BT301 Final Term Past Papers

1. Define Epistasis

Epistasis and modifier genes Epistasis is a phenomenon that consists of the effect of one gene being dependent on the presence of one or more modifier genes Type of polygenic inheritance where alleles at one gene locus can hide or prevent expression of alleles at second gene locus.

2. VNTR and Applications of VNTR

VNTR are short nucleotide sequences organized as a tandem repeats on genomes.

Found on many chromosomes

Show variations in length between individuals.

Applications of VNTR

Microbiology

DNA fingerprinting

Genetic diversity

Forensics

Mapping of genomes

Breeding patterns of wild or domesticated animals

3. Genomic Imprinting

Genomic Imprinting Epigenetic marking of a locus on the basis of parental origin. Results in monoallelic gene expression. Some genes are expressed only from the maternal genome and some only from the paternal genome. It is estimated that about 40 genes are imprinted and they can be found on several different chromosomes .

4. Point mutations
5. Frameshift mutations result in all amino acids downstream from the mutation site being completely different from wild type. These proteins are generally nonfunctional.

Mutation - Forward, Reverse and Neutral

Forward mutation

 Mutation that changes the wild type phenotype into mutant type phenotype.

 Any mutation which changes a functional wild genotype or wild phenotype to nonfunctional form.

Wild type phenotype/ genotype

reverse mutation

Most common phenotype in natural populations of the organism is called a wild type phenotype.

neutral mutation

Mutation that changes a mutant phenotype back into the wild type.

 Mutation that alters the amino acid sequence of the protein but does not change its function as replaced amino acid is chemically similar or the affected amino acid has little influence on protein function.

6. Epigenetics

the study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself. One example of an epigenetic change is DNA methylation — the addition of a methyl group, or a "chemical cap," to part of the DNA molecule, which prevents certain genes from being expressed. Another example is histone modification. Histones are proteins that DNA wraps around

Epigenetics An epigenetic trait is a stable heritable phenotype resulting from changes in chromosome without alterations in the DNA sequence.

Autosomal Dominant diseases

7. Marfan syndrome
8. Huntington's disease
9. Retinoblastoma
10. Waardenburg syndrome
11. Myotonic dystrophy
12. Polycystic kidney disease
13. Achondroplasia
14. Polydactyly
15. Heredity hearing loss

Examples of autosomal recessive disorders include cystic fibrosis, sickle cell anemia, and Tay-Sachs disease

7. Mutation nomenclature

Nomenclature

While describing sequence variants, it should be written according to HGNC rules.

All variants should be described at the most basic level, i.e. DNA level.

Descriptions should always be in relation to a reference sequence, either a genomic or a coding DNA sequence.

Although theoretically a genomic reference sequence seems best, in practice a coding DNA reference sequence is preferred.

Good for promoters, alternative splicing etc.

When the entire genomic sequence is not known, a cDNA reference sequence should be used.

To avoid confusion in the description of a variant it should be preceded by a letter indicating the type of reference sequence used.

Several different reference sequences can be used.

"c." for a coding DNA sequence (like c.76A>T)

"g." for a genomic sequence (like g.476A>T)

"m." for a mitochondrial sequence (like m.8993T>C,)

"r." for an RNA sequence (like r.76a>u)

"p." for a protein sequence (like p.Lys76Asn)

Describing genes / proteins, only official HGNC (HUGO gene nomenclature committee) gene symbols should be used ( )

9. How mutations alter gene function_to add some data

splice site mutations have severe Effects

 Splice sites site mutations usually have severe effects on protein functions.

 Often this kind of mutation produce one or more exon skipping or larger fragments of DNA. Effects of null allele and hypomorph

 Null allele results in loss of function. Usually no gene product.