Section 11-1 The Work of Gregor Mendel

1. Section 11-1The Work of Gregor Mendel

2. Gregor Mendel • Genetics – the scientific study of heredity • Gregor Mendel – used garden peas to study heredity, first to discover the theory and 3 laws of inheritance

3. Genotype & Phenotype • Mendel bred (“crossed”) plants with 7 different traits, each trait could turn out 2 different ways. • P generation – original pair of plants • F1 generation – “first generation,” P generation’s offspring • F2 generation – “second generation,” F1 generation’s offspring

4. Genotype & Phenotype • Each individual has a phenotype = observable trait or combinations of traits • Examples: “Short stem,” “axial flowers & green peas,” “blue eyes and type A blood,” “diabetes” • Mendel knew families tended to have similar phenotypes… and he wanted to know why.

5. Mendel’s Experiments • He crossed peas with the same phenotypes, and peas with different phenotypes, then counted how many of their offspring shared their parents’ traits

6. Mendel made four conclusions: • Inheritance is determined by physical factors passed on from one generation to the next. After his death, other scientists discovered: • Genes – pieces of DNA that determine a trait • Alleles – different forms of genes • “Allele is expressed” = “Allele gives the bearer its version of a trait”

7. Mendel made four conclusions: Example: All peas inherit a gene for the “seed color” trait. There are two versions (alleles) of the gene: green and yellow. Practice: All humans inherit a gene for blood type. What are the different alleles for that gene?

8. Mendel made four conclusions: • Mendel’s Law of Dominance: Not all alleles are automatically expressed. • Dominant allele – always expressed if it’s present • Usually represented by a capital letter • Recessive allele – only expressed if a dominant allele is not present • Usually represented by a lower case letter

9. Mendel made four conclusions: Genotype = An individual’s combination of alleles. Rules for writing: Keep the two alleles for a gene next to each other. If one of the alleles is dominant, put it first. • Gene & allele examples: “The gene for eye color has the alleles B and b” • Genotype examples: “Aa,” “TtYY,” XAXa,” “PPiiUuH1H2” • Mendel learned that genotype determines phenotype

10. Practice If G is the allele forpointy ears and g is the allele for floppy ears, what will be the ear shape phenotypes of the puppies with these genotypes? The dominant allele is _ for the trait ___________ The recessive allele is _ for the trait ___________ Genotype GG = Phenotype __________ Genotype Gg = Phenotype __________ Genotype gg = Phenotype ___________

11. Practice G is for pointy ears and g is for floppy ears. Also, H is for a pink nose and h is for a black nose. Genotype GGHH = Phenotype ______ and ______ Genotype GgHh = Phenotype ______ and ______ Genotype gghh = Phenotype ______ and _______ Genotype GGhh = Phenotype ______ and _______ Genotype Gghh = Phenotype ______ and _______ Genotype ggHH = Phenotype ______ and _______

12. Practice • Which of these are traits and which are phenotypes? • 1. Finger length • 2. Blue eyes • 3. Long hair • 4. Number of leaves • 5. Shape of tentacles • 6. Warbling song

13. Practice • Which of these are alleles and which are traits? • 1. Eye color • 2. Bone integrity • 3. i • 4. Insulin shape • 5. B • 6. Na

14. Practice • Which of these are phenotypes and which are genotypes? • 1. Curly hair • 2. Jj • 3. PP • 4. Arthritic knees • 5. Type B blood • 6. Spotted fur and a pink nose • 7. HHGg • 8. Purple leaves and spiny stem

15. Summary Example • There is a gene for the hair curliness trait. This trait can express as one of two phenotypes: an individual has curly hair or straight hair. • The allele for curly hair is C, the allele for straight hair is c. • If your genotype is CC, your phenotype will be curly hair.

16. Summary Example • In an alien species, there is a gene for the ____________ trait. This trait can express as one of two phenotypes: an individual has __________ or __________. • The allele for __________ is A, the allele for __________ is a. • If your genotype is Aa, your phenotype will be __________.

17. Mendel made four conclusions: • Mendel found that if he crossed peas with different phenotypes for a trait, all the F1 plants would have the same dominant phenotype. He wondered if the recessive allele had disappeared… so he let the F1 plants self-pollinate, creating the F2 generation. • The recessive phenotype reappeared in 1/4th of the F2 generation!

18. Mendel made four conclusions: 3. Mendel’s Law of Segregation: Although an individual has two alleles for every gene, s/he passes only one of them on to each offspring. • i.e., each gamete carries only a single copy of a gene, because gametes are haploid.

19. Practicing the Law of Segregation If an individual’s genotype is YY, all of that individual’s gametes will have just ONE Y allele. If an individual’s genotype is Tt, that individual’s gametes will have EITHER the T allele OR the t allele, not both. (Some gametes are written with more than one letter. If Dad’s genotype is LTLt, he will make a sperm that has the LT allele or a sperm that has the Lt allele.) Genotype YY makes gamete Y or gamete Y. Genotype Tt makes gamete T or gamete t. Genotype bb makes gamete _ or gamete _ Genotype Ii makes gamete _ orgamete _ Genotype K1K2 makes gamete __ or gamete __

20. Mendel made four conclusions: 4. We’ll learn Mendel’s final conclusion on a later date. Stay tuned!

21. Overview • Suppose there’s a gene for eye color, with the alleles B for brown eyes or b for blue eyes. • A woman has the genotype Bb, which gives her the phenotype brown eyes. • Meiosis produces her gametes… b She can make gametes that are EITHER B or b. Half of her gametes will be one, half will be the other. b b S Phase b b b b 1st Cytokinesis 2nd Cytokinesis B B B B Normal cell in G1 B B B Four Gametes