Lecture 11 - Lecture 11 Large scale chromosomal changes...

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Lecture 11 Large scale chromosomal changes
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Types of chromosome mutations Chromosome mutations may be viewed as two classes: change in structure: result in novel sequence arrangements. change in number: structure is unchanged – the number DNA molecules (chromosomes) is the basis of genetic
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Changes in chromosome number: Aberrant euploidy Euploid: a cell/organism having a chromosome number that is an exact multiple of the haploid number for the species. An organism with more or fewer than the normal number of sets is an “aberrant euploid”. Polyploids: any cell/organism having more than two sets of chromosomes Monoploid: an individual of a normally diploid ( 2n ) species having only one chromosome set ( n ). The monoploid is distinguished from a normally haploid species (also n ).
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Table 16-1 Women 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. Trisomies are named for the overrepresented chromosome (Trisomy 21, Down’s Syndrome). There are 7 autosomal trisomies that can survive to birth in human. Trisomies can also arise in sex chromosomes.
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Monoploids Monoploid animals are very rare in nature because recessive lethal mutations become unmasked, and thus they die before they are detected. Characteristically, monoploid plants are sterile. The reason of sterility is that the chromosomes have no regular pairing partners (homologous chromosomes) during meiosis, and meiotic products are deficient in one or more chromosomes. For instance, a haploid in maize (2n=20) will have 10 chromosomes and the number of chromosomes in a gamete can range from 0-10. Consequently, considerable sterility will be found in a monoploid maize. The males of many species in the order Hymenoptera are monoploid; some small marine animals like brine shrimp. These individuals develop from the unfertilized egg (parthenogenesis).
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Polyploids Polyploidy is rare in animals but very common in plants. In aberrant euploids there is often a positive correlation between the number of copies of the chromosome set and size of the organism. This appears to be a result of larger cell size rather than cell number. Epidermal leaf cell from tobacco plants with increasing ploidy level. Many agronomic species are highly polyploid, are consequently sterile, and must be propagated asexually.
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Autopolyploids and allopolyploids. Autopolyploids have multiple chromosome sets originating from within one species Allopolyploids have multiple chromosome sets from one or more different closely related species. In this case the chromosome sets are only partly homologous or ‘ homeologous
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Autopolyploids Triploids ( 3n ) are usually autoplolyploids can arise in nature can be constucted by breeding
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Lecture 11 - Lecture 11 Large scale chromosomal changes...

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