Genetic regulation of development

Question 1

Q2: What is the fate of the inactivated X chromosome in mammalian embryonic cells?

Answer 1

C) It forms a Barr body

Question 2

Which of the following species always inactivates the paternally derived X chromosome?

Answer 2

C) Duckbill platypus and kangaroos

Question 3

What does the term “maternal effect” refer to in developmental genetics?

Answer 3

B) The impact of maternal genes on early embryogenesis via cytoplasmic components

Question 4

In organisms with strong maternal effects, such as Cynthia partita, how is cell fate determined?

Answer 4

D) By uneven distribution of maternal cytoplasmic components

Question 5

Which of the following statements about early human embryogenesis is correct?

Answer 5

A) All embryonic genes are active immediately at fertilization
B) Maternal mRNA is irrelevant in human development
C) Zygotic gene expression starts at the two-cell stage
D) Maternal effect ends before the zygote divides
✅ Correct answer: C)

Question 6

In Drosophila, when are embryonic genes first expressed?

Answer 6

C) Around the blastoderm stage (∼6000 cells)

Question 7

What is the main mechanism involved in chromosome or gene imprinting

Answer 7

B) DNA methylation and protein binding

Question 8

What determines whether the maternal or paternal X chromosome is inactivated in humans?

Answer 8

C) Random selection in each cell

Question 9

What is the role of maternal effect genes?

Answer 9

C) They deposit regulatory molecules into the egg cytoplasm

Question 10

Which of the following is not a result of maternal effect in early embryogenesis?

Answer 10

A) Control of initial cell fate decisions
B) Regulation of early cleavage stages
C) Zygotic gene expression during fertilization
D) Deposition of mRNAs during oogenesis
✅ Correct Answer: C)

Question 11

Which organism shows mosaic development due to maternal effect substances?

Answer 11

B) Cynthia partita

Question 12

What developmental defect is observed when the anterior tip of a Drosophila egg is pricked?

Answer 12

C) Head and thorax segments are missing

Question 13

What conclusion can be drawn from the headless embryos observed after anterior egg pricking in Drosophila?

Answer 13

B) The anterior tip contains maternally deposited factors

Question 14

Which of the following maternal effect genes is key to head formation in Drosophila?

Answer 14

D) Bicoid

Question 15

Which mutation results in headless embryos despite the egg appearing normal?

Answer 15

A) exuperantia/exuperantia
B) hb/hb
C) bcd/bcd
D) Both A and C
✅ Correct Answer: D

Question 16

Where is bicoid mRNA localized in a wild-type Drosophila egg?

Answer 16

C) Anterior tip

Question 17

What kind of molecule is the Bicoid protein?

Answer 17

C) Transcription factor

Question 18

The Bicoid protein concentration is highest in which part of the Drosophila embryo?

Answer 18

anterior tip

Question 19

Which gene is positively regulated by the Bicoid protein?

Answer 19

hunchback gene

Question 20

Which gene is negatively regulated by the Bicoid protein in anterior regions?

Answer 20

Krüppel

Question 21

What is a morphogen?

Answer 21

B) A molecule that determines cell fate via concentration gradients

Question 22

Which gene is classified as a gap gene in Drosophila?

Answer 22

hunchback (positively regulated by bicoid protein)

Question 23

What is the role of the products of pair-rule genes?

Answer 23

C. Establish segment pairs

Question 24

What do segment polarity genes do in Drosophila embryogenesis?

Answer 24

B. Divide segments into anterior and posterior parts

Question 25

What is the final class of genes in the hierarchy of segmentation?

Answer 25

D. Homeotic genes

Question 26

Which gene mutation results in the transformation of T3 into T2 in Drosophila?

Answer 26

D. Bithorax

Question 27

What is homeosis?

Answer 27

B. Replacement of a structure by another typical of a different region

Question 28

What does the bithorax mutation cause in Drosophila?

Answer 28

C. Two pairs of wings

Question 29

Which gene type regulates expression of segment polarity genes?

Answer 29

pair-rule genes

Question 30

What is a phenocopy?

Answer 30

environmental mimmic of a genetic mutation

Question 31

What field studies abnormal development such as phenocopy?

Answer 31

teratogenesis

Question 32

What phenotype is observed in embryos from bcd/bcd mutant females?

Answer 32

headless embryos

Question 33

What is the expression pattern of zygotic hunchback in wild-type embryos?

Answer 33

C. Anterior band in future head and thorax regions

Question 34

What do gap gene products regulate?

Answer 34

expression of pair-rule gene

Question 35

What is the role of homeotic genes?

Answer 35

determine segment identity

Question 36

What is the correct order of gene classes acting in segment determination?

Answer 36

Maternal → Gap → Pair-rule → Segment Polarity → Homeotic

Question 37

What is polythely an example of?

Answer 37

atavism

Question 38

How many homeotic genes are found in the Antennapedia (ANT-C) complex?

Answer 38

5

Question 39

The homeotic genes of Drosophila are clustered in which two complexes?

Answer 39

ANT-C and BX-C

Question 40

What is the term for the full Drosophila chromosome segment that includes ANT-C and BX-C?

Answer 40

Hom-C

Question 41

In mammals, how many Hox complexes are there?

Answer 41

4

Question 42

Each mammalian Hox complex is divided into how many regions?

Answer 42

13

Question 43

What is the homeobox?

Answer 43

A 180 base pair conserved DNA sequence in homeotic genes

Question 44

What does the homeobox encode?

Answer 44

homeodomain

Question 45

What is the function of the homeodomain?

Answer 45

DNA binding by homeotic proteins

Question 46

In sea urchin embryos, what is necessary for normal development?

Answer 46

Cells from both animal and vegetal poles

Question 47

What determines the animal pole of a sea urchin embryo?

Answer 47

Polar body cells attached to the egg or zygote

Question 48

What is embryonic induction?

Answer 48

A signal from transplanted cells that instructs neighboring cells to follow a new developmental path

Question 49

Which gene controls the region where limb buds form along the anterior-posterior axis?

Answer 49

Hox6

Question 50

What is secreted by lateral plate mesoderm cells upon activation of Hox6 during limb bud formation?

Answer 50

Fibroblast Growth Factor FGF10

Question 51

What role does FGF10 play in limb bud formation?

Answer 51

It initiates limb bud formation by inducing mesodermal cell migration

Question 52

Which two genes determine forelimb and hindlimb formation respectively?

Answer 52

Tbx5 and Tbx4

Question 53

Mutation in which gene leads to Holt-Oram syndrome?

Answer 53

Tbx5

Question 54

Which developmental axis is controlled by the apical ectodermal ridge (AER) in limb buds?

Answer 54

proximal-distal

Question 55

Which molecule is required for the outgrowth of limb buds, in addition to FGF10?

Answer 55

retinoic acid

Question 56

What molecule induces the differentiation of the apical ectodermal ridge (AER)?

Answer 56

FGF10

Question 57

Which molecule is secreted by AER cells to stimulate mitosis and prevent cartilage differentiation?

Answer 57

FGF8

Question 58

What phenotype results from loss of function mutations in the HOXD13 gene?

Answer 58

Synpolydactyly (many fingers joined together)

Question 59

Which gene is expressed in the cells of the ZPA and plays a key role in anterior-posterior patterning?

Answer 59

Sonic hedgehog (Shh)

Question 60

What proteins do ZPA cells release under the influence of Sonic hedgehog, which determine positional information?

Answer 60

BMP2 & BMP7

Question 61

What does Wnt7a protein regulate in limb development?

Answer 61

Differentiation along the dorsal-ventral axis

Question 62

Which gene does Wnt7a induce in dorsal mesenchyme cells?

Answer 62

Lmx1

Question 63

What role do BMP proteins play during limb development?

Answer 63

Induce apoptosis and regulate bone formation