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Transcript
Bellringer •Please answer the following questions on your bellringer sheet: •Based off of what you remember from the Human Heredity Activity we did in class on block day, what does it mean when a trait is dominant? Recessive? Learning Targets • Please write down at the top of your notes: • Explain Mendel’s experiments and data, including the Law of Segregation. • Explain how there can be many forms of a one gene and how genes influence the development of traits. • Describe the purpose of monohybrid crosses, and use them as tools to calculate inheritance probabilities. MENDELIAN GENETICS 18 Things You Should Know About Genetics genetics video Gregor Mendel: Hereditary Genetics • Garden peas are: • Self-pollinating • Easy to experimentally cross-pollinate • Clear traits—pure purple, pure white, etc. • Trait: any single feature of an organism What Mendel Discovered! • P Generation (“Parent”) • F1 Generation (“First Filial”) (Kids) Whoa! • F2 Generation (“Second Filial”) (Grandkids) Did You Catch That? • Where did that short plant (trait) come from? • Was it hiding? Recessive Traits “Hide” Behind Dominant Traits • Sexual Organisms have two of each trait (homologous pairs) • One of each pair is passed on to offspring by each parent. Recessive Traits “Hide” Behind Dominant Traits • Different forms of the same trait are called alleles PLANT HEIGHT • What TRAIT is being studied in this experiment? “Tall” … and … “Short” • What are the TWO ALLELES (forms) of the trait being studied? Other Traits That Mendel Studied (Which word below is a synonym for “allele”?) ALLELES ALLELES Try one • What trait is being studied? • What’s the dominant allele of the trait? • What’s the recessive allele of the trait? Note the Percentages 50:50 100:0 ~75:25 50 50 Short • In P Gen: ____% Tall, ____% 100 0 • In F1 Gen: ____% Tall, ____% Short ~75 ~25 Short • In F2 Gen: ____% Tall, ____% Mendel proposed that “Factors” segregate (separate) from pairs to be passed on to offspring, one from each parent! (Sounds familiar?) Think – Pair -Share •Why does this sound familiar? During what process does this occur? Turn to your shoulder partner and discuss what you think the process is. 3 groups will be asked to share. (Sounds familiar?) (Sounds familiar?) Homologous chromosomes split up in anaphase I so that only one allele of each trait gets passed on in your gametes! 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) n N • Alleles: ___ (dominant), ___ (recessive) NN Nn nn • Genotypes: ____, ____, ____ “Homozygous Dominant” “Heterozygous” “Homozygous Recessive” The pair of alleles you have (for any trait) is called your GENOTYPE Again! NN Nn nn • Genotypes: ____, ____, ____ This genotype is described as “Homozygous _______________ Dominant” ___________ (Purebred) This genotype is This genotype is described as described as “Heterozygous” “Homozygous _____________ _______________ (hybrid or carrier) Recessive” ___________ (Purebred) NN One from Mom One from Dad Each set of alleles is a homologous pair, one from Mom and one from Dad! What is this person’s genotype? • This is called your PHENOTYPE (an expressed feature you can see!) NN ________________ Homozygous Dominant What kind of nose do they have? Round? Or Pointy? Nn • Remember: Dominant overshadows recessive! ________________ Heterozygous What is this person’s PHENOTYPE? Round? Or Pointy? nn • Recessive alleles show only if no dominant is present! ________________ Homozygous Recessive What is this person’s phenotype? Round? Or Pointy? Gregor Mendel Research and Principles • Mendel Video Mendel’s Principles • Principles of Segregation • States that every individual possesses a pair of alleles for any particular trait and that each parent passes a randomly selected copy (allele) of only one of these to its offspring. The offspring then receives its own pair of alleles for that trait. (Factors for a particular trait occur in pairs.) • Principle of Independent Assortment • States that genes for different traits can segregate independently during the formation of gametes. (Factors segregate randomly during anaphase I of meiosis.) • Principles of Dominance • States that some alleles are dominant and others are recessive. (Dominant factors mask recessive ones.) 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 is Mom’s genotype? Pp Rr Heterozygous • What is Dad’s genotype? Ova (either) Heterozygous GERM CELL Pp Sperm (either) GERM CELL 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? What if this egg meets this sperm? What if this egg meets this sperm? What if this egg meets this sperm? 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? ______ • 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% 25% 25% 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 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) 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 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 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 _____% Note the Percentages 50:50 100:0 ~75:25 50 Short 50 • In P Gen: ____% Tall, ____% 0 100 Tall, ____% • In F1 Gen: ____% Short ~25 Short ~75 Tall, ____% • In F2 Gen: ____%