Chapter 10

Question 1

Chromosomes are species-specific

Answer 1

genome content, chromosome number in a nucleus, and relative size and shape of each chromosome

are species-specific

closely related species tend to have similar numbers

Question 2

Chromosome territories

Answer 2

• specific regions where chromosomes are partitioned during interphase
• don’t occupy the same territory in each nucleus
• once situated, don’t stray till mitosis

Question 3

Karyotypes

Answer 3

• organized display of chromosomes
• arranges in descending order of size
• can identify abnormalities in number or structure

Question 4

Chromosome structure

Answer 4

centromere at the center of each chromatid

short p arm
long q arm

Question 5

Four chromosome shapes

Answer 5

1. metacentric
   - p and q same length
   - centromeres in the middle
2. submetacentric
   - short arm and long arm
   - seen in humans
3. acrocentric
   - centromere near end of chromosome
   - also seen in humans (ex. y)
4. telocentric
   - no p arm
   - centromere at the end

Question 6

FISH - fluorescent in situ hybridization

Answer 6

• uses fluorescent molecular probes to detect a target sequence
• can use diff wavelength/colour probes
• can be used to identify each chromosome in a cell

Question 7

Chromosome banding technique

Answer 7

• older than FISH
• identifies chromos based on shape, size, and banding patterns
• stop cell during metaphase
• dye

Giemsa banding used for humans

Question 8

Human chromo banding patterns

Answer 8

letters/numbers used to identify major and minor band regions

begins at centromere then goes outwards

Question 9

Euchromatin

Answer 9

light regions

chromatin is less compact

higher gene expression

Question 10

Heterochromatin

Answer 10

dark regions

chromatin is more compact

lower gene expression

Question 11

Dipteran flies chromosome banding

Answer 11

discovered by Balbiani

polytene chromosomes are produced in salivary glands

stay together while replicating

produce distinct bands when stained

used to help map genes, identify mutations, etc

Question 12

Nondisjunction

Answer 12

the failure of chromosomes and sister chromatids to properly separate during cell division

can lead to abnormalities in chromosome number

can occur in meiosis 1 or 2

Question 13

Aneuploid

Answer 13

abnormal chromosome counts

most don’t survive gestation

ex.
- autosomal trisomies (13/18/21 = patau/edwards/down)
- sex monosomy or trisomy

Question 14

Trisomy vs monosomy

Answer 14

tri
2n+1

mono
2n-1

after fusion with a normal gamete

Question 15

Meiosis 1 nondisjunction

Answer 15

• homologs fail to separate into two cells

one daughter has an extra homolog (X), one lacks a homolog

results in 4 abnormal gametes

Question 16

Meiosis 2 nondisjunction

Answer 16

homologs separate

sister chromatids fail to separate

one daughter cell lacks a homolog

results in 2 abnormal gametes

Question 17

Trisomy 21

Answer 17

down syndrome

most well known aneuploidy in humans

link between maternal age and aneuploidy

Question 18

Robertsonian translocation

Answer 18

two non-homologous chromosomes fuse to form a large chromosome

Question 19

Robertson translocation and down syndrome

Answer 19

way for down syndrome to occur not as a result of a random non-disjunction

fusion between chromos 14 and 21
= only one chromo at 21

gamete with robertson (asymptomatic) + normal gamete
= down syndrome

Question 20

Polyploidy

Answer 20

the presence of three or more sets of chromosomes

ex. triploids (3n), tetraploids (4n)

common in plants

Question 21

Two types of polyploidy

Answer 21

Autopolyploidy
- occurs from the duplication of chromos within a species

Allopolyploidy
- combining chromo sets from different species

Question 22

Causes of polyploidy (3)

Answer 22

1. meiotic nondisjunction
   - leads to diploid instead of haploid
2. mitotic nondisjunction
   - doubles chromo number so all cells have doubled count
3. combination of the two

Question 23

Autopolyploidy example

Answer 23

bigger strawberries have more chromosomes

Question 24

Allopolyploidy example

Answer 24

species with different chromo number reproduce together

60 and 62
gamete fusion = 2n = 61
mitotic nondis = 2n = 122

is fertile

Question 25

Chromosome breakage

Answer 25

causes mutation by loss, gain, and rearrangement of chromosomes can have an effect or no effect

Question 26

Chromosomal deletions

Answer 26

break occurs at chromo break point = both DNA strands severed

Question 27

Terminal deletion

Answer 27

chromo tip missing telomere lost entire arm or part of it breaks off ex causes cri du chat

Question 28

Acentric

Answer 28

lacking a centromere usually lost during cell division

Question 29

Interstitial deletions

Answer 29

internal chromosomal deletions

Question 30

Issues when chromo reattaches after breaking

Answer 30

can cause inversions and translocations if no critical/regulatory regions mutated, maybe no pheno consequences

Question 31

Chromosome inversion + 2 types

Answer 31

reattachment of the wrong end 1. paracentric - centromere outside of inversion 2. pericentric - centromere within inversion

Question 32

Chromosome translocation

Answer 32

reattachment to a non-homologous chromosome

Question 33

Recombination between inverted regions

Answer 33

- inversion usually suppresses recombination bc need homology to be exchanged BUT - can still occur using a physical inversion loop - can lead to chromo breakage and large deletions

Question 34

Unequal crossover

Answer 34

takes place between two homologs results in a partial duplication of one homolog and a partial deletion on the other rare

Question 35

Williams-Beuren syndrome

Answer 35

result of partial duplication of PMS gene due to unequal crossovers on chromo 7 naive, outgoing, intellectual disabilities, heart issues

Question 36

Deletion mapping

Answer 36

compare unknown phenotype to known mapped mutations recessive mutations relies on pseudodominance aka hemizygosity

Question 37

Pseudodominance

Answer 37

if an organism has a recessive allele on one chromosome, and a deletion on the other, the recessive allele is expressed

Question 38

Notch gene deletion mapping

Answer 38

- drosophila notch = developmental gene - affects wing phenos deletion mapping showed it's in a region on the X chromo

Question 39

Period gene deletion mapping

Answer 39

- drosophila notch = circadian rhythm clock gene within loci on X chromo pair with genetic markers for yellow and white genes