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?
Describe Becker type of muscular dystrophy?
- starts in 20-30 years old
- descending character
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
-> What are the 3 genetic phenomenons of Y-chromosome linked inheritance?
- Sex limited inheritance
- Incomplete sex restriction
- Sex-controlled inheritance
Y-chromosome linked inheritance
- Explain sex limited inheritance and then give examples
- The trait is present in the genotype of both sex, however, it is expressed only in 1 sex
- E.g, hair, menstruation, pelvic parameters
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
