MBLG2972 Lecture Notes - Lecture 17: Phenotypic Plasticity, Cell Cycle, Meiosis
5 Jul 2018
School
Department
Course
Professor
MBLG2072
Genetics and Genomics
Monica Zanuttini !
460381099
Lecture 17 "Cytogenetics !
Down-syndrome = trisomy of chromosome 21. Chromosome 21 is the smallest human autosome,
with 48 million nucleotides representing about 1.5 percent of the total DNA in cells. !
A generalised disruption of evolved genetic balance (homeostasis) in cells of affected individuals
leads to decreased developmental and physiological buffering against genetic and environmental
forces. Depends of the buffering capacity of the system. !
Euploidy: multiples of the basic chromosome set.!
Aneuploidy: gain or loss of one or more chromosomes from the set. !
n = gametic or haploid chromosome number.!
2n = somatic chromosome number.!
Monoploids: !
If inviable, lethal or deleterious genes are expressed.!
If inherited from both parents, can lead to severe genetic disorders or death before reaching the
reproductive age. !
If viable (e.g. in plants), then the organism is usually sterile. However in plants, a monoploid plant
will create gametes which may or may not contain
the gene as there is only one copy. This can be
generated in tissue culture. !
MBLG2072
Genetics and Genomics
Monica Zanuttini !
460381099
Why is double haploid important?!
Wheat X Maize example: Double haploids greatly enhances
the production of complete homozygous wheat lines in a
single generation. !
A hybrid zygote is formed in a wheat X maize cross. The maize
chromosomes are rapidly eliminated, usually during the first
three embryonic divisions. This is due to spindle fibres not
attaching. !
Colchicine doubling of chromosome number in these cells by
dissolving the spindle fibres leads to double haploid (diploid)
cells. !
Monoploids also work in male bees, ants and wasps. They are usually
haploid and develop from unfertilised eggs. !
Polyploidy: multiple chromosome sets from within one species, originating from spindle failure in
mitosis or meiosis or environmentally from colchicine (non-disjunction). !
Document Summary
Chromosome 21 is the smallest human autosome, with 48 million nucleotides representing about 1. 5 percent of the total dna in cells. A generalised disruption of evolved genetic balance (homeostasis) in cells of a ected individuals leads to decreased developmental and physiological bu ering against genetic and environmental forces. Depends of the bu ering capacity of the system. Aneuploidy: gain or loss of one or more chromosomes from the set. n = gametic or haploid chromosome number. If inviable, lethal or deleterious genes are expressed. If inherited from both parents, can lead to severe genetic disorders or death before reaching the reproductive age. If viable (e. g. in plants), then the organism is usually sterile. However in plants, a monoploid plant will create gametes which may or may not contain the gene as there is only one copy. Wheat x maize example: double haploids greatly enhances the production of complete homozygous wheat lines in a single generation.
