Download Bt - Biology

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Genetics is the study of heredity

Inherited characteristics are called traits.
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Phenotype :What you look like
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Genotype:What genes you have
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
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combination of genes in an organism
genotype usually determines the phenotype
Genotype does not always 100% determine phenotype
We can see this clearly in Identical twins who although
they share ALL of their genes they do not always appear
the same.
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A gene is a segment of DNA that is the code to make a protein

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Is starts at a start codon (code says start here!) and goes to a stop ( the
same section that enzyme translated)
Why did we spend so much work making that protein?
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Depending on what kind of protein that you make will change the trait
that you have.
 *Trait
 Blue or brown eyes
 Tall or short
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How does this affect me?
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Your body is run, maintained, and defined by the proteins working in our
cells
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Dominant

Represented by a capital letter and indicates that if this
gene is present this trait will be exhibited
 Free hanging earlobes= F
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Recessive

Represented by a lowercase letter and indicates that if both
genes passed on this trait will be exhibited, but if a
dominant gene is present then the recessive gene will not
be exhibited.
 Attached earlobes are = f
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
You have two genes for the same trait.
One was given to you by your mother, and one was
given to you by your father.
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The law of segregation
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states that gene pairs separate during gamete formation.
So you only pass on either the gene from your mother, or
father.
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Genes can exist in alternative forms
These are called alleles.
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Tall or short alleles
You can carry dominant, or recessive alleles, or one of
each ( one from each parent) Or two of the same
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Dominant Recessive
For Peas
Seed Seed Flower Flower
shape color color position
Pod
color
Pod
Plant
shape height
green
inflated
tall
constricted
short
Dominant
trait
round yellow purple
axial
(side)
Recessive
trait
wrinkled
green
white
(tips)
terminal yellow
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
Worked at a tutor, but really wanted to work do
experiments.
He joined a monastery, and was placed in charge of
gardening where he spent the rest of his life raising
food for the monks, but more important to Mendel
was working with and studying pea plants, and their
offspring.
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Homozygous

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Pure
Heterozygous
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Hybrid
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Why Peas?
Dominant
trait
Seed
shape
Recessive
trait
1. 1.Peas are easy to
raise
2. 2.He noticed that
there were a lot of
pairs of contrasting
traits. Tall short
yellow green
3. Pea plants
reproduce sexually
1. He could contol
2. Self pollination
3. Inbreeding to
produce pure
lines of traits
4. Can prevent self
pollination
5. He could choose
which plants
bred
Flower
Pod
position shape
Pod
Seed Flower
color
color
color
Plant
height
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
One trait at a time.
Mendel used Punnett squares to show possibilities
and predict ratios of offspring.
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Dominant traits are written with Capital letters, and
recessive traits are with lowercase letters
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


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
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Write down the problem.
List the Genotype of the parents.
Form the gametes. ( law of separation)
Make a Punnett square
List the genotype of the offspring
List the phenotype of the offspring.
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1 read / or write down the problem
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Cross a herterozygous brown eyed dog with a with a hybrid brown eyed
dog
2.
This means Bb x Bb
3.
B, b x B, b
4. 
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5.

6.
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25% BB or ¼
50% Bb or ½
25% bb ¼
#4
B
b
B
BB
Bb
b
Bb
bb
75% or ¾ Brown
25% or ¼ yellow
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

So lets do a problem together
Y= yellow seed color and y= green seed color
 Note that yellow seed color is dominant.
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
Cross a pea plant that is Homozygous for yellow
seed with a plant that is pure for green seeds.
Cross a hybrid yellow see with a green seed
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
P1 generation (P stands for “parent”)
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F1 generation (F stands for “filial”-son or daughter)
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This would be your parents
This would be you
F2 generation
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Your children
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Next we will work with two traits at once , and do a
Punnett square.

Do this problem (back of your last page.)
The Six steps!!!.
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
1 read / or write down the problem
B=Brown eyed b= blue eyed
T= Tall
t= short
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Cross a homozygous Tall, homozygous brown eyed man
with a
Homozygous short homozygous blue eyed woman
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
2.

3.
B,B,T,t x B, b, T,t
4. 
5.



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This means BBTT xbbtt
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bt
bt
bt
bt
BT
BbTt
BbTt
BbTt
BbTt
BT
BbTt
BbTt
BbTt
BbTt
BT
BbTt
BbTt
BbTt
BbTt
BT
BbTt
BbTt
BbTt
BbTt
BbTt= 100%
6.

#4
Brown eyes Tall =100%
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

2. BB,TT x BbTt
3. BT, BT, BT, BT x BT, Bt, bT, bt
#4
BT
BT
BT
BT
BT
BBTT
BBTT
BBTT
BBTT
Bt
BBTt
BbTt
BBTt
BBTt
bT
BbTT
BbTT
BbTT
BbTT
bt
BbTt
BbTt
BbTt
BbTt
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.
.
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#4
BT
.
BT
BBTT
BT
BBTT
BT
BBTT
BT
BBTT


Bt
bT
BBTt
BbTT
BbTt
BbTT
BBTt
BbTT
BBTt
BbTT



bt
BbTt
BbTt
BbTt


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Step 5
BBTT=4 =1/4
BBTt=4=1/4
BbTT=4=1/4
BbTt=4= 1/4
.
BbTt
Step 6
Brown eyed tall =16 or 100%
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BT
Bt
bT
bt
BT
BBTT
BBTt
BbTT
BbTt
Bt
BBTt
BBtt
BbTt
Bbtt
bT
BbTT
BbTt
bbTT
bbTt
bt
BbTt
Bbtt
bbTt
bbtt
9:3:3:1 ratio
9 Brown Tall
3 Brown short
3
blue tall
1 blue short
•
Incomplete dominance
–
The two genes that a person can carry can create three
different phenotypic results
–
For instance on page 316 ( chapter 12.20 in your book
there is an example of the snapdragon
• When a snapdragon has
– RR the flower color is red
– WW the flower is white
– RW, the flower is the third color Pink.
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When neither allele is completely dominant the letters R and R’
are used
R’ is pronounced “R prime”
R would be like R for red, and R’ would be for white.
Remember in reality the letter just represents the gene we are
talking about, and any letter can be used. R’ is how scientists
identify that the gene is another Dominant gene for a trait.
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Co-dominance
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The two genes can carry can create three different
phenotypic results
For instance on page 317 ( chapter 12.20 in your book
there is an example of the chickens….
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Sex linked inheritance when a gene is found on
the x chromosome
Color Blindness
Xr Y – Color blind man.
Xr Xr – Color blind woman
XRXr – Carrier
XRXR – cannot have color blind children
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Some traits have multiple alleles possible for them
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Blood type is one such instance
There are three different alleles for blood type
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A, B, and o
 A, and B are co-dominant
 o however is recessive to both
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So what combinations of genes can you have for
blood type?
What blood type do you have?
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Brown Blue grey green, and hazel all result from
different combinations of genes.
Brown typically is dominant to all of these, but as
seen with hazel eyes brown can be present along
with other colors.
Polygenic trait
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
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Polygenic inheritance: means that more than one
gene determines the trait expressed
These genes can be on multiple chromosomes
A good example of this is skin colors
Additive
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So what combinations of genes can you have for
blood type?
What blood type do you have?
Who can you give blood to?
Who can give you blood?
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