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
