Download Mendels Genetics

Genetics!!!
First…
Some Background Information…
What is heredity?
Heredity is the passing of traits from
parent to offspring.
You inherit traits from your parents
What are traits?
Ex. Include:
 Eye Color
Hair Color
Height
 Weight
 Body Structure
Facial Features
 Skin Color
http://www.dance-classes.ca/photos/faces/faces_2004W_comp1.jpg
What traits did you inherit
from your parents?
Turn to the Activity:
Genetic Traits
Taking a Class Survey”
in your Packet.
You will have 7 min. to complete the chart
Be prepared to share the information with
your class.
How are traits passed?
 When organisms
reproduce, traits
are passed from
parent to offspring.
 These traits are
carried in DNA,
the genetic
material found in a
cell’s nucleus.
 DNA acts like a
blueprint.
publications.nigms.nih.gov
http://www.healthsystem.virginia.edu/internet/huntdisease/i
mages/DNA.gif
Gregory Mendel’s Genetics
Father of Genetics
Studied how traits or characteristics are
passed from parents to offspring called
hereditary
Is most known for his
 experiments with
 thousands of
 pea plants to learn
 about genetics
Mendel’s Experiments:
Crossed plants with opposite traits
ex. Tall plants w/ short plants
Crossed purebreds – always produce
offspring with the same trait
Crossed :
Parents: green plant x yellow plant = all green
(F1 generation)
F1 generation: green x green = green and yellow
(F2 generation)
Dominant and Recessive Alleles:
One trait can hide or mask another
trait
Dominant trait – the trait that
always shows up when the allele is
present, hiding the other trait
Recessive trait – the trait that is
hidden or masked whenever a
dominate allele is present
Some traits are dominate,
some are recessive
Heterozygous vs. Homozygous
Heterozygous:
 2 different alleles for a specific trait
 Ex. Tt, Bb (Capital = Dom., lower case= rec.)
Pure/Homozygous:
two of the same alleles for a specific trait
Ex. tt, BB (Capital = Dom., lower case= rec.)
Homozygous recessive = 2 lower case letters
Homozygous dominant = 2 capital letters
Chromosomes
How do we know what
something will look
like?
 Ans. In the genes and
the alleles of the
organism
 Genes – small piece
of DNA for a trait
 Alleles provide the
“code” for a specific
trait
Alleles:
Carry specific information regarding a trait:
Ex.
 Gene eye color
 Alleles for eye color blue vs. brown
 And height (gene) in pea plants:
 Tall pea plant (allele)= T dominant trait (capital letter)
 Short pea plant (allele) = t recessive trait (lower case)
Homologs & Alleles
A
B
a
b
Homologs
C
c
D
d
From Dad
From Mom
 organisms have a chromosome
received from each parent.
 Called homologous
chromosomes
 This ex. has alleles of A, B, C &
D.
A & a, B & b, C & c, D & d
 A, B, C & D are at specific
loci (location)
How did Mendel cross plants to get variation
(differences) in the offspring?
Ans.
He manipulated the pollination (fertilization)
process of various traits in the flowers of
pea plants.
Reproductive structures of a flower:
Male Structures = anther and filament (pistil)
Female Structures = stigma, style and ovary
(style)
The Reproductive Structures of a Flower:
Pistil
Genetics and Probability
Punnett Squares:
A chart showing all possible combinations.
Used to determine probability of an out
come
Cross between 2 alleles
One set across top
One set down left hand side
Boxes = possible combinations
Phenotype and Genotype
 Phenotype - how it looks. Examples tall short, blue, black.
- the visible outcome of the alleles
- Ex. 75% Tall, 25% short ( not tall)
 Genotype – = the alleles represented in the Punnett square
- Ex. 25% Tt, 50 % TT, 25% tt
- genetic make-up.
- Allele combinations ex. TT, Tt, tt
 Homozygous-2 same alleles for a specific trait
 Homozygous recessive  tt
 Homozygous dominate  TT.
 Heterozygous – 2 different alleles for a trait  Tt, Bb.
Using a Punnett Square:
Used to determine probability
(Probability = the likelihood a
particular event will happen.)
Example of a
Punnett Square crossing
2 parents Tt :
Out come 1-TT, 2- Tt, 1- tt
Predicting Probability
Using alleles offspring can be predicted:
Pure dominate – TT X Pure recessive - tt =
All offspring will receive a dominant allele
100% will show the dominant trait
Can you create another cross and predict the
out come?
the visible outcome of the alleles
Ex. 75% Tall, 25% short ( not tall)
Predicting Probability
Crossing 2
heterozygo
us parents
always
gives the
ratio…
Punnett Square Examples:
In rabbits, black (B)
fur is dom. to white
(b). Cross a
homozygous black
fur w/ a heterozygous
rabbit. Identify the
genotypes and
phenotypes.
LAB: Genetics with a Smile 
Turn your packet to the page titled:
Genetics with a Smile.
With a partner, you will construct Punnett
squares to determine the outcome of your
youngin’… 
Complete at home as needed!!!!
The law of segregation
 The law of segregation states that every
individual has two alleles of each gene and
when gametes are produced, each gamete
receives one of these alleles.
 During fertilization, these gametes randomly
pair to produce four combinations of alleles.
Phenotypes and Genotypes
Tt  Tt cross
Law of segregation
 Two organisms can
look alike but have
different underlying
allele combinations.
F1
Tall plant
Tall plant
T
F2
Tall
Tall
T T
T
Tall
t
3
T
t
T
t
Short
t
t
t
1
The law of independent assortment
 Mendel’s second law states that genes for
different traits—for example, seed shape and
seed color—are inherited independently of
each other.
 This conclusion is known as the law of
independent assortment.