2.5 - Human genetics Flashcards
aneuploidy
numerical chromosome imbalance
human syndromes caused by aneuploidy (5)
- Klinefelter syndrome
- Turner syndrome
- Down syndrome
- Edwards syndrome
- Patau syndrome
effects of Klinefelter syndrome (5)
- XXY sex chromosome
- male development but small testes/ infertility
- Gynaecomastia
- tall stature
- learning difficulties
How many people are affected by Klinefelter syndrome?
1-2/1000
Turner syndrome symptoms (5)
- Monosomy X sex chromosome
- female development, no puberty
- small stature
- ovaries degenerate before birth
- kidney/heart benefits
How many people are affected by Turner syndrome?
1/2500 - 1/3000
Down syndrome symptoms (6)
- trisomy 21
- typical facial characteristics
- small stature
- congenital heart defects
- intellectual disability
- higher incidence of leukaemia/ early onset Alzheimer disease
How many people are affected by down syndrome?
1/1000
Edwards syndrome symptoms (7)
- Trisomy 18
- abnormalities affecting many organs
- congenital heart defects
- small head
5.clenched fists - severe intellectual disability
- most babies die before 1st birthday
how many people are affected by Edwards syndrome?
1/5000
Patau syndrome symptoms (7)
- Trisomy 13
- abnormalities affecting multiple organs
- congenital heart defects
- severe intellectual disability
- microphthalmia (abnormally small eyes)
- deafness
- 5-10% of children live past 1st birthday
How many people are affected by Patau syndrome?
1/16,000
What aneuploidies are live births possible with? (5)
- trisomy 13
- trisomy 18
- trisomy 21
- XXY
- monosomy X
what is the leading cause of miscarriage?
aneuploidies
maternal age effect
aneuploidy increases exponentially with maternal age (fairly unique to humans)
IVF pre-implantation genetic screening (3)
- blastocyst biopsy
- few cells analysed at genetics lab
- allows embryologist to select chromosomally normal embryos for transfer
what does the Y chromosome contain? (2)
- many repetitive palindromic sequences
- SRY
SRY
sex determining region of Y chromosome
SRY function (2)
- encodes a transcription factor
- switches on many genes required for teste development
how was the sex-determining role of Y chromosome proved?
experiments in transgenic mice
% of population born with intersex traits (abnormal sex chromosome paterns)
1.7%
X-linked recessive pedigree (3)
- more common in males
- no father-son transmission
- son of female carrier has 50% chance of having disease
X-linked dominant pedigree (3)
- male/female equally at risk
- affected mother has 50% chance of passing disease containing X chromosome to offspring
- affected father will pass X onto all daughters (no father-son transmission)
pre-implantation genetic diagnosis (2)
- parents without underlying fertility issues offered IVF with PGD
- HFEA licensed to screen for over 600 genetic disorders
