Beyond Mendel…
I.
II.
III.
IV.
V.
VI.
Mutations,
Gene Linkage,
Gene-Mapping,
Sex Linkage,
Polygenic Traits,
Non-disjunction,
disorders,
VII. Prenatal Diagnosis,
VIII. Pedigree Analysis
Mutations
A. Definition
B. Mutations in Genes
1. Point Mutations
2. Frame-shift Mutations
C. Mutations in Chromosomes
1.
2.
3.
4.
Deletion
Duplication
Inversion
Translocation
Back to
“Beyond Mendel”
Mutations
• Definition:
A change in the genetic
material (DNA or RNA) of a
cell
– Somatic: If it occurs in body
cells, it can’t be passed on
to next generation
– Germ-line: If it occurs in
gametes, it can be passed
on to next generation
Back to Mutations
Mutations in Genes
1.
Point Mutation: Affects one nucleotide
(One nucleotide is replaced by another)
- three types of point mutations
let’s look at one example…
Missense
Silent mutations:
Nonsense
mutations:
mutations:
Codes
Code
Code
forfor
same
fora adifferent
stop
amino
codon
A.A.
acid (ex. sickle-cell anemia)
Mutations in Genes
2. Frameshift Mutation: An insertion or
deletion that shifts the reading frame
a. Example of Insertion:
TA CGCATGGAATACC
b. Example of Deletion:
H
THE
TEF
ATC
FAT
CAT
ATA
TET
ATE
THE
HER RAT
AT
Back to Mutations
1. Deletion: A segment of the chromosome is removed (not just
one nuclotide)
A B C D E
F G H
A B C E
F G H
2. Duplication: A segment of the chromosome is repeated
A B C D E
F G H
A B C B C D E
A B C D E
F G H
A D C B E
F G H
3. Inversion: A segment within a chromosome is reversed
F G H
4. Translocation: A segment from one chromosome moves to
another, non-homologous one
Back to Mutations
A B C D E
F G H
M N O P Q
R
M N O C D E
A B P Q
R
F G H
Linked Genes
In flies, grey bodies (G) and normal-wing size (W) are
dominant to black bodies (g) and small wing size (w).
In this cross will the F1 grey flies always have normal
wings and will black flies always have small wings?
Actual Results
8.5%
8.5%
41.5%
41.5%
WHY?
No!
However,
mostflies
of the
F1 flies
willnormal
have either
Will
the F1 grey
always
have
wings aand
grey body
and flies
normal
wingshave
OR small
a black
body
with
will black
always
wing
sizes?
small wings, like their parents
Linked Genes
The genes for body color and
wing size are “linked”,meaning
they are found on the same
chromosome.
They will most likely be
inherited together and
will not undergo
Mendel’s Law of
Independent Assortment .
unless cross over
segregates the linked genes
G
G
g
g
W
w
W
w
Back to
“Beyond Mendel”
Gene Mapping
Grey
Body
Black
Body
Normal
wings
Small
wings
• Genes that are closer
together on the same
chromosome are less likely
to cross over, therefore
segregate.
• Genes that are farther
apart on the same
chromosome are more
likely to cross over and
segregate
• Genes that are on different
chromosomes will always
segregate independently
Back to
“Beyond Mendel”
Sex-Linkage or (X-linked)
In fruit flies, (R) is the dominant gene for red eyes, and (r)
is the recessive gene for white eyes. The gene is found on
the “X” chromosome. This is considered X-linked.
Does
the
gene
These
are
the
for
eye Y
color
X and
exist
on the “Y”
chromosomes
chromosome?
of a male fly.
Why
Howor
is why
the Ynot?
chromosome
R
r
different from
the X?
XX
r
XY
What
Whatwould
wouldbebethe
the
phenotype
phenotypeofofthis
thisfemale
male fly?
fly?
Sex-Linkage or (X-linked)
Watch this video to clarify your
knowledge of sex-linked traits
• When genes are sex-linked, we include the X
and Y as part of their genotype. For example,
the allele for red eye is not “R” but is written as
XR. How would you write the allele for white
eye?
Xr
White board practice
What is the possible
genotype(s) for this
red-eye fly if it is a
female?
What is the possible
genotype for this redeye fly if it is male?
Answer the above questions again for
this fly.
White board practice
You work in a fruit fly lab and you cross a
heterozygote red-eye female with a redeye male. Predict the F1 offspring using a
punnett square. What is the phenotypic
ratio?
White board practice
Adult on-set male-pattern
baldness
to be
Balding
is isa thought
trait that
a sex-linked recessive
can
occur
in females
trait.
Your dad
is going
bald and ityour
mother
although
is rare.
complains that if you or
What
must
your genotype
brothers were
to go
the gene
a bald
female
be infor
order
must come from
tobaldness
be
bald?
his side of the family. Use
a Punnett square to prove
Why,
then,
is balding
to your
mother
that the
wouldcommon
actually
a gene
trait more
come from her side.
in men then women?
Sex-linked or X-linked
• Time to reinforce your knowledge with a
lab!
Back to
“Beyond Mendel”
Polygenic Traits
• Definition: Traits controlled by two or
more genes
• Examples: Skin color, height
Polygenic
Traits
Skin Color
Height
Activity: Let’s
What
about
create a
our height?
histograph
of the
height
Doesofitallform
students in
the
same
class!
pattern?
Back to
“Beyond Mendel”
Non-disjunction Disorders
Meiosis
I
Definition: When members
of homologous
chromosomes fail to separate during
Meiosis I – or – when sister chromatids fail
to separate during Meiosis II.
Meiosis II
Examples: Down Syndrome, Turner’s syndrome,
Klinefelter’s syndrome
Abnormal
Gametes
Normalto
Back
Gametes
“Beyond
Mendel”
Prenatal Diagnosis: Amniocentesis
1. Amniotic fluid
withdrawn
2. Centrifuge
Fetus
(14 – 16 weeks)
Fluid
Fetal Cells
Several
weeks
later
Placenta
3. Karyotype
Uterus
Cervix
Cell culture
Prenatal Diagnosis:
Chorionic villus sampling (CVS)
Fetus
(8 – 10 weeks)
1. Suction
tube
inserted
through
cervix
Fetal cells
Placenta
Chorionic villi
Several hours
2. Karyotype
Interpret these karyotypes
Sex:
Male
Interpret these karyotypes
Klinefelter’s syndrome
Try these on-line activities
• http://www.biology.arizona.edu/human_bio
/activities/karyotyping/karyotyping2.html
Interpret these karyotypes
Down Syndrome
Genetic Disorder Brochure
Assignment
You will be assigned one of the following genetic disorders:
1) Color Blindness
3) Cystic Fibrosis
5) Down’s Syndrome
7) Duchenne Muscular Dystrophy
9) Edward’s Syndrome
11)Fragile X Syndrome
13)Hemophilia
15)Huntington’s Disease
2) Klinefelter’s syndrome
4) Marfan’s Syndrome
6) Patou’s Syndrome
8) Phenylkaptonuria
10) Sickle Cell Anemia
12) Tay-Sachs Disease
14) Turner’s Syndrome
16) Werner’s Syndrome
You will work alone on this project. If you have a disease that a
classmate has, you may collaborate during research, but you must
each create your own brochure and present it in a different way.
Your tech lit teacher will go over the details showing you how to
create a 3-fold brochure. Be careful of plagiarism! Plagiarised
projects will automatically a zero, possibly even a double zero score!
A Pedigree is…
Generally: A genetic family tree
Specifically: It is a chart of the
genetic history of family over several
generations.
Pedigree
Aa ?
A = tongue roller
a = can not roll tongue
aa
?
?
?
?
AA
aa
Aa
aa
Can you figure out the
rest of the genotypes on
your own?
male
Mating couple
female
Children/Siblings
Shaded = trait being followed
Other Pedigree Symbols
Examples of connected symbols:
• Fraternal twins
• Identical twins
Other Pedigree Symbols
•
•
•
•
Affected
X-linked
Autosomal carrier
Deceased
Back to Overview
Interpreting a Pedigree Chart
1. Determine if the pedigree chart shows an
autosomal or X-linked disease.
a. If most of the males in the pedigree are
affected the disorder is X-linked .
b. If it is a 50/50 ratio between men and
women the disorder is autosomal .
Example of Pedigree Charts
• Is it Autosomal or X-linked?
Answer
• Autosomal
Interpreting a Pedigree Chart
2. Determine whether the disorder is
dominant or recessive.
a. If the disorder is dominant, one of the
parents must have the disorder.
b. If the disorder is recessive, neither
parent has to have the disorder because
they can be heterozygous.
Example of Pedigree Charts
• Dominant or Recessive?
Answer
• Dominant
Example of Pedigree Charts
• Dominant or Recessive?
Answer
• Recessive
Summary
• Pedigrees are family trees that explain
your genetic history.
• Pedigrees are used to find out the
probability of a child having a disorder in a
particular family.
• To begin to interpret a pedigree, determine
if the disease or condition is autosomal or
X-linked and dominant or recessive.