Chromosomes

Question 1

Chromosomes which are not sex chromosomes

Answer 1

Autosomes

Question 2

Sex chromosomes males have

Answer 2

XY

Question 3

Sex chromosomes females have

Answer 3

XX

Question 4

Constriction within a chromosome which divides it into two arms

Answer 4

Centromere

Question 5

Label given to the short arm of a chromosome

Answer 5

P arm

Question 6

Label given to the long arm of a chromosome

Answer 6

Q arm

Question 7

Type of chromosome which has its centromere in the centre

Answer 7

Metacentric

Question 8

Type of chromosome which has its centromere close to the centre but one arm is slightly longer than the other

Answer 8

Submetacentric

Question 9

Type of chromosome where the centromere is significantly to one side

Answer 9

Acrocentric

Question 10

Type of chromosome where the centromere is almost completely to one side with one arm being extremely short

Answer 10

Telocentric

Question 11

Cells which contain different chromosomal numbers to the normal diploid cells

Answer 11

Aneuploid cells

Question 12

Occurrence where all cells contain three copies of each chromosome instead of two copies - so 69 total chromosomes

Answer 12

Triploidy

Question 13

Cause of triploidy

Answer 13

Non-disjunction during meiosis - one gamete has two copies of every chromosome and another gamete has no chromosomes; if the gamete with two copies of each chromosome pairs with a normal gamete the resulting foetus will be triploid

Question 14

Outcome of triploidy in human foetuses

Answer 14

Spontaneous abortion

Question 15

Non-disjunction for only one chromosome during meiosis resulting in the foetus having three copies of a single chromosome

Answer 15

Trisomy

Question 16

Non-disjunction for only one chromosome during meiosis resulting in the foetus having only one copy of a chromosome

Answer 16

Monosomy

Question 17

Trisomies of autosomes which are compatible with life

Answer 17

13
18
21

Question 18

Cause of mosaic trisomy or monosomy

Answer 18

Non-disjunction occurs during mitosis just after the two gametes fuse; resulting in two distinct cell lines, one with the normal chromosomal makeup and another with a trisomy or monosomy

Question 19

Syndrome caused by trisomy 21

Answer 19

Down’s syndrome

Question 20

Syndrome caused by trisomy 18

Answer 20

Edward’s syndrome

Question 21

Syndrome caused by trisomy 13

Answer 21

Patau syndrome

Question 22

Syndrome caused by monosomy X

Answer 22

Turner’s syndrome

Question 23

Syndrome caused by trisomy XXY

Answer 23

Klinefelter’s syndrome

Question 24

Findings before birth in Down’s syndrome

Answer 24

Reduced maternal levels of alpha fetoprotein
Increased beta HCG
Increased nuchal thickness
Increased levels of inhibin A

Question 25

Percentage of cases of Down's syndrome caused by meiotic non-disjunction

Answer 25

95%

Question 26

Three chromosomal causes of Down's syndrome

Answer 26

Meiotic non-disjunction Mosaicism Robertsonian translocation

Question 27

Percentage of cases of Down's syndrome caused by Robertsonian translocation

Answer 27

2-3%

Question 28

Percentage of cases of Down's syndrome caused by mosaicism

Answer 28

2-3%

Question 29

Steps occurring in Robertsonian translocation leading to Down's syndrome

Answer 29

When acrocentric chromosomes (including 21) break at their centromeres the long arm of chromosome 21 joins with the long arm of another acrocentric chromosome (e.g. chromosome 14) The two short arms left over are usually lost - often unimportant due to limited genetic material During meiosis the combined chromosome and the normal copy of chromosome 21 go into one gamete, while the normal chromosome 14 goes into another gamete The gamete with two copies of chromosome 21 is fertilised by another gamete with one copy of chromosome 21 The resulting foetus has three copies of chromosome 21

Question 30

Rate of Down's syndrome to mothers age 20

Answer 30

1 in 1500

Question 31

Rate of Down's syndrome in mothers aged 30

Answer 31

1 in 959

Question 32

Rate of Down's syndrome in mothers aged 40

Answer 32

1 in 100

Question 33

Rate of Down's syndrome in mothers aged 45

Answer 33

1 in 30

Question 34

Percentage of cases of trisomy 21 Down's syndrome caused by maternal meiotic error

Answer 34

95%

Question 35

Physical features of Edward's syndrome

Answer 35

Rocker bottom feet Low set ears Micrognathia Clenched hands

Question 36

Physical features of Patau syndrome

Answer 36

Polydactyly Cleft lip and palate Microcephaly Microphthalmia

Question 37

Percentage of cases of trisomy 13 caused by maternal meiotic non-disjunction

Answer 37

85%

Question 38

Percentage of cases of trisomy 18 caused by maternal meiotic non-disjunction

Answer 38

90%

Question 39

Percentage of cases of Turner's syndrome caused by paternal non-disjunction

Answer 39

80%

Question 40

Percentage of cases of Turner's syndrome caused by maternal meiotic non-disjunction

Answer 40

20%

Question 41

Physical features of Turner's syndrome

Answer 41

``` Short stature Broad chest and widely spaced nipples Webbed neck Low hairline Arms that turn out at the elbow Scoliosis ```

Question 42

Comorbidities associated with Turner's syndrome

Answer 42

Hypothyroidism and other autoimmune conditions Diabetes Osteoporosis (due to lack of oestrogen) Learning disabilities or behavioural problems (IQ usually normal) Congenital heart disease in 50% Structural abnormalities of the kidneys and ureters Middle ear issues and hearing loss

Question 43

Percentage of patients with Turner's syndrome who are able to have children without fertility treatment

Answer 43

2-5%

Question 44

Incidence of Turner's syndrome

Answer 44

1 in 2000 live born female babies

Question 45

General IQ and developmental features of patients with Turner's syndrome

Answer 45

Average or near average intelligence Weaker non-verbal skills including arithmetic Weaker visuospatial processing Weaker social skills

Question 46

Percentage of cases of Klinefelter syndrome caused by maternal non-disjunction

Answer 46

55%

Question 47

Percentage of cases of Klinefelter syndrome caused by paternal non-disjunction

Answer 47

45%

Question 48

Comorbidities associated with Klinefelter syndrome

Answer 48

Infertility in almost all patients Increased risk of breast cancer compared to other males Increased risk of autoimmune disorders

Question 49

Cognitive, developmental and psychiatric features of Klinefelter syndrome

Answer 49

Autism in 10% Increased anxiety and depression Some deficits often present in reading, language learning, and executive functions

Question 50

Facial features of Down's syndrome

Answer 50

``` Flat head Protruding tongue due to small mouth Slanted eyes and epicanthic folds Brushfield spots in iris Flat nasal bridge Small chin ```

Question 51

Non facial physical features of Down's syndrome

Answer 51

Single palmar crease Separation of first and second toes Hypotonia Short stature

Question 52

Medical comorbidities common in patients with Down's syndrome

Answer 52

Mild to moderate intellectual disability Epilepsy Visual problems - refraction errors, strabismus, cataracts Hearing problems - chronic ear infections, poor eustachian tube function Congenital heart disease - most commonly AVSD ALL, AML Hypothyroidism Diabetes Infertility GI problems - Hirschsprung's disease, duodenal atresia, constipation

Question 53

Form of Down's syndrome which has a high recurrence rate

Answer 53

Robertsonian translocation Down's syndrome

Question 54

Alleles which are found on the same chromosome

Answer 54

Syntetic

Question 55

Alleles that are close together and likely to be inherited together in the case of synapsis

Answer 55

Linked alleles

Question 56

Alleles that are close together and likely to be inherited together in the case of synapsis

Answer 56

Linked alleles

Question 57

Unit genetic distances are expressed in

Answer 57

centiMorgans (cM)

Question 58

Score used to estimate the likelihood that two loci are linked

Answer 58

LOD score

Question 59

LOD score taken to mean two loci are linked

Answer 59

>3

Question 60

LOD score taken to mean two loci are not linked

Question 61

An organism who has more than one genetically distinct population of cells arising from a single zygote

Answer 61

Mosaic

Question 62

An organism who has more than one genetically distinct population of cells arising from more than one zygote

Answer 62

Chimera

Question 63

Percentage recombination frequency equal to 1 centiMorgan

Answer 63

1%

Question 64

Number of base pairs of DNA equivalent to 1 centiMorgan

Answer 64

1 million

Question 65

Type of chromosome where the centromere makes up the whole chromosome

Answer 65

Holocentric