Download dominant allele

Bell Work: FRIDAY 2/1/13
 Go to page 79 in your science notebook:
Write a journal about what we did in
class yesterday. Discuss some of the
traits you did or did not have.
 On the same page make a “Know and
Wanna Know” chart as it pertains to
Heredity.
 If you have not taken or completed the
test from Wednesday, please see me.
 If you have work to turn in, please put it
in the drawer for your class.
Heredity
• Why don’t you look like a rhinoceros?
• The answer to this question seems simple: Neither
of your parents is a rhinoceros.
• But there is more to this answer than meets the
eye.
• As it turns out, heredity, or the passing of traits
from parents to offspring, is more complicated than
you might think.
• For example, you may have curly hair, while both of
your parents have straight hair. You might have
blue eyes while both of your parents have brown
eyes.
• How does this happen?
Who was Gregor Mendel?
• Read pg. 100
– “Who Was Gregor Mendel?
– “Unraveling the Mystery”
• Gregor Mendel discovered the principles of
heredity while studying the characteristics and
traits of pea plants.
• A characteristic is a feature that has different
forms in a population.
– For example, hair color is a characteristic of humans.
• The different forms, such as brown or red hair is
called a trait.
Review Self Pollination and
Cross Pollination
Pea plants can
also crosspollinate. In
cross-pollination,
pollen from one
plant fertilizes the
ovule of a flower
on a different
plant. There are
several ways that
this can happen.
Pollen may be
carried by insects
to a flower on a
different plant.
Pollen can also
be carried by the
wind from one
flower to another.
Self pollinating
flowers have
both male and
female
reproductive
parts. (pistil and
stamen).
During pollination
the sperm
(pollen from the
anther) attaches
to the stigma
(sticky opening
of the pistil).
self pollination
creates a true
breeding plant.
• Mendel studied one characteristic at a time
as he worked with these pea plants.
• These are some of the plant characteristics
that he worked with.
He was very careful to use only plants that had true breeding
for each of the traits he was studying. That way he would know
what to expect if they were to self pollinate.
He then decided to try cross pollinating with these flowers. He
would pull the anther off of one plant and pollinate another plant
with it. That way he knew the one flower could NOT self pollinate.
He crossed a plant with wrinkled seeds with another plant with
round seeds.
Mendel’s First
Experiments
• One trait was always present in
the first generation, and the
other trait seemed to disappear.
• Mendel chose to call the trait that
appeared the dominant trait.
• Because the other trait seemed
to fade into the background,
Mendel called it the recessive
trait.
• The recessive trait for the white
flower reappeared in the second
generation.
In human terms
• Grandma has blue
eyes.
• Grandpa has
brown eyes.
• 1st generation:
Mom has brown
eyes and so do all
of her siblings.
• 2nd generation:
Three out of four of
mom’s children
have brown eyes.
• The other one has
blue eyes.
Review: Talk with your group…
1. What is heredity?
•
The passing of genetic traits from parent to
offspring
2. Who was Gregor Mendel?
•
Discovered the principles, or ideas, of heredity
3. Which trait is present in the first
generation?
•
Dominant trait
4. Which trait is present in the second
generation?
•
Recessive trait
Review
• How did Mendel make sure that the plant
He removed the anther from one plant
didn’t self pollinate? and then cross pollinated it with another
plant.
• How many plants out of the first generation
were purple?
• How many plants out of the second
generation were purple?
• How many out of the 3rd generation do you
think would be purple?
http://www.indiana.edu/~p1013447/dictionary/mendel.htm
Bell work Tuesday, February 5
Dominant
Recessive
Trait
Charactertics
Heredity
True breeding
Pistil
Stamen
Pollination
Fertilization
Self pollinate
Cross pollinate
FIND A DEFINITION FOR EACH WORD.
Here’s the problem…you can use a maximum of 5
words to define each term. In other words, put it in
YOUR own terms. (hint: look at yesterday’s notes. )
Let’s pick the best definitions for
each word.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Traits and Inheritance
• When Mendel calculated the ratio of
dominant traits to recessive traits, he found
there was a 3:1 ratio.
:
• Mendel knew from his experiment with pea
plants that there must be two sets of
instructions for each characteristic.
• The first -generation plants carried the
instructions for both the dominant and recessive
traits.
• These instructions for an inherited trait are
called genes.
• Each parent gives one set of genes to the
offspring.
The offspring then has two forms of the
same gene for every characteristic- one
from each parent. (pouty lips/thin lips)
The two forms (often dominant and
recessive) of a gene are known as alleles.
The genes we inherit are the same for all
humans. However, how these manifest
(show) themselves is actually determined
by alleles!
Dominant and Recessive Alleles
DOMINANT alleles are shown with a capital
letter . (P for dominant purple flowers).
recessive alleles are shown with a
lowercase letter . (p for recessive white
flowers).
Phenotype & Genotype
 Genes affect the traits of an offspring.
 An organism’s appearance (the way they look) is
known as its phenotype.
 In pea plants, possible phenotypes for the
characteristic of flower color would be purple flowers
or white flowers or it could be a yellow or green seed.
 Phenotypes for humans are much
more complicated than those of peas.
The boy has inherited a trait called
albinism which prevents hair, skin,
and eyes from having normal
coloring.
The genotype of an organism is the entire genetic
makeup of an organism; the combination of genes
for a specific trait.
An organism with two dominant or two recessive
alleles is homozygous (same size letters).
RRSS = round and green
rrss = wrinkled and yellow (remind me next lesson
to discuss what it is called when there are no
dominant alleles.
An organism with one of each (Pp) is heterozygous.
RrSs= round and green
rRsS= also round and green
R= round
r= wrinkled
S=green
s= yellow
Review
1. What is an allele?
2. What is the difference in a gene and an
allele?
3. What is the difference in a phenotype and a
genotype?
4. What is the difference in a heterozygous and
a homozygous allele?
Classwork or Homework- you choose
Label the concept map and paste it in your
science notebook.
Bell Work Tuesday, Feb 12, 2013
JUSTIFY YOUR ANSWER!
Review Genes and Alleles
• The first -generation plants carried the
instructions for both the dominant and recessive
traits.
• These instructions for an inherited trait are
called genes.
• Every person has two genes for each trait. One
is from the mother and the other is from the
father. This is called an allele.
• Some of the traits that we have are based on
simple inheritance where one version of a gene
(dominant allele) masks the expression of the
other version of that gene (recessive allele).
Review
Homozygous and Heterozygous
When an organism has a pair of identical
alleles for a character, they are said to be
homozygous for that characteristic (PP, pp)
When an organism has two different alleles for
a gene (Pp) they are said to be heterozygous
for that characteristic dominance. For that
characteristic, an organism will have one of two
phenotypes.
Review
Genotype and Phenotype
When an organism has the recessive
phenotype, this means that both
recessive alleles must be present (bb).
With recessive traits, we clearly know what
the genotype is if the phenotype is
recessive.
An organism showing the dominant
phenotype can be homozygous or
heterozygous for dominant allele (PP, Pp).
It is more difficult to know genotype when
dominant allele is involved.
Let’s Put It In Human Terms
• For a simple trait like tongue rolling (curling) you have to
have 2 allele. We will label the allele that allows rolling
“R” and if it is an absent allele we will label that as “r”.
• What happens if you have RR?
• Imagine you have rr. What does this mean?
• What do you think will happen if you have Rr?
• Think of recessive as laid back. If R is dominant and r is
laid back, what does this mean for a person who has Rr?
• Does the order of the alleles matter? Talk with your
elbow partner about this.
DOMINANT
Genotypes and Phenotype
recessive
Genotype and Phenotype
RR or Rr – red antennae
rr – green antennae
SS or Ss – three body segments
ss – two body segments
CC or Cc – curly tail
cc- straight tail
LL or Ll – three pairs of legs
ll – two pairs of legs
BB or Bb – blue nose
bb – green nose
GG or Gg – green feet
gg – black feet
EE or Ee – two eyes
ee - three eyes
•Mom’s genotype: Rr, Ss, Cc, ll, bb, gg, ee
•Dad’s genotype: rr, ss, cc, Ll, Bb, Gg, Ee
•Which parent has more dominant genes?
•Describe how each parent will look. (Write the
phenotypes.)
•Get with your elbow partner and work these out!
Mom
___________________
___________________
___________________
___________________
___________________
___________________
___________________
Dad
_________________
_________________
_________________
_________________
_________________
_________________
_________________
So, in review…a genotype is
the make up of your genes.
A phenotype is how that make
up makes you look (green
eyes), be able to do (roll
tongue), or other abilities.
Punnett Square
• A Punnett square is used to
organize all possible
combinations of offspring from
particular parents.
• Genotype PP is a purebred.
(true breeding)
• What is the genotype for the
offspring to the right?
• The dominant allele P ensures
that the offspring will have
purple flowers.
• The recessive allele p may get
passed to the next generation.
• Why?
Quick Lab
pg. 107
• Work with your group
to complete the
Punnett square.
• What would be the R
phenotypes for these
offspring?
– RR= round seeds
– Rr= round seeds
– rr= wrinkled seeds
R
r
RR
Rr
(genotype- two
dominant alleles)
(genotype- one
dominant
allele,one
recessive allele)
Rr
rr
(genotype- one
dominant
allele,one
recessive allele)
(genotype- two
recessive alleles)
r
Probability
• The mathematical chance that something
will happen is known as probability.
• Genotype probability:
– Pp x Pp cross has a 50% chance of receiving
either allele from either parent.
– The probability of inheriting two p alleles is
½x½, which equals ¼, or 25%.
R= round seeds
r = wrinkled seeds
Rr x rr
Rr x rr
r
R
r
r
R= round seeds
r= wrinkled seeds
Y= yellow seeds
y= green seeds
RY
ry
ry
ry
ry
RrYy x rryy
Ry
rY
ry