Multiple choice quizzes for chapters 2 AND 4

1
Multiple choice quizzes for chapters 2 AND 4

• Due Monday Sept. 17th (midnight)

2
Outline

• Chi-squared analysis
• Extensions of Mendelian inheritance (Chapter 4)
• Inheritance pattern of single genes
• Gene interactions
• Non-Mendelian inheritance (Chapter 7)
• Maternal effect
• Epigentic inheritance
• Extranuclear inheritance

3
Hypothesis testing

• Goal determine if data from genetic crosses is
  consistent with a predicted pattern of
  inheritance (obeying Mendels laws)
• Evaluate the goodness of fit between the
  observed data and data predicted to come from a
  hypothesis
• DOES NOT prove a hypothesis is correct

4
Chi square test (?2)

• Formula
• ?2 ?

(O - E)2
E
O observed data in each category E expected
data in each category ? sum the calculation for
each category based on the experimenters
hypothesis
5
Chi square test (?2)

• Example cross
• True breeding straight wings, gray body
  (ccee)
• True breeding curved wings, ebony body (ccee)
• F1 generation is crossed to produced F2
• Do these traits follow laws of segregation and
  independent assortment?

6
Chi square test (?2)
F1 outcome all have straight wings, gray bodies
F2 outcome 193 straight wings, gray
bodies 69 straight wings, ebony bodies 64
curved wings, gray bodies 26 curved wings,
ebony bodies
7
Chi square test (?2)

• Step 1 Propose hypothesis that allows us to
  calculate the expected values based on Mendels
  laws
• 9 3 3 1 - Independent assortment
• Straight is dominant to curved
• Gray is dominant to ebony
• Step 2 Based on the hypothesis, calculate the
  expected values of the 4 phenotypes (based on 352
  individuals)
• 9/16 Straight wings, gray body 198 expected
• 3/16 Straight wings, ebony body 66 expected
• 3/16 Curved wings, gray body 66 expected
• 1/16 Curved wings, ebony body 22 expected

8
Chi square test (?2)

• Step 3 Apply values to chi square formula from
  the calculated and observed values
• ?2 1.06
• Step 4 Interpret the calculated chi square value
  using a chi square table

9
What does this table tell us?
10
How to read chi square table

• P values probabilities, allow us to determine
  the likelihood that the differences in values
  between observed and expected are due to random
  chance alone
• Low chi squared value correlates with deviation
  is due to random chance (accept hypothesis)
• Reject hypothesis if chi squared value is less
  than P 0.05
• Degrees of freedom total number of categories -
  1 (n-1) (in this case DoF 4-1)

11
?2 1.06
Accept hypothesis
12
Extensions of Mendelian InheritanceNon-Mendelia
n Inheritance

• Chapter 4
• Chapter 7

13
Outline

• Inheritance patterns of single genes
• Gene interactions
• Maternal effect
• Epigenetic Inheritance
• Extranuclear Inheritance

14
Example of simple Mendelian inheritance

• Traits affected by a single gene
• One allele is dominant over another
• Observed ratios in offspring obey Mendels laws
• i.e. self fertilization of F1 generation yield
  31 ratio

15
Dominant / Recessive relationship

• Wild-type alleles
• Most often encodes a protein that is made in
  proper amount, and functions normally
• Mutant allele
• Alleles that have been altered by mutation
• Often defective in ability to express a function
  protein
• Observed in human disease

16
Examples of recessive human diseases
Disease
Protein produced by normal gene

• Phenylketonuria
• Albainism
• Tay-Sachs
• Sandoff disease
• Cystic fibrosis
• Lesch-Nyhan syndrome

• Phenylalanine hydroxylase
• Tyrosinase
• Hexosaminidase A (lipid metabolism)
• Hexosaminidase B (lipid metabolism)
• Chloride transporter
• Hypoxanthine-guanine
• phosphoribosyl transferase
• inability to metabolize purines

17
Why are defective alleles often recessive?

• Diploid individuals have 2 copies of every gene
  (exception- sex linked traits)
• Often, in heterozygotes, 50 of the wild type
  protein is sufficient to provide wild type
  phenotype

18
Essential genes

• Defined by an absence of a specific protein
  causing a lethal phenotype
• Lethal allele is a loss of function allele of an
  essential gene
• Approximately 1/3 of all gene are essential
• Lethal alleles can kill organisms in early or
  later stages of life, depending on the function
  of the protein the gene encodes

19
When do lethal alleles cause death?

• Early stage
• Gene encodes a protein involved in cell division
• Later in life
• Huntington disease- progressive degeneration of
  the nervous system (mutation in Htt gene)
• Conditional lethal
• Temperature sensitive (ts) lethal (ex. mutant
  protein degradation at high temperature)
• Environmental exposure (ex. glucose-6-phosphate
  dehydrogenase mutation and fava bean ingestion)
• Semi-lethal - only lethal in some individuals

20
Mendelian ratios of lethal alleles

• Compare phenotypes with Punnett square
  predictions
• Ex. Chicken allele creeper
• Shortened legs, shortened wings
• Creeper phenotype observed in heterozygote
• When creeper is mated to normal chicken, ratios
  are 50 normal, 50 creeper
• When 2 creepers are crossed, the progeny are
  normal and creeper at a 12 ratio
• WHY?

21
creeper Punnett squares
C
c
C
c
c
C
c
c
normal
Creeper
CC phenotype Is lethal!
22
Incomplete dominance

• Heterozygote displays an intermediate phenotype
  between the two parental phenotypes
• Ex. the four oclock plant (Mirabilis jalapa)
• Red flowers CR
• White flowers CW
• Heterzygotes CRCW- pink flowers

23
Incomplete dominance
Contain 50 of normal protein, cannot make
same level of pigment that a plant with 100
protein can make
121 ratio red pink white
24
Mendels round/wrinkled is actually incomplete
dominance!

• Wrinkled morphology is due to loss in starch
  deposits in the seed
• Round phenotypic, but heterozygotes have an
  intermediate level of starch (microscopically)
• R (round) is dominant to r (wrinkled) for visual
  examination, but incompletely dominant at level
  of starch biosynthesis

25
Genes with multiple alleles

• An interesting example is coat color in rabbits
• Four different alleles
• C (full coat color)
• cch (chinchilla pattern of coat color)
• Partial defect in pigmentation
• ch (himalayan pattern of coat color)
• Pigmentation in only certain parts of the body
• c (albino)
• Lack of pigmentation
• The dominance hierarchy is as follows
• C cch ch c
• Figure 4.4 illustrates the relationship between
  phenotype and genotype

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Full coat color CC CCch Cch Cc
Chinchilla coat color cchcch cchch cchc
Himalayancoat color chch chc temp Sensitive!
Albino coat color cc
27
Temperature-sensitive conditional allele

• The himalayan pattern of coat color is an example
  of a temperature-sensitive conditional allele
• The enzyme encoded by this gene is functional
  only at low temperatures
• Therefore, dark fur will only occur in cooler
  areas of the body
• This is also the case in the Siamese pattern of
  coat color in cats
• Refer to Figures 4.4c and 4.5

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Fig. 4.5
29

• In a breed of dairy cattle called Brown Swiss,
  the opposite phenotype occurs
• The coat in the cooler parts of the body is
  light-colored
• The allele in this case is likely to be
  cold-sensitive
• Its enzymatic product does not work well at lower
  temperatures

30
Incomplete dominance

• Two alleles are both expressed in a heterozygous
  individual
• Ex. ABO blood type antigens
• Three alleles - IA, IB, i (i is recessive to both
  IA and IB)

31
Blood type characteristics
Blood type O A B AB Genotype ii
IAIA, IAi IBIB, IBi IAIB Surface antigen O
A B A and B Serum antibodies
?-A or B ?-B ?-A none
32
Blood type characteristics

• Individuals with type B blood have antibodies
  that recognize A antigen (but not B- you would
  not want to recognize your own blood as foreign)
• This is critical for transfusions
• Type O blood has no antigens (can be given to
  anyone)
• Type O individuals have antibodies against both A
  and B antigens
• UNIVERSAL DONOR
• Type AB blood has both A and B antigens
• Type AB individuals do NOT have antibodies
  against A and B antigens
• UNIVERSAL ACCEPTER

33
Experiment 4A

• Examine the role of dosage effect
• Look at eye color in Drosophila melanogaster
• Originally 2 alleles described- red eye and white
  eye (red allele is dominant to white)
• This trait is X-linked (located on the X
  chromosome- well learn more about this later . .
  .)
• Third allele discovered, called eosin

34
Eosin eye color allele

• Morgan and Bridges identified this allele
• When present in females (homozygous) the color is
  darker than males (one copy of X chromosome)
• Male color is called light eosin
• Hypothesized that having two copies (two doses)
  in females, the allele provides more color
• In the case of the red allele, one is enough for
  full color
• Test this by examining results of crosses
  designed to examine the various allele
  combinations

35
Set up the following crosses
Red eyed XwY
White eyed XwXw
Light eosin Xw-eY
Red eyed XwXw
White eyed XwY
Eosin Xw-eXw-e
36
Predicted offspring
Red eyed XwY
White eyed XwXw
XWXW XWY females males red eyed white eyed
1 1 ratio
37
Predicted offspring
Light eosin Xw-eY
Red eyed XwXw
XwXw-e female Red eyed
XwY male Red eyed
11 ratio
38
Set up the following crosses
White eyed XwY
Eosin Xw-eXw-e
Light eosin female Xw-eXw
Light eosin male Xw-eY
1 1 ratio
39
Data
40
Results

• Prediction of the eosin allele having a dosage
  effect were correct
• Females with one copy of the eosin allele and one
  copy of the white allele had the light eosin
  phenotype

41
Overdominance

• Phenomenon when the heterozygote has a survival
  or reproductive advantage over either homozygote
• Referred to as over-dominance or heterozygote
  advantage
• Related to a similar phenomenon called hybrid
  vigor or heterosis (observed in breeding and
  agriculture situations)

42
Example of overdominance

• Sickle cell anemia
• Healthy individuals carry HbA allele, make
  hemoglobin A, leading to wt blood cell formation
• Sickle cell patients are homozygous for HbS,
  making hemoglobin S, and RBCs form sickle shape
  during low oxygen concentration
• Abnormal sickle shaped cells can become clogged
  in arteries, leading to localized areas of oxygen
  depravation (PAINFUL)
• Heterozygote (HbA HbS) has only slightly reduced
  hemoglobin function (incomplete dominance)

43
Example of overdominance

• However- consider the disease malaria. . .
• Malaria is caused by a protozan (Apicomplexa)
  Plasmodium sp.- spread by the Anopheles mosquito
• This organism is spread to the blood by a the
  mosquito bite, and enters RBCs, to replicate
• Individuals heterozygous for the hemoglobin S
  allele produce RBCs that are likely to rupture
  when infected with the protozoa- protecting them
  from infection

44
3 possible mechanisms for overdominance
Ex. Sickle cell anemia Malaria infection
Heterodimer may exhibit greater activity
Mixture of both enzymes would give a wider range
for environmental survival
45
Incomplete penetrance

• Refers to occasional occurrence when a dominant
  allele in a heterozygote does not cause a
  phenotype
• If 60 of heterozygotes with the allele have the
  corresponding phenotype, the allele is said to by
  60 penetrant
• This way, the phenotype can skip generations
• Example polydacytly

46
Incomplete penetrance
Low expressivity
47
Environmental influence on trait expression

• Surrounding environment can have an impact on
  individual phenotype
• Examples- heterozygote snapdragon flower color
• PKU

48
Sex-influence inheritance

• Cases in which an allele is dominant in one sex,
  but recessive in the other
• Only observed in heterozygotes
• Fathers can pass these traits onto sons-
  therefore NOT sex-linked
• Example pattern baldness in humans (loss of hair
  on the front and top, but not sides of head)

49
Pattern baldness
Genotype Phenotype males females BB bald bald
Bb bald nonbald bb nonbald nonbald
thinning hair later in life
-Baldness phenotype is related to levels of male
sex hormones -If a female heterozygote has a rare
adrenal gland tumor, and produces high level of
male hormones hair will fall out, but will grow
back upon tumor removal!
50
Adams Family Baldness
Example pedigree Bald individuals are in black
51
Sex-limited traits

• Traits that can occur in only one of the two
  sexes
• Ex. Breast development in humans
• bird plumage
• Roosters have larger comb and waddles, longer
  neck, tail and sickle feathers

Genotype Phenotype Females males hh hen-feathe
red cock-feathered Hh hen-feathered hen-feather
ed HH hen-feathered hen-feathered
Depends on production of sex hormones
52
Gene interactions

• When two or more different genes influence the
  outcome of a single trait

Examine crosses in general AaBb x AaBb A is
dominant to a B is dominant to b
If these genes control two traits, the laws of
segregation and independent assortment would
dictate a 9331 ratio of offspring
53
Two gene interaction resulting in 4 phenotypes

• Observed in comb morphology of chickens
• Discovered by William Bateson and Reginald
  Punnett in 1906
• Examine the cross of two true breeding lines- a
  rose comb and a pea comb
• All F1 offspring had a walnut comb
• F2 generation resulted in
• 9 walnut 3 rose 3 pea 1 single

54
2 gene determination of comb morphology

• 9 walnut 3 rose 3 pea 1 single

Data from crosses determined that R (rose comb)
is dominant to r P (pea comb) is dominant to p RP
are co-dominant - yielding walnut comb rrpp
produces a single comb
RP Rp rP rp
RP Rp rP rp
55
97 ratio due to epistasis

• Examine sweet pea flowers
• True breeding purple and white lines
• F1 when crossed resulted in all purple
• F2 contained purple and white in a 31 ratio
• Crossed two different white lines
• F1 ALL PURPLE FLOWERS??
• F2- purple and white in a 9 7 ratio (?!?)
• Decided there are 2 genes involved

56
Flower color explanation

• 2 gene interaction

C (purple color producing) is dominant to c
(white) P (purple color producing) is dominant to
p (white) cc or pp masks C or P alleles- causing
white
CP cP Cp cp
CcPp
CCPc
CcPP
CCPP
CP
ccPp
CcPp
ccPP
CcPP
cP
Ccpp
CCpp
CcPc
CCPp
Cp
ccpp
Ccpp
ccPp
CcPp
cp
57
Flower color explanation

• 2 gene interaction
• Epistasis- when one gene can mask the phenotypic
  effects of a different gene
• Epistatic interactions occur when multiple
  proteins are participating in a common cellular
  functions (ie. Enzymatic pathway)

Colorless precursor
Colorless intermediate
Purple pigment
Enzyme C
Enzyme B
58
Experiment 4B

• Bridges (the fly geneticist) identified another
  eye color allele- cream color allele
• Occurrence of cream colored eyes was rare
• Hypothesized that this would be functioning in
  one of two ways
• Cream color was a new mutation that changes eosin
  to cream color
• A different gene has a mutation that modifies the
  expression of the eosin allele (gene interaction)

59
Derivation of cream colored eye stock

• Obtained from a culture with eosin eyes
• Allele called cream a
• Fly was used to produce a true breeding stock
  with cream colored eyes

60
Set up crosses
Red eyed CCXWXW
Cream colored eyes cacaXw-eY
Red eyed CcaXWY
Red eyed CcaXWXw-e
61
Data
104 females w/ red eyes 47 males w/ red eyes 44
males w/ light eosin 14 males w/ cream

• Suppose
• C is normal allele (which does nothing to eosin)
• ca is a cream allele that modifies a would-be
  eosin phenotype to cream
• F1 genotype is CcaXWXw-e (females) and CcaWY
  (males)

62
Punnett square
Prediction 8 red eyed females 4 red eyed males 3
eosin males 1 cream male
104 females w/ red eyes 47 males w/ red eyes 44
males w/ light eosin 14 males w/ cream
63
Non-mendelian inheritance

• Maternal effect
• Epigenetic inheritance
• Extranuclear inheritance

• Inheritance patterns that deviate from a
  Mendelian pattern
• Genotypes of offspring do not directly govern the
  phenotype in ways predicted by Mendel
• Due to specific timing of nuclear gene expression
  and nuclear gene inactivation
• Inheritance of and influence on traits by
  extranuclear genetic material

64
Maternal effect

• Inheritance pattern observed for nuclear genes
• Genotype of the mother directly determines the
  phenotypic traits of the offspring
• Genotypes of the neither individual itself, nor
  the father participate in the phenotype
• Due to the mother providing gene products to the
  developing eggs

65
Maternal effect

• Ist studied by A. E. Boycott in 1920s using
  Limnea peregra (water snails)
• Shell shape can be either
• Right hand facing (dextral)
• Left hand facing (sinistral)
• Direction is decided on by the egg cleavage
  pattern immediately after fertilization
• Genetic crosses were completed to examine the
  transmission of this trait

66
Inheritance pattern of snail coiling
67
Oogenesis in female animals

• Oocyte is surrounded by nurse cells during
  maturation
• Nurse cells are diploid
• If nurse cells are heterozygotic, their genes are
  activated to produce mRNA and protein
• Gene products are transported to the oocyte
• It makes does not matter what the oocyte allele
  is- just what the gene products the nurse cells
  are producing

68
Mechanism of maternal effect
69
Maternal effect genes and gene products

• Maternal effect genes encode RNA and proteins
  critical in embryogenesis
• Participate in cell division, cleavage
  patterning, and body axis orientation
• Mutations in maternal effect alleles can often be
  severe/ even lethal
• Many studies have been done in Drosophila and the
  maternal effect on antero-posterior and
  dorso-ventral axis patterning (will cover in
  chapter 23)

70
Epigenetic inheritance

• Modification is made to nuclear genes or
  chromosomes, altering gene expression
  transiently, but not permanently change DNA
  sequence
• Modifications occur during oogenesis,
  spermatogenesis, early embryogenesis- permanently
  effecting the traits of the individual
• Two examples
• Dosage compensation
• Genomic imprinting

71
Dosage compensation

• Mechanism to offset differences in sex
  chromosomes between males and females
• Required to equilibrate the level of expression
  in both sexes even though the male and female
  complement of sex chromosomes are different
• Termed in 1932 by Hermann Muller in response to
  eye color mutations in Drosophila (on X
  chromosome)

72
Drosophila dosage compensation

• X linked gene leading to apricot eye color is a
  similar phenotype in homzygous females and
  hemizygous males
• Heterozygous females (apricot and deletion) have
  a paler color- one copy in females does not equal
  one copy in males
• Copy number is compensated by increased
  expression level in males
• Dosage compensation does not occur in all X
  linked genes - why?

73
Types of dosage compensation
Sex chromosomes
Females Males
Placental Mammals Marsupial Mammals Drosophilia
melanogaster Caenorhabditis elegans
XX XY
One X chromosome is inactivated Paternally
derived X chromosome is inactivated Expression of
X chromosome in males is increased 2x Expression
level of both X chromosomes is decreased 50 in
hermaphrodites
XX XY
XX XY
XX XO
Process is unclear for birds and fish
74
Random X inactivation

• Theory proposed in 1961 by Mary Lyon, Liane
  Russell
• First evidence was cytological- 1949 Murry Barr
  and Ewart Bertram
• Condensed structure observed in somatic cell
  nuclei during interphase, only in female cats

Barr Body
Highly condensed X chromosome
75
Calico cat X inactivation

• All calico cats are females
• Heterozygous for X-linked gene with an orange or
  black allele (white coloring is due to a separate
  gene)
• Orange and black patches are distributed randomly
• X inactivation of one of the two alleles in
  somatic cells

76
Mechanism of X- inactivation

• Lyon Hypothesis
• Examined in mice with variegated coat color
• Inherit allele for white coat color from mother
  (Xb), black coat color from father (XB)
• Patches of epithelial tissue derived from
  embryonic cell in which one of the X chromosomes
  were inactivated
• Compaction of DNA during inactivation prevent
  gene expression

77
Mechanism of X inactivation
78
Experiment 7A

• Test of Lyon hypothesis at the cellular level
• Use an gene on the X chromosome that encodes
  glucose-6-phosphate dehydrogenase
• There are two alleles that produce protein
  variants that run either fast or slow when
  subjected to gel electrophoresis
• Heterozygous adult female produce both enzyme
  variants, while males produce only one

79
Experimental technique

• Isolate tissue from a heterozygous female
• Culture on solid media to produce colonies -
  groups of cells that originated from one single
  progenitor cell
• Identify whether these clonal populations express
  only one G-6-PD variant

80
Hypothesis

• Single somatic cells from a heterozygous female
  should only produce one variant of the G-6-PD
  enzyme

81
Experimental set up
82
Experimental set up (cont.)
83
Data
Result single somatic clones only express one
form of the enzyme
84
How does X inactivation occur?

• Human cells are able to count the X
  chromosomes, and allow only 1 to remain active
• In females- 2 Xs are counted, one is inactivated
• In males- 1 X is counted, none are inactivated
• If there is an abnormality in the number of sex
  chromosomes, counting still occurs, and more or
  less Barr bodies are produced

85
X- inactivation center (Xic)

• Region on the X chromosome plays a critical role
  in X inactivation (process still not fully
  understood)
• The number of Xics are counted
• If a chromosome is missing an Xic- no X
  chromosomes are inactivated - this is embryonic
  lethal!

86
Xist gene
Successful compaction requires first the
activation of Xist gene on inactivated X
chromosome Xist gene product is an untranslated
RNA molecule that coats the X chromosome to be
inactivated The promotes binding of other
proteins to the chromosome and compaction into a
Barr body
87
Xce region
There are multiple Xce alleles Heterozygous
females with a strong Xce allele will favor the
other for inactivation, skewing the inactivation
(usually not to more than 70) Tsix gene produces
an RNA complementary to Xist RNA
(antisense) Expression of Tsix is thought to
prevent inactivation during embryonic development
88
Stages of X inactivation

• Initiation
• One X is targeted for inactivation
• One X is chosen to remain active
• Spreading
• Chosen X is inactivated
• Expression of Xist, coating of X, condensation
• begins near X-inactivation center and spreads
  outward
• Maintenance
• Inactivated X chromosome maintained during
  somatic divisions

Embryonic stages
89
Initiation Occurs during embryonic development.
The number of X inactivation centers (Xics)
are counted and one of the X chromosomes remains
active and the other is targeted for inactivation.
To be inactivated
Xic
Xic
Spreading Occurs during embryonic development.
It begins at the Xist and progresses toward both
ends until the entire chromosome is inactivated.
The Xist gene encodes an mRNA that coats the X
chromosome and promotes its compaction into a
Barr body.
Xic
Xic
Further spreading
Barr body
Maintenance Occurs from embryonic development
through adult life. The inactivated X chromosome
is maintained as such during subsequent cell
divisions.
90
Escape X inactivation

• Some genes are expressed on inactivated X
  chromosome
• Xist
• Pseudoautosomal genes also found on Y chromosome

91
Genomic Imprinting

• Segment of DNA is marked
• Mark is retained and recognized throughout the
  life of the organism inheriting the marked DNA
• Causes non-Mendelian patterns, due to the ability
  to distinguish between maternally and paternally
  inherited alleles
• Offspring express one of the marked alleles, not
  both (monoallelic expression)

92
Imprinting example IgF-2 allele

• Encodes murine growth hormone- insulin-like
  growth factor 2
• Imprinting results in expression of paternal
  allele, but NOT maternal
• Paternal allele is transcribed, maternal allele
  is transcriptionally silent
• Mutant of Igf-2 (Igf-2m) can cause dwarfism but
  only if inherited from the male parent

93
Igf-2 imprinting in mouse
mother
father
mother
father
Igf-2m Igf-2m x Igf-2 Igf-2
Igf-2m Igf-2m x Igf-2 Igf-2
Igf-2m Igf-2
Igf-2 Igf-2m
silent
expressed
94
3 stages of imprinting

• Establishment of imprint during gametogenesis
• Maintenance of imprint
• Erasure and restablishment of imprint in germ
  cells

95
(No Transcript)
96
Imprinting via DNA methylation

• DMR (differentially methylated regions) near
  imprinted genes
• Methylated in sperm or oocytes, not both
• Methylation results in inhibition of gene
  expression (most of the time) via enhancing the
  binding of inhibitors or inhibiting the binding
  of enhancers
• But, as usual, there are interesting exceptions

97
H19 and Igf-2 expression in humans

• 2 imprinted human genes
• Controlled by the same DMR
• DMR region also contains regulatory binding sites
  for transcription of both H19 and Igf-2 genes
• Highly methylated on paternal chromosome
• Maternal chromosomal region is unmethylated

98
H19 and Igf-2 expression in humans
Only Igf-2 mRNA expressed believed methylation
prevents an inhibitor of Igf-2 from Binding to
DMR region
Only H19 mRNA expressed
99
Human disorders as a result of imprinting

• Prader-Willi syndrome and Angelman syndrome
• Prader-Willi patients- reduced motor function,
  obsesity and mental deficiencies
• Angelman patients- hyperactive, unusual seizures,
  repetitive symmetrical muscle movements, mental
  deficiencies
• Both due to small deletion of chromosome 15
• If inherited from paternal parent- Prader-Willi
• If inherited from maternal parent- Angelman

100
Angelman syndrome

• Results from the lack of expression of a single
  gene UBE3A, located in this region of chromosome
  15
• Paternal allele is silenced- therefore if the
  inherited maternal chromosome is lacking this
  region- there is an overall lack of expression

101
Prader-Willi syndrome

• Genes responsible not yet determined
• Although there are several known imprinted genes
  in this region that would be good candidates,
  including SNRPN, involved in gene splicing

102
(No Transcript)
103
Extranuclear Inheritance

• Organellar genetic material
• Mitochondria and chloroplasts have genetic
  material
• Located inside the nucleoid
• Genetic material is circular, double stranded DNA
• There is variation in size and number of copies
  of this DNA

104
mtDNA

• About 17,000 bp in length
• Encode ribosomal and tRNA, required for synthesis
  of proteins inside mitochondrian
• Encode 13 polypeptides involved in oxidative
  phosphorylation, to allow synthesis of ATP

105
Extrachromosomal inheritance

• Non-Mendelian pattern
• Ex. Pigmentation of Mirabilis jalapa is solely
  due to maternal parent
• Called maternal inheritance
• Pigment production genes are inherited only
  through chloroplasts- only in egg (pollen does
  not transmit plastids/chloroplasts to offspring)

106
Organelle Transmission
107
Endosymbyosis theory

• Theory that the ancient origin of plastids whas
  when a primordial bacterium took up residence
  in a eukaryotic cell