Unit 5 – Other Forms of Inheritance
Not all traits are simply dominant or recessive, with only ______possible alleles.
1. ______= BLENDING in heterozygotes
· ______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 ______letters to represent each possible allele (instead of Rr use RW since there is not dominant or recessive allele)
· Examples: Beta fish, 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 = RW
Sample Cross…
Cross a red parent with a white parent & give phenotype and genotype ratios of offspring.
R R
W
W
Phenotype Ratio= ______Pink
Genotype Ratio= ______heterozygous
You practice:
Cross two pink flowers and give the genotype and phenotype ratios of their offspring.
2. ______= TOGETHER or SPOTTED – both traits are FULLY and SEPARATELY expressed
· Co means together, and ______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 Rr use RW since there is not dominant or recessive alleles)
Sample cross…black and white fur in cows.
BB = Black
WW = White
BW = Black AND White hairs together
Cross a cow and a bull that have black and white hairs.
B W
BB / BWBW / WW
B
W
Phenotype: ______
Genotype: ______
You practice: Cross a white cow with a black bull. Give the genotype and phenotype ratios of the offspring.
3. Human Blood Types/Multiple Alleles: Use both co-dominance and regular dominant/recessive.
· A and B are co-dominant. O is recessive.
· Use the chart to help with crosses.
*Note: You may use the letter subscripts when doing Punnett crosses, OR just use the letters (i.e. A, B, O)
Cross a person who is homozygous for type A blood with a person who has type AB blood.
A A
A
B
Practice: Cross someone with Type O blood with someone who is heterozygous for type B blood.
3. (cont) Multiple alleles are when there are more than ______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 Practice
Cross a black hair parent with a blond hair parent whose mother had black hair. Give phenotypes and genotypes
4. Polygenic traits are the result of the interaction of several ______(2 or more genes)
Poly = ______, Genic = ______
Examples: human skin color, human eye color
5. Sex-Linked: Use sex chromosomes and alleles.
· 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. Since females have 2 copies of the X chromosome, the dominant allele will cancel out the recessive allele. 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.
Practice Cross:
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 males
25% Color Blind males
Genotype: 25% XBXb (Carrier)
25% XbY
25% XBXB
25% XBY
Practice: Cross a carrier female with a colorblind male and give the genotype and phenotype ratios of the offspring.
Sex-Linked Pedigree