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GeneticsGenetics

The Science of HeredityThe Science of Heredity

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What does heredity mean?What does heredity mean?

• Inheritance:Inheritance: The process of passing on The process of passing on traitstraits from from parentsparents to to offspringoffspring. .

• Heredity:Heredity: The passing of The passing of physicalphysical characteristics from parent to offspring.characteristics from parent to offspring.

• Traits:Traits: Characteristics (examples): Characteristics (examples):

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Gregor MendelGregor Mendel

MendelMendel was a famous geneticist, he laid was a famous geneticist, he laid the foundation of the foundation of geneticsgenetics today. today.

Much of what we have discovered can be Much of what we have discovered can be attributed to Mendel’s work with attributed to Mendel’s work with peapea plantsplants

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The Year was 1861The Year was 1861

• Gregor Mendel was a young priest from a monastery Gregor Mendel was a young priest from a monastery in Central Europe.in Central Europe.

• He attended the University of Vienna to study He attended the University of Vienna to study mathematics and science.mathematics and science.

• He then returned to the monastery to teach at a He then returned to the monastery to teach at a nearby high school.nearby high school.

• Mendel also cared for the monastery’s garden, where Mendel also cared for the monastery’s garden, where he began to become curious about how plants of the he began to become curious about how plants of the same species had different characteristics or traits. same species had different characteristics or traits. For example, some pea plants grew tall while others For example, some pea plants grew tall while others grew short.grew short.

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Understanding VocabularyUnderstanding Vocabulary

• Traits:Traits: characteristics characteristics• Heredity:Heredity: The passing of traits from parents to The passing of traits from parents to

offspring.offspring.• Genetics:Genetics: The study of heredity The study of heredity• Purebred:Purebred: one that always produces one that always produces

offspring with the offspring with the samesame form of a trait as the form of a trait as the parent. (parent. (homozygoushomozygous))

• Hybrid:Hybrid: has both forms of a trait has both forms of a trait ((heterozygousheterozygous))

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GenerationsGenerations

P-Generation (P-Generation (ParentsParents))

FF11 Generation ( Generation (11stst Generation of Generation of Parents PParents P))

FF22 Generation ( Generation (22ndnd Generation of Generation of Offspring Offspring

F1F1))

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Genes are factors that control Genes are factors that control traitstraits• Different forms of genes are called Different forms of genes are called allelesalleles..• Each offspring inherits a Each offspring inherits a combinationcombination of two of two

alleles from its parents.alleles from its parents.

• Individual alleles control the inheritance of Individual alleles control the inheritance of traits.traits.

• Some alleles are Some alleles are dominantdominant and other alleles and other alleles are are recessiverecessive..

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Dominant AllelesDominant Alleles

• A A dominantdominant allele is one that can be allele is one that can be seen in the seen in the phenotypephenotype (physical (physical characteristics).characteristics).

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Recessive AllelesRecessive Alleles

• RecessiveRecessive alleles are masked or alleles are masked or covered up by the dominant alleles and covered up by the dominant alleles and cannotcannot be seen in the be seen in the phenotypephenotype..

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HybridHybrid

• An organism that contains two An organism that contains two differentdifferent alleles for a trait. (alleles for a trait. (heterozygousheterozygous))

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Using Symbols in GeneticsUsing Symbols in Genetics

• Geneticists today use a standard shorthand Geneticists today use a standard shorthand method to write about alleles in genetic method to write about alleles in genetic crosses.crosses.

• InsteadInstead of using of using wordswords such as “tall” to such as “tall” to represent an allele they use represent an allele they use lettersletters..

• A A dominantdominant allele is represented by allele is represented by capitalcapital lettersletters

• A A recessiverecessive allele is represented by allele is represented by lowercaselowercase letters. letters.

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Let’s refresh!Let’s refresh!

• TTTT = both = both dominantdominant alleles, also known alleles, also known as a purebred or as a purebred or homozygoushomozygous..

• tttt= both = both recessiverecessive alleles, also known alleles, also known as as homozygoushomozygous..

• TtTt= a = a dominantdominant allele and a allele and a recessiverecessive allele are present. Also known as a allele are present. Also known as a hybrid or hybrid or heterozygousheterozygous..

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Genotype vs PhenotypeGenotype vs Phenotype

• GenotypeGenotype: genetic makeup (BB,Bb,bb): genetic makeup (BB,Bb,bb)

• PhenotypePhenotype: physical makeup (brown : physical makeup (brown eyes or blue eyes, tall or short)eyes or blue eyes, tall or short)

Punnett SquaresPunnett Squares

• The gene combinations that might result The gene combinations that might result from a genetic cross can be determined from a genetic cross can be determined by by drawingdrawing a diagram known as the a diagram known as the punnett square.punnett square.

• CapitalCapital Letter represents the Letter represents the dominantdominant allele.allele.

• LowercaseLowercase letter represents the letter represents the recessiverecessive allele. allele.

Punnett SquarePunnett Square

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Parent 1 ( Bb)

Parent 2

(Bb)

Try These!Try These!

1.1. TT X ttTT X tt

2.2. Bb x bbBb x bb

3.3. BB x bbBB x bb

4.4. Tt x TtTt x Tt

Genotype vs PhenotypeGenotype vs Phenotype

• Genotype is an organisms genetic makeup. Genotype is an organisms genetic makeup. For example Bb or BB or bbFor example Bb or BB or bb

• Phenotype is the physical characteristics or Phenotype is the physical characteristics or what they look like. For example if we were what they look like. For example if we were talking about eye color, the phenotype would talking about eye color, the phenotype would be blue or brown eyes.be blue or brown eyes.

• If B =brown eyes and b= blue eyesIf B =brown eyes and b= blue eyes• Bb=would have brown eyesBb=would have brown eyes• BB= brown eyesBB= brown eyes• bb = blue eyesbb = blue eyes

Beyond Dominant and Recessive Beyond Dominant and Recessive AllelesAlleles• Some alleles are neither dominant or recessive, Some alleles are neither dominant or recessive,

and many traits are controlled by multiple alleles and many traits are controlled by multiple alleles or multiple genes.or multiple genes.

• Incomplete dominance:Incomplete dominance: one allele is not one allele is not completely dominant over another. A red flower completely dominant over another. A red flower crossed with a white flower, produce pink crossed with a white flower, produce pink flowers. (blending)flowers. (blending)

• Codominance:Codominance: Both alleles contribute to the Both alleles contribute to the phenotype of the organism. Black chicken phenotype of the organism. Black chicken crossed to a white chicken produce a black and crossed to a white chicken produce a black and white chickenwhite chicken

Homozygous vs Homozygous vs HeterozygousHeterozygous• Homozygous and purebred = BBHomozygous and purebred = BB

• Heterozygous and hybrid= BbHeterozygous and hybrid= Bb