Mendelian Inheritance Flashcards
What is mendelian inheritance
Simple: Refers to inheritance of traits controlled by a single gene with 2 alleles
What are ways in which traits can be studied
Pedigree
Punnet square
What is a pedigree and what does it show
Chart representation of an individual ancestry and relatedness of family member
Shows:
▪️relationships and identifies individuals with a given trait
▪️how trait is passed from generation to generation within a family
▪️determines mode of inheritance of a trait
▪️allows accurate risk calculation
What is a punnet square
Chart that allows determination of expected ratios of possible genotypes in the offspring of 2 parents
What are the characteristics of AD inheritance
▪️Affect both males and females in equal portions
▪️All forms of transmission between sexes are observed
▪️Affected people are usually born to at least one affected parent
▪️pedigree usually shows vertical transmission of trait through generations
▪️usually involves genes encoding regulatory proteins of complex metabolic pathways
▪️usually heterozygous
What are the exceptions yo AD inheritance in phenotype
Cases originating from fresh mutations in a gamete of a phenotypically normal parent
Cases in which the disorder is not expressed
Variable expressivity
What is the genetic risk of AD inheritance
Child of an affected heterozygous parent has a 50% risk of being affected independent of sex
What are examples of AD inheritance
Nervous system:neurofibromatosis
Hematology:hereditary spherocytosis
What is AR inheritance and its characteristics
Both alleles must be abnormal for disease to be expressed
▪️Males and females are equally likely to be affected
▪️Transmitted by either sex
▪️Affected people are usually born to un affected parents
▪️More commonly observed with consanguinity
▪️Shows horizontal transmission
▪️Usually involves genes of enzymes and proteins
▪️affected children may be homozygous or mat be compound heterozygotes for two diff mutations
What is the genetic risk for AR inheritance
Couples who are heterozygous of a recessive mutant allele have a 25% chance of having an affected child with each pregnancy
Thus among healthy siblings there is a 67% chance if a being a carrier
Examples of AR inheritance
Metabolic disorders: cystic fibrosis, phenylketonuria, lysosomal storage disorders
Hematology: sickle cell anemia and thalassemia
