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