Aneuploidy (Lec 12)

Question 1

Define Aneuploidy

Answer 1

a change in the number of individual chromosomes

Question 2

A type of aneuploidy where there is a loss of both members of a pair of homologous chromosomes is called what?

Answer 2

nullisomy

Question 3

A type of aneuploidy where there is a loss of a single chromosome (2n-1) is called what?

Answer 3

monosomy

Question 4

A type of aneuploidy where there is a gain of a single chromosome (2n+1) is called what?

Answer 4

trisomy

Question 5

A type of aneuploidy where there is a gain of two homologous chromosomes (2n+2) is called what?

Answer 5

tetrasomy

Question 6

What is double trisomy?

Answer 6

gain of two non homologous chromosomes (2n+1+1)

Question 7

What is double monosomy?

Answer 7

loss of two non homologous chromosomes (2n-1-1)

Question 8

What is double tetrasomy?

Answer 8

gain of two extra pairs of homologous chromosomes (2n+2+2)

Question 9

If nondisjunction occurs in meiosis I, what are the resulting zygotes?

Answer 9

trisomic (2n+1) or monosomic (2n-1)

Question 10

If nondisjunction occurs in meiosis II, what are the resulting zygotes?

Answer 10

trisomic (2n+1), monosomic (2n-1), or normal diploid (2n)

Question 11

Aneuploidy affects number of gene copies but not nucleotide sequences, therefore, effects of aneuploidy are most likely due to what?

Answer 11

abnormal gene dosage

Question 12

True or false?

X-inactivation in mammalian females is an example of dosage compensation

Answer 12

true

Question 13

In regards to aneuploidy in humans, what type of chromosomes are most commonly involved?

Answer 13

sex chromosomes

Question 14

Primary Down Syndrome (trisomy 21) usually arises from nondisjunction in which part of meiosis I?

Answer 14

oogenesis of meiosis I

Question 15

About 4% of those with Down syndrome have 46 chromosomes with extra part of chromosome via translocation. This type of Down syndrome that arises from carriers of chromosomes that have undergone a Robertsonian translocation is called what?

Answer 15

Familial Down syndrome

Question 16

Between what two chromosomes does the Robertsonian translocation occur in Familial Down syndrome?

Answer 16

14 and 21

Question 17

In regards to Familial Down syndrome, how many chromosomes do the translocation carriers have and do they have down syndrome?

Answer 17

45; no they do not have Down syndrome

Question 18

In regards to Familial Down syndrome, what are the three possible ways for segregation to occur in a translocation carrier?

Answer 18

Translocation chromosome may separate from normal 14 and 21 chromosomes

gametes = half with translocation chromosomes and half with normal 14 and 21 chromosomes

gametes = half with normal 21+ translocation chromosome and half with 14 but no 21 chromosome

gametes = half with normal 14+ translocation chromosome and half with 21 but no 14

Question 19

If a normal person mates with a translocation carrier, what percentage of offspring will be healthy and what percentage will have down syndrome?

Answer 19

2/3 healthy, including the translocation carriers

1/3 will have Down syndrome

note: other chromosomal combinations result in aborted embryos

Question 20

What are some characteristics of Trisomy 10: Edward syndrome?

Answer 20

1 in 8,000 births
severely retarded
low-set ears
short neck
deformed feet
clenched fingers
heart problems
die within a year typically

Question 21

What are some characteristics of Trisomy 13: Patau syndrome?

Answer 21

1 in 15,000 births
severe mental retardation
small head
sloping forehead
small eyes
cleft lip and palate
extra fingers and toes
half die within a month of birth, rest by age of 3

Question 22

What are some characteristics of Trisomy 8?

Answer 22

mental retardation
contracted fingers and toes
low-set malformed ears
prominent forehead
often a normal life expectancy

Question 23

The following condition occurs when both chromosomes of a homologous pair are inherited from the same parent - most cases probably arise as a trisomy with one of the three homologs chromosomes lost early in development

Answer 23

uniparental disomy

note: trisomics typically do not survive
ex: cystic fibrosis and prader-willi

Question 24

What is Mosaicism?

Answer 24

occurs when there is nondisjunction in mitosis and is often found in Turner’s syndrome (45, XX/46, XX)

Question 25

Define polyploidy

Answer 25

changes in number of haploid SETS of chromosomes

note: more common in plants than animals

Question 26

What is autopolyploidy?

Answer 26

extra sets of chromosomes are derived from same species

Question 27

What is allopolyploidy?

Answer 27

extra sets of chromosomes are derived from two or more species

Question 28

What is the significance to cell size, attributes, and evolution of polyploidy?

Answer 28

increase in cell size; larger plant attributes; evolution: may give rise to new species

Question 29

A diploid (2n) cell that experiences nondisjunction in mitosis will result in what type of cell?

Answer 29

autotetraploid (4n)

note: separation of chromosomes occurs but since there is nondisjunction, there is no cell division

Question 30

A diploid (2n) cell that experiences nondisjunction in meiosis I will result in what type of gamete and zygote?

Answer 30

two 2n gametes

when one of these 2n gametes fuses with a 1n gamete, an autotriploid (3n) zygote will be formed

Question 31

What happens in a tirploid (3n) cell when none of the chromosomes pair in meiosis I?

Answer 31

all three chromosomes will move to the same cell creating two 3n gametes

Question 32

In regards to hybridization between two diploid species, (2n = 14) x (2n = 14) / 2 -> ?

Answer 32

(2n = 14)

explanation: nondisjunction leads to doubling of all chromosomes (2n = 28) and then proper chromosome pairing and segregation produce two balanced (2n = 14) gametes