1. Heredity
Chapter 5

2. Heredity and Genetics section 5-1 H.W. pg 132 ques. 1-5
Heredity is the passing down of traits from parent to offspring.
You inherit traits or body features from your parents, and them from their parents, etc…
All of the traits that you express and carry are inside your DNA on what we call alleles.
An allele is basically one half, of one piece of DNA that is responsible for gene.

3. Heredity and Genetics
Sex cells contain one half of all of the alleles in your DNA (or half of your DNA).
So when a sperm and egg fertilize each other, their alleles combine to produce genes. (now full DNA,46 Chromosomes)
And the study of how traits are inherited through the interactions of alleles is what we call genetics.

4. Mendel
An Austrian monk named Gregor Mendel is known as the father of genetics.
Through science and mathematics, he studied how traits get passed on from generations to generation, using pea plants.
He used pea plants because they grew quickly and they had different colored pea flowers. This made it easy to see where the traits were passed on to.

5. Mendel
He looked at characteristics like the color of the peas, color of the pea pod, shape of the pea pod, height of the pea plant, and color of the flowers.
The way he studied the plants is by cross mating two pea plants that expressed totally different traits.
He found that the offspring from these 2 different plants produced an offspring which always looked like on of the parent plants.
He called these offspring plants Hybrids, because they received different alleles for a trait from each parent.

6. Mendel
He found that it was easy to breed pea plants that had pure traits. That means that an organism that always produces the same traits generation after generation, and is called a pure breed.
An example is that tall plants will always produce tall offspring.
To see how genetics worked in nature he took pollen from short plants and fertilized a tall plant seed, just like a bee might carry pollen randomly from one plant to another.
When you mate two pure breeds of different traits (short and tall for example) it is called cross breeding.

7. Mendel
The result of this cross breeding, was that all the offspring were tall. Whatever it was that made the short plants short appeared to be gone.
He than referred to the tall trait as a dominant trait because it overcame the short trait or covered it up.
He referred to the short trait as recessive because it seemed to disappear.
However, he found that these recessive traits didn’t disappear because as he kept cross breeding his pea plants he found that they reappeared.
So, the recessive traits did not disappear, they were just not expressed because a dominant trait was present.

8. Alleles and Punnett Squares
Almost every cell in your body has two alleles for every trait. One from mommy and one from daddy.
These alleles are on your chromosomes inside the nucleus of your cells.
An organism that has two alleles that are the same for one trait is said to be called homozygous. TT
An organism that has two different alleles for a single trait is called heterozygous. Tt
We use these terms to express an organisms phenotype, or a trait that can physically can be seen without knowing what alleles it has.
Ex: I have black hair, so my phenotype for hair color is black.

9. Alleles and Punnett Squares
We also use these terms to express what is called, an organisms genotype. This is genetic make up of the alleles an organism has.
Ex: I might have black hair, but I might not have 2 alleles for black hair, but b/c one allele is black, and black is dominant over any other color allele, I have black hair. Bb
We can not assume what an organisms genotype is just by looking at its phenotype.

10. Alleles and Punnett Squares
To test the probability of what traits will get passed down from the cross breeding of parent genotypes, to offspring, we use Punnett squares.
In a Punnett square we use 2 letter abbreviations for traits.
Capital letters stand for dominant traits and lower case letters represent recessive traits.

11. Punnett Square

12. Alleles and Punnett Squares
Even though Mendel didn’t know about DNA and Chromosomes he did teach us 3 principles of heredity.
1) Traits are controlled by alleles on chromosomes.
2) An allele can be dominant or recessive.
3) When a pair of chromosomes separate during meiosis, the different alleles for a trait move into separate sex cells.

13. Genetics Since Mendel section 5-2 H.W. pg 140 ques. 1-4
Since we have found what is called incomplete dominance. This is when the offspring of 2 homozygous parents produce an intermediate or middle offspring.
Ex: A pure white flower and a pure red flower could give a pink flower.
This occurs with hair color of horses and other animals and feather color of birds.

14. Multiple alleles
We also learned that many traits are controlled by more than just two traits.
A trait that is controlled by more than two alleles is said to be controlled by multiple alleles.
An example is blood type. There are 3 alleles for blood type: A B O
A could be AA or AO
B could be BB or BO
AB is only AB
O is only OO

15. Polygenic Inheritance
Some traits are produced because many genes combine to form it. When a group of genes act together to produce a trait its called polygenic inheritance.
An example is skin color. It is estimated that 3-6 genes control what skin color an offspring will have.
Eye color is also a polygenic trait, among others.

16. Mutations
Sometimes during cell division DNA is not copied correctly. And these incorrect copies of DNA are called mutations and can be harmful or advantages to an organism. (diseases or a 4 leaf clover)
There can also be chromosome disorders. These disorders occur when an organism contains to few or to many chromosomes.
When this happens the fetus or embryo usually dies before birth.
If it does live it could result in mental or physical disorders like down syndrome (3 chromosome 21’s)

17. Recessive Genetic disorders
A lot human genetic disorders, like cystic fibrosis, are caused by mutated recessive genes.
To get this disease one would have to inherit 2 recessive alleles. aa
This could mean that the parents of this offspring could have only been carriers of the disease and had no shown symptoms of it.

18. Sex Determination
The sex of an organism is determined by special sex chromosomes.
The female sex chromosome is the X chromosome and the male is the Y chromosome.
In order for a female to be produced it needs to inherit 2 X chromosomes: XX
If a Y is inherited the result is a male: XY
YY is not possible

19. Sex linked disorders
Some genetic disorder occur because of mutations of genes on sex chromosomes or sex linked genes.
These disorders can only be expressed in certain sexes.
Ex: Color blindness is only expressed on the X chromosome. So men only need one allele for colorblindness to become color blind where women will need two.

20. Pedigree Chart
We use a pedigree chart to find out how a trait was passed on from generation to generation.

21. Genetic Engineering
Genetic engineering is used to correct genetic disorder. We want to fix a piece of DNA that is damaged or missing something.
We do it in a couple of ways: one way is with recombinant DNA. We do this with diabetics a lot.
Here we place DNA for insulin inside of a bacteria’s DNA.
This will cause the bacteria to produce insulin that can be used for people with diabetes.

22. Genetic Engineering H.W. pg 149 & 150 ques 1-18
Another way is called gene therapy. Here we try to fix a bad gene inside of a cell.
We take a good gene and place it into a virus genome. Then we infect a person that doesn’t have the good gene with this virus and hopefully it corrects the problem.

23. Test on Chapter 5 in one Week!!!!!