Download Final Concepts for Chapter 9 Mendelian Genetics

Final Concepts for Chapter 11
Mendelian Genetics
Allele
Dominant
Recessive
P-generation
F1
generation
F2 generation
Law of independent
assortment
Law of segregation
Chromosomes
Pure breed
Trait
•Codominance
•Complete dominance
•Dihybrid cross
•Genotype
•Genotypic ratio
•Heterozygous
•Homozygous
•Incomplete dominance
•Monohybrid cross
•Phenotype
•Phenotypic ratio
•Probability
•Punnett square
•Testcross
•Expected/predicted
results
•Actual/observed
results
•Karyotype
•Amniocentesis
•Linked genes
•Sex-linked disorders
•Autosomal disorders
Independent Assortment vs. Linked
Genes
Mendel did not know about chromosomes
when he proposed the Law of
Independent Assortment.
 The pea traits he studied happened to be
located on different chromosomes – so
they did assort independently.

Independent Assortment vs. Linked
Genes

Question: How many traits do you have?

Question: How many chromosomes (per
cell) do you have?

Question: Is it possible to have only one
trait per chromosome?
– No, lots of genes are carried or linked
together on the same chromosome.
Independent Assortment vs. Linked
Genes

Do the punnett square for the following
cross – assume independent assortment.
Cross two heterozygous tall, heterozygous
red flowered plants
T=tall
R=red flower
t= short
r = white flower
Independent Assortment vs. Linked
Genes
What is the
phenotypic ratio?
TR
TR
Tr
tR
tr
TtRr x TtRr
Tr
tR
tr
TTRR
TTRr
TtRR
TtRr
TTRr
TTrr
TtRr
Ttrr
TtRR
TtRr
ttRR
ttRr
TtRr
Ttrr
ttRr
ttrr
Independent Assortment vs. Linked
Genes
9:3:3:1 ratio
9
3
3
1
=
=
=
=
tall and red
tall and white
short and red
short and white
PROBABILITY:
From this cross, 48 offspring
were produced.
1. How many offspring would
you expect to be tall and
red?
2. How many would expect
to be tall and white?
3. How many would you
expect to be short and
white?
Independent Assortment vs. Linked
Genes
Now, do the following cross BUT the genes
for tallness and red flowers are linked.
Cross two heterozygous tall,
heterozygous red flowered plants
T=tall
t= short
R=red flower
r = white flower
Independent Assortment vs. Linked
Genes

Hint
TtRr X TtRr
T
t
R
r
Is it possible to
produce a Tr
gamete?
Independent Assortment vs. Linked
Genes
TtRr X TtRr
TR
TR
tr
TTRR
TtRr
tr
TtRr
ttrr
What is the
phenotypic ratio?
3:1
3 = Tall and Red
1 = Short and
white
Independent Assortment vs. Linked
Genes

So… out of the 48 offspring, if the genes
are linked, how many would be
– 1. tall and red?
– 2. tall and white?
– 3. short and red?
– 4. short and white?
Answer:
tall and red = 36
short and white = 12
EXPECTED
RESULTS!
tall/white = 0
short/red = 0
Independent Assortment vs. Linked
Genes
Is it possible for our Actual Results to
show any flowers that are tall/white or
short/red?
Yes – how?
Crossing over
Crossing over occurs in meiosis
Pieces of the chromosomes actual switch
places.
Complete vs Incomplete
Dominance
Codominance – the alleles are
equally dominant
Roan Cow
Human Blood Type
Sex-linked Traits

Traits carried on the X chromosome
Fill in the genotypes
on the pedigree.
Autosomal disorders
Disorders carried on non-sex
chromosomes (first 22 pairs)
 Some are autosomal dominant

– Huntington’s disease

Most are autosomal recessive
– Sickle-cell anemia
– Cystic fibrosis
Question: How do you know if the pure
bred dog you just paid big bucks for is
actually pure?
GG?
Gg?
Test Cross
Cross using a homozygous recessive
individual with a dominant individual to
determine if the dominant individual is
heterozygous or homozygous dominant
(pure)
 Why use a homozygous recessive
individual?

Test Cross
Do the punnett squares for each case:
GG x gg
Gg x gg
Test Cross

All offspring produced should show the
dominant characteristics if the dominant
parent is pure (GG) for the trait.
9-1 Mendel’s Legacy

F1 generation are the offspring produced
from the original parental group whereas
2.
The dominant factor gets expressed in
the individual and the recessive factor
can only be expressed when the
dominant factor is absent.
Ex. Pure Mendelian traits such as Pea Seed
Shape
S= smooth
s = wrinkled
3. An allele is a hereditary factor whereas a
gene is a segment of DNA that dictates a
trait. Two alleles for every trait: one from
mom and one from dad
Multiple Choice
1.
 2.
 3.
 4.

C
A
D
B
SHORT ANSWER
1. Strain = the body of descendants of a
common ancestor, genetic crosses show
how “strains” display family traits
2. Meiosis accounts for both the Law of
independent assort. and Law of
Segregation because the chromosomes
are pulled apart randomly during
anaphase 1 and 2 of meiosis

3. F= orange and f = red, then orange is
the dominant color
– All flowers in the F1 generation would be
orange.

4 Critical Thinking: If Mendel studied
traits that were linked on the same
chromosomes his observations would have
led him to very different conclusions. For
example, he would not be able to
conclude that heredity factors are
independent of one another because some
would always be displayed together.

EX: round seeds would be produced by
red flowering plants only
R r B b
RB
Rb
r B
r b
9-2 Genetic Crosses
Complete dominance – one allele completely
masks the expression of another
 Incomplete dominance – both alleles are
partially dominant causing an intermediate
phenotype (Ex. red and white flower produce a
pink flower)
 Codominance – both alleles are expressed
equally Ex. blood type AB, both A and B
antigens are produced

Multiple Choice
1.
 2.
 3.
 4.
 5.

B
A 266 short/ total possible of 1,064
C
D (test cross)
C
Short Answer
1. A homozygous individual has two of
the same alleles for a trait (AA or aa)
whereas a heterozygous individual has
two different alleles for a trait (Aa)
 2. .25 X 80 = 20 individuals
 3. AA, Aa are the possible genotypes,
100% of offspring will show dominant
phenotype

Critical Thinking

4. One offspring is not sufficient enough
to show if the cow is pure bred or not.
The larger the sample size the more
accurate the conclusion.
WwRr X WwRr
9 – dominant for both traits
 4 will have same genotype as parents
 1 will be homozygous dominant for both
traits
 1 will be homozygous recessive for both
traits

Gregor Mendel: Father
of genetics