Download 1.6-Genetic Diversity and Heredity

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Lesson# 1.6Genetic Diversity and
Heredity
Gregor Mendel (1822-1884)
• Pioneer of genetics
• Austrian monk
• Explained the
mechanism of gene
Inheritance
• Basis for understanding heredity
What is heredity?
• The passing on of characteristics
(traits) from parents to offspring
• Genetics is the study of heredity
Mendel’s Research
• Used pea plants
• They reproduce sexually
• They have two distinct, male and
female, sex cells called gametes
• Their traits are easy to isolate
Mendel…
• Cross-pollinated plants to see the
outcomes and later to manipulate
desired combinations
Mendel’s Research
• Fertilization - the uniting of male
and female gametes
• Cross - combining gametes from
parents with different traits
= Cross-Fertilization OR
Cross-Pollination
Cross-Pollination
stigma
anther
style
filament
ovary
ovule
petal
sepal
peduncle
receptacle
Mendel’s Observations
• Results were ALWAYS the SAME
• Example: He crossed
– TALL pea plant x SHORT pea plant
• Result: TALL pea plants, ~100% of the time
– ROUND pea plant x WRINKLED pea plant
• Result: ROUND pea plants, ~100% of the time
Mendel’s Observations
What Did Mendel Find?
• Each organism has two alleles for each
trait
• Alleles - different forms of the same
gene
• Genes - located on chromosomes,
they control how an organism
develops
What does this mean…?
• Mendel concluded that there had to
be factors that controlled the traits
expressed in plants
– Genes
• He realized that genes control what
traits are passed on to offspring
• Different variation/version of a gene:
alleles
gene: plant height, alleles: tall, short
Gene for flower colour
GENETIC WHEEL Activity
Dominant or Recessive?
• Dominant: alleles of this type determine
the expression of the genetic trait in
offspring
• Recessive: alleles of this type are
overruled by dominant alleles
The Symbol System
• Used letters of the alphabet to show
what traits were passed on to offspring
• UPPERCASE letters = Dominant
• lowercase letters = recessive
Y = yellow pea plant
y = green pea plant
The Crossing of 2…
• A yellow pea plant might inherit the
alleles Yy (one from each parent)
• Since there is a dominant allele (Y)
the expressed colour is YELLOW
• YY = Yellow (dominant)
• Yy = Yellow (dominant)
• yy = green (recessive)
Example:
YY
Parents
yy
x
Meiosis (segregation
of homologs)
Y
y
Y
y
gametes
Cross-fertilization
F1 gen.
100% Tall
Yy
Yy
Yy
Meiosis (segregation
of homologs)
Y
YY
y
Y
Yy
y
Yy
gametes
Cross-fertilization
Yy
yy
F2 gen. 75% Tall
25% Short
What Did Mendel Find?
• Mendel discovered different laws
and rules that explain factors
affecting heredity…
Mendel’s Laws of
Heredity
1. Law of Segregation
2. Law of Independent Assortment
3. Law of Dominance
1. Law of Segregation
• The two alleles for a trait
must separate when
gametes are formed
2. Law of Independent
Assortment
• The genes for different traits are
inherited independently of each
other.
• A parent randomly passes only
one allele for each trait to each
offspring
3. Law of Dominance
• The trait that is observed in the
offspring is the dominant trait
–(UPPERCASE)
• The trait that disappears in the
offspring is the recessive trait
–(lowercase)
Single –Trait Inheritance
• Genotype: the alleles an organism
contains
– Tall plant can have the genotype TT or
Tt, short plant only one  tt
• Phenotype: the traits you can SEE
– A plant can either be TALL or SHORT
– A pea can be yellow or green
• Homozygous: genotype that has 2
alleles that are the same (TT or tt)
• Heterozygous: genotype that has
two different alleles (Tt)
Single –Trait Inheritance
• Monohybrid Cross: a cross that
includes only one trait
– Ex. Height or colour
• Punnett Square: a chart used to
show the possible combinations of
alleles in offspring
Punnett Square
Let’s look at the
possible crosses
Plant height:
• TT x TT = all TT
• TT x Tt = 2 TT, 2 Tt
• TT x tt = all Tt
• Tt x Tt = TT, 2 Tt, tt
• Tt x tt = 2 Tt. 2 tt
• tt x tt = all tt
T
T TT
T
TT
t
TT
Tt Tt
T
Tt TT
Tt
tt
Tt
Tt TT
tt Tt
Tt
tt
t Tt
T
TT
T
Tt
TT
Tt
t
TT
tt
Tt
Tt
Tt
tt
tt
Activity:
• Simple Genetics Practice Problems
#s 1-3
Monohybrid Crosses
Cross a pea plant that is heterozygous
for round seeds and a pea plant that has
wrinkled seeds.
The allele for round seeds is dominant.
Use the symbols R=round and
r=wrinkled
*Determine the phenotypes and
genotypes of the offspring in the F1
generation
Monohybrid Crosses
TRAIT: seed shape
• Parent phenotypes: round x wrinkled
• Parent genotypes:
Rr x rr
• Parent gametes:
R, r, x r, r
R
r Rr
r
rr
F1 Phenotypes:
r Rr
rr
50% Rr, 50% rr
50% round, 50% wrinkled
F1 Genotypes:
Reverse Monohybrid Cross
• PURPOSE: to determine the
genotypes/phenotypes of the
parents if the offspring phenotypic
ratio is known
• Question: Determine the genotypes
of the parents given the information
Offspring Genotype
Numbers
Round seed
5472
Wrinkled seed
1850
Activity:
• Simple Genetics Practice Problems
#s 4-15
• Practice Quiz
• In-Class Assignment
Test Cross
• An organism showing a dominant
phenotype can have two possible
genotypes:
– Homozygous dominant (TT)
– Heterozygous dominant (Tt)
• Therefore, a test cross is performed
to determine the genotype of the
unknown parent
Test Cross
• A test cross is always performed by
crossing the unknown genotype with
a homozygous recessive (T? x tt)
• The genotype of the unknown parent
can be deduced from the
appearance of the offspring:
– IF half the offspring show the recessive
trait  unknown parent = heterozygous
– IF all the offspring show the dominant
trait  unknown parent = homozygous
Activity
Let’s say you decide to make your living as
a mink farmer. In mink, black fur is
dominant over white fur. Since the market
for black mink coats is higher than white
mink, you (being the entrepreneur that you
are) decide to only raise black mink.
Everything is going well but the guy you
bought your mink from seemed a little
sketchy! You want to make sure they are
pure breeds so you run a test-cross.
#1
Give the phenotypes of the mink in your
test-cross:
white
black
____________x___________
#2
In your fist test-cross, 30 out of 60 offspring
are black and the rest are white! No wonder
you got such a good deal! What are the
genotypes of the mink used in your testcross? (Use “B” and “b”)
Bb
bb
___________X__________
B
B
B
b
b Bb Bb
b Bb bb
b Bb Bb
b Bb bb
#3
Was the black-furred mink you chose for
your test-cross a pure breed?
Bb
What is his genotype? ______________
Try it!
In fruit flies, red eyes are dominant over sepia
(brownish) eyes. Being the great genetic student
that you are, you happen to have a culture of
pure red eye and pure sepia eye flies in your
laboratory. While working in your lab late one
night, a cute, fuzzy, and fantastically friendly, red
eyed fruit fly came in for a crash landing on your
banana. Wanting (naturally) to know more about
your new friend, you decide to run a test-cross on
your little, buzzing buddy.
…answer these..
1.Give the phenotypes of the flies in your
test-cross: ___________X___________
Red eyes
Sepia eyes
2. If all of the offspring turn out to be redeyed (all 347 of them!!!) what are the
genotypes of the flies used in your testcross? (Use “R” and “r”)
___________X__________
RR
rr
…but what about….
If instead, 179 of the 347 show up with
sepia eyes, what was the actual
genotype of your new found friend?
Rr
_______________
Genetic diversity is due to…
• “Crossing over” during Meiosis I
– Prophase I
• Independent assortment during
Meiosis I and II
– Metaphase I and II
• Random fertilization of gametes
• Certain reproductive technologies
• Mutations
Types of Reproductive
Technologies
•
•
•
•
Selective Breeding
Inbreeding
Hybridization
Mutations
Selective Breeding
• Humans take advantage of naturally
occurring variation in organisms and
choose advantageous traits to pass
down to the next generation
– Example: domestic animals and
desirable crops
Types of Reproductive
Technologies
•
•
•
•
Selective Breeding
Inbreeding
Hybridization
Mutations
Inbreeding
• Continued breeding of individuals
with similar characteristics to
maintain the desired characteristics
of a line
– Example: Pure breeds
• Increases breed’s susceptibility to
diseases and deformations
Types of Reproductive
Technologies
•
•
•
•
Selective Breeding
Inbreeding
Hybridization
Mutations
Hybridization
• Crossing dissimilar individuals to
bring together the best (most
desirable) traits of both
• Produces “hybrids”
• New varieties of plants and animals
are developed
Types of Reproductive
Technologies
•
•
•
•
Selective Breeding
Inbreeding
Hybridization
Mutations
Mutations
• Definition: the changing of one or
more genes
• Breeders can increase variation in a
population by causing mutations in
the DNA
– Example: oil-eating bacteria, new
species of flowers, etc.
• Mutations can either occur
spontaneously or can be induced by
radiation and chemicals