Gross Anatomy of the Eye...6 Graw (2010) in Seminars in Developmental Biology 90: 343.11 Primary Eye...
Transcript of Gross Anatomy of the Eye...6 Graw (2010) in Seminars in Developmental Biology 90: 343.11 Primary Eye...
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PHOP Core Fall 2018
Intro to Genetics and Ocular Development
D. C. Otteson PhD UHCO 1
Gross Anatomy of the Eye
Graw, Eye Development. (2010) in
Current Topics in Developmental Biology (Volume 90) p. 343. 2
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From the National Eye Institute
http://www.nei.nih.gov/photo/ 3
Body Axis Terminology
Caudal
(posterior)
Ventral
Dorsal
Medial
Lateral
Rostral
(anterior)
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Eye-specific Axis Terminology
Dorsal / Superior
Ventral / Inferior
Posterior Anterior
Nasal
Temporal
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http://www.becomehealthynow.com/article/bodyembryo/789/1
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GastrulationInduction and cell migration forms three germ layers
Ectoderm
Mesoderm
Endoderm
Gastrulation initiates at posterior end
Figure from Developmental Biology by Scott Gilbert. Sinauer
Associates, Inc. 7
(From Martin, Neuroanatomy
Text and Atlas, Elsevier press)
Neural Crest
8
5
Neural tube segmentation: brain vesicles
(From Martin, Neuroanatomy Text and
Atlas, Elsevier press)
Mouse: day 8 post fertilization day 10-11 post fertilization
Human: week 4 week 5
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Growth of
cranial nerves
Dekaban, A.S. and Sadowsky, D, Ann. Neurology, 4:345-356, 1978
3-vesicle
stage5-vesicle stage
Telencephalon
grows
Cortical maturation
and expansion
NOT TO SCALE !!!!
EYE
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Graw (2010)
in Seminars in Developmental Biology 90: 343.
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Primary Eye Field in Anterior Neural Plate
Eyes develop from cells in
anterior neural plate
Eye field contains cells
competent to form eye
structures
Not all cells will actually
contribute to eye structures
Early genes important in
specification of eye fields:
Pax6, Rax/Rx, Six3,
Tbx3, Six6, Otx2, Lhx2,
TllSpecies: Mouse E7 ~Human E17
http://www.med.unc.edu/embryo_images/12
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Neurulation: Folding of Neural Plate
Neural plate grows rapidly
Eye fields in rostral neural
plate expand
Eye fields separate at
midline
Secreted sonic hedgehog
(SHH) from notocord
specifies ventral midline
http://www.med.unc.edu/embryo_images/
Species: Mouse E8 ~ Human E21
View: Frontal13
PAX2 specifies ventral optic cup and optic stalk
Mutations: loss of ventral diencephalon, optic chiasm,
ventral optic nerve coloboma, kidney and ear defects
Homozygous: lethal: no chiasm, no uritogenital tract
SHH secreted from notocord early embryo
induces ventral and midline structures in neural plate
required for separation of eye fields
Mutations: holoprosencephaly, cyclopia, midline facial
defects, microcephaly
PAX6 specifies dorsal and lateral structuresneural retina, RPE, lens, cornea (+ non-ocular structures)
Mutations: heterozygous: aniridia, glaucoma
homozygous: (lethal) anophthalmia, failure to form nasal
passage, brain defects
Separation of Eye Fields
SHH represses PAX6, induces PAX2
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Cells in Eye Fields Invaginate Forming Optic
Grooves (a.k.a. optic sulci, optic pits)
Mouse E8.5 ~ Human E24
Fronto-LateralMouse E8 ~ Human E22
View: Frontal
http://www.med.unc.edu/embryo_images/ 15
Neural tube, rat development
showing optic vesicles
Zhang, Fu, Barnstable (2002)
Molec. Neurobiol. 26:137-152.
Rat embryo, E11.
Rostral view of neural tube
Head ectoderm removed
Arrows show
anterior neuropore
ov=optic vesicles
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9
Species: Mouse E8.5 to 9 (~Human E25)
http://www.med.unc.edu/embryo_images/
Optic vesicle/Lens induction
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Mouse E 9 (~Human E28) Mouse E10 (~ Human E29)
http://www.med.unc.edu/embryo_images/
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Species: Mouse E11 (~Human E36)
View: Coronal
Lens placode invaginates to form
lens vesicle
Invagination of optic vesicle forms
bilayered optic cup
Lens vesicle pinches off surface
ectoderm
Overlying ectoderm becomes
cornea
http://www.med.unc.edu/embryo_images/
Lens Vesicle and Optic Cup
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Species: Mouse E 11
(~Human E36)
View: Coronal Cut
http://www.med.unc.edu/embryo_images/
Retina/RPE
Pax6 (+Mitf in RPE)
Lens vesicle
Pax6, Sox2/3
Optic Stalk
Pax2
Irido-pupillary
Membrane
From neural crest
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Lens DevelopmentPrimary
Fiber elongation
Secondary
Fiber elongation
Graw (2010)
in Seminars in Developmental Biology 90: 343.
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A model of a genetic switch composed of SOX2/SOX3 and Pax6, which regulates initiation of lens development.
Kamachi Y et al. Genes Dev. 2001;15:1272-1286
©2001 by Cold Spring Harbor Laboratory Press 22
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Lens maturation
Proliferation of cells at the equator
Elongation of cells at bow
Fiber cells
nuclei are gone in central lens
cells remain connected by gap junctions
Species: Human 8 Weeks
http://www.med.unc.edu/embryo_images/23
Lens Fiber Cells
Song et al J Clin Invest. 2009;119(7):1837–1848
Scanning electron micrographs of bovine lens fiber cells
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induced by lens
• outer epithelial layer forms from surface
ectoderm
• inner layers primarily from neural crest
cells
Image of cornea from: T. Caceci (2001)
Anatomy and Physiology of the Eye V2.0
http://www.med.unc.edu/embryo_images/
Cornea
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RPE: Outer pigmented layer becomes relatively thinner
Single cell layer
RPE cells express PAX6 and MITF. Expression of MITF helps
specify RPE identity and this transcription factor directly regulates genes
that are responsible for pigment formation in RPE.
RETINA: Inner, neural portion thickens
Pseudostratefied epithelium
Differentiation begins at ~E11.5
Mouse Day E14 (~ Human 7 weeks) http://www.med.unc.edu/embryo_images/
RPE
Ventricle/
Sub-retinal
Space
Retina
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The tunica vasculosa lentis
From human fetus
(a) Hyaloid artery
(b) Posterior ciliary artery
From Duanes Ophthalmology 2006
Chapter 15: Lens, Kleiman and Worgul
Vasculature
Mouse(Gerhardt et al., 2003)
Superficial Plexus
Deep Plexus
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Iris and Ciliary Body Formation
Human ~15 Weeks
http://www.med.unc.edu/embryo_images/
Human 8 Weeks
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Ittner et al. Journal of Biology 2005 4:11
Neural Crest Derivatives in Eye
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Neural Crest
Ittner et al. Journal of Biology 2005 4:11 30
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Human: 8 Weeks
Eyelids
•begin to form at end of embryonic period
•fuse at the start of 2nd trimester
•reopen at the beginning of the 3rd trimester
Human: 10 Weeks
http://www.med.unc.edu/embryo_images/31
Loci for Inherited Retinal Disease
RetNet; Stephen P Daiger PhD
The University of Texas Health Science Center, Houston, Texas
http://www.sph.uth.tmc.edu/RetNet
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genetics
DNA Replication and Inheritance
The basis of
perpetuation of life and
transmission of
traits/genes
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Inherited vs. Non-inherited Mutations
• Germ-line mutations lead to inherited mutations– Occurs in germ line tissue
– If mutation passes into gametes (egg, sperm), it will be passed
on to next generation. • e.g. sickle cell anaemia
• Retinitis pigmentosa,
• Keratoconus
• Somatic mutations occur in somatic tissues – Population of identical cells derived from a single mutated
somatic cell is a clone
– Often results in a patch of phenotypically mutant cells
– Not inherited
– Many tumours result from somatic mutation
– Two-hit theory of cancer e.g. retinoblastoma
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Heritable Genetic Changes
Single gene mutation
Change in allele of a gene
• Protein not expressed or
• Protein non-functional or
• Protein acquires novel/harmful/beneficial functions
• Contributes to evolution
Chromosome mutation: multiple genes
Changes in segments of chromosome
Deletion, duplication, inversion, translocation
Loss/duplication of whole chromosome
Epigenetic Changes
DNA modifications that can permanently change gene
expression
Genes + Environment= Phenotype
genes environmentphenotype
Contributions from genotype/environment varies with disease
Some diseases have both genetic and environmental components
e.g. macular degeneration; cataract; heart disease
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Classifying Mutations : Phenotypic Aspects
• Morphological mutations– Visible/measurable change in phenotype– e.g. eye color; ocular coloboma
• Lethal mutations– Heterozygous: normal– Homozygotes: do not survive– e.g. Cystic Fibrosis= mutation in CFTR gene–
• Conditional mutations – Phenotype only presents under specific conditions – e.g. predisposition for developing disease: diabetes, heart
disease, cancer: can change life-style and reduce risk
• Biochemical mutations– Change in enzyme, biochemical pathway components– e.g. Albinism (inability to synthesize melanin) mutations in
Tyrosinase and other enzymes of melanin biosynthesis
8-38
Mutations: Mechanistic Aspects
• Silent mutations/Polymorphisms
• Change in DNA sequence:
• doesn’t change sequence of protein (synonymous)
– or
• occurs in non-critical region of gene
– Used for:
– DNA “fingerprinting”
– paternity analysis
– genetic mapping (linkage analysis)
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Consequences of point
mutations
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Gametes get one copy of each chromosome
Gene R is on a separate chromosome from A and B and segregates independently of A and B
All allelic combinations are found: AB +R AB + r ab + R ab + r
Therefore, R is not linked to the A or B genes
Genes A and B are on the same chromosome
Parental allelic combinations inherited together (AB or ab)
A and B genes are linked
Independent assortment of
chromosomes during meiosis
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Predicting Patterns of Inheritance: Punnett Square
Genotype:
B/B B/b b/b
1 : 2 : 1
Phenotype:
Black brown
3 : 1
diploid
diploid
haploid
Shown: two alleles of a single gene
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Mendelian Non-Mendelian
Autosomal Epigenetic
Sex-linked Mitochondrial
Recessive Imprinting
Dominant Multifactorial
Monogenic
Other including complex
Syndromic
Semi-dominant/co-dominant
Sporadic/spontaneous
Digenic
Patterns of Inheritance
• Autosomal inheritance
– Based on the variation of single genes on regular chromosomes
(autosomes)
• Sex-linked inheritance
– Based on the variation of single genes on sex-determining
chromosomes
• Cytoplasmic inheritance
– Based on the variation of single genes on organelle’s
chromosomes (e.g. Mitochondrial)
Patterns of Inheritance
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Patterns of Inheritance: Recessive
Appearance of macula in Usher syndrome
Fundus pigmentation in Usher
syndrome
Usher Syndrome I (human) USHIB
mutations in MYO7A (Myosin7A)
• Heterozygous (-/+) normal
• Homozygous (-/-)
• profound congenital hearing
impairment
• unintelligible speech
• early retinitis pigmentosa (<10 yrs
• vestibular dysfunction
• defects in cilia (photoreceptor
connecting cilium; hair cells)
Patterns of Inheritance: Recessive
•How to detect this pattern in
patients?
•Can you distinguish this from
spontaneous mutation?
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Parents:
heterozygous
(+/-)
normal
+
CSNB
-
normal
+
CSNB
-Genotypes: +/+ +/- -/-
Ratios (genotype)
Phenotypes
Ratios (phenotypes)
Patterns of Inheritance: Recessive
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Parents:
heterozygous
(+/-)
normal
+
CSNB
-
normal
++/+ -/+
CSNB
-+/- -/-
Genotypes: +/+ +/- -/-
Ratios (genotype)
Phenotypes
Ratios (phenotypes)
1 2 1
Normal Normal mutant
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Patterns of Inheritance: Recessive
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Parents:
Heterozyous (+/-)
Homozygous (+/+)+ -
+
+
Genotypes: +/+ +/- -/-
Ratios (genotype)
Phenotypes
Ratios (phenotypes)
Patterns of Inheritance: Recessive
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Parents:
Heterozyous (+/-)
Homozygous (+/+)+ -
+ +/+ -/+
+ +/+ -/+
Genotypes: +/+ +/- -/-
Ratios (genotype)
Phenotypes
Ratios (phenotypes)
1 1 0
Normal Normal
1 0
Patterns of Inheritance: Recessive
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• Recessive genes are not major contributors in
human genetic disease unless:
• highly consanguineous group
• frequency of mutant allele in general population is
high
• Difficult to determine if this is inherited or
spontaneous if only one affected individual
Patterns of Inheritance: Recessive
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Patterns of Inheritance: Dominant
• Dominant: Mutant allele is fully expressed and masks
the expression of the allele.
• With true dominant, individuals heterozygous and
homozygous for the mutated allele show the same
phenotype.
• Haplo-insufficient: Absence of one allele results in
intermediary phenotype; often referred to as semi-
dominant
• Co-dominant: both alleles are fully expressed
• e.g. blood groups (A, AB, B, O)
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genetics53
Patterns of Inheritance: Dominant
Retinitis Pigmentosa
Phenotype:
• Constriction of the visual fields
• Night blindness
• Fundus changes
• “bone spicule” lumps of pigment
• Photoreceptor Degeneration
• Variable age of onset
Multiple patterns of inheritance
• Autosomal dominant
• Autosomal recessive
• X-linked
More than 3100 distinct mutations in
56 genes in have been identified(Daiger et al 2013 Clinical Genetics 84:132.)
From: www.stlukeseye.com/
genetics54
Male unaffected
Male affected
Female
unaffected
Female affected
Patterns of Inheritance: Dominant
Retinitis Pigmentosa
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genetics55
Genotypes: +/+ +/- -/-Ratios (genotype)
Phenotypes
Ratios (phenotypes)
Parents
Heterozyous (+/-)
Homozygous (+/+) + +
+
-
Patterns of Inheritance: Dominant
Retinitis Pigmentosa
genetics56
Genotypes: +/+ +/- -/-Ratios (genotype)
Phenotypes
Ratios (phenotypes)
1 1 0
Normal Mutant Mutant
1 1 0
Parents
Heterozyous (+/-)
Homozygous (+/+) + +
+ +/+ +/+
- +/- +/-
Patterns of Inheritance: Dominant
Retinitis Pigmentosa
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genetics57
Patterns of Inheritance: Semi-Dominant Haploinsufficient
Aniridia
• Mutations in transcription factor Pax6
• Haploinsufficient
• Homozygous lethal
• Heterozygotes: anterior segment malformations:• aniridia
• corneal clouding with variable iridolenticulocorneal adhesions
• Peters anomaly (central corneal leukoma, absence of the posterior corneal stroma and Descemet membrane, and a variable degree of iris and lenticular attachments to the central aspect of the posterior cornea)
• foveal hypoplasia
• glaucoma
• autosomal dominant keratitis
A normal eye is pictured above.
Below is the eye of a child with
aniridia, a congenital eye disorder.
People born with the disease have
no iris and are generally legally
blind.
CREDIT ANIRIDIA FOUNDATION
genetics58
Genotypes: +/+ +/- -/-Ratios (genotype)
Phenotypes
Ratios (phenotypes)
Parents
Heterozyous (+/-)+ -
+
-
Patterns of Inheritance: Semi-Dominant / Haploinsufficient
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genetics59
Genotypes: +/+ +/- -/-Ratios (genotype)
Phenotypes
Ratios (phenotypes)
1 2 1
Normal Mutant More severe
1 2 1
Parents
Heterozyous (+/-)+ -
+ +/+ +/-
- +/- -/-
Patterns of Inheritance: Semi-Dominant Haploinsufficient
genetics60
• Mutation on X chromosome
• Females: XX
• Males: XY
• Mutation/disease phenotype manifests in males
• Females are carriers, typically normal
– But may manifest mosaic defects
• Generation skipping pattern
Patterns of Inheritance: X-linked
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genetics61
Examples of X-linked Retinal Diseases
OA1 X-linked ocular albinism
RP23,RP6, X-linked Retinitis Pimentosa
RS1 Retinoschisis
OPA2 X-linked optic atrophy
NDP Norrie disease; familial exudative
vitreoretinopathy
Colorblindness (mutations in red/green opsin genes):
OPN1SW protan (red deficient)
OPN1LW deutan (green deficient)
blue cone monochromacy (red & green deficient)
X-linked Diseases: X-inactivation
X chromosomes:
Males have 1
Females have 2
How to maintain same level of
transcription (RNA levels) from
X chromosome genes?
Random X-inactivation
(Lyonization) in females
after Mary Lyon
e.g. coat color in cats62
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X-inactivation of B-gal
transgene in retina
http://mentor.lscf.ucsb.edu/course/winter/mcdb101b/x-inactivation/xinactivation.html
X-inactivation in the
cornea
John West
http://www.cip.ed.ac.uk/gallery/index.htm
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Mutant phenotype present in males x* Y
Carrier females may show mosaic defects Xx*
Skips generations
carrier
XY Xx*
XX x*Y XY Xx* XY x*Y XX
XY Xx* Xx* Xx* Xx* XY x*Y XX XX x*Y Xx* Xx* XY
Patterns of Inheritance: X-linked
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genetics66
Genotypes: X*X XX X*Y XY
Ratios (genotype)
Phenotypes
Ratios (phenotypes)Normal
*carrier
Normal Affected Normal
Parents
Father affected X* Y
X
X
Patterns of Inheritance: X-linked
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genetics67
Genotypes: X*X XX X*Y XY
Ratios (genotype)
Phenotypes
Ratios (phenotypes)
0 1 0 1
Normal
*carrier
Normal Affected Normal
1 0 0 1
Parents
Father affected X* Y
X X*X XY
X X*X XY
Patterns of Inheritance: X-linked
genetics68
Genotypes: X*X XX X*Y XY
Ratios (genotype)
Phenotypes
Ratios (phenotypes)Normal
*carrier
Normal Affected Normal
Parents
Mother-carrier X Y
X*
X
Patterns of Inheritance: X-linked
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genetics69
Genotypes: X*X XX X*Y XY
Ratios (genotype)
Phenotypes
Ratios (phenotypes)
1 1 1 1
Normal
*carrier
Normal Affected Normal
1 1 1 1
Parents
Mother-carrier X Y
X* X*X X*Y
X XX XY
Patterns of Inheritance: X-linked
Mitochondrial diseases affecting the eye
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Ophthalmic manifestations of mitochondrial diseases:
cataract, retinopathy, optic atrophy, cortical visual loss, ptosis and
ophthalmoplegia
• Leber’s Hereditary Optic Neuropathy (LHON)
• Kearns-Sayre Syndrome (KSS)
• Mitochondrial Encephalopathy, Lactic Acidosis Stroke (MELAS)
• Myoclonic Epilepsy and Ragged Red Fiber myopathy
(MERRF)
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genetics71
Patterns of Inheritance: Mitochondrial
Leber Optic Atrophy
• Presents in mid-life as acute or sub
acute central vision loss leading to central
scotoma and blindness
• Associated with many missense
mutations in the mtDNA
• Mutations can act autonomously or in
association with other mt mutations
• Final visual acuity can range from 20/50
to no light perception, depending on
severity of the mutations
Leber Optic Neuropathy with
temporal optic nerve pallor in both
eyes.
http://www.revoptom.com/continuing_education/ta
bviewtest/lessonid/108143/
Healthy optic disc
http://www.intechopen.com/books/the-mystery-of-glaucoma/
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http://www.usc.edu/dept/mda/180evolution/IMAGES/wmho.html
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Patterns of Inheritance: Mitochondrial
Mitochondrial mutations:
•inherited ONLY from the mother
•NEVER from the father
ROM1/ROM1; ROM1/ROM1; +/ROM1 ; +/ROM1;
RDS/RDS +/RDS RDS/RDS +/RDS
ROM1/ROM1; ROM1/ROM1; +/ROM1; +/ROM1;
RDS/+ +/+ RDS+ +/+
+/ROM1; ROM1/+; +/+; +/+;
RDS/RDS +/RDS RDS/RDS +/RDS
ROM1/+; ROM1/+; +/+; +/+;
+/RDS +/+ RDS/+ +/+
Mode of inheritance: multigenic
ROM1/+; RDS/+ x ROM1/+; RDS/+
ROM1; RDS ROM1; + +; RDS +; +
ROM1; RDS
ROM1; +
+; RDS
+;+
Genotypes 1:2:1:2:4:2:1:2:1
Phenotypes: 1:3:2:1:9