Genetics
Q: What is GENETICS?
A:
Q: How do we inherit our traits?
A:
Q: How do we know so much about genetics today?
A: The work of Gregor Mendel in the 1850’and 1860’s. He studied pea plants and
noticed that pea plants had opposite traits in many cases. He saw that the plants were
either tall or short, had yellow or green pea color, had wrinkled or smooth seeds, and so
forth. *See pages 80-85 in orange books.
List 10 Specific traits that you have below:
1.
6.
2.
7.
3.
8.
4.
9.
5.
10.
The specific trait that you have for any type of characteristic is also called the
phenotype. The phenotype is the physical expression of the genes. In other words,
what the genes give a code for. For example, my eye-color genes give a code for BLUE
EYES. Blue eyes is my phenotype for that trait. Also, I have a gene that gives a code for
ASTHMA, whereas many people have a gene that gives a code NOT to have asthma. My
phenotype is “having asthma”.
Facts about our genes:
1. We have
pairs of chromosomes in each cell.
2. Each chromosome has
genes on it.
3. Chromosomes come in pairs because
. Therefore, the genes ON
the chromosomes always come in pairs. This means we have 2 alternate genes for each
trait. They could be the same, or they could be different. These 2 alternate genes are
called Alleles.
Alleles:
Dominant Allele – The “Strongest Gene”.
The allele that is always expressed over
the other one. This means that if you have 1 dominant allele for any trait, you will have
that dominant trait.
We write dominant alleles with a capitol letter. For example, a capitol B for green or
brown eyes.
Recessive Allele –The “Weakest Gene”.
The allele that doesn’t show up unless there
are two of them for the trait. If you have one dominant allele and one recessive allele, you
will have the dominant trait.
We write recessive alleles with a lower case letter. For example, lower case b for
blue eyes.
Genotype – The genotype is the actual alleles that you have for any given trait.
You
have 3 possibilities for your genotype for any trait:
1. You could have both dominant alleles (For example, BB)
Q: What would be your PHENOTYPE for this genotype?
2. You could have one dominant and one recessive allele (For example, Bb)
Q: What would be your phenotype for this genotype?
3. You could have both recessive alleles (For example, bb)
Q: What would be your phenotype for this genotype?
There are 2 types of genotypes:
1.
Purebred (homozygous)—When both alleles are the same.
2.
Hybrid (heterozygous)—When the alleles are different.
In other
words, both alleles are dominant or both alleles are recessive. You would
write that with both capitol letters or both letters are lower-case. For example,
BB or bb
One is
dominant and one is recessive. Therefore, you write one capitol letter and one
lower-case letter. For example, Bb
Punnett Squares:
Q: What are punnett sqares?
A: A method of predicting what genes the offspring between 2 parents will have. We
use them to do genetic crosses, which are how make this prediction.
*We can predict the Probability of offspring inheriting particular traits.
Probability means
Chance something will
happen
.
Examples:
1. If b = Blue eyes and B = brown or green eyes, what would be the genotype of a
hybrid parent?
Bb
What colored eyes would this person have?
BROWN OR
GREEN
What would be the genotype of a blue eyed person?
bb
Step One: Write down the genotypes of both of the parents, one at a time.
Step Two: Draw a punnett square. One box, broken up into 4 smaller
boxes.
Step Three: Put one parent across the top of the box and one parent down
the left side of the box.
Step Four: Combine the letters inside the square.
Examples:
1. Cross a hybrid green eyed parent with a blue eyed parent.
What is the probability of these parents having a blue-eyed offspring?
More Punnett Square Examples:
2. If T = tall height, and t = short height, cross a purebred tall
person with a hybrid person. What is the probability of these
two parents having a short offspring?
3. If G = having green pea pods, and g = having yellow pea pods,
cross 2 hybrid plants together. What is the probability of the
offspring having green pods?
4. If H = happy personality, cross 2 hybrid parents together. What is the
probability of these parents having an offspring who is not happy?
5. In whitetail deer, having albino fur is caused by a recessive gene (a).
Cross a purebred deer with normal fur with an albino deer. What is
the probability of the offspring being albino?
6. If having normal breathing is dominant (A) over having asthma, cross
2 hybrid parents together. What is the probability of the offspring
breathing normally?
7. In people with diabetes, the gene that produces insulin is faulty. This
is caused by a recessive gene (i). Cross a hybrid parent with a parent
that has diabetes. What is the probability of the offspring having
diabetes?
Blood type Punnett Squares:
*Different because there are 3 different alleles. Instead of one being
dominant and 1 being recessive, two are dominant, and one is recessive.
A= type A blood (dominant)
B=type B blood (dominant)
O=type O blood (recessive)
A and B together are codominant which gives type AB blood
The only way to get type O blood is to have “OO” as your genotype.
Examples:
1. Cross AB x OO. List all phenotypic ratios
2. Cross a hybrid type A (AO) and a hybrid type B (BO) person. List all
phenotypic ratios.
3. Cross AA X AB
Pedigree Charts:
*Show the relationships between traits of family members.
Pg. 118 orange books.
Rules:
Circle=female
Square=male
Fully shaded in=they have that trait
Half shaded in (always a female)= don’t have the trait, but carry a gene for it
(hybrid genotype)
Not shaded in = don’t have that trait.
The most current generation (children or grandchildren) are at the bottom.
1. How many children did the original parents have?
2. How many grandchildren are there?
3. How many total family members have the disease?
4. Write down the genotype of the daughter
]
Pedigree Charts:
What is a pedigree chart?
A family tree that traces the inheritance of sex linked traits in humans.
Example:
*Look at page 118 in orange books. Copy this pedigree chart below:
Questions about pedigree chart on page 118:
1. How many children did the original parents have?
2. What % of the grandchildren have colorblindness?
3. What % of the grandchildren are carriers for the disease (hybrid)?
4. What % of the grandchildren have normal vision?
Vocabulary, Unit 6
Genetics
Pedigree chart
Phenotype
Genotype
Dominant
Recessive
Allele
Sex linked trait
Codominance—when more than one allele are dominant together (Ex: blood type)
Purebred (homozygous)
Hybrid (heterozygous)
Punnett Square
Genetic Crosses—What we do in the punnett square to predict the offspring
Greg Mendel
Probability