Cell Division and Numerical Chromosomal Abnormalities

Question 1

4 stages during Interphase?

Difference during Metaphase I of meiosis?

What’s the area of crossing over called?

Answer 1

• • Prophase; chromosomes condense, spindle forms at both ends of cell
  • Metaphase; chromosomes line up along equator and attach to spindle
  • Anaphase - sister chromatids pulled apart
  • Telophase - nuclear membrane forms around each set and chromosomes uncoil
• In meiosis I, homologous chromosomes align to form a bivalent/tetrad using a synaptonemal complex, allowing genetic material to be exchanged
• Chiasma

Question 2

How do numerical chromosomal abnormalities arise?

What is segregation?

What is Non-disjunction?

What are the 2 types of Non-disjunction?

Answer 2

• Due to failure of mitotic/meiotic non-disjunction
• When chromosomes separate
• Failure to separate chromosomes = a cell with too many/few chromosomes
• • Polyploid = multiple of haploid number
  • Aneuploid = chromosome number is not an exact multiple of haploid number; Due to extra/missing chromosome e.g. Trisomy, Monosomy

Question 3

Autosomal Aneuploidies:
What is Patau’s Syndrome? Features?

What is Edward’s Syndrome? Features?

What is Down’s Syndrome? Features?

Answer 3

• Trisomy 13 - 2 in 10,000 births
  o Midline defects – Holoprosencephaly, Cleft lip/palate, Scalp defects, Cutis aplasia
  o Polydactyly, Cardiac Abnormalities, Exomphalos
• Trisomy 18 - 3 in 10,000 births
  o Intrauterine growth retardation, Micrognathia (small jaw), Cleft lip, Overlapping fingers & Rocker bottom feet, Cardiac abnormalities, GI/Renal Abnormalities, Exomphalos
• Trisomy 21 - 15 in 10,000 births
  o Flat nasal bridge, Single palmar crease, Short stature, Hypotonia, Developmental delay, Cardiac abnormalities, Hypothyroidism, Dementia

Question 4

Sex Chromosome Aneuploidies:
What is Turner’s Syndrome? Features?

What is Triple X Syndrome?

What is Klinefelter’s Syndrome? Features?

What is XYY Syndrome? Features?

Answer 4

• Monosomy 45X - 1 in 5,000 female births
  o Normal IQ, Oedema of hands + feet, Broad/Webbed neck, Cardiac abnormalities, Renal abnormalities, Short statue, Absent puberty, Infertility, Low hairline
• 47XXX - 1 in 1,000 female births
• 47XXY - 1 in 1,000 male births
  o Tall, Female fat distribution, Gynaecomastia, Hypergonadotropic hypogonadism, Small testes, Higher rate of autism and ADHD
• 47XYY - 1 in 1,000 male births
  o Normal IQ, Tall, No significant medical problems, Behavioral issues, Puberty and fertility normal

Question 5

What is Mosaicism?

What is Translocation?

Answer 5

• Due to mitotic non-disjunction; 2 or more genetically different cell populations formed
• Rearrangement of chromosomes between homologous pairs