Module 2:8 Chromosomal Variations

Question 1

How does gene dosage relate to diploidy?

Question 2

how does meiosis work to generate haploid gametes?

Question 3

what features of meiosis contribute to genetic variation? how?

Question 4

for chromosomal mutations: identify, what are chromosomal features associated with it? what are the causes? what are the effects on the cell?

Question 5

what is aneuploidy - how does it occur? why is aneuploidy in somatic cells not such a big deal? how does non-disjunction relate to aneuploidy in germ-line cells?

Question 6

what is polyploidy? how is it different from aneuploidy? what causes it? what is different between an auto and allo tetraploid?

Question 7

meiosis

Answer 7

the process by which the sex cells are produced

double division
-reduction division: reduce chromosomes by half, separate homologous chromosomes
-separation division: separate sister chromatids

Question 8

end result of meiosis

Answer 8

4, separate, haploid gametes

Question 9

meiosis - homolog pairing

Answer 9

maintained by a group of proteins that unite homologous pairs

cleavage of these proteins assures synchronous and complete separation of homologs

mistakes or errors in protein attachment/cleavage can affect cell

Question 10

important features of meiosis

Answer 10

crossing over - homologous recombination

segregation of homologous chromosomes

independent assortment

Question 11

what are the two types of mutation?

Answer 11

gene mutation
chromosomal mutation

Question 12

chromosomal mutation: rearrangements

Answer 12

affect structure and location

Question 13

chromosomal mutation: aneuploidy

Answer 13

gain or loss of one to a few chromosomes

Question 14

chromosomal mutation: polyploidy

Answer 14

gain of complete genome, an increase in n

Question 15

chromosomal rearrangements: what are the 3 types of duplications

Answer 15

tandem duplication
displaced duplication
reverse duplication

Question 16

how are chromosomal duplications detected?

Answer 16

by examining meiotic chromosomes

Question 17

how do you determine which chromosome is normal when dealing with duplications?

Question 18

what are the effects of chromosomal duplications?

Answer 18

increased copy number can change the phenotypes

duplications allow for divergence in gene function and thus evolution

Question 19

chromosomal deletions

Answer 19

removal of chromosomal segments

Question 20

how can chromosomal deletions be detected?

Answer 20

by examining paired homologs during meiosis

Question 21

what are the consequences of chromosomal deletions?

Answer 21

-loss of function is often lethal
-low gene dosage effects: haploinsufficiency
-loss of a dominant allele, leads to expression of recessive: pseudodominance
-loss of centromere: chromosomal loss

Question 22

what is the most likely cause of duplication/deletion?

Answer 22

unequal crossing over or mistakes in recombination repair mechanisms

Question 23

chromosomal inversions

Answer 23

paracentric or pericentric

Question 24

what is the cause of chromosomal inversions?

Answer 24

breaks in DNA that cause section to be inverted
-could be by unusual recombination events

Question 25

what are the effects of chromosomal inversions?

Answer 25

-conservation of gene sequence -gene breaks (loss-of function) -positional effects (think chromatin)

Question 26

translocations

Answer 26

caused by double strand breaks as with deletions and inversions may break genes (loss-of-function) or have positional effects

Question 27

robertsonian translocation

Answer 27

involved between 2 acrocentric chromosomes -reduces chromosome number die to small, non-functional chromosome

Question 28

aneuploidy

Answer 28

change in number of individual chromosomes nullisomy: no copies (2n-2) monosomy: one copy (2n-1) trisomy: three copies (2n+1) tetrasomy: four copies (2n +1 +1)

Question 29

what does aneuploidy result from?

Answer 29

non-disjunction - failure of segregation

Question 30

what are the effects of aneuploidy?

Answer 30

most are lethal - loss of genes, change gene dosage affects the phenotype

Question 31

impact of trisomies

Answer 31

severe developmental defects and greatly reduced life expectancy (if survive to term)

Question 32

mosaics

Answer 32

distinct, mixed populations of cells types

Question 33

polyploidy

Answer 33

possession of more than two sets of chromosomes -most common in plants and very rare in animals

Question 34

autopolyploids

Answer 34

organism has more than 2 sets of homologous chromosomes, all derived from the same organism rarely fertile due to failure of homologous chromosomes to pair in meiosis (they could form pairs but rarely do)

Question 35

allopolyploids

Answer 35

organisms with complete sets of chromosomes from two different species -normally produce non-functional gametes -through mitotic non-disjunction can form amphipolyploids, functional polyploids -tetraploid can be: 1n+3n, 2n+2n, 3n+1n

Question 36

transposable elements

Answer 36

genes able to move locations; insertion at a new site leads to mutation or chromosomal rearrangement

Question 37

classes/types of transposable elements

Answer 37

Class I -DNA transposons: moveable component of DNA Class II -Retrotransposons: transpose through an RNA intermediate (DNA copied to RNA, which is then reverse transcribed to DNA)

Question 38

replicative transposable elements

Answer 38

copy and paste copy themselves with each new copy inserted at a new site, inc in number of transposons

Question 39

non-replicative transposable elements

Answer 39

conservative; cut and paste the same transposon is cut and moved to a new site, no increase in number of transposons

Question 40

mechanism of transposition

Answer 40

many transposons encode their own enzyme called transposase different mechanisms for transposition -staggered breaks generated in target site by transposase - generally a canonical sequence -transposon is joined to single stranded ends of target -DNA in single strand gaps is replicated/filled in

Question 41

insertional mutagenesis

Answer 41

large pieces of DNA that interrupt a gene or insert into the promoter region prevent: -proper transcription and/or translation of the gene -transcriptional activation of the gene

Question 42

Because replicative transposons are essentially identical...

Answer 42

...they can align and recombine these recombinations can alter the structure of chromosomes