DNA, Mutations, Chromosomes,
and Reproduction Review
DNA: The Genetic Code
• Genes
– main function 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
DNA Structure
• DNA structure
– 4 Nitrogen bases: Adenine (A),
Thymine (T), Guanine (G), and
Cytosine (C).
– Form the rungs of the DNA “ladder”
– Adenine always binds with Thymine
– Guanine always Binds Cytosine
• RNA
– Thymine is replaced by Uracil
– So Adenine binds with Uracil
Genes
• A section of DNA
– Contains the
information to code
for one specific
protein
– Made up of a
series of bases in
a row
Making Proteins
• During protein synthesis, the cell uses
information from a gene on a chromosome
to produce a specific protein
Mutations
• Any change in a gene or chromosome
– Can cause a cell to produce an incorrect
protein during protein synthesis
– The trait or phenotype may be different
• Body cell mutations will not be passed on
to offspring
• If the mutation is in a sex cell, the mutation
can be passed on to an offspring and
affect the offspring’s phenotype
Question
• If a cat gets hit by a car and loses a leg,
does this mean it will have kittens that are
also missing a leg?
Effects of Mutations
• Introduce changes in an
organism
– Can be a source of genetic
variety
– Some are harmful, some are
helpful, others are neither
helpful nor harmful
• A mutation is harmful if it
reduces the organism’s
chance for survival and
reproduction
Chromosome Theory of Inheritance
• Sutton discovered that sex cells contain
half the number of chromosomes as body
cells.
• One set of alleles comes from the male
parent; the second set comes from the
female parent
• Chromosome theory of inheritance
– Genes are carried from parents to their
offspring on chromosomes
Mitosis
• Mitosis (asexual reproduction)
– No change in genetic variability
– No genetic loss from meiosis or
recombination
– Good in stable environments…ones that are
NOT always changing
– Occurs in body cells
– Results in 2 cells
– Results in cells with the same # of
chromosomes as the original parent cell
Meiosis
• Sexual Reproduction
– Rearranging the genome creates variability
– Almost 50% of genetic material is lost during
recombination
– Good in variable environments…ones that are
always changing
– Occurs only in sex cells
– Results in 4 cells
– Results in cells with half the chromosome #
as the parent cell