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Genetics
What is genetics?
Study of how traits are passed from parent to offspring
Vocab
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Trait: Physical characteristic (hair color, eye color)
Heredity: Passing of trait from parent to offspring
Allele: Different form of a trait (blue or brown eyes)
Dominant: The trait expressed when two alleles are present
Recessive: The trait hidden when two alleles are present
• Pure breed: Two of the same genes. 2 recessive or 2
Dominant
• Hybrid: One of each gene. 1 dominant and 1 recessive
Transmission of characteristics from
parent to offspring is called
___________________.
heredity
The science that studies how those
characteristics are passed on from one
generation to the next is called
Genetics
____________
Different genes
for a the same
trait are called
ALLELES
___________.
Eye color is an
example
http://sps.k12.ar.us/massengale/genetics%20tutorial.htm
Method of Heredity
• Heredity is possible due to Chromosomes.
• Each chromosome contains hundreds of
genes that carry the genetic code for traits
• To make sure the species survives there
are two ways to reproduce using
Chromosomes.
• Mitosis (making the exact copy of the cell)
• Meiosis (cutting the chromosome number in half so
when they join it will make a complete full set)
Chromosomes
• 2 main jobs
• Direct actions of cell parts
• Allow cells to reproduce
• Found inside the nucleus of the cells
• Two types of cells
– Body cells (liver, skin, stomach, muscle, etc.)
• Have full set of chromosomes in pairs
– Sex cells (egg and sperm)
• Have a half of set of chromosomes 1 copy of each
chromosome
Group of chromosomes
Chromosomes Continued
• Because sperm and egg have ½ a set of
chromosomes; when they meet they make
a complete set.
Each
chromosome
is made of
tightly coiled
DNA strands.
Genes
• Genes are the small sections of a
chromosome that determine a specific trait
• There are thousands of traits for every
living thing.
• Every gene has a pair on the other
chromosome of the same pair.
Passing of trait on genes
• Each sperm and egg have one copy of a
gene from their original owner.
Gregor Mendel
•father of genetics
•studied the inheritance traits
in pea plants.
• Mendel showed that the
inheritance of these traits
follow two particular laws.
Mendel’s Experiments
• Did his work with peas for four reasons:
– Peas are simple plants with little number of
traits
– Peas are cheap to grow compared to humans
– Peas have a quick life cycle
– Peas were available for use
Mendel’s results
Trait
Dominant trait
Recessive trait
Total
Color of pod
Green-428
Yellow-152
580
Shape of pea
Round-5474
Wrinkled-1850
7324
Color of pea
Yellow-6022
Green-2001
8023
Flower color
Red-705
White-224
929
Law of Segregation
• The Law of Segregation states that when any
individual produces gametes (egg or sperm), the
copies of a gene separate, so that each gamete
receives only one copy.
• A gamete will receive one allele or the other.
• In meiosis the chromosomes get separated and
the alleles with the characters are segregated
into two different gametes.
Law of Independent Assortment
• Alleles of different genes assort independently of one another
during egg and sperm formation.
• So there is no relation, for example, between a cat's color and
tail length.
• This increases genetic diversity by producing different genetic
combinations.
• In independent assortment the chromosomes that end up in a
newly-formed offspring are randomly sorted from all possible
combinations of mother and father chromosomes.
• Because gametes end up with a random mix instead of a predefined "set" from either parent, gametes are therefore
considered assorted independently.
• The offspring can end up with any combination of traits.
• For human gametes, with 23 pairs of chromosomes, the
number of possibilities is 2^23 or 8,388,608 possible
combinations.
Review
• Alleles are different expressions of a
single trait (different eye colors)
• Gregor Mendel is the first person who
studied genetics using peas
• He developed two laws
– Law of segregation you only get 1 copy of a
trait from each parent
– Law of independent assortment each trait will
separate randomly
• Using these two laws and a
little more information you can
determine the possible
outcome of offspring.
• The possibilities are calculated
in a tool called a punnett
square.
DOMINANT
Gene
__________________ = An
allele that is expressed in
the presence of a weaker
allele.
RECESSIVE
Gene
__________________ = An
allele that is not expressed
in the presence of a
dominant Allele
• Homozygous= the same genes (AA or BB
or aa or bb) it also means pure bred.
• When an egg or sperm are made from a
Homozygous trait it only has one type of
gene to give both are the same.
• Heterozygous= different genes (Aa or Bb)
it also means hybrid.
• When an egg or sperm are made from a
heterozygous trait it can give either the
dominant or recessive gene.
HOMOZYGOUS/
HETEROZYGOUS
When alleles in the pair are
the same the organism is called
HOMOZYGOUS or ______
PURE
_________________
TT
tt
EX: ____
or ___
When both alleles in the pair are Different,
the organism is __________________
HETEROZYGOUS or
HYBRID
___________
Tt
Ex: ____
DOMINANT/RECESSIVE
_____________
Dominant allele is represented by a
capital letter.
(usually the first letter of the trait)
Recessive allele is represented by the
____________
(SAME) lower-case letter.
T
EX: Tall = ______
Short
t
NOT
=______
S for short
DOMINANT TRAIT
eye color
brown eyes
vision
farsightedness
normal vision
normal vision
normal vision
dark hair
non-red hair
curly hair
full head of hair
widow's peak
RECESSIVE TRAIT
grey, green, hazel,
blue eyes
normal vision
nearsightedness
night blindness
color blindness
blonde, light, red hair
red hair
straight hair
baldness
normal hairline
dimples
unattached earlobes
freckles
broad lips
no dimples
attached earlobes
no freckles
thin lips
hair
facial features
Digits
other
Dominant Trait
Recessive trait
extra digits
fused digits
short digits
fingers lack 1 joint
limb dwarfing
clubbed thumb
double-jointed
immunity to poison ivy
normal pigmented skin
normal blood clotting
normal hearing
normal hearing and speaking
normal- no PKU
normal number
normal digits
normal digits
normal joints
normal proportion
normal thumb
normal joints
susceptibility to poison ivy
albinism
hemophilia
congenital deafness
deaf/ mute
phenylketonuria (PKU)
Expected and Observed results
• Knowing the outcome of offspring an
individual may have could be helpful
• A punnett square is used to show all the
possible combinations of offspring parents
may have.
• Knowing the genetic make up of the
alleles is all you need to make it happen.
Reading a punnett Square
• Two things can be read from a punnett
square.
• Genotype: The actual genes that make up
the trait
• Ex: AA, or AaBb
• Phenotype: The physical appearance of
the trait
• Ex: blue eyes, brown hair
Punnett Squares
• You can mathematically find the percent of
off spring by using this method
• You can figure out the chances of having a
boy or girl
• Using a punnett square with plants you
can figure out what color flowers will
bloom, or whether the plants will be short
or tall.
Making Punnett Squares
• The first step is to separate the parents genes (just like
the egg and sperm)
• If one of the parents is T T for Tall plant and the other
parent has t t for a short plant
• Place the genes on the outside
of the box for the parents.
• Then place the letters on
the inside of the box.
• The results inside the box are
the possible offspring of
the parents
•A punnett square of
multiple parents is on the
sheet to the left.
• The first Punnett square
has been filled in for you.
TT
TT
TT
Tt
TT
TT
Tt
tt
•Fill in the other 3 punnett
squares into your
notebook
•For the first and last example:
•100% chance for a
Homozygous Offspring.
TT
TT
Tt
Tt
tt
tt
•For the second example:
•25% recessive
tt
tt
•75 % dominant
• The punnett squares in the
examples you just filled in where
for one trait these are called
Monohybrid Crosses
• One = Mono
• The next examples are for two
traits or Dihybrid Crosses
• Two = Di
Dihybrid crosses
• We will look at two traits say Heterozygous
Eye Color (A) and Hair Color (B)
• Since there are more than one
combination of gene you need to find out
the four different combinations that can
occur with the cross.
• To find the correct combinations we use
F.O.I.L.
F.O.I.L
• First, Outer, Inner, Last letters of each letter.
• The first parent has the following genotype:
• A* a** B* b*
• first combination is AB the First letter of each
gene.
• The second will be Ab the Outer letters of the
parent.
• The third combination will be aB the Inner
letters.
• The last combination will be ab the Last
letters
F.O.I.L. Combinations
• So the parents sperm and egg can make 4
different possible combinations of genes
for two traits.
• AB, Ab, aB, and ab
• These combination get put onto the
outside of the di-hybrid cross punnett
square.
From here it is the
same as the one
trait cross.
AA BB
AA Bb
Aa BB
Aa Bb
Place the two A’s
into the box
AA Bb
AA bb
Aa Bb
Aa bb
Then the two B’s
Aa BB
Aa Bb
aa BB
aa Bb
Always place the
A’s before the B’s
Aa Bb
Aa bb
aa Bb
aa bb
Practice problem 1
• Parent 1 is Heterozygous for trait (A)
• Parent 2 is Heterozygous for trait (A)
• What are the parents Phenotypes and
Dominant and _______
Dominant
genotypes? Phenotype ________
Aa
Aa
Genotype _____
and _____
• Fill in the Punnett square below
A
a
A
AA
Aa
a
Aa
aa
Practice problem 2
• Parent 1 is Homozygous for trait (a)
• Parent 2 is Heterozygous for trait (A)
• What are the parents Phenotypes and
Recessive and _______
Dominant
genotypes? Phenotype ________
aa
Aa
Genotype _____
and _____
• Fill in the Punnett square below
a
a
A
Aa
Aa
a
aa
aa
Practice problem 3
• Parent 1 is Homozygous for trait (A)
• Parent 2 is Homozygous for trait (a)
• What are the parents Phenotypes and
Dominant and _______
Recessive
genotypes? Phenotype ________
AA
aa
Genotype _____
and _____
• Fill in the Punnett square below
A
A
a
Aa
Aa
a
Aa
Aa
Review
• Chromosomes are threadlike parts of a cell that
control traits
• Body cells have 2 times as many chromosomes
as sex cells
• Dominant traits keep recessive traits from
showing
• An individual that is Heterozygous (Aa) can
make two types of sex cells (A) or (a) an
individual that is homozygous (AA) can make
only one (A)
Review
• The punnett square helps to predict the
combinations of genes in all offspring
• Expected results are predicted. While
Observed results are what we see.
• Mendel reported how traits were inherited
in pea plants
• Mendel explained the basic principles of
genetics and inheritance.