Download Mendelian Genetics Notes

 Genes & Alleles
 Genotype & Phenotype
 Homozygous & Heterozygous
Gregor Mendel known as::
THE FATHER OF GENETICS.
- laid the foundations for the SCIENCE
OF GENETICS through his study of
inheritance patterns of traits in pea
plants.
What is heredity or inheritance?
 Passing of traits from parent to offspring
or from one generation to the next.
 Genes are the coded instructions that
define our traits.
How are genes inherited?
 Humans have 2 sets of chromosomes for a total of
46 chromosomes. Each parent contributes only 1
set of chromosomes to their child.
 When a sperm cell (23 chromosomes) and an egg
cell (23 chromosomes) join during fertilization, it
results in a zygote (46 chromosomes).
What is a trait?
 Notable feature or quality in a person.
What are the two types of traits?
 Physical traits are traits that can be
seen such as eye or hair color
 Behavioral traits demonstrate the way
one acts such as “the fetching behavior
of golden retrievers”.
Phenotype
 Phenotype is another word for physical
trait (in other words, it describes how
someone looks)
 Examples of phenotypic words are:
tall, short, brown hair, straight hair, fat,
skinny, fair skin, freckles, etc.
Can you think of anymore?
On your notes, write at least 4 phenotypic
words that describe YOU!
REMEMBER!!
 Phenotype describes things you can see!!!
What do you think person’s phenotype
would be?
How would you describe this phenotype?
 REMEMBER: Mom gives you one half of
Remember??
your genes, and your dad gives you the
other half….
 sperm + egg = YOU!
Together, these two genes (one from mom
and one from dad) represent your genotype
 Each gene is represented by one letter.
Genotype
 Genotype is the genetic makeup of an
organism’s traits represented by letters
Genotype codes for phenotype
T = tall
t = short
The factors that carry all traits =
Two different forms of the same gene =
Example
 Gene = height
 Alleles = tall; short
Example
 Gene = eye color
 Alleles = green, blue, brown
Example
 Gene – hair texture
 Alleles – straight, wavy, curly
Example
 Gene – thumb
 Alleles – hitchhiker’s thumb, straight thumb
Dominant vs. Recessive
 Think of a person who never lets you talk during a
conversation – that person DOMINATES the
conversation.
A Dominant Allele: allele that is
expressed (the one that you see).
A Recessive Allele: allele that is masked
or hidden (not shown)
Which allele is
expressed over another
and represented by a
capital letter?
Which allele is usually
masked or appears less in
the population and
represented by a
lowercase letter?
Dominant or Recessive?
A
F
r
h
G
t
d
Check Yourself
A – dominant
F - dominant
r – recessive
h - recessive
G - dominant
t - recessive
d - recessive
B = brown hair b = red hair
homozygous
for brown hair
heterozygous
for brown hair
 When both
alleles are the
SAME it is called
HOMOZYGOUS
homozygous
for red hair
 When the alleles
are DIFFERENT it
is called
HETEROZYGOUS
Homozygous or Heterozygous?
RR
Jj
tt
Hh
aa
Check Yourself
RR - homozygous
Jj - heterozygous
tt - homozygous
Hh - heterozygous
aa - homozygous
You inherit two alleles for each gene (trait).
1 from MOM!
 PHENOTYPE –
physical
characteristics that
you SEE
1 from DAD!
 Ex. Straight
hair, red hair,
freckles, lactose
intolerant, tall,
blue eyes
 GENOTYPE –
 Ex. RR, Tt,
genetic makeup
represented by
letters
Ffgg, YyEePp
Mendel’s 1st Law of Inheritance
 Principle of Dominance: when there
is a dominant allele and a recessive
allele inherited together for a particular
gene, the dominant allele will ALWAYS
be expressed.
Dominant
Brown
hair
allele
Recessive
red
hair
allele
Express the dominant
allele for brown hair