1. Genetics
A. The work of Gregor Mendel
1. Monohybrid crosses
2. Dominant and recessive alleles
3. Law of Segregation
B. Mendel and meiosis

5. 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

7. 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!!

8. 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
Also allowed for study in an ‘either-or’ rather than a ‘more or less’ manner

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

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

11. 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

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

13. Mendel’s hybridization experiments…
Monohybrid crosses:
Parental Generation
True-breeding purple flower
True-breeding white flower x
All purple flowers (the hybrids)
F1 generation
Allowed F1 offspring to self-fertilize
F2 generation
705 purple
224 white

15. The results of Mendel’s monohybrid crosses led him to propose…
All organisms contain two “units of heredity” for each trait (alleles).
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).
The Law of Segregation – during gamete formation, alleles separate randomly into separate gametes.

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

17. More jargon… homozygous vs. heterozygous P 2 of the same alleles:
PP or pp
2 different alleles: Pp p

18. Even more jargon…
True breeding: When the plants self-pollinate, all their
offspring are of the same variety.
Hybridization: Mating, or crossing, of two varieties.
Monohybrid cross: A cross that tracks the inheritance of
a single character.
P generation: True breeding parents.
F1 generation: (first filial) Hybrid offspring of the
P generation.
F2 generation: (second filial) Offspring from the
self-fertilization of the F1 hybrids.

19. A Punnett square

20. A Punnett square… Gametes from one parent p P PP Pp P
Gametes from other parent
purple
purple pp Pp p
purple
white
Ratio: 3:1 or ¾ purple, ¼ white

22. Let’s relate Mendel’s findings to what we now know about gamete formation
True-breeding white flower
True-breeding purple flower x
all purple P P p p P p P P P P p p p p

23. Mendel’s Laws of Genetics

24. Law of Dominance
In a cross of parents that are pure for contrasting traits,
only one form of the trait will appear in the next generation.
All the offspring will be heterozygous and express only the dominant trait.
Example:
RR (round seeds) x
rr (wrinkled seeds)
yields
all Rr (round seeds)

25. Law of Segregation
During the formation of gametes (meaning eggs or sperm), the two alleles responsible for a trait separate from each other.
Alleles for a trait are then “recombined” at fertilization, producing the genotype for the traits of the offspring.
Cool – but what does this mean????

26. Law of Segregation (continued)

27. Law of Independent Assortment
Alleles for different traits are distributed to sex cells (and offspring) independently of one another.
Check out this example –
See how not every yellow seed is round?

28. P P P P P P P P purple hybrid x purple hybrid F1 generation p p p p p
pp - white

29. Join to your partner and together, work on the following…
Determine the phenotypic and genotypic ratios for each of the following monohybrid crosses.
Phenotypic ratio
Genotypic ratio
Aa x Aa
3:1 (dom:rec)
1:2:1 (hd:h:hr)
AA x Aa
1:0 (dom:rec)
or all dominant
1:1:0 (hd:h:hr)
aa x Aa
1:1 (dom:rec)
0:1:1 (hd:h:hr)
AA x aa
1:0 (dom:rec)
or all dominant
0:1:0 (hd:h:hr)
hd = homozygous dominant; h = heterozygous; hr = homozygous recessive

30. SO, NOW IT’S YOUR TURN TO WORK ALONE
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