WEEK 5 (Chromosome mutations) Flashcards
What is Aneuploidy?
An abnormal number of chromosomes such as having a single extra chromosome (47) or a missing chromosome (45)
[an organism gains or loses one or more chromosomes but not a complete set]
What is an Aneuploid?
Any chromosome number that is not euploid
Define Monosomy
The loss of a single chromosome from an otherwise diploid genome
Define Trisomy
The gain of one chromosome
What is Euploidy?
Where complete haploid sets of chromosomes are present
What is Polyploidy?
When more than two sets of chromosomes are present
What are organisms with three and four sets of chromosomes called?
- Three sets = TRIPLOID
- Four sets = TETRAPLOID
How do chromosomal variations originate?
NONDISJUNCTION
during the formation of games where PAIRED HOMOLOGS fail to disjoin during SEGREGATION -> disrupts the NORMAL DISTRIBUTION of chromosomes into gametes
What is Klinefelter syndrome and what are the symptoms?
Klinefelter syndrome is when boys are born with an extra X chromosome (XXY). To compensate for the extra X chromosome, one X chromosome will be inactivated (Barr body).
SYMPTOMS:
- Taller than average stature
- Longer legs due to delayed epiphyseal closure which leads to increased long bone length
- Absent, delayed or incomplete puberty
- After puberty, less muscle and less facial and body hair compared with other teens
- Small, firm testicles (TESTICULAR ATROPHY)
- Small penis
- Enlarged breast tissue (GYNECOMASTIA)
- Abnormal Leydig cell function - decrease testosterone and increase LH and oestrogen
What is Turner syndrome and what are the symptoms?
Turner syndrome, a condition that affects only females, results when one of the X chromosomes (sex chromosomes) is missing or partially missing (XO).
Sex chromosome (X, or rarely Y) is loss often due to NONDISJUNCTION during meiosis or mitosis. Meiosis errors usually occur in paternal gametes (sperm missing the sex chromosome) and Mitosis errors occur after zygote formation (loss of sex chromosome in some but not all cells).
SYMPTOMS:
- Short stature (SHOX gene, preventable with growth hormone therapy)
- lymphatic defects resulting in WEBBED NECK
- 1st degree amenorrhea (late period)
- menopause before even starting period (pregnancy is possible using IVF & progesterone)
- decrease in oestrogen leads to increase in LH & FSH
- No Barr body
- Shield chest
What is Double Y syndrome and what are the symptoms?
Double Y syndrome is a chromosomal mutation in which boys have an extra Y chromosome (XYY)
Frequency: 1 in 250 males
SIGNS AND SYMPTOMS:
- Phenotypically normal (usually undiagnosed)
- Very tall
- Normal fertility
- May be associated with severe acne
- Often less than average IQ
- Learning disabilities & autism spectrum disorders
- High levels of male hormones
- Delayed speech and language skills
What are the 5As of Down syndrome?
- Advanced maternal age
- Atresia (duodenal)
- Atrioventricular septal defect
- Alzheimer disease
- AML/ALL
______________ is the most common viable chromosomal disorder and most common cause of genetic intellectual disability
Down syndrome
How is Down syndrome diagnosed?
The first trimester ultrasound commonly shows increased nuchal translucency and hypoplastic nasal bone
markers for Down syndrome are increased hCG and increased inhibin
What are the causes of Down Syndrome?
- 95% of cases due to meiotic NONDISJUNCTION (most commonly during meiosis)
- 4% of cases due to UNBALANCED ROBERTSONIAN TRANSLOCATION (most typically between chromosomes 14 and 21)
- 1% of cases due to POST FERTILISATION MITOTIC ERROR
