Download Chapter 8 - TeacherWeb

Chapter 8
Genetics
Traits Inventory Lab
Detached
Earlobes
Rolling
Tongue
Dimples
Right handed
Freckles
Curly
Hair
Allergies
Left over
Right
See
green
and red
Straight
Hairline
HH
Thumb
__________
Heredity - is the passing of traits from parents
to offspring.
The study of heredity started with an Austrian
Gregor Johann Mendel
Monk named _______________________
. He
“Father of Genetics”
was considered the _______________________.
Background Information
- He was a peasant and grew up in a family of farmers.
- Became a priest.
-Went to the University of Vienna and studied
math and science
- He wanted to study genetics and so, repeated experiments
that had been done by a former British scientist named
T.A. Knightly. Mendel counted the offspring that he
and analyzed data.
He studied garden peas
bred
Why Pea Plants???
1. There are several characteristics that are ___________________________.
clearly distinct and different
male and female reproductive parts are on the same plant. They
2. The _______________
self-pollinate
can __________________
or pollinate each other.
3. The plants are _______________
small
, _________________________
mature quickly
and
produce many offspring
____________________________
so results can be observed quickly.
Mendel’s Results
monohybrid cross – a cross between two plants for
Mendel performed a ________________
one trait. He focused on __________________.
flower color
Step 1 – He allowed plants to self pollinate
called _________________,
to ensure that
true-breeding
the plants only carried two genes for the
same trait.
*He called them the P (parent) generation.
Step 2 – He crossed 2 true-bred plants with
opposing traits (Ex. one white and one purple)
*He called them the F1 (filial) generation.
Step 3 – He crossed 2 plants from the first
generation.
*He called them the F2 (filial) generation.
Mendel Discovered: In the P generation, the plant only had the gene it was bred
for. In the F1 generation, the four offspring were carriers of the recessive gene but
is was not expressed. The recessive gene started to show in the F2 generation.
Mendel’s 4 Hypothesis
1. For each trait, you get one gene from your
mother and one gene from your father.
2. There are alternative versions of each gene.
Like brown and blue eye color. These versions
are called alleles.
3. When two genes come together, one might
be completely expressed (observable) and
the other one might not be observable. These
are called dominant and recessive traits.
4. When gametes are formed, they separate
and only have one allele for each trait.
People thought that offspring were a blend of
their parents – not so. Each organism
inherits one copy of a trait from each
parent. Therefore each organism carries
2
_______
genes for each trait. The variety
of genes that an organism can inherit for
a particular trait is called an
____________.
allele
Mendel Had Two Laws!
_______________________
Law of Segregation
- the two alleles
that a person carries for a trait separates
during meiosis when the sperm or egg are
formed.
_____________________________
Law of Independent Assortment - alleles for
different genes separate independently of one
another when sperm and egg are formed. In other
words, just because the allele for blonde hair and
brown eyes are on the same chromosome does not
mean they will end up in the same gamete (do to
crossing over)
There are two types of genes
Dominant
Recessive
1. Represented by a capital letter.
1. Represented by a lower case letter.
2. If it is present, it will always be expressed.
2. It is a trait that will never be
expressed if a dominant allele is
present. The only way the trait will be
expressed is if the organism has two
recessive alleles for the same trait.
Examples include: free earlobes (A),
freckles, dimples, curly hair, rolling tongue,
long eye lashes
Examples include: attached earlobes
(B), no freckles, no dimples, straight
hair, not being able to roll the tongue,
long eye lashes.
A person has two alleles for each gene. They can either be
Homozygous
-____________________
- two of the same alleles (two
dominant or two recessive).
Heterozygous
-____________________
- the organism has one dominant
and one recessive allele.
genotype
________________
– the actual genes you have (using the letters)
phenotype
________________
- the physical appearance of the genes (how the person looks)
Expected and Observed Results
We can only predict what possible traits a
child will have. The only way to truly know
what a child will look like or how his or her
body will work, is by observing the child after
birth.
To predict the possible traits of a child, will
punnett square
use a _______________.
Step 1 – Determine the two genes that each
parent is carrying for a particular trait.
- Determine what the trait is:
Example - eye color, hair color, long ears.
- Determine the letter that represents that trait.
-
Determine what each parent is:
Homozygous Dominant - 2 capital letters
Heterozygous – 1 capital and 1 lower case letter
Homozygous Recessive – 2 lower case letters.
Dominant traits are represented
capital letter
by a ________________
Recessive traits are represented
lower case letter
by a _________________
Capital letters are always written first!
Draw a square. Place the mother’s two genes on
the top and the father’s two genes on the left side.
Cross a mother and a father
who are both heterozygous for
free ear lobes. Free ear lobes
are represented by a “F”.