Download L1 Genetics overview

GENETICS
Lesson 1
Introduction and
Terms
Genetics
•  Genetics is the study of heredity
•  In Genetics we look at how characteristics
are passed from one generation to the
next.
•  Genes carry the hereditary information on
chromosomes.
People share 7% of genetic material with the E.coli bacteria,
21% with worms, 90% with mice and 98% with chimpanzees.
Genetics
•  Let us look at the human characteristic of
having a free or attached earlobe
•  Click on the attached lobe
YES This ear is attached
This lobe is FREE
Genetics
Attached lobe
Free lobe
Attached lobe
ee
• Genes occur in pairs
• If we represent the gene for
attached ear lobe as little “e”
• Then this persons gene pair
will be “ee”
Genetic Terms
ee
PHENOTYPE
The characteristic
expressed by the
gene e.g. attached
ear lobe
ALLELE
genes are partners
of each other:“e”
is an allele of “e”
GENOTYPE
The genes that code
for a characteristic
e.g. ee
Looking at the genes on Chromosomes
Attached lobe
e
e
The genes occur
in pairs on
chromosomes
Free lobe
E
E
The gene for free
lobe is “E”
Attached lobe
e
e
Free lobe
E
E
The genes occur at special positions on
chromosomes called loci.
One version of the gene is inherited from
the father , the other from the mother
If the two genes are the same e.g. ee or
EE they are homozygous.
E
e
There can be a mixture of attached and
free ear lobe genes (Ee)- heterozygous.
One gene, in this case (E) is dominant
over unattached lobe (e) which is called
recessive
In this case the E gene completely
supresses the expression of e gene so this
persons will have free ear lobes
Summary Three possible genotypes…
PHENOTYPE
Free lobe
Attached lobe
GENOTYPE
e
e
Homozygous
recessive
E
E
Homozygous
dominant
E
e
Heterozygous
dominant
Examples of different traits
Trait
Genotype
Phenotype
Dominant/
Recessive
Albinism
aa
No skin
pigment
Recessive
Normal skin
(not albino)
AA or Aa
Normal skin
Dominant
Second toe
longest
TT or Tt
Longer
second toe
Dominant
Big toe
longest
tt
Big toe
longest
Recessive
2nd toe longer (Morton’s Toe)
Dominant trait
Albino
Black
Person
Recessive trait
Widows peak
Hitchhkers Thumb
Rolling Tongue
Cleft Chin
Dominant trait
Dimples
Dominant trait?
Assignment
•  Read 181-184
•  Do Patterns of Heredity Worksheet