Inheritance Patterns

Last updated 20.09.12

 

Index

 

-  Autosomal Dominant

-  Autosomal Recessive

-  X-Linked

 

Punnet Square

-  Used to calculate inheritence pattern

 

Punnet Square

 

General

-  Allele = particular point on a gene, 1 on each pair of the autosomes

-  Gene = DNA coding region for protein on a chromosome

-  Chromatid = 1/2 of chromosome, 1 of pair

-  Chromosome = DNA sequences

-  22 pairs of autosomes (46)

-  2 sex chromosomes (X, Y)

 

Genes

 

Autosomal

-  Defect on 1+ of non-sex chromosomes

 

-  Autosomal Dominant

-  Only 1 effected allele is required

-  Effects both sexes equally

-  Children of single effected parent have 50% chance of aquiring defect

-  Dd + dd = Dd, Dd, dd, dd

 

 

-  Autosomal Recessive

-  If both alleles (RR) then effected by disease

-  If 1 allele (Rr) then carrier

-  For a child to be effected (RR) both parents must be effected or carriers (Rr + Rr or RR + Rr = RR)

-  More common in consanguineous (related) parents

-  Most common: haemochromatosis, CF, alpha thalassaemia, sickle cell anaemia

 

 

X-Linked

-  Defect on X chromosome

-  Daughter (XX) can get from mother (XX) or father (XY)

-  Son (XY) can only get from mother (XX) not father (XY) as fathers genese determine sex

-  X --> girl (XX), Y --> boy (XY)

-  Mother (XX) alway gives X

-  Usually diseases of males

-  Females might be effected if heterozygous

 

X Linked