Molecular gene family

gene families and gene clusters

1. SUBMITTED TO :- SUBMITTED BY :- Mr. P.C.GUPTA NAVREET KAUR RAI (M.Sc. (Ag.) Pre. Yr. GPB Sem-I) Deptt. Of Genetics And Plant Breeding COLLEGE OF AGRICULTURE SWAMI KESHWANAND RAJASTHAN AGRICULTURE UNIVERSITY An Assignment O n Gene F amilies A nd G ene C lusters

2. A gene family is a set of several similar genes, formed by duplication of a single original gene, and generally with similar biochemical functions. One such family are the genes for human haemoglobin subunits; the ten genes are in two clusters on different chromosomes, called the alpha-globin and beta-globin loci. GENE FAMILY

3. A gene family is a set of homologous genes within one organism. Genes are categorised into families based on shared nucleotide or protein sequences. The position of exons within the coding sequence can be used to infer common ancestry. When a gene is present in two or more copies per genome, the condition is known as “ redundancy ”.

4. The members of a gene family may be either clustered together, dispersed on different chromosomes or present in a combination of both. If the gene of a gene family encode proteins, the term “ protein family ” is often used in an analogous manner to gene family. One example for such family are the genes for Human haemoglobin subunits.

5. Gene families are group of related genes that share a common ancestor. Members of gene families may be paralogs or orthologs. Gene paralogs- genes with similar sequence from within the same species. Gene orthologs- genes with similar sequence in different species. Gene families are highly variable in size, sequence diversity and arrangement. BASIC STRUCTURE -

6. Depending on the diversity and functions of the genes within the family, families can be classified as a multigene families or superfamilies. MULTIGENE FAMILIES- Typically consist of members with similar sequences and functions, though a high degree of divergence ( at the seq. &/or functional level ) doesnot lead to the removal of a gene from a gene family. Individual genes in the family may be arranged close together on the same chromosome or dispersed throughout the genome on different chromosomes.

7. SUPERFAMILIES – These families are much larger than single multigene families. Superfamilies contain upto hundreds of genes, including multiple families as well as single, individual gene members. The genes are diverse in sequence and function displaying various levels of expression and seperate regulation controls. Some gene families also contain pseudogenes, sequences of DNA that closely resemble established gene sequences but are non-functional.

8. A gene cluster is a part of a gene family. A gene cluster is a group of two or more genes found within an organism’s DNA that encode for similar polypeptides or proteins,which collectively share a generalised function and are located within a few thousand base pairs of each other. The size of gene clusters can vary significantly, from a few genes to several hundred genes. GENE CLUSTERS -

9. Genes found in a gene cluster may be observed near one another on the same chromosome or on different, but homologous chromosomes. Extensive tanden repetition of a gene normally occurs when the gene product is needed in unusually large amounts. Eg., genes for rRNA, histone genes, etc. Sometimes all the members of a gene family are functional, but often some members are nonfunctional pseudogenes .

10. In a tandem repeat, the nucleotide sequence is repeated in the same orientation. For example, the trinucleotide sequence GAA is repeated two times in the DNA segment- GAAGAA- GAA GAA CTT CTT tandem repeat TANDEM REPEAT-

11. Genes encoding the various globin proteins evolved from one common ancestral globin gene,which duplicated and diverged about 450-500 million years ago. After the duplication events, differences between the genes in globin family arose from the accumulation of mutations. GLOBIN GENES-

12. The haemoglobin molecule is a tetramer and is composed of two similar polypeptides, the alpha and beta chains,encoded by two distinct genes. Each polypeptide incorporates a hemi-group, that reversibly binds oxygen. The genes are co-ordinatedly turned on and turned off during the embryonic, foetal and adult stages of development. The genes for alpha-globin lie in a cluster on chromosome 16, while those for beta-globin are located on chromosome 11. HAEMOGLOBIN GENES-

13. Myoglobin is an iron- and oxygen- binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is releated to haemoglobin, which is the iron- and oxygen- binding protein in blood, specifically in the red blood cells. In humans, myoglobin is only found in the bloodstream after muscle injury. MYOGLOBIN GENES-

14. Myoglobin is the primary oxygen- carrying pigmen t of muscle tissues. High concentrations of myoglobin in muscle cells allow organisms to hold their breath for a longer period of time. Diving mammals such as whales and seals have muscles with particularly high abundance of myoglobin In humans,myoglobin is encoded by MB gene.

15. Histones are highly alkaline proteins found in eukaryotic cell nuclei that package and order the DNA into structural units called “nucleosomes”. They are the cheif protein components of chromatin,acting as spools around which DNA winds, and play a role in gene regulation. Without histones, the unwounded DNA in chromosomes would be very long. HISTONE GENES

16. Histones are found in the nuclei of the eukaryotic cells and in certain Archaea, but not in bacteria. The unicellular algae known as dinoflagellates are the only eukaryotes that are known to completely lack histones. Histone protein are among the highly conserved proteins in eukaryotes. Histone genes are of 5 types namely, H1 , H2A, H2B, H3 and H4 .

17. Large quantities of histones are required during the S phase of cell cycle to package the newly synthesised DNA. To meet this demand multiple copies of each of the five histone genes are present per genome in clusters of tandemly repeated units. A repeat unit contains one copy each of five histone genes seperated from each other by non transcribed spacer regions. The histone genes don’t have intron sequences. All the exon sequences are highly conserved.

18. 1. HISTONE H1:- H1 is one of the five main histone protein families which are components of chromatin in eukaryotic cells. Unlike other histones,H1 doesn’t make up the nucleosome bead. It sits on the top of the structure, keeping in place the DNA that has wrapped around the nucleosome. TYPES OF HISTONE GENES

19. Histone H2A is one of the five main histone proteins involved in the structure of the chromatin in eukaryotic cells. H2A is important for packaging DNA into chromatin. H2A plays a major role in determining the overall structure of the chromatin. 2. HISTONE H2A :-

20. It is also a main component of histone protein involved in structure of chromatin in eukaryotic cells. H2B is involved with the structure of the nucleosomes of the ‘beads on a string’ structure. 3. H ISTONE H2B :-

21. Histone H3 is one of the five main histone proteins involved in the structure of chromatin in eukaryotic cells. H3 is involved with the structure of the nucleosomes of the ‘beads on a string’ structure. 4. HISTONE H3 :-

22. Histone H 4 is one of the five main histone proteins involved in the structure of chromatin in eukaryotic cells. H4 is structural component of the nucleosome, and is subjected to some modifications including acetylation and methylation, which may alter expression of genes located on DNA associated with its parent histone octamer. 5. H ISTONE H4 :-

23. THANK YOU