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Chapter 5- Heredity
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Chapter 5- Heredity


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  • 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!!!!!