Embryology to gastrulation

Question 1

What chromosomes do human somatic cells contain

Answer 1

46 chromosomes
2 sex chromosomes
Remaining autosomes
Every cell has 22 homologous sets of paired chromosomes

Question 2

Describe fertilisation briefly

Answer 2

Fusion of 2 gametes (spermatozoa and ova)

Leads to formation of zygote

Question 3

Meaning of diploid and haploid

Answer 3

Diploid- complete number of chromosomes in somatic cells

Haploid- half number of chromosomes in gametes

Question 4

Meiosis

Answer 4

Produces germ cells with half the number of chromosomes of the somatic cell

Question 5

Mitosis

Answer 5

Division of somatic cells

Question 6

Before mitotic cell division begins…..

Answer 6

DNA replicates, amount doubled to value tetraploid

Which is 4 times the amount of DNA found in germ cell

Question 7

Down syndrome

Answer 7

Trisomy 21
Fertilisation, gamete containing 24 chromosomes fuses with a normal gamete containing 23, zygote will possess 47 chromosomes

One homologous pair has third component, thus cells are trisomic

Question 8

Features of Down syndrome

Answer 8

Facial cleft
Shortened palate
Protruding and fissured tongue
Delayed eruption of teeth0

Question 9

Turner Syndrome: X0

Answer 9

One member of the homologous chromosome pair is missing, rare condition known as monosomy of the X chromosome prevails

Question 10

Features of Turner syndrome

Answer 10

Dystrophic stigmata
Short stature
Sexual infantilism

Question 11

Klinefelter syndrome: xxy

Answer 11

One member of the homologous chromosomes pair is extra

Taller than average
Less muscle
Less hair
Gynaecomastia
Abnormalities

Question 12

2 ways alteration of genes are transmitted

Answer 12

1– autosomal dominant inheritance: achondroplasia
Cleidocranial dystosis
Osteogenesis imperfecta
Dentinogenesis imperfecta

2- autosomal recessive inheritance: chondroectodermal dysplasia
Microcephaly
Cystic fibrosis

Question 13

Achondroplasia

Answer 13

“Without cartilage formation”
Short limbed dwarfism

Question 14

Cleidocranial dysostosis

Answer 14

Abnormal bone forming in skull and collar bones

“Dystosis” means abnormal bone forming

Question 15

Osteogenesis imperfecta

Answer 15

Bones fracture and break easily

Question 16

Chondroectodermal dysplasia

Answer 16

Affects bone development and growth

Question 17

How do epigenetic changes affect gene expression?

Answer 17

DNA methylation
Histone modification
Non-coding RNA

Question 18

Formation of the three layered embryo

Answer 18

Fertilised egg undergoes rapid divisions
Lead to formation of cells called ‘morula’
Fluid builds inside morula
Cells realign to form ‘blastocyst’

Question 19

Structure of blastocyst

Answer 19

Outer layer-trophoblast, will eventually form placenta

Embryoblast- give rise to tissues of the body

Primary yolk sac, gives space for embryoblast

Question 20

Day 8 of gestation

Answer 20

Embryoblast cells differentiate into 2 layered disk called bilaminar germ dis

Cells dorsally or ectodermal layer, columnar and form amniotic cavity

Those on ventral aspect, endodermal layer, cuboidal and form roof of secondary cavity (secondary yolk sac)

Question 21

Epiblast

Answer 21

Another name for ectoderm

Question 22

Hypoblast

Answer 22

Another name for endoderm

Question 23

When is the axis of embryo established

Answer 23

After 2 weeks
Slight enlargement of the ectodermal and endodermal cells

Head end of embryo prochordal plate

Tail end is cecal plate