Ch. 6 Chromosome Variation

Question 1

What is the “ploidy” status of cultivated bananas?

Answer 1

Polyploidy (3n, 4n, or higher)

Question 2

The Cavendish strain of bananas is threatened by what?

Answer 2

Soil Fungus more recently but also pests and diseases

Question 3

The banana of choice before the Cavendish was what?

Answer 3

Gros Michel (until disease in 1950’s - 1960’s wiped it out)

Question 4

Why can’t we just replant the Gros Michel?

Answer 4

Because they would all be genetically identical cultivated and vulnerable to the same pathogen and pests as before.

Question 5

How are we helping the banana issue?

Answer 5

Using genome sequence scientists have already identified several genes that play a role in resistance to fungal diseases and are exploring ways to breed and genetically engineer bananas

Question 6

Chromosome mutations

Answer 6

Variations in the number and structure of chromosomes

Question 7

Karyotype

Answer 7

Complete set of chromosomes possessed by an organism

Question 8

What types of cells are karyotypes prepared from?

Answer 8

actively dividing cells such as wbc, bonemarrow cells, treated with chemical (colchicine) to prevent them from entering anaphase.

Question 9

special staining techniques within karyotyping help to reveal what?

Answer 9

“bands of DNA (G band, C band, Q band, R band)

G bands - DNA rich in A-T base pairs
Q bands - differences of c-g and a-t base pairs
C bands - regions of DNA occupied by centromeric heterochromatin
R bands - DNA rich in C-G base pairs

Question 10

three basic categories of chromosome mutations

Answer 10

• 6.2 chromosome rearrangements (alter structure)
• 6.3 aneuploidy (add number)
• 6.4 polyploidy (add sets)

Question 11

*** 6.2 Chromosome rearrangements

Answer 11

alter the STRUCTURE of chromosomes (duplicated, deleted or inverted)

Question 12

*** 6.3 aneuploidy

Answer 12

NUMBER of individual chromosomes is altered (addition or deletion)

Question 13

*** 6.4 polyploidy

Answer 13

SETS of chromosomes are added (3n, 4n, or more etc. . ..)

Question 14

6.2 Chromosome duplication

Answer 14

mutation in which part of the chromosome has been doubled. Example: instead of ABCDEFG the duplication might be ABCDEF-EF-G (tandem duplication)

Question 15

6.2 Tandem duplication

Answer 15

the type of duplication in which the duplicated segment is immediately adjacent to the original segment
ABCDEFG
ABCDEFEFG

Question 16

6.2 Displaced duplication

Answer 16

if the duplicated segment is located some distance from the original segment either on the same chromosome or on a different one
ABCDEFG
ABCDEFGEF

Question 17

6.2 reverse duplication

Answer 17

duplication is inverted
ABCDEFG
ABCDEFFEG

Question 18

6.2 Deletion

Answer 18

a segment of the chromosome is deleted
ABCDEFG
ABCDG

Question 19

6.2 Inversion

Answer 19

segment of the chromosome is turned 180 degrees.

ABCDEFG
ABCFEDG

Question 20

6.2 Translocation

Answer 20

segment of a chromosome moves from one chromosome to a nonhomologous chromosome or to another place on the same chromosome.

Question 21

Loop segment in meiosis

Answer 21

a way to detect duplication or deletion in a heterozygous for duplication. within meiosis the duplicated region must loop out to allow the homologous sequences of the chromosomes to align.

Question 22

how do duplications and deletions often arise?

Answer 22

Duplications and deletions often arise from unequal crossing over, in which duplicated segments of chromosomes misalign during the process.

Question 23

What’s the most frequent cause of red-green color blindness in humans?

Answer 23

unequal crossing over

Question 24

Segmental duplication

Answer 24

duplications greater than 1000 base pairs in length.

Question 25

pseudodominance

Answer 25

expression of a normally recessive mutation. it is an indication that one of the homologous chromosomes has a deletion.

Question 26

paracentric inversions

Answer 26

inversions that DO NOT include the centromere

Question 27

pericentric inversions

Answer 27

inversions that DO include the centromere.

Question 28

position effect

Answer 28

many genes are regulated in a position-depentednt manner; if their positions are altered by an inversion, their expression may be altered i.e. position effect.

Question 29

dicentric chromatid

acentric chromatid

Answer 29

• two centromeres

- no centromere

Question 30

How is recombination reduced within pericentric inversions?

Answer 30

no dicentric bridges or acentric fragments are produced, but the recombinant chromosomes have too many copies of some genes and no copies of others, so gametes that receive the recombinant chromosomes cannot produce viable progeny

Question 31

nonreciprocal translocation

Answer 31

genetic material moves from one chromosome to another without any reciprocal exchange.

Question 32

Reciprocal translocation

Answer 32

two way exchange of segments between the chromosomes

Question 33

Robertsonian Translocation

Answer 33

the long arms of two acrocentric chromosomes become joined to a common centromere through a translocation generating a metacentric chromosome with two long arms and another chromosome with two very short arms.

Question 34

fragile sites

Answer 34

chromosome regions susceptible to breakage under certain conditions.

Question 35

fragile-X syndrome

Answer 35

one of the most intensively studied fragile sites on the human x chromosome. a disorder that includes intellectual disability. x linked inheritance 1 in 5000 male births. results due to the increase in the number of repeats of a CGG trinucleotide.

Question 36

What is the outcome of a Robertsonian translocation?

Answer 36

One large chromosome and one very small chromosome with two very short arms.

Question 37

copy number variations (CNVs)

Answer 37

include duplications and deletions that range in length from thousands of base pairs to several million base pairs. Many of these variants encompass at least one gene and may encompass several genes.

Question 38

3 main ways aneuploidy can arise?

Answer 38

1. chromosome may be lost in the course of mitosis or meiosis.
2. the small chromosome generated by a robertsonian translocation may be lost in mitosis or meiosis.
3. nondisjunction. failure of homologous chromosomes or sister chromatids to separate in meiosis or mitosis. some gametic cells will gain a single chromosome some will lose a single chromosome.

Question 39

Aneuploidy - nullisomy

Answer 39

loss of both members of a homologous pair of chromosomes. 2n-2

Question 40

Aneuploidy - Monosomy

Answer 40

Loss of a single chromosome 2n-1

Question 41

Aneuploidy - Trisomy

Answer 41

gain of a single chromosome 2n+1

Question 42

Aneuploiody - Tetrasomy

Answer 42

gain of two homologous chromosomes 2n+2

Question 43

Down syndrome

Answer 43

trisomy 21. most common autosomal aneuploidy in humans.

Question 44

primary down syndrome

Answer 44

three full copies of chromosome 21. arises from spontaneous nondisjunction in egg formation: about 75% of the nondisjunction events that cause down syndrome are maternal in origin most arising in meiosis 1.

Question 45

familial down syndrome

Answer 45

4% of people with down syndrome have this type. NOT TRISOMIC. extra copy of part of chromosome 21 is attached to another chromoosome through translocation. so still 46 chromosomes but the second part of 21 tacs on to another chromosome so karyotype might look like 45. .

Question 46

translocation carrier

Answer 46

increased chance of producing children with down syndrome although they themselves don’t have down syndrome.

Question 47

Trisomy 18 (Edward Syndrome)

Answer 47

severe intellectual disability low set ears, short neck, deformed feet, clenched fingers heart problems. life expectency <1 year.

Question 48

Trisomy 13 (Patau syndrome)

Answer 48

severe intellectual disability, small head, sloping forehead, small eyes, cleft lip and palate, extra fingers and toes and numerous other problems. life expectency < 3 years.

Question 49

Trisomy 8

Answer 49

Most rare of trisomies- intelectual disability, contracted fingers and toes, low set malformed ears, prominent forehead. normal life expectancy.

Question 50

Does the frequency of Aneuploidy increase or decrease with maternal age?

Answer 50

it increases with maternal age. due to being associated with nondisjunction.

Question 51

Autopolyploidy

Answer 51

all chromosome sets are from a single species

Question 52

Allopolyploidy

Answer 52

chromosome sets are from two or more species

Question 53

two types of polyploidy

Answer 53

• autopolyploidy

- allopolyploidy

Question 54

unbalanced gametes

Answer 54

various number of chromosomes in gametes due to random segregation when multiple are involved.

Question 55

amphidiploid

Answer 55

type of allopolyploid consisting of two combined diploid genomes.