7.2 complex patterns of...

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7.2 Complex Patterns of Inheritance

!  7.2 Complex Patterns of Inheritance

SC.912.L.16.2 •  Discuss observed inheritance patterns caused by

various modes of inheritance, including dominant, recessive, codominant, sex-linked, polygenic, and multiple alleles

•  Scenarios that refer to codominance & incomplete dominance

•  Evaluate polygenic traits and the effect of environmental factors on phenotype


!  Dominant and Recessive Alleles

•  Dominant Alleles code for specific proteins

•  Recessive Alleles code for variations (differences) of a protein with little or no effect.

Don’t forget: genes contain the information needed to make functional molecules called proteins. 2 Major steps (1) transcription (DNA-RNA (2) translation (RNA-Protein)

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!  Incomplete Dominance

•  When two traits are not completely dominant over each other •  Heterozygous phenotype between 2 homologous phenotypes •  BLENDING of 2 traits •  Both alleles are expressed (combined phenotype) •  Example 4 O’ Clock flowers (open at 4PM daily)


!  Four O’ Clock Plants

•  R = red flower •  W = white flower •  Neither allele is

dominant or recessive Genotype & Phenotype •  RR = red flowers •  WW = white flowers •  RW = pink flowers

(blend) •  Ratio both 1:2:1

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!  Example: Incomplete Dominance. Draw a Punnett Square. List the genotype & phenotype

1.  In certain species of fish, blue scales and yellow scales are incompletely dominant. Predict the outcome of two heterozygous fish. Hint: 1st create a key, 2nd determine the parents


!  Answer example #1

Key BB = Blue yy = yellow By = green

B y

B

y

BB

By

By

yy

Genotype Phenotype 25% BB BB = blue 50% By By = green 25% yy yy = yellow

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!  Look at figure 7.5. How can you tell that the 2 color alleles show incomplete dominance? (Pause ) •  Answer: The color of the heterozygote

(royal blue) is a combination of blue and green


!  Phenotype can depend on interactions of alleles.

–  Heterozygous phenotype is intermediate between the two homozygous phenotypes

–  Homozygous parental phenotypes not seen in F1 offspring

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!  Codominance

•  When two traits are both equally dominant •  Both alleles are dominate at the same time

FBFB = black feathers

FWFW = white feathers FBFW = black & white spotted/speakled feathers


!  In some species of frog green skin and purple skin are codominant. Predict the outcome between two heterozygous frogs.

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!  In some species of frogs, green skin & purple skin are codominant. Predict the outcome between two heterozygous frogs.


Human ABO blood types result from codominant alleles Blood Types: IA = type A codominant IB = type B codominant O = type O recessive

Genotype/phenotype: IAIA & IAO = type A IBIB & IBO = type B IAIB = type AB (universal donor) codominant OO = type O universal donor) homozygous recessive Karl Landsteiner-Dr. who developed ABO system

Antigen – marker proteins on the surface of RBC

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Multiple Alleles

•  More than 2 alleles for the trait

•  Example rabbit fur


Polygenic Traits

•  Traits produced by 2 or more genes

•  Several genes must interact together to create the trait

•  Examples: human skin color, eye color

•  More dominate = darker skin

•  More recessive = lighter skin

Order of dominance: brown > green > blue

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!  How the environment interacts with genotype?.

•  Height is an example of a phenotype strongly affected by the environment.

•  The sex of sea turtles depends on both genes and the environment

•  Eggs in warmer area develop into females. In cooler areas develop into males.

•  Phenotype is a combination of genotype and environment. •  Food, temperature, living conditions

7.2 complex patterns of...

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