Transcript Chapter 5-1 Genetics

Thursday February 14, 2013
Warm Up:
Draw a Punnett Square to
represent a cross between a
homozygous recessive plant and
a heterozygous plant.
• Trait is height
• Tall is dominant
Happy Valentine’s
Day
Love,
Ms. Archie and Ms. Johnson
MYP Unit Question- How did
you get those traits you have?
Area of Interaction- Human
Ingenuity
Learning Target: Today I will
learn why punnett squares are
useful because they allow me to
see the chance of what genes
will be handed down to the
offspring.
Chapter 5-1
Genetics
Heredity
is the passing of traits
from the parents to the
offspring and is controlled
by genes
Gregor Mendel
Father of Genetics
Gregor Mendel
 Born in 1822 in Austria
and lived in Europe.
 Was a monk who studied
mathematics and science.
 Determined the basic
laws of Genetics.
Mendel’s Garden
 As a boy, he worked in his
father’s orchard and
became interested in plants
 He experimented with
peas.
 Self-Pollinating Peas have
both male and female
reproductive structures. So,
pollen from one flower can
fertilize the ovule of the
same flower.
 When a true-breeding plant
self pollinates, all of the
offspring will have the same
trait as the parent.
 Pea plants can also cross-pollinate.
Pollen from one plant fertilizes the
ovule of a flower on a different plant.
 The image below shows crosspollination and self-pollination.
Characteristics
 Characteristics Mendel studied
only one pea characteristic at a
time. A characteristic is a
feature that has different
forms in a population.
Ex: Human hair color
 Different forms of a
characteristic are called traits.
Gregor Mendel
Called the form of a trait
that appears to dominate
or mask another form of
the same trait dominant.
Gregor Mendel
Called the weak form of a
trait that is prevented
from showing up by a
dominant trait recessive.
Chapter 5 section 2
So, what is
genetics?
Genetics is the study of
how traits are inherited
through the actions of
alleles.
What are genes?
 Instructions for an inherited
trait.
 Made of segments of DNA
 Control the traits of an organism
 Found on the chromosomes
 Have different forms called
alleles
What are alleles?
Alleles are the different
forms that a gene can
have for a trait.
Alleles
determine the traits of the
organisms
Alleles
 An organism with the
same two alleles for a
trait is homozygous.
 An organism with two
different alleles for a
trait is heterozygous.
Therefore:
 An organism’s genetic
makeup is it’s genotype.
 An organism’s physical
makeup is it’s phenotype.
Punnett Square
The tool used to predict
the probability of certain
traits in offspring that
show the different ways
alleles can combine.
Punnett Square
Dominant allele is Upper
case letter
=G
Recessive allele is Lower
case letter
=g
G
G
g
Gg
Gg
g
Gg
Gg
Punnett Square
Lets try one:
Lets cross a true breeding white
flower (pp) with a true breeding
purple flower (PP).
Probability
• The branch of mathematics
that helps you predict the
chance something will happen is
called probability
• Probability is most often
written as a fraction
½
If you roll a pair of dice, what is
the probability that you will roll 2
three?
Step 1: count the number of faces on a single die. Put this
number in the denominator:
__
6
Step 2: Then count how many ways you can roll a three with
one die. Put that number in the numerator:
1
6
Step 3: To find the probability of rolling 2 threes multiply
1/6 x 1/6 = 1/36
Genotype Probability Example
Use a punnett square to determine the
possible genotypes of offspring of a
BB x Bb
Incomplete Dominance
• One trait is not completely dominant over
the another.
When a plant which is homozygous for red flowers (AA) is
crossed with a plant which is homozygous for white flowers
(aa), the plants of the F1 generation produce pink flowers
which is a blend of red and white condition. This result
clearly indicates that neither red flowered condition nor
white flowered condition is dominant.
Thank You
Exit Ticket:
Write down one thing they are
still confused about regarding
genetics.