Transcript FUNDAMENTALS OF GENETICS

FUNDAMENTALS OF
GENETICS
USEFUL MATERIALS
Video- Garden of Inheritance
Guinea Pig Work sheet
Text pages 159-176
Worksheet and word search
Vocabulary
• 75. Independent
assortment
• Monohybrid cross
• True breeding
• Cross pollination
• Self pollination
• Alleles
• Homozygous
dominant
• Heterozygous
• Homozygous
recessive
• Genotype
• Phenotype
• Test cross
Read: 159-170
Remember this about
chromosomes?
• X = shorthand for chromosomes
• 46 total – 23 from mom and 23 from dad
(23 pairs)
centromere
Chromatids
(2)
Types of Chromosomes
• Autosomes – do not determine sex (1-22)
• Sex Chromosomes – determine sex (X
and Y) = 23rd
– XY – male
– XX - female
Hereditary Terms
• Trait – genetic characteristic of an
organism
• Gene – DNA sequence that codes for a
protein (may lead to a trait)
• Allele – different forms of a gene
I. Principles of Heredity
• There are two factors which determine
what and who you are, or what an
organism looks like and how it behaves.
– HEREDITY - the genetic make-up
– ENVIRONMENT- conditions during
development
• Is it “NATURE OR NURTURE” that
determines the ultimate product?
– Studies on TWINS are inconclusive
II. PARADOX OF HEREDITY
• A paradox is a seeming contradiction.
– “Success is measured sweetest by those who
never succeed.” – Dickens
– “We are most lonely at times when we are
among many men” H. D. Thoreau
– Consider a situation in which a father and his son
are driving down the road. The car collides with a
tree and the father is killed. The boy is rushed to the
nearest hospital where he is prepared for
emergency surgery. On entering the surgery suite,
the surgeon says, "I can't operate on this boy. He's
my son."
So what is the paradox of
heredity?
• Why are some characteristics inherited
exactly and others are variable?
– Species Characteristics: 5 fingers,
walk erect, nervous system, appendix, 2
eyes
– Individual Characteristics: height, hair
color, skin color, hair line
Diagram 2 homologous pairs of
chromosomes with alleles on each pair
X X
Useful Terms
• Phenotype- observable feature (eye color,
hair color, blood type)
• Genotype- arrangement of alleles (Aa, Tt,
Bb Gg)
III. History
• Gregor Mendel: Austrian Monk (18221884)
– Published the results of scientific research on
Garden Peas (Pisium sativum) in 1865.
Why study peas?
– Great natural variation- stem length, seed
color, pod shape ,pod color, small, edible,
easy to grow, many offspring, easy to cross
fertilize, grow well in tne climate
Floral Anatomy
• pollination
• fertilization
Floral Anatomy
More Useful Terms
• P generation (parental): true breeding
• F1 (first filial) offspring of P generation
• F2 (second filial) offspring from F1 cross
IV. EXPERIMENTAL CROSSES
FOR INDIVIDUAL TRAITS
Must begin with PURE BREEDING parents:
HYBRID offspring
F1
First Filia Generation
Cross Pollination
P
yellow
F1
X green
yellow
tall X
tall
short
wrinkled
X round
round
these are TEST CROSSES to determine
dominance and recessiveness
P
F1
yellow
X green
yellow
allowed to Self Pollination
F1
yellow
X yellow
F2
3 yellow
1 green
Tall X
3 tall
Tall
1 short
Round X
3 round
Round
1 wrinkled
**Large sample sizes are needed to get an accurate
picture of the frequency
P
red
F1
F2
705
X
white
red (self)
red
224 white
V. PUNNETT SQUARE
Method for determining possible allele combination
for the offspring
Gametes outside
Offspring Inside
Who was Punnett?
• REGINALD CRUNDALL
PUNNETT (1875-1967)
was among the first
English geneticists. He
created the “Punnett
Square” – a diagram to
work out the possible
allele combinations of the
offspring of two parents.
How are gametes produced?
• Meiosis!
– Where does this process happen in a flower?
• If a person is a tongue roller with the
genotype Tt, what happens to the alleles
during meiosis? Draw the process.
Draw summary and short hand of meiosis with 1 pair of chromosomes
Tongue Rolling
Chromosomes with alleles
Gene: tongue rolling
Alleles:
T- can roll
t – unable to roll
X X
VI. TEST CROSSES
• Monohybrid (one feature)
• Dihybrid (two features)
Some more terms…
• Homozygous Dominant – TT – given two
dominant alleles from parents
• Homozygous Recessive – rr – given two
recessive alleles from parents
• Heterozygous – Gg – given one dominant
allele and one recessive allele from
parents
Setting up a Punnett Square
• Brown eyes (B) are
dominant to blue eyes (b)
• Cross a homozygous
brown-eyed person with
a blue-eyed person
•
BB vs. bb
B
B
b
Bb
Bb
b
Bb
Bb
What is the probability of having an offspring with
heterozygous brown eyes?
4/4 or 100%
Another Example
• Tongue rolling(T) is
dominant to nontongue rolling (t)
• Cross a
homozygous tongue
roller with a
heterozygous
tongue roller
• TT vs. Tt
T
T
T
TT
TT
t
Tt
Tt
What are the genotype possibilities?
2/4 or 50% TT and 2/4 or 50% Tt
Useful Terms
• Phenotypic ratio- Pattern of offspring
distribution according to phenotype
Usually written as a fraction.
observable feature (eye color, hair color, blood type)
• Genotypic ratio- Pattern of offspring
distribution according to genotype. Usually
written as a fraction.
• arrangement of alleles (Aa, Tt, Bb Gg)
Practice Problems
•
•
•
•
•
Pea Plants: green – G
GG x gg
GG x Gg
Gg x gg
Gg x Gg
Genotypic/phenotypic ratios:
yellow – g
GG x Gg
Gg x gg
Gg x Gg
Albinism is the result
of the expression of a
recessive allele for
skin pigment
There are
several forms
of albinism
• A normal pigmented male (who has an albino
mom) and an albino female get married and
have two children. What are the phenotypic
ratios and genotypic ratios? What alleles will you use?
Genotypic Ratio:
Phenotypic Ratio:
Some more practice problems:
• Two “normal” heighted but heterozygous
people have a child who is a midget. The wife
is pregnant. What is the chance that their
second child will be of normal height? What
alleles will you use?
Genotypic Ratio:
Phenotypic Ratio:
• Dimples is a dominant trait. A heterozygous
mom and a homozygous recessive dad have a
child. What is the phenotypic ratio and
genotypic ratio of the possible offspring? What
is the genotype and phenotype of the parents?
Finding phenotypes and
genotypes for 2 traits.
• Read lab
• Observed ratio- a record of the results of
an event that has occurred
• Expected ratio- mathematically calculated
results of an event prior to it occurring
Finding phenotypes and
genotypes for 2 traits.
• Chance- not planned, accidental, not
expected
• Sample Size- number of events recorded
large sample side is needed to reduce
the influence of chance and allow the true
patterns to emerge.
Dihybrid Cross
Cross 2 pea plants that are both heterozygous purple
flowered and heterozygous for smooth seeds.
P= purple
p= white
N= non-wrinkled (smooth) n= wrinkled
• Step 1: Figure out the different gametes for each
parent
• Step 2: Set-up the cross and complete
• Step 3: Calculate the genotypic and phenotypic
ratios
Example of Ratios
Data summary from dihybrid lab
Data summary from dihybrid lab
VII. Mendel’s Laws
Mendel was a patient and keen observer.
• Some characteristics mask others yet
reappear.
– Principle of Dominance and Recessiveness
• Features can skip a generation.
• Theorized there were 2 factors for each
trait.
– Principle of Segregation of Alleles
• Pairs of factors separate into gametes
without influenceing each other.
– Principle of Independent Assortment
Quiz Topics –FRIDAY 3/5
Read: 159-170
• Vocab 90-101
• Worksheets (pg 127 and pg 129)
• Mendel and his laws
• Terminology (P, F1, F2, heterozygous,
homozygous dom, homozygous rec, phenotype,
genotype, trait, gene, allele)
• Monohybrid vs Dihybrid crosses
• Doing monohybrid problems
Review Questions
•
•
•
•
RRTT
RrTt
RRtt
Rrtt
• List gametes possible from these parents
• (T) is the allele for tall humans and is dominant over
the allele (t) for short humans. The allele for
widows peak (W) is dominant over (w) non-widows
peak hairlines.
What are the phenotypes for the following parents?
TtWw - _________________
TTww - _________________
What are the possible gametes formed by the
parents listed above?
AND
• 1. A woman with free ear lobes marries a
man with attached ear lobes. Two of their
children have attached ear lobes and two
have free ear lobes. The alleles are (E) free (e) - attached
•
A. what is the genotypes of the
woman?
•
B. what is the genotype of the man?
•
C. What are the chances of the 5th
child having free ear lobes?
• (F) striped fur is dominant over (f) white fur in
Australian cats.
What is the result of a cross between a
homozygous recessive parent and a
heterozygous parent? Give phenotypic ratios
and genotypic ratios.
Genotypic Ratio:
Phenotypic Ratio:
PTC tasting
Reality Show?
Do you recognize
this family?
*Hint: They are
from a TV show
• They are the Roloff
family from TLC’s
show Little People
Big World
• How are the
members of this
family the same?
• How are they
different?
• Great! You probably
noticed that the family
members share facial
features, hair color etc.
• They are different
because of their height
• Some family members
(including the parents)
exhibit the characteristic
short stature of
Achondriplasia, a
dominant genetic
disorder that results in a
form of dwarfism.
• How is it possible
for Matt and Amy
(the parents) to
have a child like
Zach with
Achondriplasia
and three
children who do
not have the
disease?
• The key is understanding
dominant and recessive
genes and the concept of
segregation
• Zach and Jeremy are
Fraternal Twins – what does
that tell us about their genes?
• Fraternal twins have genes
that are different genetically, they are no more
similar than any other set of
siblings.
• If Zach and Jeremy were
Identical Twins, how would
this picture change?
• Both boys would either
display the short stature of
Achondriplasia or be of
normal height – Identical twins
have identical genes!
Zach
Jeremy