dna, genes and chromosomes. frederick griffith 1928 are genes made up of dna or protein? griffith...
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![Page 1: DNA, Genes and Chromosomes. Frederick Griffith 1928 Are genes made up of DNA or protein? Griffith did an experiment with mice and two different strains](https://reader036.vdocument.in/reader036/viewer/2022062300/56649dff5503460f94ae869c/html5/thumbnails/1.jpg)
DNA, Genes and Chromosomes
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Frederick Griffith 1928
• Are genes made up of DNA or protein?• Griffith did an experiment with mice and
two different strains of bacteria called Streptococcus pneumoniae
• One variety strain S looks smooth and causes pneumonia in mice.
• The other strain R has a rough coat and does not cause pneumonia in mice
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Griffith’s experiment
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Now, you answer these questions.
• 1. What happened to the mouse injected with just strain S?
• 2. What happened to the mouse injected with just strain R?
• 3. What happened to the mouse injected with a mix of strain R and strain S which had been HEATED up?
• 4. What happened to a mix of R and S when only the S had been heated?
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What’s the big idea?
* TRANSFORMATION
Griffith hypothesized that the heat-killed S bacteria had transformed the live R strain changing it into S bacteria.
He concluded that the transforming material was genetic material.
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In 1944 Oswald Avery
• Discovered that only DNA from strain S bacteria was necessary to transform strain R bacteria into S strain
• The importance- His findings supported that DNA not protein was the genetic material
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DNA or Protein?????
• In 1952 Alfred Hershey and Martha Chase conducted and important experiment in order to prove that DNA was in fact the genetic material.
• They used special viruses which can infect bacteria called Bacteriophages.
• A bacteriophage is made up of two components- DNA and protein. Hmm good choice!
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Hershey and Chase experiment
• Cell Culture 1• Cell Culture 2
BacteriophageWith Radioactive
DNA
Bacteriophage With Radioactive
protein
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Experiment summary
• In culture 1 the phages with radioactive DNA infected the bacteria and the bacteria BECAME radioactive too! SO, the DNA went inside the bacteria.
• In culture 2, when the phages with radioactive protein infected the bacteria, the bacteria DID NOT become radioactive because the protein remained on the outside. SO, DNA is the heredity material!
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The next big question was what does DNA look like?
• DNA is made up of 4 Nitrogenous bases:• Adenine& Thymine• Guanine& Cytosine• And a Phosphate and Deoxyribose (sugar)
backbone
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DNA nucleotides
• A DNA nucleotide is made up of :• One of the 4 Nitrogenous bases (A,T,G,C)• A Phosphate• And a sugar (Deoxyribose)
The bases are divided into two groups:
Purines- Adenine and Guanine
Pyrimidines- Thymine and Cytosine
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The history of the race to the double helix
• 1952-Edwin Chargaff discovers that in all living organisms the amount of adenine equals the amount of thymine and the amount of cytosine equals the amount of guanine.
• This discovery about the specific amount of these bases became known as Chargaff’s rules.
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Maurine Wilkins and Rosalind Franklin
• Both of these scientists especially the brilliant Rosalind Franklin took pictures of DNA using a special technique called
• X-ray Crystallography• One of Rosalind’s pictures proved to be
the missing link in solving the puzzle of how DNA looked.
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Rosalind Franklin
• Rosalind Franklin and her famous picture of DNA. Two scientists Watson and Crick used this to discover the secret of DNA
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1953 James Watson and Francis Crick
• Discovered the structure of DNA and built the first model of DNA. They used Rosalind Franklins picture to figure out that the A and T’s went together and the G and C’s went together. Each base letter was bonded to a sugar and a phosphate to make a sugar-phosphate backbone
• =double helix• NOBEL prize recipients for their work.
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The famous Watson and Crick
James WatsonFrancis Crick
Wow, James its amazing what you can make
these daysout of tinker toys!!
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DNA replication
• Turn in your books to page 162.• Write down the 3 steps in your notes.• 1.
• 2.
• 3. • What does DNA polymerase do?
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Linked genes
• Genes that are on the same chromosome are linked.
• That’s why we can have only 46 chromosomes with thousands of characteristics!
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Refining Mendel’s laws
• Geneticists William Bateson and R.C. Punnett discovered that some genes are linked when they experimented with flower color in sweet pea plants.
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Do genes shuffle?
• YES!• In meiosis in prophase I the tetrads snap
together and the arms of the chromatids cross allowing for genes to be exchanged.
• The result: LOTS of variation!
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Sex Linkage
• Involves Sex chromosomes ONLY• Traits that are the X chromosome are
found more often in males than females. • Females are X
• Males are XY
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Sex linked Conditions
• Color blindness in humans• XNXN= normal female• XNXn= Normal female carrier• XNY= Normal male• XnY= Color blind male• Hemophilia (Bleeder’s disease) Humans• White eyes in fruit flies
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Sex –linked crossN= Normal n= colorblind
XNXN XNXn
XNY XnY
XN Xn
XN
Y
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Sex- limited traits
• Traits that are only expressed in the presence of SEX hormones and are only observed in one sex or the other.
• Beard growth in males• Milk production in females• Differences in female and male bird
feathers.
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Sex-influenced traits
• Traits that are expressed in both sexes but they are expressed differently.
• Baldness in males is dominant and in females recessive.
• Males Females• BB=bald BB= hair• Bb= bald Bb= hair• bb=hair bb= bald
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Karyotype• A picture of one’s chromosomes taken when they are lined up in metaphase.
• An amniocentesis is done to obtain the cells from the amniotic fluid surrounding the fetus.
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The Human Genome Project
• A project established in 1988 to sequence all of the DNA in the human body.
• That means all 23 chromosomes pairs with 90,000 genes and 3 billion bases!
• Goal: Use the knowledge to cure disease and improve life.
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Chromosome Problems
• Nondisjunction- Down’s Syndrome. • A child with 3 number 21 chromosomes
which total up to 47 in a somatic cell instead of 46
• Called a Trisomy
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Polyploidy
• Nondisjunction occurs in all the pairs.
• Generally happens only in plants.
• Potatoes, oats, bananas, apples, strawberries…