to breathe and can interfer with digestion.
2. Sickle-cell disease
- a genetic disorder that affects the blood. The red blood cells have a sickle (half moon) shape instead of the normal donut shape. They cannot carry enough oxygen and they block the blood vessels causing pain and weakness.
3.Hemophilia
- a genetic disorder in which a person's blood clots slowly or not at all. Minor cuts and bruises can cause major bleeding or death. It is caused by a recessive allele on the X chromosome. Therefore it is a sex-linked disorder.
4. Downs Syndrome
- a genetic disorder that results from an extra copy of chromosome #21. People with this disorder have a distinctive physical appearance and some degree of mental retardation.
The image below is a karyotype of a person with Down Syndrome.
A genetic disorder is an abnormal condition that a person inherits through genes or chromosomes. They are caused by mutations or changes in a person's DNA.
examples:
1. Cystic fibrosis
- a genetic disorder in which the body produces abnormally thick mucus in the lungs and intestines. This makes in hard for the person to breathe and can interfer with digestion.
2. Sickle-cell disease
- a genetic disorder that affects the blood. The red blood cells have a sickle (half moon) shape instead of the normal donut shape. They cannot carry enough oxygen and they block the blood vessels causing pain and weakness.
3.Hemophilia
- a genetic disorder in which a person's blood clots slowly or not at all. Minor cuts and bruises can cause major bleeding or death. It is caused by a recessive allele on the X chromosome. Therefore it is a sex-linked disorder.
4. Downs Syndrome
- a genetic disorder that results from an extra copy of chromosome #21. People with this disorder have a distinctive physical appearance and some degree of mental retardation.
The image below is a karyotype of a person with Down Syndrome.
Section 3, Advances in Genetics
Selective Breeding -- the process of selecting a few organisms with desired traits to serve as parents for the next generation.
1. Inbreeding -- crossing two organisms that have the same or similar sets of traits
examples:
Selective Breeding -- the process of selecting a few organisms with desired traits to serve as parents for the next generation.
1. Inbreeding -- crossing two organisms that have the same or similar sets of traits
examples:
Breeding dogs to get puppies that are just like the parents and just like each other.
2. Hybridization -- crossing two organisms that have two different desirable traits
examples:
examples:
Breeding a yellow flower with wide, ruffled petals with a pink flower with more narrow petals to get a pink flower with (longer) wide, ruffled petals.
Cloning -- producing offspring genetically identical to a single parent
- in plants cloning can be done by cuttings or runners
- in plants cloning can be done by cuttings or runners
- in animals an example is Dolly the sheep who was cloned in 1997
Genetic Engineering -- taking genes from one organism and transferring them directly into the DNA of another organism.
examples:
-"gene splicing" a gene for a protein that controls human blood clotting is inserted into the cells of a cow which then produces that protein in her milk. The milk can then be used to treat human hemophilia.
examples:
-"gene splicing" a gene for a protein that controls human blood clotting is inserted into the cells of a cow which then produces that protein in her milk. The milk can then be used to treat human hemophilia.
Book C, Chapter 5
Changes Over Time
Changes Over Time
-- he observed the huge variety of plants
and animals
- today we think that there are 2,500,000 different kinds of organisms
- in 1835 he came to Galapagos Islands
and animals
- today we think that there are 2,500,000 different kinds of organisms
- in 1835 he came to Galapagos Islands
Here he found that many plants and animals were exactly like those on the mainland but a few had some differences.
Here he found that many plants and animals were exactly like those on the mainland but a few had some differences.
examples: (see p. 142)
Iguanas on the island had big claws to grasp the slippery rocks. The ones on the mainland had smaller claws.
- he decided to call these changes adaptations
(An adaptation is a characteristic of an organism
that helps it survive and reproduce.)
-he said that gradual changes in organisms over
many years would produce organisms that were better
adapted to their environment. He called this
process evolution.
- he then needed to decide what made these changes happen.
- he noticed that many organisms overproduced
offspring. (They had so many offspring that not all could survive.)
- the offspring would compete with each other to
survive.
He called this “survival of the fittest”
or natural selection
Here he found that many plants and animals were exactly like those on the mainland but a few had some differences.
examples: (see p. 142)
Iguanas on the island had big claws to grasp the slippery rocks. The ones on the mainland had smaller claws.
- he decided to call these changes adaptations
(An adaptation is a characteristic of an organism
that helps it survive and reproduce.)
-he said that gradual changes in organisms over
many years would produce organisms that were better
adapted to their environment. He called this
process evolution.
- he then needed to decide what made these changes happen.
- he noticed that many organisms overproduced
offspring. (They had so many offspring that not all could survive.)
- the offspring would compete with each other to
survive.
He called this “survival of the fittest”
or natural selection