Transcript DNA and Sex Chromosomes

DNA and Sex
Chromosomes
DNA Structure
 The DNA structure is like a twisted ladder with
each step made of nitrogen bases
 The four nitrogen bases are:
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Adenine (A)
Thymine (T)
Guanine (G)
Cytosine ( C)
 Adenine only pairs with Thymine
 Guanine only pairs with Cytosine
DNA Replication
DNA replication begins when the two sides of the DNA molecule begin
to “unzip”
 Next, nitrogen bases that are floating in the
nucleus pair up with the bases on each half of the
DNA molecule.
 Because of the way in which the nitrogen bases
pair with one another, the order of the bases in
each new DNA molecule exactly matches the
order in the original DNA molecule
Mendal Revisited
 Earlier we learned about Mendal’s work with pea
plants
 Mendal discovered traits but he did not have
knowledge of DNA or genes
 His work proved that genes existed by no one knew
what they looked like or where they were located
 Enter Walter Sutton…….
Walter Sutton (1903)
 Sutton wanted to now how egg and sperm cells
formed
 While studying grasshoppers he proposed that
chromosomes were the key to why offspring look
like their parents
Sex Cells
The large egg is a female sex cell, and the smaller sperm is a male sex cell
The Chromosome Theory
of Inheritance
 By studying the fretilization of sex cells in
grasshoppers Sutton developed the chromosome
theory of inheritance
 According to the chromosome theory of
inheritance, genes are carried from parents to their
offspring on chromosomes
Meiosis
 Meiosis- the process by which sex cells are
formed; the process by which the number of
chromosomes is reduced by half to form sex
cells—sperm and eggs.
Meiosis I
Meiosis II
Taking a Look Back at
Punnett Squares
Genes
 Although you have only
23 pairs of chromosomes,
your body cells each
contain about
35,000 genes.
 Each gene controls a trait.
The Genetic Code
Proteins
 The main function of genes is to control the
production of proteins in an organism’s cells
 Proteins help to determine the size, shape, color, and
many other traits of an organism
 Recall what DNA is made of
 …..The four nitrogen bases are…?
Order of the Bases
 A gene contains the code for the structure of a
protein
 The order of the nitrogen bases along a gene forms
a genetic code
 That code determines what type of protein will be
produced
Protein Synthesis
 The production of proteins
is called protein synthesis
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During protein
synthesis, the cell uses
information from a gene
on a chromosome to
produce a specific
protein
RNA
Messenger RNA
 RNA that copies the coded
message from DNA in the
nucleus and carries the
message into the
cytoplasm.
Transfer RNA
 RNA in the cytoplasm that
carries an amino acid to
the ribosome and adds it
to the growing protein
chain.