inheritance and disorders Flashcards
1
Q
what is sex linked inheritance
A
- male: XY
- female: XX
- sex-linked genes in humans are usually carried on the X chromosome
2
Q
what is y linkage / x inactivation
A
- Y: very rare, father to son (never to females)
- X: inactivation of one X during embryonic development, do not produce twice as many X linked proteins, phenotype of both alleles can be expressed (mosaic of cells with varying X chromosomes inactivated)
3
Q
what are mutations
A
- change in gene or chromosome
- new characteristic displayed
- harmful, beneficial or no effect
- dysfunctional / no protein
- gene or chromosome mutation
- occurs during replication before cell division
- mutagen: environmental factor that increases rate at which mutations occur
4
Q
what is a genetic disorder
A
- harmful effect of detrimental allele
- mild: albinism (loss of pigmentation)
- severe: cystic fibrosis
- rarity: affected individuals usually die at younger age and cannot reproduce)
- uneven distribution, different genetic histories, geographic isolation
5
Q
what is tay Sachs
A
- homozygous = show disease
- incurable, disorder of lipid metabolism, accumulation of fat in the nervous system leads to deterioration, very rare
- lethal if not masked, if born, child develops normally for few months before developing mental and physical disability
- ashkenazi: jewish population, occurs 1:3,500 in comparison to 1:300,000 worldwide
- phenotypic categorisation: incomplete dominance at organism level and co-dominance at molecular level
6
Q
what is sickle cell anaemia
A
- substitution of valine for glutamic acid
- haemoglobin gene, changes shape of RBC / haemoglobin, not efficient in carrying oxygen in blood
- leads to clumping / clogging
- 1:400 people of african descent are affected
- areas of malaria: 2 SCA alleles = fatal, 2 normal alleles = susceptible to malaria, 1 of each = resistant to malaria and no signs of SCA (selective / survival advantage, co-dominance at molecular level)
- pleiotropy: multiple effects of one gene
7
Q
what is cystic fibrosis
A
- chromosome 7, recessive
- abnormal ion channels, thick mucous, salty skin, persistent coughing
- 4% of european descent are carriers, 1:3,500 are affected
8
Q
what is duchenne muscular dystrophy
A
- fault in gene for dystrophin (recessive) on X chromosome
- mother passes to son
- wasting of limb muscles, die of respiratory failure
9
Q
what is ichthyosis
A
- mutation of sulfatase gene
- lack functional allele (I), have recessive (i)
- large patches of dry, scaly skin
10
Q
what is a lethal recessive and an example
A
- less common
- dominant = kills offspring before maturity (not passed on, unlike recessive alleles)
- huntington’s: escapes elimination, death occurs later, reach life expectancy to have children
11
Q
what are pedigrees
A
- used to study human disorders, family tree focusing on traits
12
Q
what is non-disjunction
A
- aneuploidy
- homologous chromosomes / sister chromatids fail to separate correctly (meiosis 1 or 2)
- checkpoints don’t work effectively
- monosomy: -1 chromosome, loss of autosome = gamete dies, gamete that gains chromosome may survive
- trisomy: +1 chromosome
13
Q
what is an example of non-disjunction in autosomes
A
- down syndrome: additional chromosome 21, can be whole / part of chromosome (varying degree of symptoms)
- symptoms: distinct facial appearance, stunted growth, degree of mental disability
- partial trisomy: part of chromosome is present, symptoms may occur but not to full extent
14
Q
what are examples of non-disjunction in sex chromosomes
A
- klinefelter (XXY): deficiency of male hormones, sterile, female traits (enlarged breasts, sparse body hair), reduced mental capacity, small testes,
- turners (XO): 1 in 2000 births, short stature, infertile, lack secondary characteristics, infertile (do not menstruate)
- jacobs (XYY): 1 in 1000 births, ‘super male’, fertile males of normal appearance, high frequency in sexual homicide perpetrators