Lecture 45

Question 1

Cause of trisomy 21

Answer 1

• trisomy due to most frequently meiosis nondisjunction during oogenesis (mostly meiosis 1) - most common cause
• Usually, individual has two maternal chromosome 21 and 1 paternal chromosome 21. If two maternal chromosomes are same, that means nondisjunction meiosis II has occured, If two maternal chromosomes are different, nondisjunction at meiosis I occurred.
• robertsonian translocation between chromosome 9 and 21

Question 2

menifestation of trisomy 21

Answer 2

• intellectual disability
• depressed nasal bridge and epicanthal folds
• congenital heart defects
• single palmar crease

Question 3

What is trisomy 18

Answer 3

Edward syndrome

Question 4

Genetic mechanism of trisomy 18

Answer 4

nondisjunction during oogenesis

Question 5

Manifestation of trisomy 18

Answer 5

clenched fist, overlapping of finger

• rocker bottom feet
• congenital heart defects
• micrognathia(small lower jaw)
• microcephaly
• intellectual disability

Question 6

What is trisomy 13

Answer 6

Patau syndrome

Question 7

Cause of trisomy 13

Answer 7

nondisjunction during oogenesis

Question 8

Manifestation of trisomy 13

Answer 8

polydactyly

• cleft lip and palate
• microphthalmia
• microcephaly
• intellectual disability
• cardiac anomalies

Question 9

What is genotype of Turner syndrome

Answer 9

45,X (cells with no barr body)

Question 10

Manifestation of turner syndrome

Answer 10

short stature

• webbed neck (neck swelling)
• primary amenorrhea
• gonadal dysgenesis
• streak ovaries
• poor breast development

Question 11

Cause of turner syndrome

Answer 11

nondisjunction during spermatogenesis

• could also happen post-fertilization mitosis as one of the X chromosomes evicted during cell division leading to mosaicism.
• also causedby isochromosome X

Question 12

What is genotype of klinefelter syndrome

Answer 12

47,XXY

Question 13

Manifestation of klinefelter syndrome

Answer 13

• gynecomastia (enlargement of breast in male)
• female distribution of hair
• infertility and testicular atrophy
• feminization of features

Question 14

Cause of klinefelter syndrome

Answer 14

• meiosis I or II in mom

- nondisjunction during meiosis I in dad

Question 15

2 ways that a person could be mosaic for down syndrome

Answer 15

1. post-fertilization non-disjunction, leading to mosaic

2. Nondisjunction in oogenesis, then there is trisomy rescue during post-fertilization mitosis, leading to mosaicism.

Question 16

What is philadelphia chromosome

Answer 16

Reciprocal translocation between chromosome 9 and 21, leading to fused gene (BCR and ABL). This leads to activation of BCR-ABL tyrosine kinase which is a proto-oncogene in hematopoietic cells. (Condition : Chronic myelogenous leukemia (CML))

Question 17

What does translocation between chromosome 8 and 14 lead to?

Answer 17

Burkitt lymphoma caused by dysregulation of c-myc gene expression

Question 18

Isochromosome

Answer 18

Loss of one arm of a chromosome and duplication of the other arm

Question 19

Girls with isochromosome X

Answer 19

Turner syndrome