Download GENETICS

•In the 19th century Gregor Mendel, an Austrian
monk, discovered that living things inherit their
physical feature due to discrete genetic traits that
we now call GENES.
•We know that these traits are made of DNA.
http://learn.genetics.utah.edu/
What is DNA?
• DNA (deoxyribonucleic acid) is a molecule
that contains all the instructions and
What is DNA?
information
to:
 Help and organism live and grow.
 Allow cells to? know what role they play
in the body.
• DNA is found in the nucleus of eukaryotic
cells as well as in bacterial cells.
• DNA can contain information due to it’s
structure.
• DNA is a long molecule made
in the form of a double helix
(twisted ladder)
What is DNA?
• The “rungs” are built with 4 DNA “letters” or
bases A, C, T & G.
?
 A always pairs with T
 C always pairs with G
A -> adenine
C -> cytosine
T -> thymine
G -> guanine
What is a Gene?
• Genes (“ DNA words”) are parts of the DNA
molecule made of groups base pairs triplets
(“3 DNA letters = 1 word or gene)
• Each gene instructs the body to make 1
protein
• These proteins include enzymes, structural
proteins, hormones etc. Together these
proteins allow an organism to live, grow and
have specific characteristics.
What is a Chromosome ?
• If the DNA in one cell were stretched out into
one line it would be 3 meter long.
• To fit into the cell the DNA is packaged into
compact units called chromosomes.
• To fit all of the DNA into chromosomes the
DNA is first twisted into a double helix then
further twisted around protein molecules.
• Humans have 23 pairs of chromosomes giving
a total of 46.
(see cell size & scale)
• Organisms that reproduce sexually get half of
their genetic material from the female parent
and half from the male parent.
• In humans the genetic material from one
chromosome in each pair comes from the
mother and genetic material from the other
chromosome in the pair comes from the
father.
• The sex chromosomes are both the same in a
female (XX) but different in a male (XY).
• Only a male parent can pass on a Y
chromosome therefore it is the male parent
who determines the gender of the child.
What is Heredity?
• Heredity involves the passing down of “traits” from
parents to their children
• Our genes encode instructions that define our traits.
• The environment can also affect our traits (ex hair gets
lighter in the sunlight).
• Humans have two complete sets of 23 chromosomes (2
x 23=46)
• To pass down genetic traits to an offspring -> each
parent gives 1 set (23) of chromosomes to their child
What is a trait?
• A trait is a notable feature or quality in a person.
• We inherit a unique combination of traits from
our parents.
• We pass a different combination of traits to our
children.
• Traits can be:
–Physical (ex eye colour or height).
–Behavioural (ex a dogs instinct to fetch)
–Medical -> these give a predisposition to a
disease or condition such a diabetes or sickle
cell anemia
HOW WE INHERIT TRAITS
• For each trait we have 2 alleles (one from each parent).
• Some alleles have the code for a dominant trait
(the trait is seen) other alleles are recessive (the
trait can be hidden).
• For each trait we might have:
 2 dominant alleles or 2 recessive alleles
(Homozygous -> both alleles are the same)
 1 dominant & 1recessive allele
(Heterozygous -> both alleles are different)
• http://www.cellsalive.com/