Transcript heredity

Bell Work: Monday February 4, 2013
 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. Due today
unless you were absent last week.
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
Traits and Inheritance
• Mendel knew from his experiment with pea plants
that there must be two sets of instructions for each
characteristic.
• 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.
• The two forms (often dominant and recessive) of a
gene are known as 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.
• 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).
– An organism with one of each (Pp) is heterozygous.
Punnett Square
• A Punnett square is used to
organize all possible
combinations of offspring from
particular parents.
• Genotype PP is a purebred.
• 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%.
Monohybrid vs. Dihybrid Punnett Square
• A monohybrid Punnett
• A dihybrid Punnett
square is one where only
square is one where two
one trait is crossed.
traits are crossed.
– Example: A tall pea
• Example: a tall, green
plant TT is crosses with
flowered plant TtGg is
a short pea plant tt.
crossed with a short,
yellow flowered plant ttgg.
T
t
t
Tt
Tt
T
Tt
Tt
TG
Tg
tG
tg
tg
TtGg
Ttgg
ttGg
Ttgg
tg
TtGg
Ttgg
ttGg
Ttgg
tg
TtGg
Ttgg
ttGg
Ttgg
tg
TtGg
Ttgg
ttGg
Ttgg
Rr x rr
RrYy x rryy