Download Human Heredity: Chapter 14

Chapter 14
Thomas Hunt Morgan (1933)
• Used fruit flies (Drosophilia melanogaster)
• Females had 8 paired chromosomes while
males have 3 pairs and 1 mismatched pair
How is sex determined?
• Sex Chromosomes – mismatched chroms
that determine sex
• In humans, X or Y - Always a 50:50 chance of
a boy or a girl with males determining sex of
child
• Humans have 46 chrom/body cell. Last two
are sex chroms. 22 autosomes & 2 sex
chroms
X
Y
X
XX
XY
X
XX
XY
Sex Linkage
• Morgan noticed that some traits in fruit flies were
inherited differently in males than in females. Males
seem to inherit certain traits w/ a greater frequency
than females.
P1:
F1:
F2:
Wild type female
X
White eyed male
Wild type
75% Wild type
(All females & ½
of the males)
25% White males
(Only males)
How was the gene for eye color related to
being a male?
• Conclusion: The gene for eye color is
carried on the X chromosomes. The Y
chromosome is shorter than the X and
has no corresponding gene for eye color.
Normal female Carrier female Female w/ trait Normal male Male w/trait
Crosses:
Cross a carrier red-eyed
female w/ a white eyed
male.
•
XRXr x
PR:
XrY
• Cross a red eyed male
w/ a carrier red eyed
female.
•
XRY x XRXr
Can a female have white eyes?
• Cross a Carrier red eyed female with a
white eyed male.
• XRXr x XrY
PR:
Sex-linked traits in humans
1. Red-Green color blindness –
recessive. Can’t distinquish between
colors
2. Muscular dystrophy- recessive –
weakens then destroys muscle tissue
3. Hemophilia – recessive – lacks ability
to produce clotting factor – bleeders
– Ran rampant through the royal families
of Europe – “Royal Hemophilia”
Here is a test for you. Look at the figures below and
write down what you see. Do not talk or make any
comments4. during this test!
If you could not see the 29, 45,
56, 6 or 8, you are color blind!!
12 – 20% of the population has
this trait.
How colorblind people see colors
Parisi Family Colorblindness Pedigree
I
Mary
Joseph
II
Mary
Ed
Dom
Rose
Helen
Josephine
Theresa
Bob
Joan
III
Mary Terese
Bonnie
Charles
Donna
Joe Ralph
Hank
ME! MA
Joe
Bobby
Alisa
IV
V
1.
2.
3.
4.
Which individuals are we not able to determine their genotype for colorblindness?
Which individuals were not in danger of ever having to worry about inheriting colorblindness from this family?
Which individual was the best at transferring the colorblind gene to their offspring?
What could have been the genotypes of Mary P’s parents?
Sex Linked
Problems
Cross a colorblind male with
a carrier female
What percent of the boys may have hemophilia if their mother is
pure normal and their father is a hemophiliac?
If both parents are normal vision, show the cross that
could result in a colorblind son
If 2 parents are normal and nd their son has MD, what
must have been the genotypes of the parents?
In humans, the gene for color vision is dominant to the
gene for red-green colorblindness.
XNXN, XNY = Normal color vision
XNXn = Carrier for colorblindness but normal vision
XnXn, XnY = Colorblind
• Show the cross between a normal visioned carrier
female and a normal male.
• What is the likelihood of them having a colorblind
son? Daughter?
Show the cross between a carrier mother and a
colorblind father.
What is the probability of them having a son that is
colorblind? A daughter?
In humans, the dominant allele for a rare form of
rickets (Vitamin D deficiency), is located on the X
chromosome. This condition can be successfully
treated with Vitamin D therapy.
Let “R” = the rickets allele & “r” = the normal
allele
XR XR, XR Y = Affected female, male
XR Xr = Affected female
Xr Xr , Xr Y = normal female, male
A couple goes to a genetic counselor to
find out the chances of them having
children with rickets. The wife is
normal, without any family history while
the husband is affected by this disease.
Phenotype:
________________________________________
Genotype:
________________________________________
What if the wife were affected (but had a normal father)
& the husband was normal?
Phenotype:
___________________________________
Genotype:
___________________________________
In cats, the black coat pigment (R) is codominant
with the orange coat pigment (O). These two
alleles are found only on the X chromosome.
XB XB , XB Y = Black coated female, Black male
XO XO, XO Y = Orange coated female, Orange male
XB XO = Tortoiseshell coat (intermingled black and
orange in fur)
Notice, only females can have tortoiseshell coats.
A female tortoiseshell cat mated with an unknown
male cat giving birth to 6 kittens (2 orange females, 1
tortoise female, 1 black male and 2 orange males.
What was the genotype and phenotype of the father?
Phenotype: ____________________
Genotype: _________
The owner of a black female cat wants to know
which cat fathered her two tortoiseshell female
and 2 black male kittens. Was it the same male
cat from above?
• Pedigrees - like a flow chart of a
family’s genetic history. Traces a
family’s genes
Roman
numerals show
each Generation
This pedigree chart shows inheritance of the gene
that causes albinism (autosomal recessive trait).
N = Normal pigmentation
n = Albino gene
A pedigree chart for the inheritance of achondroplasia
(ay-kon-druh-play-zhuh), a form of dwarfism. Dwarfism
is a dominant autosomal trait
D = Dwarfism
d = normal height
Karyotypes
Diagrams or photo of how chromosomes are
arranged and which ones are present from
an individual.
Chromosome smear
Karyotypes can be used to determine
abnormalities in chromosome makeup.
A Normal female
A Normal Male
Amniocentesis
• Method of extracting amniotic fluid w/
fetal cells. Can give sex of child and
also a karyotype is produced.
Mutations – aka: what can go wrong.
Changes in the genetic material of a cell
Types:
• Gene mutation – affects gametes
therefore inheritable – Point &
frameshift
• Chromosomal mutations – involves
segments, whole chroms or an entire
set of chroms
• Somatic mutations – affect body cells.
Not inheritable. Cancers (skin, etc)
Nondisjuction
• Involves a whole chromosome or an
entire set of chromosomes that fail to
separate during meiosis.
Gametes may contain extra
chromosomes (or missing
chromosomes)
• Another animation
If Sex chromosomes fail to separate properly
• a. Turner’s Syndrome - 45 XO
#1280
•
Sterile, underdeveloped, short, webbed neck, low
hairline
•
May have learning problems
•
1/2500 births
• b. Klinefelter’s syndrome – 47 XXY#1281
•
Underdeveloped, sterile, female characteristics but is
a male.
•
1/1000 births
• 45YO – Dead – need an X chromosome to survive
• 47XXX – Triple female – normal mental capacity. Tend to
be lighter than normal. Very passive. Are fertile. 1/1000
• 47XYY – Triple males. 1/1000. Very physical. Fertile.
Tends to be more aggressive. 2% of convicts of violent
crimes
46XX
Descriptions
45X0
47XXY
46XY
If Autosomes fail to separate
• Trisomy 21 (or other type of trisomy) –
aka; Down’s syndrome
• Extra #21 chromosome
• Mild to serious mental deficiency
• 1/800 births
Down’s Syndrome
or Trisomy 21
Extra #21 chromosome
Klinefelter’s syndrome 47XXY
Turner’s Syndrome - 45XO
Polyploidy
• Entire set or sets of chromosomes fail
to separate
• Fatal in animals
• In plants, leads to larger, hardier plants
• 3N, 4N
Polyploidy
• An entire set of chromosomes fails to
separate.
• Fatal in animals
• In plants, leads to larger, hardier plants
• 3N, 4N…
Chromosomal mutations
•
Deletions – loss of a part of a
chromosome
#1178
•
Additions – gain of a part of a
chromosome (duplication)
•
Inversions – Part of a chrom becomes
oriented in the reverse of its normal
direction
•
Translocation - crossing over of
nonhomologous chroms