MENDELIAN GENETICS

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) “Short” trait disappears… F2 Generation (“Second Filial”) (Grandkids) …then reappears! Whoa!

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

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. (p265)

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

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 In P Gen: ____% Tall, ____% Short In F1 Gen: ____% Tall, ____% Short In F2 Gen: ____% Tall, ____% Short 50:50 100:0 ~75: ~75~25 WHY?

Mendel proposed that “Factors” segregate (separate) from pairs to be passed on to offspring, one from each parent! (p ) (Sound familiar?)

(Sound 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 Alleles: ___ (dominant), ___ (recessive) Genotypes: ____, ____, ____ 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 NN Nn nn “Homozygous Dominant” “Heterozygous” “Homozygous Recessive”

This genotype is described as _______________ ___________ The pair of alleles you have (for any trait) is called your GENOTYPE Genotypes: ____, ____, ____ Again! NNNn nn This genotype is described as _______________ ___________ “Heterozygous” (hybrid or carrier) “Homozygous Recessive” (Purebred) This genotype is described as _____________ “Homozygous Dominant” (Purebred)

One from DadOne from Mom Each set of alleles is a homologous pair, one from Mom and one from Dad! NN

What is this person’s genotype? This is called your PHENOTYPE (an expressed feature you can see!) What kind of nose do they have? Round? Or Pointy? NN ________________ Homozygous Dominant

Remember: Dominant overshadows recessive! What is this person’s PHENOTYPE? Round? Or Pointy? Nn ________________ Heterozygous

Recessive alleles show only if no dominant is present! What is this person’s phenotype? Round? Or Pointy? nn ________________ Homozygous Recessive

Another Example: What’s the TRAIT? What are the ALLELES? Which is dominant? PPpp PpPp

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

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

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

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

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

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? ____ X ____ AA Aa Offspring Genotype: - HD (AA) = ___% - Het (Aa)= ___% - HR (aa)= ___% Offspring Phenotype: - Healthy* = ___% - Disease = ___% - * (Healthy) Carrier = _____% DadMom AAAa Aa A A

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

Note the Percentages In P Gen: ____% Tall, ____% Short In F1 Gen: ____% Tall, ____% Short In F2 Gen: ____% Tall, ____% Short 50:50 100:0 ~75: ~75 ~25 NOW YOU KNOW WHY!