Genetics 1 (Mrs Jones)

Question 1

What are the 7 types of congenital abnormalities and birth defects?

Answer 1

• Malformation: primary structural defect, single organ shows multi-factorial inheritance
• Disruption: not genetic, secondary abnormal structure of organ/tissue
• Dysplasia: abnormal organisation of cells into tissues
• Deformation: abnormal mechanical force distorts structure
• Sequence: multiple abnormalities initiated by primary factor
• Association: non-random occurrence of abnormalities, cause unknown
• Syndrome: consistent pattern of abnormalities with specific underlying cause

Question 2

What are examples of the 7 congenital abnormalities?

Answer 2

• Malformation: cleft lip/atrial septal defect
• Disruption: amniotic bands lead to digital amputation
• Dysplasia: thanatophoric dysplasia
• Deformation: club foot/hip dislocation
• Sequence: potters sequence
• Association: vater association
• Syndrome: down’s syndrome

Question 3

What is the most common cause of Sequence?

Answer 3

Oligohydraminos

Question 4

How does chromosome banding work?

Answer 4

• Starts at 11 at the centromere

- different banding for different stains

Question 5

What are the three different types of chromosomal abnormality?

Answer 5

• Aneuploidy: loss/gain of chromosomes
• Structural
• Mosaicism: different cell lineages (cells of same individual have different numbers/arrangement of chromosomes)

Question 6

What is the difference between a balanced and unbalanced translocation?

Answer 6

Unbalanced has a loss of genetic material

Question 7

What are some clinical features of Down Syndrome?

Answer 7

• newborn: excess nuchal skin, sleepy, severe hypotonia
• craniofacial: macroglossia, eye folds, small ears, spots in iris
• limbs: single palmar crease, sandal gap
• Cardiac abnormalities – A and V septal defects
• short stature

Question 8

What are three possible causes of Down syndrome?

Answer 8

• Non-disjunction during meiosis I or meiosis II
• Robertsonian translocation (2 acrocentric chromosomes break at the centromere and fuses to form a new chromosome)
• Mosaicism (<1%)

Question 9

What are two trisomy disorders, not Down’s syndrome?

Answer 9

• 13: Patau syndrome (heart defects, mental retardation, holoprosencephaly)
• 18: Edward’s syndrome (heart defects, mental retardation, kidney malformation, digestive tract defects)

Question 10

What is monosomy X in females and what are the clinical features?

Answer 10

• Turner’s Syndrome (45, X)

- webbed neck, infertile, low set ears, low posterior hairline, short stature, diabetes, hypothyroidism

Question 11

What is polysomy X in males and what are the clinical features?

Answer 11

• Klinefelter’s syndrome (47, XXY)

- tall, reduced verbal IQ, infertile, enlargement of breast tissue

Question 12

How can someone who has sex chromosomes XX be male?

Answer 12

Due to translocation where sex determining region on Y (SRY) is translocated onto X chromosome

Question 13

What are the different types of aneuploidy?

Answer 13

• monosomy: loss of single chromosome (lethal)
• trisomy: gain of one chromosome (tolerated)
• tetrasomy: gain of two chromosomes (tolerated)

Question 14

What are the 5 structural problems of chromosomes?

Answer 14

• translocations
• deletions
• insertions
• inversions
• rings

Question 15

When does X-inactivation in females occur?

Answer 15

early embryonic development