Topic 5 Flashcards
What’s the differences between gene mutations and chromosome mutations?
Gene mutations are changes that take place within a gene
Chromosome mutations are changes in a chromosome region encompassing multiple genes
Chromosome mutations divide into 2 groups:
Changes in chromosome number (# of DNA molecules changed)
Changes in chromosomes structure (result in novel sequence arrangements within one or more DNA double helicies
Slide 3
What are the 2 types of changes in chromosomes number?
Changes in whole chromosome sets (results in condition called aberrant euploidy
Changes in parts of chromosome sets (resulting in condition called aneuploidy
What is cytogenetics?
Geneticists use stains to identify specific chromosomes and to analyze their structures
Slides 4-6
What do each of these terms mean: Euploid Polyploid Aneuploid Monosomic Trisomic
Euploid- having a chromosome number that is an exact multiple of the monoploid number
(Monoploid=1n, diploid=2n, triploid=3n)
Polyploid- extra copy/copies of each chromosome of species that normally are diploid (polyploid >2n)
Aneuploid- abnormal number of one or more of the chromosomes, but not all
Monosomic- one missing chromosome compared to the 2n wild type
Chromosome #= 2n-1
Trisomic- one extra chromosome compared to the 2n wild type chromosome number
Chromosome #= 2n+1
Slide 7-10
What is autopolyploid?
What is allopolyploid?
Autopolyploid- all the chromosomes originated from the same organism
Increasing ploidy levels can generate traits that are more valued by the consumer
Allopolyploid- one set of chromosomes originated from one organism and the other from another (original hybrid)
The parent organisms need to be related to produce viable progeny
Mixing 2 genomes can lead to new phenotypes in the offspring
Slide 11-13
What are the 2 ways autopolyploid are generated?
Naturally formed autopolyploids- mistakes in meiosis that lead to failure in executing one of the meiotic divisions produces a gamete with twice as many chromosomes as wild type gamete
Induced autopolyploids in plants-
Treat meiotic or mitotic cells with microtubules inhibitor to arrest cells in metaphase, identify variable polyploid individuals by karyotyping
Slide 14-16
What are polyploid tissues?
In some tissues the cells replicate the DNA in S phase but not divide, leading to the formation of a polyploid tissue in an otherwise non polyploid organism
To become polyploid cells replicate their DNA (S), but do not divide
Polyploid can be a mechanism of increasing cell volume and/or call metabolism
Slide 17-19
What are the agricultural advantages of monoploids?
Used in research for:
Combining recessive mutations in one genotype
Screening for resistance to chemicals, easier to do as a haploid, the the resistance is recessive
Slide 20
What are monosomies?
What are trisomies?
Aneuploidy is gain or loss of 1 chromosome due to non-disjunction errors in meiosis
Monosomies- one missing chromosome, in humans autosomic monosomies die in utero Turner syndrome (XO)
Trisomies- one extra chromosome, in humans only autosomic monosomies for large chromosomes die in utero
Down syndrome
Klinefelter syndrome
Slide 21-26
What are trisomies/monosomies so deleterious?
The product of genes typically do not work in their own pathway, but interact with other to contribute to a process/pathway
Gene imbalance is often not sufficient to perturb a pathway, however the combo of many pathways slightly perturbed may lead to an embryo that can not develop
The amount of gene product (transcription) is in part dependant on how many template (copies) of the gene there are for the RNA polymerase to act upon
Too much transcription (trisomies) and too little transcription (monosomies)
Slides 27-31
Why are trisomies for sex chromosomes less deleterious compared to trisomies for autosomes?
Imbalance of the Y chromosomes will have a effect in fertility since this chromosome encodes mostly for genes involved in sex determination and function
Imbalance of X chromosomes will have a minor effect since the X chromosome has naturally evolved to be dosage compensated between the 2 sexes
Slide 32-34
How do abnormalities in chromosome number appear?
Lack of crossovers causes non disjunction in the first meiotic division (homologs don’t separate)
Defect in chromosomes cohesion cause non disjunction in the second meiotic division (sister chromatids don’t separate)
Trisomies increase in frequency with increased maternal age
Slides 35-40
Study the 5 types of chromosomal changes slide 41-42
Translocation Inversion Duplication Deletion Gain of genetic material
Slide 41-42
What is unbalanced vs balanced rearrangements?
Unbalanced rearrangements- lead to change gene number, these can be caused by deletions and duplications, when they involve atleast one gene
Balanced rearrangements- do not lead to change gene number, will be rearrangements that change gene order, like inversions and reciprocal translocations
Slide 43
What is the effect of a deletion?
Unmasking of recessive mutation
Pseudodominance- recessive alleles uncovered by the deletion will appear as if they are dominant
Can lead to defects if deletion involves haplinisufficient genes (genes that need to be expressed in both homologs to provide enough protein)
Slide 44
Slide 46-47
