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Unit 5 – GeneticsOther forms of inheritance Not all traits are simply dominant or recessive, with only 2 possible alleles.
Incomplete Dominance = BLENDING in heterozygotes Neither allele is dominant over the other,
so individuals with a heterozygous genotype show a blended phenotype somewhere in the middle. (i.e. red + white=pink)
Use different letters to represent each possible allele (instead of Rr use RW since there is not dominant or recessive allele)
Examples: feather color in chickens, flower color such as roses or snapdragons.
EXAMPLE: ◦Red flowers x White Flowers = Pink flowers
Choose letters to represent each phenotype
Red = RR White = WW Pink = RWCross a red parent with a white
parent & give phenotype and genotype ratios of offspring.
Phenotype ratio: 100% PinkGenotype ratio: 100% heterozygous
You PracticeCross 2 pink flowers
RR RW
RW WW
R W
R
W
Phenotype: 25% Red, 25% White, 50% Pink
Genotype: 25% Homozygous Red, 25% Homozygous White, 50% Heterozygous
Co-dominance = TOGETHER or SPOTTED – both traits are FULLY and SEPARATELY expressed Co means together, and BOTH
alleles are dominant so they show up together. Ex: hair color in humans, fur color in cattle.
Use different letters to represent each possible allele (instead of Bb use BW since there is not dominant or recessive alleles)
Sample cross…black and white fur in cows.
BB = BlackWW = WhiteBW = Black AND White hairs togetherCross a cow and a bull that have black and white hairs.
BB BW
BW WW
B W
B
W
Phenotype: 25% Black, 25% white, 50% black and white Genotype: 25% homozygous black, 25% homozygous white,
50% Hetero
You PracticeCross a white cow with a black
bull.
BW BW
BW BW
W W
B
B
Phenotype: 100% Black and White Hairs
Genotype: 100% Heterozygous
Human Blood Types: Use both co-dominance and regular dominant/recessive. A and B are co-dominant. O is
recessive.Use the chart to help with
crosses.
Cross a person who is homozygous for type A blood with a person who has type AB blood.
AA AA
AB AB
A A
A
B
Phenotype Ratio: 50% Type A, 50% Type ABGenotype Ratio: 50% Homozygous AA, 50% Heterozygous AB
You PracticeCross type O blood, with
heterozygous type B blood.
Bi Bi
ii ii
i i
B
i
Phenotype: 50% Type B, 50% Type O
Genotype: 50% Heterozygous Bi, 50% Homozygous Recessive
Sex-Linked: Use sex chromosomes and alleles.
Some disorders are carried on the X chromosome. Examples of these disorders are color blindness, and hemophilia.
Some disorders are carried on the X chromosome. Examples of these disorders are color blindness, and hemophilia.
Only females can be carriers (heterozygous) because they have two X chromosomes
Males either have the allele (and hence show the trait) or they don’t. Males only get 1 X, so whatever they inherit on that 1 X is what you see.
When doing Punnett Squares, you must first use sex chromosomes (XX for female, XY for male) then assign letters to the trait and put them as superscripts on the sex chromosomes.
B = normal vision, b = color blind.
Cross a heterozygous normal vision female with a normal vision male. (First cross sex chromosomes, then put on alleles and cross them).
Phenotype: 50% Normal vision females 25% Normal vision males25% Color Blind males Genotype: 25% XBXb
(Carrier) 25% XbY
25% XBXB 25% XBY
You PracticeCross a carrier female with a
colorblind male and give the genotype and phenotype %.
XBXb XbXb
XBY XbY
XB Xb
Xb
Y
Phenotype: 25% Normal Vision Carrier Female 25% Colorblind Female 25% Normal Vision Male 25% Colorblind Male
Genotype: 25% XBXb, 25% XbXb, 25% XBY, 25% XbY
Sex-Linked Pedigree
Multiple AllelesMultiple alleles are when there
are more than 2 forms of a gene. Ex: human blood type (ABO), human hair colors.
HBr = brown HBd = blonde hR = red hbk = black
The possible genotypes and phenotypes: HBdHBd or HBdhbk = blonde HBdHBr = mousy brown HBdhR = strawberry blonde HBrHBr or HBr hbk = brown HBrhR = auburn hRhR or hRhbk = red hbkhbk = black
You PracticeCross a black hair parent with a
blond hair parent whose mother had black hair.
P = hbk hbk x HBdhbk
HBdhbk HBdhbk
hbkhbk hbkhbk
hbk hbk
HBd
hbk
Phenotype: 50% Blond, 50% BlackGenotype: 50% HBdhbk, 50% hbkhbk
PolygenicPolygenic traits are the result of the
interaction of several genes (2 or more genes) Poly = many, Genic = “genes”
Examples: human skin color, human eye color