W7LECT - Sex inheritance Flashcards
What is Sex Inheritance?
- Inheritance of genetic material in gametes.
- Females- two times X chromosome, thus can be homozygous or heterozygous.
- Males- one X chromosome and one Y chromosome. Considered hemizygous.
Compare sex inheritance to autosomal inheritance
- Females and males are not equally affected.
- Transmission of trait depends on sex.
What are the 5 features of X-linked Dominant Inheritance (XD)?
- Affected females to males ratio is about 2:1
- Vertical pedigree pattern (every generation)
- Daughters of an affected male have the disease
- No male-to-male transmission (helps distinguish it from autosomal inheritance)
- Affected females may have affected offspring of both sexes
What are the 5 features of X-linked Recessive Inheritance (XR)?
- Much more common in males than in females (males hemizygoyes XaY)
- Horizontal pedigree pattern (skip generations)
- Criss-cross pattern- affected male transmit the disease-causing mutation to a heterozygous daughter, who is asymptomatic carrier, which transmit the disease-causing allele to her sons
- No male-to-male transmission
- Father and all sons of affected women (rare) are affected, daughters are asymptomatic carriers
What is Criss-cross pattern?
Criss-cross pattern
- affected male transmit the disease-causing mutation to a heterozygous daughter, who is asymptomatic carrier, which transmit the disease-causing allele to her sons
What are 5 examples of X-linked Dominant Inheritance (XD)?
Hypophosphatemia, formerly vitamin D-resistant rickets (PHEX: phosphate-regulating endopeptidase)
Fragile X syndrome (FMR1)
Incontinentia pigmenti (IKBKG; NEMO protein)
Rett syndrome (MECP2)
Amelogensis imperfecta (amelogenin)
= Heterozygote Female Is Readily Affected
What are 3 examples of X-linked Recessive Inheritance (XD)?
- Hemophilia A / B (coagulation factors VIII / IX)
- Duchenne and Becker muscular dystrophy (DMD; dystrophin)
- Red-green color blindness
What are the 4 features of Y-linked Inheritance?
- Only males are affected
- Male-to-male transmission
- Affected males have affected father (if not new mutation) and all of the sons of the man are affected
- Vertical pedigree pattern (every generation)
*Male only can indicate this pattern
What are the examples of Y-linked Inheritance?
Examples: (Gene affected: Protein affected)
SRY gene
*Azoospermia is not inheritable but always new mutation
What are the features of Mitochondrial Inheritance?
- Inherited from the mother only
- Affected females transmit the disease to all of their children
- Affected males do not transmit to their children
- Does not follow Mendalian rules
- Heteroplasmy: the presence of more than one type of mtDNA in the mitochondria of a single individual’s cell
- Homoplasmy: all mitochondria carry the same mtDNA
Mitochondrial Inheritance
-> What is Heteroplasmy?
the presence of more than one type of mtDNA in the mitochondria of a single individual’s cell
Mitochondrial Inheritance
-> What is Homoplasmy?
all mitochondria carry the same mtDNA
What are examples of Mitochondrial Inheritance?
Leber’s hereditary optic atrophy
Describe inheritance pattern of amelogenesis imperfecta
- X - dominant
- Synthesis of enamel (external layer of teeth) is affected
- Heterozygote female - columnar pattern) X’X
- Homozygote female and hemizygote male - severe clinical forms
AMELOGENESIS IMPERFECTA
=> What are the genes affected? (Pathological proteins of enamel)
AMELX
Describe the inheritance pattern of incontinentia pigment
Describe inheritance pattern of Hypophosphataemia
Describe inheritance pattern of hemophilia A
- Deficiency in blood clotting
- Factor VIII deficiency
+) 45% inversion (F8A)
+) Insertion of LINE-1 sequence - 6% antibodies are developed to factor VIII
Describe inheritance pattern of hemophilia B
- Deficiency in blood clotting
- Factor IX deficiency (protease precursor)
- 2% deletion
-Insertion (ALU sequence)
Describe inheritance pattern of color blindness
- X-recessive
- Cones of retina detect the 3 basic colors
- Opsin genes
- Mutation in RCP gene: PROTANOPIA
- Mutation in GCP gene: DEUTERANOPIA
- Mutation in BCP gene: TRITANOPIA
What are the features of Rett syndrome
What is the genetic pattern of Rett syndrome?
What are the features of Duchenne muscular dystrophy?
- X-recessive
- The most frequent muscular dystrophy
- There are 2 types: Duchenne type and Becker type
Describe Duchenne type of Duchenne muscular dystrophy?
What is the geneticrn of Duchenne muscular dystrophy
Give the Comparison of Duchenne (DMD) and Becker (BMD) muscular dystrophies
What is Utrophin?
A potential replacement of the missing dystrophies
What is the genetic patter of fragile X syndrome?
- Mutations of Xq28 FRAXA gene - CGG trinucleotide-repeat
- Expansion takes place at the “maternal-transfer”
- Affected region is the gene 5’ region of the gene (not transcribed region)
- Pathological elongation is escorted by methylation which inhibits expression
- FMR-1 protein is an RNA binding protein (fragile X mental retardation)
How many repeats on FMR-1 gene that will indicate a healthy, pre-mutation or full mutation?
Describe the inheritance pattern of fragile X syndrome
Y-chromosome linked inheritance
- Explain incomplete sex restriction and then give examples
crossing over between pseudoautosomal regions of X and Y chromosomes
Y-chromosome linked inheritance
- Explain sex controlled inheritance then give examples
- The trait is expressed in both sexes, however, its degree is different
