1. Objective:
SWBAT to complete Punnett squares for monohybrid crosses.

2. Do Now!
What is probability?
What are ratios?

6. Who was this Mendel and what the heck is he doing in a monastery?
born in 1822
trained himself to be a naturalist early in life
worked as a substitute science teacher
failed the qualifying exams to be a regular high school teacher!
joined a monastery in Brunn, Austria
sent to Vienna U. to study science and math

8. MendelWeb
Mendel’s first published work: "Versuche über Pflanzen-Hybriden“ or Experiments in Plant Hybridization was a landmark in clarity and insight!
Trained as a mathematician and a biologist, he figured out the laws of inheritance… mathematically!!

9. The work of Gregor Mendel
worked with pea plants…
…he called them his children!
Why pea plants???
There was a long-standing tradition of breeding pea plants at the monastery where Mendel lived and worked

10. Science Humor

11. So…they were readily available and they come in lots of varieties!
…there were plants with different flower colors, seed color, flower position etc..

12. Mendel’ Pea Plants
Mendel based his laws on his studies of garden pea plants. Mendel was able to observe differences in multiple traits over many generations because pea plants reproduce rapidly, and have many visible traits such as:
Pod color
Seed Color
Plant Height
Green
Yellow
Green
Yellow
Seed Shape
Short
Pod Shape
Tall
Wrinkled
Round
Smooth
Pinched

13. ‘Brother Greg... We grow tired of peas again!!!’

14. And best of all… Pea plants flowers can reproduce by themselves
This allowed Mendel to see if strains were true breeding and to produce hybrids

15. How Mendel made hybrids…
He’d then tie little bags around the flowers to prevent contact with stray pollen.

16. Mendel’s Experiments
Mendel noticed that some plants always produced offspring that had a form of a trait exactly like the parent plant. He called these plants “purebred” plants. For instance, purebred short plants always produced short offspring and purebred tall plants always produced tall offspring. X
Short Offspring
Purebred Short Parents X
Purebred Tall Parents
Tall Offspring

17. Mendel’s First Experiment
Mendel crossed purebred plants with opposite forms of a trait. He called these plants the parental generation , or P generation. For instance, purebred tall plants were crossed with purebred short plants. X
Parent Short P generation
Parent Tall P generation
Offspring Tall F1 generation
Mendel observed that all of the offspring grew to be tall plants. None resembled the short short parent. He called this generation of offspring the first filial , or F1 generation, (The word filial means “son” in Latin.)

18. Mendel’s Second Experiment
Mendel then crossed two of the offspring tall plants produced from his first experiment.
Parent Plants
Offspring X
Tall F1 generation
3⁄4 Tall & 1⁄4 Short F2 generation
Mendel called this second generation of plants the second filial, F2, generation. To his surprise, Mendel observed that this generation had a mix of tall and short plants. This occurred even though none of the F1 parents were short.

20. The results of Mendel’s monohybrid crosses led him to propose…
All organisms contain two “units of heredity” for each trait (alleles).
Genes- a segment of DNA that carries hereditary instructions and is passed from parent to offspring
Alleles- multiple forms of the same gene
Heredity- the passing of traits from parent to offspring.

21. Dominant and recessive alleles…
…and organisms can have any combination of the two alleles (2 dominants, 2 recessives or a mixture 1 dominant and 1 recessive).
Dominant trait- the trait observed when at least one dominant allele for a characteristic is inherited
Recessive trait- a trait that is apparent only when two recessive alleles for the same characteristic are inherited

22. Purebred - all of the offspring will have the same trait as the parent when self-pollinated
Hybrid- an organism has two different alleles for a trait
The Law of Segregation – during gamete formation, alleles separate randomly into separate gametes.

23. Mendel’s Law of Segregation
Mendel’s first law, the Law of Segregation, has three parts. From his experiments, Mendel concluded that:
1. Plant traits are handed down through “hereditary factors” in the sperm and egg.
2. Because offspring obtain hereditary factors from both parents, each plant must contain two factors for every trait.
3. The factors in a pair segregate (separate) during the formation of sex cells, and each sperm or egg receives only one member of the pair.

24. A bit of genetic jargon…
phenotype vs. genotype
What the organism looks like –
its
Physical
makeup
What alleles the organism has - its genetic makeup

25. More jargon… homozygous vs. heterozygous P 2 of the same alleles:
RR or rr
2 different alleles: Rr p

26. A Punnett square

27. Dominant & Recessive Practice
TT - Represent offspring with straight hair
Tt - Represent offspring with straight hair
tt - Represents offspring with curly hair
T – straight hair
t - curly hair

29. Practice naming what traits will show

30. Punnett Squares
Punnett Square – Diagram showing the gene combinations that might result from a genetic cross
Used to calculate the probability of inheriting a particular trait
Probability – The chance that a given event will occur

31. A Punnett square… Gametes from one parent r R RR Rr R
Gametes from other parent
round
round rr Rr r
round
wrinkled
Ratio: 3:1 or ¾ round, ¼ wrinkled

32. Punnett Square
Parent
Offspring
Parent

33. How to Complete a Punnett Square

34. Y-Yellow
y-white
Genotype:
1:2:1
(YY:Yy:yy)
Phenotype:
3 Yellow
1 White

35. You Try It Now!
Give the genotype and phenotype for the following cross: TT x tt (T = Tall and t = Short)

36. TT x tt
Step One: Set Up Punnett Square (put one parent on the top and the other along the side)
T T t

37. TT x tt
Step Two: Complete the Punnett Square
T T t Tt

38. TT x tt Tt t Genotype: 4 - Tt Phenotype: 100% Tall
Step Three: Write the genotype and phenotype
T T t
Genotype:
4 - Tt
Phenotype:
100% Tall Tt
Remember: Each box is 25%