Topic heteroploidy

For students studying genetics as a subject.

1. Ploidy Heteroploidy Types of heteroploidy Euploidy - it’s definition, types with sub-types, examples and origin Change in ploidy - types and causes. HETEROPLOIDY SAKSHI

2. What is ploidy ? P loidy : T he number of sets of chromosomes in a cell, or in the cells of an organism . For eg . In human there are 46 chromosomes i.e. 23 pairs of chromosomes. There are 2 sets of chromosomes so we are having a di ploidy or we can say we are diploid organisms. So a ploidy shows the no. of sets of chromosomes in a organism.

3. Hetero is a Greek word which means “different ” or “other”. So the literal meaning of heteroploidy is “a set of chromosomes having different chromosome number than t he normal set of it has”. Having an abnormal chromosome number that deviates from the normal diploid number of a given species is called as heteroploidy . Heteroploidy

4. Types of heteroploidy

5. Euploidy is the state of a cell or organism having one or more than one set of the same set of chromosomes, possibly excluding the sex-determining chromosomes . For example , most human cells have 2 of each of the 23 homologous monoploid chromosomes, for a total of 46 chromosomes. A human cell with an extra set out of the 23 normal ones would be considered euploid . Euploid karyotypes would consequentially be a multiple of the haploid number, which in humans is 23. a single extra chromosome (such as Down syndrome ). karyotypes are given names with the suffix-ploidy , used for euploid karyotypes ). EUPLOIDY

6. TYPES OF EUPLOIDY

7. The nucleus of a eukaryotic cell is haploid if it has a single set of chromosomes, each one not being part of a pair . By extension a cell may be called haploid if its nucleus is haploid, and an organism may be called haploid if its body cells (somatic cells) are haploid. The number of chromosomes in a single set is called the haploid number, given the symbol n. MONOPLOIDY OR HAPLOIDY

8. Haploids can be artificially produced by any one of the following methods: X-rays treatment, delayed pollination, temperature shocks, colchicine treatment , distant (interspecific or intergeneric) hybridization , anther or pollen culture. ORIGIN OF HAPLOIDY

9. Haploids in some cases as in male insects (Hymenoptera) are found as a routine and are produced due to parthenogenesis. In these insects, queen and drones are diploid females. Haploids may also originate spontaneously due to parthenogenetic development of egg in flowering plants. Such rare haploids have actually been obtained in tomatoes and cotton under cultivation. Rarely haploids may originate from pollen tube rather than form egg, synergids or antipodals of embryo sac. These haploids will be called  androgenic haploids.  NATURALLY OCCURING HAPLOIDS

10. The state of being diploid, that is having two sets of the chromosomes (and therefore two copies of genes), especially in somatic cells. Word DIPLOID is originated from Greek  diplous , which means “double”.   For example : a human somatic cell is in diploid state since it contains 46 chromosomes (in contrast to the sex cell that contains only 23 chromosomes). The 46 chromosomes in somatic cell results from the presence of two sets of chromosomes – one set derived from the father and another set from the mother (during the zygote stage). DIPLOIDY

11. Polyploid  cells and organisms are those containing more than two paired ( homologous ) sets of chromosomes .   polyploidy  is found in some organisms and is especially common in plants. In addition, polyploidy occurs in some tissues of animals that are otherwise diploid, such as human muscle  tissues. For e.g. H ighly differentiated human tissues in the liver, heart muscle and bone marrow. It occurs in the somatic cells of some animals, such as  goldfish ,   salmon , and  salamanders , but is especially common among  ferns  and flowering  plants  (see  Hibiscus rosa-sinensis ), including both wild and cultivated  species . POLYPLOIDY

12. Types of polyploidy

13. Autoploidy

14. Alloploidy

15. An  aneuploid  is an individual organism whose chromosome number differs from the wild type by part of a chromosome set. Generally , the aneuploid chromosome set differs from wild type by only one or a small number of chromosomes . Aneuploids can have a chromosome number either greater or smaller than that of the wild type. Aneuploid nomenclature is based on the number of copies of the specific chromosome in the aneuploid state. For example, the aneuploid condition 2 n −1 is called  monosomic  (meaning “one chromosome”) because only one copy of some specific chromosome is present instead of the usual two found in its diploid progenitor. The aneuploid 2 n + 1 is called  trisomic,2 n −2 is  nullisomic , and  n + 1 is  disomic . ANEUPLOIDY

16. TYPES OF ANEYPLOIDY

17. Monosomy  is a form of aneuploidy with the presence of only one chromosome from a pair. Partial monosomy occurs when only a portion of the chromosome has one copy, while the rest has two copies. Monosomic  chromosome complements are generally deleterious for two main reasons. First, the missing chromosome perturbs the overall gene balance in the  chromosome set . (We encountered this effect earlier). Second, having a chromosome missing allows any deleterious recessive allele on the single chromosome to be hemizygous and thus to be directly expressed phenotypically. Notice that these are the same effects produced by deletions. MONOSOMY

18. Turner syndrome  – People with Turner syndrome typically have one X chromosome instead of the usual two sex chromosomes. Turner syndrome is the only full monosomy that is seen in humans—all other cases of full monosomy are lethal and the individual will not survive development . MONOSOMY IN HUMAN

19. 1p36 deletion syndrome  – a partial monosomy caused by a deletion at the end of the short p arm of  chromosome 1 Cri du chat   syndrome – (French for "cry of the cat" after the distinctive noise by affected persons' malformed larynx) a partial monosomy caused by a deletion of the end of the short p (from the word  petit , French for "small") arm of  chromosome 5

20. Nullisomic  is a genetic condition involving the lack of both the normal chromosomal pairs for a species (2n-2). Humans with this condition will not survive . Causes Nullisomy is caused by non-disjunction during meiosis that causes two of the gametes to have no chromosomal material, leaving the other two gametes to have double the amount of chromosomal material (disomic). Due to the lack of genetic information, the nullisomic gametes are rendered unviable for fertilization . NULLISOMY

21. A  trisomy  is a type of  polysomy  in which there are three instances of a particular chromosome, instead of the normal two. If the chromosome pairs fail to separate properly during cell division, the egg or sperm may end up with a second copy of one of the chromosomes(non-disjunction). If such a gamete results in fertilization and an embryo, the resulting embryo may also have an entire copy of the extra chromosome. TRISOMY

22. The most common types of  autosomal  trisomy that survive to birth in humans are: Trisomy 21 ( Down syndrome ) Trisomy 18 ( Edwards syndrome ) Trisomy 13 ( Patau syndrome ) Trisomy 9 Trisomy 8  ( Warkany syndrome 2) Trisomy 22 Of these, Trisomy 21 and Trisomy 18 are the most common. In rare cases, a fetus with Trisomy 13 can survive, giving rise to  Patau syndrome . Autosomal trisomy can be associated with birth defects,  intellectual disability  and shortened life expectancy . Trisomy of  sex chromosomes  can also occur and include : XXX ( Triple X syndrome ) XXY ( Klinefelter syndrome ) XYY TRISOMY IN HUMAN

23. A  tetrasomy  is a form of  aneuploidy with the presence of four copies, instead of the normal two, of a particular chromosome . Causes Full tetrasomy of an individual occurs due to non-disjunction when the cells are dividing (meiosis I or II) to form egg and sperm cells (gametogenesis). This can result in extra chromosomes in a sperm or egg cell . For e.g. After fertilization, in human the resulting fetus has 48  chromosomes instead of the typical 46. TETRASOMY

24. Autosomal tetrasomies Cat eye syndrome  where tetrasomy of chromosome 22 is present Pallister-Killian syndrome  ( tetrasomy 12p) Tetrasomy 9p Tetrasomy 18p Sex-chromosome tetrasomies 48, XXXX syndrome 48, XXYY syndrome Klinefelter's syndrome , where XXXY tetrasomy is present TETRASOMY