Traits & Inheritance Ch 5.2 7th

8/8/2019 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.

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Traits & Inheritance Ch 5.2 7th