Lecture 5: Inheritance and Genetic Diseases Flashcards
what generates genetic variation
- mutation
- diploid cells and inheriting one set of chromosomes from each parent
- homologous recombination between chromosomes during meiosis
- independent segregation
what is non-disjunction and what does it cause
- when the chromosomes aren’t pulled apart into separate cells
- causes monosomy or trisomy
what causes Down’s syndrome
trisomy 21
what causes Patau’s syndrome
trisomy 18
babies usually die within the first year
how common is monosomy
uncommon as it is fatal unless it is on the X chromosome, which has evolved to be viable with one copy
what is X monosomy
Turner’s syndrome
- causes pubertal failure
- infertility
- may have neck webbing, heart defects and horseshoe kidneys
what are the sex chromosome syndromes
X = Turner's syndrome XXY = Klinefelter syndrome: male, lower IQ and fertility XXX = undiagnosed XYY = undiagnosed
what is X inactivation
- in female nucleuses, one X chromosome is very tightly folded, forming heterochromatin so it’s not expressed
- in every cell, a different X chromosome is inactivated
why does trisomy become more likely as maternal age increases
over time, cohesins get stickier and spindle fibres become weaker, making it harder to pull apart chromosomes efficiently
what sort of disease is cystic fibrosis
autosomal recessive loss of function
what sort of disease is sickle cell anaemia
- autosomal incomplete recessive loss of function
- being a carrier gives heterozygote advantage of malaria resistance
what sort of disease is Huntington’s disease
autosomal dominant gain of function
what is Haemophilia A
- X linked recessive disorder
- lack of factor VIII clotting factor
- causes bleeding, easy bruising and haemorrhaging
what are some examples of X-linked disorders
- haemophilia A
- colourblindness
- muscular dystrophy
