MENDELIAN GENETICS How does Genetics connect with DNA

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MENDELIAN GENETICS

MENDELIAN GENETICS

How does Genetics connect with DNA? • DNA RNA Amino Acids Protein • Genes

How does Genetics connect with DNA? • DNA RNA Amino Acids Protein • Genes Traits • Thus, different variations of each trait, known as alleles, arise when mutations in DNA = different Amino Acid sequences, which = different proteins, which = different traits.

 Mendel and His Beloved Peas • Garden peas are: • Self-pollinating • Easy

Mendel and His Beloved Peas • Garden peas are: • Self-pollinating • Easy to experimentally cross-pollinate • Clear traits—pure purple, pure white, etc.

Trait: any single feature of an organism Traits That Mendel Studied ALLELES

Trait: any single feature of an organism Traits That Mendel Studied ALLELES

Gregor Mendel: Classical Genetics • Principle of Dominance • Principle of Segregation • Principle

Gregor Mendel: Classical Genetics • Principle of Dominance • Principle of Segregation • Principle of Independent Assortment • Video clip: Alleles & Genes

Principle of Dominance • Some alleles are dominant, others are recessive. • Dominant alleles

Principle of Dominance • Some alleles are dominant, others are recessive. • Dominant alleles “overpower” the recessive. • EXCEPTIONS: • Incomplete Dominance • Codominance

 What Mendel Noticed: • P Generation (“Parent”) • F 1 Generation (“First Filial”)

What Mendel Noticed: • P Generation (“Parent”) • F 1 Generation (“First Filial”) (Kids) • “Short” trait disappears… Whoa! • F 2 Generation (“Second Filial”) (Grandkids) • …then reappears!

Did You Catch That? • Where did that short plant (trait) come from?

Did You Catch That? • Where did that short plant (trait) come from?

 Recessive Traits “Hide” Behind Dominant Traits • Sexual organisms have two of alleles

Recessive Traits “Hide” Behind Dominant Traits • Sexual organisms have two of alleles for each trait, one allele on each chromosome of a homologous pair. • One homologue of each pair is passed on to offspring by each parent. (p 265)

 Recessive Traits “Hide” Behind Dominant Traits PLANT HEIGHT • Different forms of the

Recessive Traits “Hide” Behind Dominant Traits PLANT HEIGHT • Different forms of the same trait are called alleles • What TRAIT is being studied in this experiment? “Tall” … and … “Short” • What are the TWO ALLELES (forms) of the trait being studied?

Principle of Segregation • Alleles are separate from one another; each gamete only carries

Principle of Segregation • Alleles are separate from one another; each gamete only carries a single copy of each gene • EXCEPTION: • Nondisjuntion

 Mendel proposed that “Factors” segregate (separate) from pairs to be passed on to

Mendel proposed that “Factors” segregate (separate) from pairs to be passed on to offspring, one from each parent! (p 265 -266)

Homologous chromosomes split up in Anaphase II so that only one allele of each

Homologous chromosomes split up in Anaphase II so that only one allele of each trait gets passed on in your gametes!

Principle of Independent Assortment • Genes for different traits segregate independently of one another

Principle of Independent Assortment • Genes for different traits segregate independently of one another during the formation of gametes (sperm/egg) • EXCEPTION: • When genes for different traits are on the same chromosome they are likely to travel together and are called “linked” traits.

This principle assumes that each trait is carried on a different chromosome, thus alleles

This principle assumes that each trait is carried on a different chromosome, thus alleles for each trait sort into gametes (sperm/egg) independently, regardless of which alleles for other traits a gamete will receive.

 The pair of alleles you have (for any trait) is called your GENOTYPE

The pair of alleles you have (for any trait) is called your GENOTYPE Example Trait: Nose Shape (Let us pretend that round nose is dominant to pointy nose) (usually, letters are used to represent alleles, upper case for dominant) • Alleles: ___ (dominant), ___ (recessive) n N • Genotypes: ____, ____ NN Nn nn “Homozygous Dominant” (Purebred) “Heterozygous” (hybrid or carrier) “Homozygous Recessive” (Purebred)

Another Example: • What’s the TRAIT? • What are the ALLELES? • Which is

Another Example: • What’s the TRAIT? • What are the ALLELES? • Which is dominant? PP pp Pp

Remember: Only one of each allele is passed on from each parent! • What

Remember: Only one of each allele is passed on from each parent! • What is Mom’s genotype? Heterozygous • What is Dad’s genotype? Ova (either) Heterozygous GERM CELL Pp Pp Sperm (either) GERM CELL

Let’s Look At the Offspring Probabilities Ova (either) • What if this egg meets

Let’s Look At the Offspring Probabilities Ova (either) • What if this egg meets this sperm? Sperm (either) What if this egg meets this sperm?

 This Is Called A Punnett Square • Punnett squares allow us to predict

This Is Called A Punnett Square • Punnett squares allow us to predict probabilities about offspring

What percentages does this Punnett square predict? • How many 75% (3/4) Purple? ______

What percentages does this Punnett square predict? • How many 75% (3/4) Purple? ______ • How many White? ______ 25% (1/4) • How many homozygous dominant? 25% ___(1/4) • How many heterozygous? ______ 50% (2/4) • How many homozygous recessive? ___ 25% (1/4) 25% 25%

What is the probability that this couple will have a baby with the “a”

What is the probability that this couple will have a baby with the “a” disease? • Healthy allelle = A • Disease allele = a 25% (1/4)

What is the probability that this couple will have a baby who is a

What is the probability that this couple will have a baby who is a CARRIER for the “a” disease? • Healthy allelle = A • Disease allele = a 50% (2/4) A CARRIER is a heterozygote (he or she can “pass on” the trait but does not exhibit it)

 Your Turn! (For disease “A”): What if a homozygous dominant man marries a

Your Turn! (For disease “A”): What if a homozygous dominant man marries a carrier woman? AA Aa ____ X ____ Dad Mom A a A AA Aa Offspring Genotype: - HD (AA) = ___% 50 - Het (Aa)= ___% 50 - HR (aa)= ___% 0 Offspring Phenotype: - Healthy* = ___% 100 - Disease = ___% 0 - *(Healthy) Carrier = 50 _____%

 One More Time! (For disease “A”): What if a carrier man marries a

One More Time! (For disease “A”): What if a carrier man marries a woman with the disease? Aa ____ X aa ____ Dad Mom a a A Aa Aa a aa aa Offspring Genotype: 0 - HD (AA) = ___% 50 - Het (Aa)= ___% 50 - HR (aa)= ___% Offspring Phenotype: - Healthy* = 50 ___% 50 - Disease = ___% - *(Healthy) Carrier = 50 _____%