Section 6-4

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Section 6-4Traits genes

• Write everything that is BLACK

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KEY CONCEPT Genes encode proteins that produce a
diverse range of traits
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State Standards

• 4. Genes are a set of instructions encoded in the
  DNA sequence of each organism that specify the
  sequence of amino acids in proteins
  characteristic of that organism. As a basis for
  understanding this concept
• D. Students know specialization of cells in multi
  cellular organisms is usually due to different
  patterns of gene expression rather than to
  differences of the genes themselves.

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The same gene can have many versions

• Alleles are made up of genes. A Gene is a piece
  of DNA that directs a cell
• to make a certain protein
• Each gene has a locus,
• a specific position
• on a pair of
• homologous chromosomes

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• Again a gene is a piece of DNA that directs a
  cell to make a certain
• protein

DNA Brain POP w/ activity
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• An allele is an alternative form of a gene
• Each parent donates one allele for every gene

• Pea plants have 2 alleles for shape - they
  receive one from each parent
• For shape, there is a wrinkled allele and a round
  allele

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• What are proteins made of?
• Proteins are made up of smaller building blocks
  called amino acids,
• joined together in
• chains. There are 20
• different amino acids.
• Some proteins are just
• a few amino acids long,
• while others are made
• up of several
• thousands.

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Gene Expression Transcription The majority of
genes are expressed as the proteins they encode.
The process occurs in two steps Transcription
DNA ? RNA Translation RNA ? protein Taken
together, they make up the "central dogma" of
biology DNA ? RNA ? protein.
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Genes influence the development of traits

• All of an organisms genetic material is called
  the genome
• A genotype refers to the actual genes
• A phenotype is the physical expression of a trait

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Genotype

• The gene combination of an organism
• It consists of 2 alleles
• For example
• Pure dominant, 2 dominant genes
• Pure recessive, 2 recessive genes
• Hybrid, 1 dominant and 1 recessive gene

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Phenotype

• The way an organism looks
• No matter what genes are present, phenotype of a
  tall pea plant is tall and a short pea plant is
  short

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• A dominant allele is expressed as a phenotype
  when at least one allele is dominant
• A recessive allele is expressed as a phenotype
  only when two copies are present
• Dominant alleles are represented by uppercase
  letters
• Recessive alleles by lowercase letters

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Mendels observed traits

• Dominant traits covers up the other traits
• Recessive traits traits that disappear
• Rule of Dominance When a dominant trait is
  present the recessive trait is hidden

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Step 1
Label the dominant and recessive traits
R Red flower r Purple flower
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Step 2
Write the genotypes of each parent to be crossed
Purple (since it is recessive it has to be
homozygous)
Hybrid Red (means heterozygous)
Rr
rr
Rr x rr
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Step 3
Set up the punnett square. Each parent will give
up one gene or the other so there will be one
gene per box for each parent
R r
r r
Rr rr Rr rr
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Step 4 Analyze the genotypes
2 of the 4 (50) offspring will be pure recessive
2 of the 4 (50) will be hybrids
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Step 5 Analyze the phenotypes
Punnett Square Handout
50 of the offspring will be red
50 of the offspring will be purple
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DNA Structure and Function
DNA Model Lab

• DNA contains the genetic information that codes
  for the RNA and proteins necessary for cell
  function.
• All DNA in the chromosomes has to be copied
  (replicated) and transmitted to daughter cells
  via mitosis.
• Non-faithful replication or inability to correct
  errors and damage to DNA results in mutations.
• Structure of DNA

A Adenine T Thymine C Cytosine G Guanine RNA
ONLY U Uracil
Four nucleotides (A,T,C,G) are chemically joined
through sugar and phosphate molecules in the
backbone.
During synthesis of mRNA (where U is used instead
of T)
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RNA carries DNAs instructions

• The central dogma is the basic concept proposed
  by Crick (one of the scientists that discovered
  DNA)
• It states that information flows in one
  direction from DNA to RNA to proteins

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• The central dogma includes three processes

Brain POP- Mutation

• Replication
• Transcription
• Translation

Transcription DNA ? RNA Translation RNA ?
protein

• RNA is a link between DNA and proteins

Mistake in Replication Mutation
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• RNA differs from DNA in 4 ways

• RNA has a ribose sugar
• RNA has uracil instead of thymine
• RNA is a single-stranded structure
• RNA can leave the nucleus and go into the
  cytoplasm DNA cant

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Transcription makes three types of RNA

• Transcription copies DNA to make a strand of RNA

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• The RNA strand detaches from the DNA once the
  gene is transcribed

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Amino acids are coded by mRNA base sequences

• Translation converts mRNA messages into
  polypeptides (protein)
• A codon is a sequence of three nucleotides that
  codes for an amino acid

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• A change in the order in which codons are read
  changes the resulting protein

• Regardless of the organism, codons code for the
  same amino acid

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Amino acids are linked together by a peptide bond
to become a protein

• An anticodon is a set of three nucleotides that
  is complementary (opposite) to an mRNA codon
• An anticodon is carried by a tRNA transfer RNA
  (translation)

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Transcription vs. Translation Review

• Transcription
• Process by which genetic information encoded in
  DNA is copied onto messenger RNA
• Occurs in the nucleus
• DNA mRNA (DNA unzipped)

• Translation
• Process by which information encoded in mRNA is
  used to assemble a protein at a ribosome
• Occurs on a Ribosome
• mRNA protein

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Why are proteins important?

• Well, for starters, you are made of proteins. 50
  of the dry weight of a cell is protein of one
  form or another. Meanwhile, proteins also do all
  of the heavy lifting in your body digestion,
  circulation, immunity, communication between
  cells, motion-all are made possible by one or
  more of the estimated 100,000 different proteins
  that your body makes.
• Here are several examples of how RNA codes for
  amino acids. These codons are for tryptophan, the
  amino acid that contributes to the sleepy feeling
  you may have after eating turkey phenylalanine,
  an amino acid used in the aspartame sweetener in
  diet soda tyrosine, an important amino acid in
  intracellular signaling processes and cystine.

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• Genes control the genetic traits, and genes are
  DNA, which is organized into chromosomes

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Codon Bingo Lab
Brain POPs next slide
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Brain POPs

• Genetics w/ vocab sheet
• Genetic Mutations w/ vocab sheets