suo pericentric inversion, the centromeres are contained within the inverted region. Consequently, the chromosomes that have engaged in crossing over separate in the normal fashion, without the creation of a bridge (Figure 17-29). However, the crossover produces chromatids that contain a duplication and a deletion for different parts of the chromosome. In this case, if a gamete carrying a crossover chromosome is fertilized, the zygote dies because of gene imbalance. Again, the result is that only noncrossover chromatids are present in viable prog- eny. Hence, the RF value of genes within a pericentric inver- Paracentric inversions can lead to deletion products A Paracentric- inversion heterozygote A D CBE Pairing Crossover in loop sion also is zero. Inversions affect recombination in another way, too. Inver- sion heterozygotes often have mechanical pairing problems in the region of the inversion. The inversion loop causes a large distortion that can extend beyond the loop itself. This distor- tion reduces the opportunity for crossing over in the neigh- boring regions. Let us consider an example of the effects of an inversion on recombinant frequency. A wild-type Drosophila specimen from a natural population is crossed with a homozygous recessive laboratory stock dp en /dp cn. (The dp allele encodes dumpy wings and cn encodes cinnabar eyes. The two genes are known to be 45 map units apart on chromosome 2.) The F, generation is wild type. When an F, female is crossed with the recessive parent, the progeny are Segregation A B C DE A B C D E Acentric fragment (lost) D Dicentric bridge breaks randomly ++/ dp cn 246 dumpy cinnabar dp cn / dp cn 250 wild type ADCBE ADCB E 5 dumpy dp + / dp cn 7 cinnabar + en / dp cn ABC DE Normal product A Авср B Deletion product FIGURE 17-28 A crossover in the loop of a paracen- tric-inversion heterozygote gives rise to chromosomes Deletion product containing deletions. AD CBE LounchPad ANIMATED ART: Chromosome rearrangements: meiotic behavior of paracentric inversions Inversion product

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Question

In Figure 17-28, what would be the consequence of a
crossover between the centromere and locus A?

suo
pericentric inversion, the centromeres are contained within
the inverted region. Consequently, the chromosomes that
have engaged in crossing over separate in the normal fashion,
without the creation of a bridge (Figure 17-29). However, the
crossover produces chromatids that contain a duplication and
a deletion for different parts of the chromosome. In this case,
if a gamete carrying a crossover chromosome is fertilized, the
zygote dies because of gene imbalance. Again, the result is
that only noncrossover chromatids are present in viable prog-
eny. Hence, the RF value of genes within a pericentric inver-
Paracentric inversions can lead
to deletion products
A
Paracentric-
inversion heterozygote
A D CBE
Pairing
Crossover
in loop
sion also is zero.
Inversions affect recombination in another way, too. Inver-
sion heterozygotes often have mechanical pairing problems in
the region of the inversion. The inversion loop causes a large
distortion that can extend beyond the loop itself. This distor-
tion reduces the opportunity for crossing over in the neigh-
boring regions.
Let us consider an example of the effects of an inversion
on recombinant frequency. A wild-type Drosophila specimen
from a natural population is crossed with a homozygous
recessive laboratory stock dp en /dp cn. (The dp allele encodes
dumpy wings and cn encodes cinnabar eyes. The two genes
are known to be 45 map units apart on chromosome 2.) The
F, generation is wild type. When an F, female is crossed with
the recessive parent, the progeny are
Segregation
A B C DE
A B C D E
Acentric
fragment
(lost)
D
Dicentric bridge
breaks randomly
++/ dp cn
246 dumpy cinnabar dp cn / dp cn
250 wild type
ADCBE
ADCB E
5 dumpy
dp + / dp cn
7 cinnabar
+ en / dp cn
ABC DE
Normal product
A
Авср
B
Deletion product
FIGURE 17-28 A crossover in the loop of a paracen-
tric-inversion heterozygote gives rise to chromosomes
Deletion product
containing deletions.
AD CBE
LounchPad ANIMATED ART: Chromosome rearrangements:
meiotic behavior of paracentric inversions
Inversion product
Transcribed Image Text:suo pericentric inversion, the centromeres are contained within the inverted region. Consequently, the chromosomes that have engaged in crossing over separate in the normal fashion, without the creation of a bridge (Figure 17-29). However, the crossover produces chromatids that contain a duplication and a deletion for different parts of the chromosome. In this case, if a gamete carrying a crossover chromosome is fertilized, the zygote dies because of gene imbalance. Again, the result is that only noncrossover chromatids are present in viable prog- eny. Hence, the RF value of genes within a pericentric inver- Paracentric inversions can lead to deletion products A Paracentric- inversion heterozygote A D CBE Pairing Crossover in loop sion also is zero. Inversions affect recombination in another way, too. Inver- sion heterozygotes often have mechanical pairing problems in the region of the inversion. The inversion loop causes a large distortion that can extend beyond the loop itself. This distor- tion reduces the opportunity for crossing over in the neigh- boring regions. Let us consider an example of the effects of an inversion on recombinant frequency. A wild-type Drosophila specimen from a natural population is crossed with a homozygous recessive laboratory stock dp en /dp cn. (The dp allele encodes dumpy wings and cn encodes cinnabar eyes. The two genes are known to be 45 map units apart on chromosome 2.) The F, generation is wild type. When an F, female is crossed with the recessive parent, the progeny are Segregation A B C DE A B C D E Acentric fragment (lost) D Dicentric bridge breaks randomly ++/ dp cn 246 dumpy cinnabar dp cn / dp cn 250 wild type ADCBE ADCB E 5 dumpy dp + / dp cn 7 cinnabar + en / dp cn ABC DE Normal product A Авср B Deletion product FIGURE 17-28 A crossover in the loop of a paracen- tric-inversion heterozygote gives rise to chromosomes Deletion product containing deletions. AD CBE LounchPad ANIMATED ART: Chromosome rearrangements: meiotic behavior of paracentric inversions Inversion product
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