12. Human Genetics Chromosomal Abnormalities

Question 1

How can humans end up having a genome containing too many or too few chromosomes?

Answer 1

• failure in meiosis (non-disjunction)
• non-disjunction in M1 is the failure of one tetrad set to separate during anaphase I (impacts all gametes)
• non-disjunction in M2 is when in anaphase II one sister chromatid fails to separate (impacts half the gametes)

Question 2

Draw non-disjunction in M1 and M2.

Answer 2

https://www.researchgate.net/publication/48171971/figure/fig3/AS:306079633297417@1449986479573/Nondisjunction-in-meiosis-I-and-meiosis-II.png

Question 3

Define karyotype and the two techniques used to determine prenatal karyotypes in humans?

Answer 3

A karyotype is an individual’s complete set of chromosomes

Amniocentesis
- collects fetal cells at 9 to 15 weeks gestation from the amniotic fluid; results in 3 – 5 weeks
Chorionic Villi Sampling (CVS)
- collects cells from the placental tissue at 8 weeks for examination; results in 48 hours

Question 4

What is Trisomy 21 (aka Down Syndrome)?

Answer 4

• Extra chromosome 21 (2n + 1 (n+1 and n))
• Affects development of brain, immune system, heart and skeleton
• Mentally challenged
• Physical effects: broad face with flat nasal bridge; wide set eyes, transverse simian crease in hands…

Question 5

What is Turner’s Syndrome?

Answer 5

• only females (X0 instead of XX)
• 2n - 1 (n-1 and n)
• short stature, webbed neck and non-functioning ovaries which causes infertility

Question 6

What is Klinefelter Syndrome Karyotype?

Answer 6

• only males (XXY instead of XY)
• n + 1
• Taller than average stature.
• Feminine body type
• May have incomplete breast development.
• Absent, delayed or incomplete puberty

Question 7

What is Metafemale Syndrome (Trisomy X Females Karyotype)?

Answer 7

• only females (XXX instead of XX)
• May be taller than other girls.
• May have problems with spoken language and processing spoken words
• Coordination problems, and weaker muscles.

Question 8

What is Jacob’s Syndrome Karyotype?

Answer 8

• only males (XYY instead of XY)
• delayed motor skill development, such as with writing.
• delayed or difficult speech.
• emotional or behavioral issues.
• hand trembling or involuntary muscle movements.
• weak muscle tone

Question 9

Explain how a karyotype is prepared

Answer 9

1. Fetal cells are grown (cultured) to increase their number and promote cell division.
2. Cell growth is stopped during mitosis
3. Metaphase cells collected, and then squished between two slides, photographed and paired by homologue and grouped by size.

Question 10

Can you have a Y chromosome alone?

Answer 10

No, genes on X chromosome required for development and survival