Download - Traits & Inheritance Ch 5.2 7th
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Chapter 5 Section 2
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y Explain how genes and alleles are related to genotypeand phenotype
y Use the information in a Punnett square
y Explain how probability can be used to predictpossible genotypes in offspring
y Describe 3 exceptions to Mendels observations
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y Genes: a set of instructions for an inherited trait; eachparent gives one set to their offspring
y Alleles: different forms of a gene (dominant orrecessive)y Dominant alleles are represented by a capital letter (ex.
B)
y
Recessive alleles are represented by a lowercase letter(ex:b)
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y An organisms appearance = phenotype
y Ex: pea plants phenotype for flower color (purple or
white)
y Human phenotypes are more complicated
y Ex:Albinism in humans (lack of pigment for hair, skin,hair)
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y Both inherited alleles together form an organismsgenotype
y Ex: Purple flowers (B) is dominant
y 2 dominant or 2 recessive alleles are homozygous (BBor bb)
y Bb is said to be heterozygous
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y Used to organize all possible combinations of offspringfrom particular parents
b b
B
B
Bb Bb
Bb Bb
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http://www.biology.iupui.edu/biocourses/n100/images/10F1.gif
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y Self-pollination cross of a plant with the genotype Bb
B b
B
b
Only one combination results in white flowers, bb
BB Bb
Bb bb
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y When the alleles are different (Bb), offspring areequally likely to receive either allele (50%)
y Probability= the mathematical chance thatsomething will happen
y Written as a fraction 50% chance written as
y Math practice page 123 of text
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y Lets use the example of a coin toss:
y What is the probability of getting 2 heads in a row?
y Multiply the probability of tossing the 1st head (1/2 or50%) by the probability of tossing the 2nd head (1/2 or50%)
y The probability of tossing 2 heads in a row is (1/4or25%)
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y What is the probability of having white flowers in apea plant?
y The pea plant must have a b allele from each parent
y Each offspring of a Bb xBb cross has a 50% chance ofreceiving either allele from either parent
y The probability of inheriting 2 b alleles is x or (25%)
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y Information determined about traits and inheritancewas more complex than Mendel imagined
y These are exceptions to Mendels principles:y Incomplete Inheritance
y One gene, many traits
y Many genes, one trait
y The Importance ofEnvironment
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y Sometimes one trait is not completely dominant overanother
y Each allele has its own degree of influence:INCOMPLETE DOMINANCE
y Ex: Cross between the Red snapdragon (p. 124, fig. 5)
and true-breeding white snapdragon all phenotypesare PINK because both alleles of the gene have someinfluence
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y One gene can inf luence more than one trait
y Ex:White tiger white fur is caused by a single gene;
this gene influences eye color too
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y Sometimes several genes work together to determinetraits such as eye color, hair, skin
y It is hard to tell if the trait is the result of a dominantor recessive gene
y Different combination of alleles result in different eye-
color shades
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y Genes arent the only influences on traits
y The environment influences how you grow
y Ahealthy diet can also work towards determining yourheight
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y Holt Science and Technology: Life Science.Austin: HoltRinehart & Winston, 2007. Print.