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GENETICS – PART IIIPatterns of Inheritance
PATTERNS OF INHERITANCE
•Dominant / Recessive• Incomplete Dominance•Co-dominance•Sex-linked•Multiple alleles•Polygenic
DOMINANT / RECESSIVEA = red a = white
Genotype PhenotypeHomozygous Dominant AA red Heterozygous* Aa red
Homozygous Recessive aa white
Heterozygous expresses (shows) the dominant trait.
INCOMPLETE DOMINANCE• Incomplete ≠ Complete• The dominant trait does not completely dominate the heterozygous • does not show the dominant trait• does not show the recessive trait
• The heterozygous is a blend (mix) of the dominant and recessive phenotype to create a 3rd phenotype
INCOMPLETE DOMINANCE
INCOMPLETE DOMINANCEA = red a = white
Genotype Phenotype
Homozygous Dominant AA red Heterozygous* Aa pink
Homozygous Recessive aa white
Heterozygous expresses (shows) a 3rd phenotype that is a blend of the dominant trait and the recessive trait.
CO-DOMINANCE
•Co- = together• co-worker• cooperate
•Both the dominant trait and the recessive trait shows in the heterozygous
CO-DOMINANCE
CO-DOMINANCEA = red a = white or A = red W = white
or CA= red CW = white
Genotype PhenotypeHomozygous Dominant AA or
CACAred
Heterozygous Aa or AWor CACW
Red and white
Homozygous Recessive aa or WWor CWCW
white
INCOMPLETE OR CO-DOMINANCE?
Parents
A. B.
INCOMPLETE OR CO-DOMINANCE?
Parents
A. B.
INCOMPLETE OR CO-DOMINANCE?
Parents
A. B.
INCOMPLETE OR CO-DOMINANCE?
A. B.
• Write your name and label the heterozygous
dominant/recessive
incomplete dominance
co-dominance
G = green g = blue
GgGg
WHICH PATTERN? CO-DOMINANCE INCOMPLETE DOMINANCE, OR DOMINANT-RECESSIVE?
Y = yellow y = blue YY or Yy or yy?
1. ______________________ 2. ________________________ 3. _____________________
MULTIPLE ALLELES
•Usually a gene has two versions (alleles)• A or a B or b C or c
•Some genes have more than two alleles (versions). An example is human blood type.
HUMAN BLOOD TYPE
• The gene for human blood type has 3 alleles• A or IA
• B or IB
• O or II or ii
•6 possible combinationsGenotype Blood Type
AA (or IAIA) AAO (or IAI or IAi) A
BB (or IBIB) BBO (or IBI or IBi) B
AB (or IAIB) ABOO (or II or ii) O
POLYGENIC
Poly- = many or more than one
Polygenic means that more than one gene codes for a trait
MCAS QUESTIONS
When red-flowered snapdragon plants are crossed with white-flowered snapdragon plants, all the offspring have pink flowers. Based on these results, which of the following inheritance patterns determines flower color in snapdragons?
A. incomplete dominanceB. multiple alleleC. polygenicD. sex-linked
In Japanese quail, the allele for curly feathers (c) is recessive to the allele for smooth feathers (C). Which of the following best describes the offspring of quail parents that each have the genotype Cc?
A. Most offspring are expected to have curly feathers.
B. Most offspring are expected to have smoothfeathers.
C. All offspring are expected to have curly feathers.
D. All offspring are expected to have smooth feathers.
Human HLA genes have as many as 100 different alleles per gene. Which of the following terms best describes the inheritance pattern for each HLA gene?
A. codominantB. linked geneC. multiple alleleD. recessive
The table below gives information aboutthe genetics of white spotting in cats.
If a partially white cat mates with a black cat, what are the expected phenotypes of the kittens?
A. All the kittens will be black.B. Half the kittens will be black, and half will be
partially white.C. Three-quarters of the kittens will be black, and
one-quarter will be partially white.D. Three-quarters of the kittens will be partially
white, and one-quarter will be mostly white.
In betta fish, alleles for color are incompletely dominant. Green fish have genotype CC, dark blue fish have genotype cc, and royal blue fish have genotype Cc. Two royal blue betta fish are crossed. What percentage of the offspring is expected to be green?
A. 0%B. 25% C. 50% D. 75%
A particular species of moth can have green or yellow scales on its wings. The scale color is controlled by a single gene with two alleles, the green allele and the yellow allele. When moths that are homozygous for green scales are mated with moths that are homozygous for yellow scales, 100% of the offspring have green scales. Based on this information, how do the alleles for scale color interact?
A. The green allele is dominant to the yellow allele.
B. The green allele is recessive to the yellow allele.
C. The green allele and the yellow allele are codominant.
D. The green allele and the yellow allele are incompletely dominant.
In four o’clock plants, the allele for red flower color is incompletely dominant to the allele for white flower color. As a result, plants that are heterozygous for flower color have pink flowers.If two plants with pink flowers are crossed, what are the expected percentages of phenotypes in the offspring?
A. 0% red, 100% pink, 0% whiteB. 25% red, 50% pink, 25% whiteC. 50% red, 0% pink, 50% whiteD. 50% red, 50% pink, 0% white
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