Mendel and Genetics

1. Mendel and Genetics

3. Gregor Mendel • Austrian Monk • Worked with pea plants • Small • Easier to use and control (breeding) • Produce hundreds of offspring • Grew quickly • Self pollinating • Short life cycle • Have many visible traits/characteristics • Other organisms? • Fruit flies • Zebra fish

4. What do Pea Plants Have to Do with Genetics? • “All living things have DNA” • Peas plants are living organisms; therefore, they also have DNA. • “All living things reproduce” • Pea plants are living organisms; therefore, they reproduce. • Pea plants reproduce sexually – combination of two sex cells (gametes)

5. the next few images may be graphic in nature

6. Anatomy of a Flower

7. Fertilization in Plants

8. Anatomy of a Pea Flower

9. Pea Plant Pollination

10. How did he do it??? • Stamen = male reproductive part of a flower • Anther – produces pollen • Filament – holds up the anther • Pollen – holds sperm cells • Carpel/Pistil = female reproductive part of a flower • Stigma – top of carpel; sticky to catch pollen • Style – structure that leads to ovules/ovaries

11. Developing Truebreeders • Truebreeders – organisms whose offspring are always identical to the parents • Their traits are the same in each generation. • Trait – specific characteristic or feature of an individual that is controlled by genes • Ex. – tall plants always produce tall plants; short plants always produce short plants; purple flowers always produce purple flowers…etc.

12. Crossbreeding • Mendel wanted to learn how traits are passed on from parent to offspring. • He used a process called crossbreeding and produced plants that has different parents. • Used pollen from one type to pollinate • Fertilized the female parts of another flower of another type • The offspring of crosses between parents with different traits are called hybrids.

13. What’s a Hybrid??? Just kidding!! These are hybrids because they have both an electric engine and a gas engine.

14. Animal Hybrids

16. GregorMendel’s Observations • Noticed a pattern in offspring after the P generation, F1 generation, and F2 generation • Developed “true breeding” plants • Offspring always resembled parents • White always gave rise to white flowers • Purple always gave rise to purple flowers • Mendel crossed one true breeding plant with another with a different trait to produce a hybrid.

17. Crossed Purple Flowers with White Flowers • True breeding purple and white flowers are known as the parent (P) generation • Offspring of P generation are known as Filial 1 (F1) generation. • All the offspring from the F1 generation were hybrids • All of F1 were purple. No white flowers! P x P F1 Purple x White 100% Purple

18. F1 Purple X F1 Purple • When F1 is crossed with F1, their offspring is called the second Filial or F2 generation. • When Mendel crossed a purple F1 with another purple F1, he got both purple and white flowers! • He kept a record of numbers and noticed a pattern. • For every 3 purple flowers, there was 1 white. In other words, there was a 3:1 ratio.

19. Mendel and Genes • Mendel did not know about DNA and genes. • He realized there must be something that determines the traits of the pea plants and called them factors. • Genes can have several (at least two) forms. These forms of genes are called alleles.

20. Genes vs. Alleles • Genes are segments of DNA that has instructions for making proteins (traits). • Alleles are specific forms of genes that code for a specific trait. • Mendel dealt with genes for plant height. • Mendel crossed plants with the tall allele and short allele. • Mendel dealt with genes for pea color. • Mendel crossed plants with the yellow allele and green allele.

21. Not only flower color!!! • Mendel saw the same pattern and ratio happening with other traits as well • Pea color (green vs. yellow) • Pea texture (smooth vs. wrinkled) • Pod shape (full vs. constricted) • Plant height (tall vs. short) • 3:1 ratio!!! • Characteristics are called phenotypes • Genotypes – genetic makeup; actual genes/alleles

22. Mendel didn’t know about genes • Since we now know about genes, we have an explanation for what Mendel observed • Two types of traits • Dominant – trait that is always expressed • Recessive – trait that is only expressed when dominant allele is not present • We use letters to represent the genes • Capital letters = dominant alleles • Lowercase letters = recessive alleles

23. Segregation Through meiosis, the alleles, (T) (t), are segregated into their gametes. Through fertilization, the alleles, (T) (t), are recombined when zygotes are formed.

24. Summary of Mendel’s Results In the P generation, truebreeding tall plants and truebreeding short plants are cross pollinated. In the F1 generation 100% of the offspring are tall plants. Short plants seem to have disappeared. F1 plants are crossed with F1 plants to get the F2 generation. In the F2, short plants reappeared! 75% are tall, 25% are short. There is a 3:1 ratio of tall to short plants.

25. Reminder about Genes • Genes are segments of DNA that codes for protein; protein shows up as trait • Genes are found on chromosomes (chromosome theory) • Chromosomes are found in pairs (homologous) • Therefore, genes are also found in pairs • If both genes are alike (both dominant or both recessive) we use the term homozygous • If genes are different (one dominant, other recessive) we use the term heterozygous

26. Homozygous dominant Homozygous recessive P = purple p = white X P P p p P generation Segregation P P p p gametes Pp P p P p P p Heterozygous Heterozygous Heterozygous Heterozygous F1 Generation

27. P p P p F1 Generation ??? segregation P p p P pp Pp Pp PP F2 Generation

29. Punnett Square • Tool used by geneticists use to predict the possible genotypes/phenotypes of offspring • Chart shows • allele of gametes of parents on the top and side of the chart • All possible allele combinations of offspring

30. Punnett Square - diagram used to show the possible genetic combinations from a particular cross P generation: PP x pp p p Note: All offspring have the genotype: Pp phenotype: purple F1 Generation P P p P p P P p P p

31. F1 generation: Pp X Pp P p In the F2 generation the possible genotypes are : 1 PP, 2 Pp, and 1 pp or a 1:2:1 ratio Phenotypes are: 3 Purple and 1 white or a 3:1 ratio F2 generation: P PP P p P p p p p

32. Independent Assortment • Mendel wondered if alleles for one trait affected the alleles for another trait. • Mendel set up a cross that enabled him to study two different genes (dihybrid) at the same time. • Two different genes = two different traits. • Seed color: yellow vs. green • Seed shape: round vs. wrinkled

33. Getting the F1 Generation • Crossed round/yellow (RRYY) with wrinkled/green (rryy) • The gametes from RRYY all carry RY. • The gametes from rryy all carry ry. • The only possible combination of alleles in the F1 is RrYy. • All are round/yellow.

34. Getting the F2 Generation • Crossed RrYy with RrYy • Each parent has 4 possible combination of alleles in gametes • Not only were there round/yellow and wrinkled/green, there were other combinations • Round/green and wrinkled/yellow • Showed 9:3:3:1 ratio

35. Dihybrid Revelation • New combinations other than parents revealed another property of genetics. • Independent assortment – alleles of different genes segregate independently or separately during gamete formation • In other words, traits do NOT come in specific combinations. • Round does not necessarily mean yellow • Wrinkled does not necessarily mean green