What determines
who we are?
Genes
and
Chromosomes
Evolution
• Evolution is the process by which species
change over time.
• This is done by natural selection: random
changes to an animal are passed on if
those changes help the animal survive and
reproduce.
• These random changes are called
mutations. How do they happen?
Mutations
• Mutations are random changes to the genetic
information of a plant or an animal and can
cause the animal to grow in a new and different
way.
• Most mutations are neutral – they do not affect
an animal’s fitness positively or negatively.
• Some mutations are negative – such as
deformed limbs or malfunctioning organs.
• Some mutations are positive – such as larger
brains, webbed feet, or better camouflage.
Genes
• Genes hold your
personal information
• They control hereditary
traits like eye colour
and body function
• Genes are segments
of DNA
• DNA makes up your
chromosomes
• Each human cell has
23 pairs of chromosomes
Chromosomes
• There are 22
autosome pairs
and one pair of
sex chromosomes
• Sex chromosomes
control gender
• Females have 2 X chromosomes and
males have an X and a Y chromosome
• Autosomes determine other traits
So what does this have to do with
mutation?
• Mutation happens at the genetic level
• This happens when the information in the
genes gets mixed up
• We know certain syndromes come from
mutations in specific chromosomes:
-for example Down’s Syndrome comes
from having an extra chromosome 21
• One possible mutation:
Recap (1)
• Cells contain chromosomes
• Each chromosome is made up of DNA
• A segment of DNA which controls a trait or
body function is called a gene
• When the information in genes is mixed up
it is called mutation
• Mutations may or may not change an
individual for better or for worse
Recap (2)
• When the mutation helps, the individual is
more likely to reproduce and pass on the
mutation to future generations.
• When the mutation is harmful, the
individual is less likely to reproduce.
• This process is called evolution by natural
selection and allows species to change
over long periods of time.
Dominant vs. Recessive Genes
• We get one set of 23 chromosomes from each
parent
• When the gene
from one set
overrules the gene
from the other set,
that gene is called
“dominant”.
• The other gene is
called “recessive”.
• The gene for brown eyes is dominant.
Bibliography of images
• http://www.oncolink.org/library/images/id8181.gif
• http://ghr.nlm.nih.gov/handbook/illustrations/chro
mosomes.jpg
• http://www.biologyonline.org/images/gene_inversion.gif
• http://www.ashg.org/images/dominant.jpg
• http://www.detectingdesign.com/images/Defining
Evolution/defini8.jpg
• http://evolution.berkeley.edu/evosite/evo101/ima
ges/drosophila_experiment.gif