L15 - Errors in Meiosis and X-inactivation

Question 1

Define aneuploidy

Answer 1

An abnormal number of a particular chromosome

Question 2

What is a common example of Aneuploidy in humans?

Answer 2

Down syndrome

Question 3

In Down syndrome, what chromosome does trisomy occur in?

Answer 3

Chromosome 21

Question 4

What is trisomy?

Answer 4

3 copies of a particular chromosome

Question 5

Define non-disjunction

Answer 5

The failure of chromosomes to separate properly during meiosis

Question 6

Which of first and second meiosis does disjunction occur during?

Answer 6

Can occur during first or second meiosis

Question 7

How many chromosomes are in the resulting daughter cells when non-disjunction occurs during meiosis I?

Answer 7

n+1, n+1, n-1, n-1

Question 8

How many chromosomes are in the resulting daughter cells when non-disjunction occurs during meiosis II?

Answer 8

n+1, n-1, n, n

Question 9

What is the sex genotype os someone with Klinefelter Syndrome?

Answer 9

XXY

Question 10

What are some characteristics of Klinefelter Syndrome?

Answer 10

• Male, with some female characteristics
• Some intellectual impairment
• Tall

Question 11

What is the sex genotype of someone with Turner Syndrome?

Answer 11

XO

Question 12

What are some characteristics of Turner Syndrome?

Answer 12

• Folds of skin at neck
• Some intellectual impairment
• Where on spectrum depends on whether X from mum or dad

Question 13

Define polyploidy

Answer 13

Possession of multiple sets of chromosomes

Question 14

Is polyploidy more common in plants or animals?

Answer 14

Plants

Question 15

What is is called when 2 polyploid cells fuse to form a zygote?

Answer 15

Autopolyploid

Question 16

What is an autopolyploid?

Answer 16

The zygote formed when 2 polyploid cells fuse

Question 17

Why is an autopolyploid organism generally viable and fertile?

Answer 17

Because it has a full copy of genetic material, and can divide to produce cells that also have a full copy of DNA

Question 18

Name 3 polyploidy organisms

Answer 18

Raddage, bananas, New Mexico Whiptail lizard

Question 19

Why aren’t eating bananas fertile?

Answer 19

Because they have an odd number of chromosomes, which results in non-disjunction and thus unsuccessful zygotes that have a hodgepodge of cells with lots of different numbers of chromosomes

Question 20

Describe how New Mexico Whiptail lizards reproduce

Answer 20

These lizards are all female and reproduce parthenogenetically (lay unfertilised eggs) resulting in offspring with identical genetic material (clones)

Question 21

Name 4 other chromosomal aberrations

Answer 21

• deletion
• duplication
• inversion
• translocation

Question 22

Describe a deletion

Answer 22

A deletion removes a chromosomal segment

Question 23

Describe a duplication

Answer 23

A duplication repeats a segment (usually inserted right beside segment)

Question 24

Describe an inversion

Answer 24

An inversion reverses a segment within a chromosome

Question 25

Describe a translocation

Answer 25

A translocation moves a segment from one chromosome to a non-homologous chromosome

Question 26

Lejeune/Cri du chat syndrome is an example of...

Answer 26

deletion

Question 27

Which part of what chromosome is deleted in Lejeune/Cri du chat syndrome?

Answer 27

The tip of the short arm of chromosome 5

Question 28

Name 2 characteristics and the severity of Lejeune/Cri du chat syndrome

Answer 28

- Very severe ○ Intellectual impairment, make cat meow sound ○ Often don't survive past childhood

Question 29

How are humans impacted by gene inversion

Answer 29

Individual has all genetic material and is therefore effected very little, however their fertility is affected

Question 30

How is the fertility of a person with an inversion affected?

Answer 30

Chromosomes cannot align during crossing over, resulting chromosomes have the wrong genetic information

Question 31

Describe a Philadelphia Translocation

Answer 31

Reciprocal translocation between chromosomes 9 and 22

Question 32

What is typically the result of a Philadelphia Translocation?

Answer 32

Gene on translocated chromosome 22 cannot be turned off because broken in wrong place = leukaemia

Question 33

What is the difference between Familial Down Syndrome and trisomy Down Syndrome?

Answer 33

Familial Down Syndrome has some inheritance pattern due to the translocation of chromosome 21

Question 34

Describe the karyotype of a person with Familial Down Syndrome

Answer 34

They have 46 chromosomes, however one copy of chromosome 14 consists of the fused long arms of chromosome 14 and 21. Thus there is effectively 3 copies of chromosome 21

Question 35

What is a Barr body?

Answer 35

A condensed X chromosome

Question 36

Who discovered Barr bodies in the nucleus of cells?

Answer 36

Mary Lyon

Question 37

In what sex chromosome genotypes is a Barr body found

Answer 37

XX and XXY (2 found in XXX - very uncommon)

Question 38

At what stage of development is an X chromosome deactivated?

Answer 38

When embryo is 4 days old = 100 cells

Question 39

What 3 changes at the molecular level to allow the X chromosome to be deactivated?

Answer 39

○ Histone proteins change signalling deactivation ○ Structural proteins wrap it tighter ○ Methyl groups (markers) signal that it shouldn't be read

Question 40

What happens to the X chromosome that is not inactivated? What is the purpose of this?

Answer 40

It is spread out, histone tails have different confirmation, signalling that it is active. Makes it easier to be read, transcribed

Question 41

Why must all calico cats be female?

Answer 41

Fur colour is a sex linked gene and the striped appearance is due to the expression of heterozygous alleles on 2 X chromosome. Therefore all calico cats must be female