Examples Flashcards
What is an example of incomplete dominance
Mirabilis japonica. Red x White: F1 all pink. F2: 1:2:1
Tay Sachs
Incomplete Dominance seen at molecular level
What is Codominance. Examples
Expression of both alleles fully and simultaneously. Both alleles are seen in the phenotype.
Red cows x White cows: Red cow with white spots
Sickle Cell anaemia: hetrozygotes are distiguishable
ABO blood group
What is multiple alleles
Multiple alleles at one loci effect the phenotype
Drosophilla, traditional white eye/red eye. Other alleles produce other colour e.g. apricot eyes
Human blood group, ABO
What is Lethal alleles
Homozygotes are lethal.
Affects the ratio seen: 2:1
Yellos mice x Yellow mice : Yy x Yy, yy dies
Y allele dominant for coat colour, recessive for viability
Manx Cat, no tail. Brachydactly homo dom normal, hetro short limbs, homo rec, lethal
Pleiotropy
One gene has many effects
Blue eyed cats are deaf. Tabby cats are aggressive
Sickle cell anaemia: aneamic, heart failiure, paralysis, enlarged spleen, bossed skulls… + malaria resistance
Gene interaction
Expression of an allele at one locus is affected by another allele at another locus
Albinism in mice.
Sex limitation. Certain phenotypes are limited to one gender: patterned baldness, breast cancer.
Due to the activation of certain genes by testosterone
Coat Colour in mice, 5+ interacting loci Wild type agouti: dark shaft yellow band (A). (a) removes yellow band. B codes for hair colour: B for black b for brown 9:Agouti 3:cinnamon 3:black 1:brown
Epistatis
Example of gene interaction: Gene at one loci can lead to the inexpression of another gene at another loci
Albinism: C allele codes for pigment. Recessive is albino
9:3:4 ratio. No pigment regarless of genes at other loci
D controls to what degree pigment is expressed: D fully, d dilute
S, S- not spotted, ss pleibald, patches of colour
ABO: Se
Complementation
Different homozygous recessive at different loci produce the same phenotype
White plant from 2 strains, homo at different loci
F1: all Purple, complement colour. Heterozygous at both loci. Genes complement to give a new colour
F2: 9:7 ratio. homozygosity at any loci gives white plant
Complementation test:
Organism with different mutation. When crossed, F1 all 1 of the mutations, no complementation. If F1 is a new phenotype, complement, The loci complement
Human deafness, Many loci coding for different parts of the hearing system. Mutation at one leads to the same phenotype, deafness.
If two deaf people with mutation at different loci: offspring will be hearing, complementation between the two loci`
What is sex linkage
..
What is the evidence for chromosome theory
F1
What is the inheritance of eye colour in drosphilla
Red female x White male= F1 all red, F2 all females red half males red, half males white
Red males x White males = F1 red females.
F2: Fem half red, half white. Males half red, half white
Showed that the locus for each colour is carried on the X chromosome
Inheritance of allele is like that inheritance of a solid object
What occus if alleles fail to segregate
Aneuploidy. Drosophilla: XX x Xy
XwXwX. female dies. XwXwY female, white
XO: red male. YO dies
What aneuploidy is viable in humans
XO: turner diesease, XXX viable. Both female
XXY: Kleinfelter syndrome viable male: Not fertiles, small testicles and little terstosterone due to extra X
Mosaic KS: some cells are aneuploidy, some arent. mild effects
Trisomy of chromosome 21
Edward’s Syndrome, trisomy of 18
Sex determination in other animals
Birds, Butterflies: ZZ male, ZW female
How dosage equalised
Lyonisation in humans: X inactivation specific transciprt. Xist, produces RNA with now protein, coats X chromosome. Barr body can be seen in karyotype
Drosophilla, 2 X = normal expression. In males, X chromosome is doubly expressed
Conditons related to the inactivation of X chromosome
Tortise shell cat. Cells inacitvate X chromosome randomly. Half orange, half black
Hetro women for colour blindness have patches of red green retina along with colour blind patches
What is patau syndrome
Trisomy of chro 13
What is a chromsome
Single molecule of DNA. Organised by size.
1 largest, y smallest
Cetromeres, attachment point for spindles
Telomeres, repeated sequence at the end. Protection
P short, Q long. Acrocentric uneven. Metacentric
Telocentric
What is a method of mapping?
Somatic cell hybridisation
Flourescent In Situ Hybridisation (FISH)
Explainthe process of SCH
Cellculture of Human and mice cells. Sendai virus has multiple point of attachment, thus, can attach two cells together.
Virus is very small, membranes overlap. Leads to fusions and formation of a binucleate heterokaryon.
Fusion of nuclei to form uninucleate synkaryon.
Hybrid can be slected for:
De novo pathwayu of DNA synthesis is blocked by aminoptetrin. Only salvage pathway can be used
2 key enzymes in salvage: Thymine kinase, HPGRT
1 organism has 1 enzyme. Other has the other
Both is needed for DNA synthesis
Only hybrids will survive. Human DNA is spat out over time as it is less stable (Griffiths et al, 2000)
Elimination of human DNA can be studied using microscopes
Which conditions are observed with deletions
Notch wing drosophilla.
Cri-du-Chat humans. Tip of chro 5 lost
Duplication conditions
Deletions caused by base mispairing
Huntington’s disease
Bar eyes in drosophilla
Translocation conditons
2 non-homologous proteins exchange parts
Burkitt’s: t(8,14)
Myelpid leukaemia: t(9,22)
Chromosome number alterations
Aneuploidy: cells do not have typical number of chro
Nondisjunction: lack of segregation at anaphase I,II. Responsible for trisomy and monosomy
Polyploidisation: change in number of chromsome sets. Lethal in humans. Linked to fertility
Alloploidy: fusion of distinct chromosome sets
Autoploidy: duplication of a diploid set of chromosomes
What is the back-test cross
F1 crossed with parent. 1:1:1:1 ratio
Crossed with double mutant of parent
If genes are linked, vast majority are parent’s genotype, very few are the recombinants
Recombinant formed by the chiasma of 2 hologuous chromosomes during prophase 1
What is interference.
Interferance the chiasma at one loci influences (reduces) the probabilty of a chiasma at another loci.
Observed/expected. Coeffiecient= 1-(observed/expected)
What can gene expression be affected by
Temperature: Siamese cats. cold activates melanin gene
Also: white blood drosoophilla. Fly development at 15 degrees= dark eye, 30 degrees = light coloured eyes
Light: expression of cryptocchrome determine day length
Artic hares, long hours of sun dark fur. winter light
Chemicals: Some bacteria can only grow on certain food. E-Coli which lack the gene to synthesise AA can not grow on plate with those AA
Phenylketonuria. Human can’t break down phenylalanine, build up of Phe can be lethal
George II, porphyria, unable to break down haemin. Gene expression sensitive to light
Expressoin of some genes is affected by drugs. Barbituates can be lethal at lower doses in porphyria
Obese mutation in mice: mice have gene, can’t stop eating
Age: Hutington is not seen until for over 50s. Same with cancer and heart disease
Incomplete Penetrance
Someone who has disease genotype does not have disease. It’snot expressed
Sex limitation
Effects of hormonal environment:
Dorsett horn sheep, male have horns, females do not
patternes baldness, loci on autosomal chromosome, but dependent on the expression of genes on Y chromosome
