Transcript DNA and Heredity - Dr. Diamond`s Website

DNA and Heredity
What Mendel didn’t know
Genes
• Are on chromosomes
• Chromosomes are
made of DNA (+
protein)
• DNA is composed of
subunits called
nucleotides
• There are two basic
types of nucleotides
(one ring or two ring)
Nucleotides
• 4 different nucleotides
–
–
–
–
Adenine (2-ring)
Thymine(1-ring)
Guanine (2-ring)
Cytosine (1-ring)
• Chargaff’s rule
– The amount of adenine in
DNA is always = to the
amount of thymine
– The amount of guanine is
always = to the amount of
cytosine
DNA Structure
• DNA has a ‘twisted
ladder’ structure
(double-helix)
• Nucleotides pair
specifically to make
two sides of the
ladder
• A–T
• G–C
Base-pairing rule mnemonic
• All Tigers Can Grin
(A with T; G with C)
DNA (Chromosome) Replication
• How do
chromosomes copy
themselves?
• DNA ‘unzips’
• Each side of ladder
serves as a template
• More nucleotides
come to base-pair
with existing
nucleotides
Summary
From cell to DNA
More about traits
• Incomplete
dominance
– Not like blending paint
– White is an absence
of color
– Less color means
you get pink instead
of red
Still more…Traits
• One gene may affect
more than one trait
• Mendel observed that
– Plants with colored
seed coats had
colored flowers
– Plants with colorless
seed coats had white
flowers
• Tiger has white coat
and blue eyes
More…. About traits
• More than one gene
may affect a trait
(e.g., height, skin
color, eye color)
• These are polygenic
traits (controlled by
multiple genes)
• Results in a range of
outcomes
And yet more… about traits
• Environmental
influences (e.g.,
nutrition, temperature)
• In Siamese cats,
production of dark
color depends on
temperature (cooler
temperature on ears,
tail, paws, face)
From Gene to Trait
• Genes are made of
DNA nucleotides
• The order of the
nucleotides
determines the gene
product
• To express a gene, it
must first be copied
Gene Product
• Copying takes place in
the nucleus (where the
DNA is located; the
‘master’ recipe)
• The copy (of the recipe
for the gene product)
goes to the cytoplasm
• The recipe is read by the
ribosome
• A protein is made
according to the recipe
Changes in Genes
• Each ‘word’ in the recipe
has three letters
(nucleotides)
• A change in a word is
called a mutation
• It may cause a change in
the recipe for a protein
• A mutation may be
helpful, harmful or neither
• Sickle cell anemia is an
example of the result of a
harmful mutation
Pedigrees
(Family Trees)
• Used to trace a trait
through a family
• Important for genetic
counselors in tracking
a hereditary disease
• Example – hemophilia
in the British royal
family
Hemophilia in the British royal
family
Other examples