Chapter 14 . Genetics. Introduction. Pre 1800s – blending hypothesis 1850s – Gregor Mendel. Pisum sativum – what makes pea good genetic model? - - - - Pea character (gene) = Pea trait (allele) = . self fertilization Vs. cross fertilization. The monohybrid cross.
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Pisumsativum– what makes pea good genetic model?
Vs. cross fertilization
F1 plants all purple
F2 plants = ~250 white ~750 purple
Is this quantitative or qualitative data?
Allele = Alternative version of gene
Dominant allele PRecessive allele p
Each individual inherits 2 alleles/gene
PP homozygous dominant
pp homozygous recessive
Find the dominant allele
What is the phenotype of plant with genotype Rr?
What is genotype of a green plant?
Pea chromosome 1
Genotype of plant?
Phenotype of plant?
Human chromosome 11 gene for beta globin
In mice, black fur is dominant over white fur
Cross heterozygous mouse with homozygous recessive mouse
3. Write the phenotypes under the genotypes
4. Determine the parental gametes (random segregation)
5. Add to Punnett square
6. Determine offspring
What is the expected ratio of phenotypes?
In a litter of 3, how many are expected to be white?
Which phenotype is the recessive phenotype?
The Scottish fold is a dominant trait
Genotypes FF Ffff
The original Scottish Fold was a white barn cat named Susie, found in Scotland
Scottish fold cat -> Is she Ff or FF?
If FF, then cross toff kittens?
If Ff, then cross to ff kittens?
A test cross is always a cross to a homozygous individual.
B = black fur allele
b = white fur allele
Y = yellow pea alleleR = round pea allele
y = green pea alleler = wrinkled
Phenotypes of peas
True-breeding yellow, round X true-breeding green, wrinkled
Gametes? (always 4 per parent in 2 gene cross)
R = round allele Y = yellow
r = wrinkled y = green
RY and ry
Parental generation: RRYY X rryy
Gametes of F1 generation?
Ratio of genotypes?
Ratio of phenotypes?
Both alleles expressed in phenotype
Ex. Blood type I gene
Alleles IA IB
Phenotype of IA IB ?
Ex. blood type
Alleles IA IB i
IAIA IBIB IA IB
multiple genes affect characteristic
Ex. skin – at least 3 genes
A particular genotype may have a phenotypic range
A allele normal protein
a allele malfunctioning or no protein
Aa heterozygotes are carriers
disorders range from fetal lethal to mild
bb = blond hair
bb = blue eyes
ii = type O blood
A allele abnormal protein
a allele normal protein
Genetic component + environment (aging, diet, chemicals, radiation, etc.)