No genetic recombination during gametogenesis seen with?
Ans. d (Mitochondrial chromosome) (Ref. Robbin's pathology 7th/ 185; Harper's Biochem 26th/ 323; Ganong Physiology 22nd/pg. 11,27).# Non-Mendelian inheritance mechanisms include mitochondrial inheritance (exhibiting maternal transmission), expansion of triplet repeats (exhibiting anticipation in pedigrees as in the fragile X syndrome), and genomic imprinting (exhibiting different phenotypes according to maternal or paternal origin of the aberrant genes).The mitochondrial genome does not recombine and is inherited through the maternal line because sperm does not contribute significant cytoplasmic components to the zygote. A noncoding region of the mitochondrial chromo- some, referred to as D- loop, is highly polymorphic. This property, together with the absence of mtDNA recombination, makes it a valuable tool for studies tracing human migration and evolution, and it is also used for specific forensic applications. Inherited mitochondrial disorders are transmitted in a matrilineal fashion; all children from an affected mother will inherit the disease, but it will not be transmitted from an affected father to his children. The resulting heterogeneity in the proportion of mitochondria with and without a mutation is referred to as heteroplasmia and underlies the phenotypic variability that is characteristic of mitochondrial diseases.Mitochondrial Disorders# The mitochondrial genome does not recombine and is inherited in a matrilineal fashion (all children from an affected mother will inherit the disease, but it will not be transmitted from an affected father to his children because sperm does not contribute significant cytoplasmic components to the zygote).# Heterogeneity in the proportion of mitochondria with and without a mutation is referred to as heteroplasmia and underlies the phenotypic variability that is characteristic of mitochondrial diseases.# Acquired somatic mutations in mitochondria are thought to be involved in age-dependent degenerative disorders affecting predominantly muscle and nervous system (e.g., Alzheimer's and Parkinson's disease).# Alterations in the mtDNA affecting enzymes required for oxidative phosphorylation lead to reduction of ATP supply, generation of free radicals, and induction of apoptosis.# Azidothymidine (AZT) causes acquired mitochondrial myopathy through depletion of muscular mtDNA.# A noncoding region of the mitochondrial chromosome, referred to as D-loop, is highly polymorphic. This property, together with the absence of mtDNA recombination, makes it a valuable tool for studies tracing human migration and evolution, and it is also used for specific forensic applications.# Diseases transmitted by mitochondrial inheritance:- Leber's hereditary optic atrophy,- Leigh disease,- NARP- Familial progressive external ophthalmoplegia,- MERRF syndrome,- MELAS syndrome,- Succinic dehydrogenase complex-II deficiency & Cytochrome C oxidase complex-IV dt.MITOCHONDRIAL DNA (mtDNA)# It is small (16.5 kb) circular, double-stranded, and composed of heavy and light chains.# One percent of cellular DNA is in mitochondria.# Contains very few untranslated sequences.# High mutation rate (5-10 times more than nuclear DNA)# Genetic codes differ slightly from the standard code:- UGA (standard stop codon) is read as Trp.- AG A and AGG (standard codon for Arg) are read as stop codons.# Functions:- Encodes t and rRNAs, and 13 proteins of the respiratory chain involved in oxidative phosphorylation and ATP generation.
X chromosome
Y chromosome
Autosome 21
Mitochondrial chromosome
Genetics