The human genome
diploid, 22 pairs of autosomal chromosomes and 1 pair of sex chromosomes thus 46 pairs of chromosomes. Of a pair of chromosomes , 1 is maternal the other paternal. Sex chromosomes determine is individual is male XY or female XX
Chromosome makeup of an individual
Each chromosome of the karyotype is sorted and numbered according to size
What is lyonisation and why is it necessary
Lyonisation: when one X chromosome in each cell is inactivated during early development of the embryo.
Necessary to stop female from having double the expression of all X chromosome proteins in her cells where such overexpression would be harmful and very likely fatal.
inactivated chromosome that is excluded from the nucleus
esult in visible changes in the chromosomes.
Aneuploidy cause is non-disjunction( non-seperation) of chromatids or parts of chromatids during meisosis.
Occur when entire chromosome is affected. Whole chromosome may be deleted or duplicated or there may be large breakage, deletions or duplications within chromosome. A euploid person has 23 pairs of chromosomes
An aneuploid does not have 23 pairs e.g Down syndrome
List the chromosomal disorders
E.g of chromosomal disorders:
Down syndrome (trisomy 21) extra chromosome
Kleinfelter syndrome (47 XXY) extra X chromoxome
Turner syndrome (45 XO) second sex chromosome is lacking
Due to mutation in a single gene on an autosome. May be dominant ( one damaged allele)or recessive (both alleles damaged)
Dominant autosomal disorder
tends to affect structural proteins
disease affects heterozygotes
onset of disease may be delayed
neither parent may have the disease
When inherited, generations may be skipped
Half building blocks are defective, cell cannot assemble structure properly. Is an autosomal dominant disorder due to mutation in one of the fibrillin genes.
Recessive autosomal disorder
disease occurs in homozygotes
more uniform expression
onset of disease is early in life
Generally both parents have disease or are carriers
more common than autosomal dominant
when inherited generations may be skipped
autosomal recessive disorder
inherited on the X chromosome
Most are recessive, disease expressed when X chromosome is abnormal.
Female affected if the X chromosomes are abnormal, has Turner syndrome or as a result of lyonisation. Only males are affected and daughters inherit the disease from father, sons don't inherit
Females are carriers
All daughters of affected male are carriers
red-green colour- blindness
Duchenne muscular dystrophy
All mitochondria inherited through the female line
Typically progressive and not obvious at birth and affect cells non-uniformly
Mitochondria are important in neurological tissues and skeletal muscles
Cannot be inherited from father
e.g lebers hereditary optic atrophy