3- Chromosomal disorders diseases and embryonic development

What are the types of chromosome mutations? 

• Translocation 

• Inversion 

• Deletion 

• Duplication 

What is translocation? 

When segments of different chromosomes are exchanged 

What is inversion? 

A segment of chromosome is inverted 

What is deletion? 

A segment of chromosome is deleted  

What is duplication? 

Segment of one chromosome moves to the same location on a homologous chromosome 

Why is trisomy 21 relatively common and the other autosomal trisomy's not? 

• It's the smallest autosomal chromosome- causes down syndrome. 

• Mainly due to chromosome size vs gene content 

What is a nondisjunction? 

• When the chromosome fails to separate during meiosis 

• This produces gametes with either a missing chromosome or extra chromosome 

What is aneuploidy? 

When gametes contain an abnormal amount of chromosomes, it is referred to as having ''aneuploidy'' 

Describe the lengthy Meiosis process in Oocytogenisis 

• The development of mature egg, is a prolonged process 

• Immature eggs form in the female embryo but do not complete their development until years of decades later 

• One egg is prepared in a follicle and released ~every 28 days between start of puberty  and menopause (not during pregnancy or hormonal induced menstral suppresion) 

What is fertilization? 

Formation of a diploid zygote from a haploid egg and sperm 

What occurs during fertilization? (detailed pls)

• Cleavage-a period of rapid mitotic devision without growth 

• Morula is formed- a compact mass of cells (solid ball of cells) 

• After 5 days, a blastocyst is formed (hollow ball of cells) 

Give a summary of the formation of the human zygote and early post fertilization events. 

1. Ovulation 

2. Fertilization 

3. Cleavage 

4. Cleavage continues 

5. Implantation 

Describe how an embryo develops and leads to the formation of a human 

1. Fertilisation 

• Sperm fuses with egg in falopian tube 

• Forms a zygote 

2. Cleavage and blastocyst formation 

• Zygote undegoes rapid mitotic divisions (cleavage) 

• Becomes a morula (solid mass of balls) 

• Fluid enters, forming the blastocyst with: Inner cell mass (forming the embryo) and Trophoblast (becoming the placenta). 

3. Implantation 

• Blastocyst embeds itself into the uterus lining 

• Trophoblast cells form the placenta, supporting nutrient and gas exchange 

4. Gastrulation 

• ICM (Inner cell mass) reorganizes into: Ectoderm (skin, nervous system), Endoderm (organ linings, guts, lungs, liver), Mesoderm (muscles, bones, blood, kidneys) 

5. Neurulation 

• Ectoderm folds to form the neural tube which becomes the brain and spinal chord 

• Neural crest cells migrate to form peripheral nerves, facial structures, and more.  

6. Organogenesis 

• Major organs begin forming.  

• Heart starts beating around week 4. 

• Limb buds, eyes, and early facial features appear. 

  7. Fetal Development 

  • Embryo is now called a fetus.  

  • Growth accelerates; organs mature. 

  • Nervous system becomes more complex. 

  • By birth, systems are developed enough to function independently. 

What occurs during clavage and blastocyst formation?

• Zygote undegoes rapid mitotic divisions (cleavage) 

• Becomes a morula (solid mass of balls) 

• Fluid enters, forming the blastocyst with: Inner cell mass (forming the embryo) and Trophoblast (becoming the placenta). 

What occurs during implantation?

• Blastocyst embeds itself into the uterus lining 

• Trophoblast cells form the placenta, supporting nutrient and gas exchange 

What occurs during gastrolation?

ICM (Inner cell mass) reorganizes into: Ectoderm (skin, nervous system), Endoderm (organ linings, guts, lungs, liver), Mesoderm (muscles, bones, blood, kidneys) 

What occurs during neurulation?

• Ectoderm folds to form the neural tube which becomes the brain and spinal chord 

• Neural crest cells migrate to form peripheral nerves, facial structures, and more.  

What occurs during organogenesis?

• Major organs begin forming.  

• Heart starts beating around week 4. 

• Limb buds, eyes, and early facial features appear. 

What occurs during fetal development?

• Embryo is now called a fetus.  

• Growth accelerates; organs mature. 

• Nervous system becomes more complex. 

• By birth, systems are developed enough to function independently. 

What are the different layers of  an embryo and what tissues do they for? 

• Three layers are called created by a process called gastrula 

• The three layers are called germ layers- ectoderm, mesoderm and endoderm 

Ectoderms- epidermis of skin, the nervous system (including brain), sensory organs 

Mesoderm- The skeleton, muscles, blood vessels, heart, blood, kidneys 

Endoderm- lining of internal organs, including those of the digestive system, respiratory system, liver and pancreas 

Describe the development of male and female specific parts of the anatomy, how is this regulated? 

1. Bipotential Stage (Weeks 4–6) 

• Embryos start with indifferent gonads (can become testes or ovaries). 

• Both sexes initially have Müllerian ducts and Wolffian ducts. 

• Development depends on genetic signals and hormones. 

2.  Male Development (XY) 

Key Regulator: SRY gene (on Y chromosome) 

• SRY → triggers testis formation. 

• Testes produce:  

  • Testosterone → maintains Wolffian ducts → epididymis, vas deferens, seminal vesicles. 

  • Anti‑Müllerian Hormone (AMH) → causes Müllerian duct regression. 

• DHT (dihydrotestosterone) (from testosterone) → forms external genitalia: penis, scrotum, prostate.  

3. Female Development (XX) 

Key Concept: Default pathway 

• No SRY → gonads become ovaries. 

• No AMH → Müllerian ducts persist → uterus, fallopian tubes, upper vagina. 

• No testosterone → Wolffian ducts regress. 

• External genitalia develop into clitoris, labia, lower vagina.