1. Please write AT THE TOP of your dragon picture…
Your names
Your egg number
The name of your baby dragon

2. Take home message from Dragon Genetics Project...
You should understand…
Alleles are genes (DNA)
Each organism gets 2 alleles per trait
1 from mom; 1 from dad
Alleles are on chromosomes
Gametes give alleles to “babies”

3. Introduction to Mendel Honors Genetics Ms. Gaynor
Heredity
Introduction to Mendel
Honors Genetics
Ms. Gaynor

4. Transmission (passing down) of Traits
How?
One possible explanation of heredity is a “blending” hypothesis
genetic material contributed by two parents mixes

5. Another Hypothesis
An alternative to the blending model is the hypothesis of inheritance (genes)
Parents pass on discrete heritable units (factors) called genes

6. Gregor Johann Mendel 1843
Documented a mechanism of inheritance through his experiments with garden peas
Figure 14.1

7. Gregor Johann Mendel
Mendel discovered the basic principles of heredity
By breeding garden peas in carefully planned experiments

8. Mendel’s Experimental Method
Why use pea plants?
available in many varieties
easy to get
he could strictly control which plants mated with which
Grow quickly

10. Pea Plant Fertilization
Self fertilization : mate with self  produce identical offspring
TRUE or PURE breeds
Cross fertilization : mate with another  can produce different offspring
HYBRIDS

13. SELF
Cross B A

14. Procedure: Crossing pea plants

15. Mendel’s Procedures Mendel chose to track
Only those characteristics (traits) that varied in an “either-or” manner
Mendel also made sure that
He started his experiments with varieties that were “true-breeding”

16. True Breeding vs. Hybridization
In a typical breeding experiment
Mendel mated 2 DIFFERENT, true-breeding varieties
called hybridization
The true-breeding parents (Pure breeding
made through true breeding mated two of the SAME varieties so these plants are “TRUE” for only 1 trait (can only make offspring w/ this trait)

17. Mendel’s Generations Original Parents Are called the P generation
The next generations is called the F1 generation
When 2 F1 individuals are mated together it produces the F2 generation

18. Generations (in general)
P = parental generation of a cross
F1 = the first generation after the parental (the results of the 1st cross)
F2 = a cross between F1 individuals yields F2 (2nd cross)

19. Mendel’s Results When Mendel crossed contrasting, true-breeding traits
All of the offspring showed only ONE of the 2 traits
When Mendel crossed two of these F1 plants
Many of the plants had the F1 shown trait, but some had the other trait that wasn’t shown in F1

20. Mendel discovered Where did the white color go?
A ratio of about 3:1, purple to white flowers, in the F2 generation
P Generation
(true-breeding
parents)
Purple
flowers
White 
F1 Generation
(hybrids)
All plants had
purple flowers
F2 Generation
Where did the white color go?
Figure 14.3

21. Mendel’s Conclusions Mendel reasoned that
In F1 plants, only purple flower factor was affecting flower color in the hybrids
Purple flower color was dominant, and white flower color was recessive
Some FACTOR was being transferred from parent to offspring

22. Alleles Alleles = alternative forms of genes (Mendel’s “factors”)
Each individual has 2 alleles for the same gene (because there are 2 homologous chromosomes)
Each parent passes one allele for each gene to his/her offspring

23. Useful Genetic Vocabulary
Homozygous
A pair of IDENTICAL alleles for that gene
Exhibits true-breeding
aa = homozygous recessive (or just recessive)
HH = homozygous dominant
Heterozygous
A pair of alleles that are different for that gene
Aa or Hh

24. Recessive is… Recessive
an allele that does NOT produce a characteristic effect when present with a dominant allele
only expressed when the determining allele is present in the homozygous condition
aa or hh

25. Dominant is…
Dominant
an allele that produces the same phenotypic effect whether inherited with a homozygous or heterozygous allele
Aa or AA, Hh or HH
The allele that is expressed
Not necessarily better, stronger, etc.

26. Mendel’s Law of Segregation
The two alleles for a characteristic separate (segregate) during gamete formation (Anaphase I of meiosis) end up in different gametes
Each gamete gets 1 allele ONLY for each gene

27. Mendel’s Model Mendel developed a model to predict inheritance
Mendelian Genetics states
There will be a 3:1 inheritance pattern in his F2 offspring if 2 of his F1 offspring were crossed

29. Allele for purple flowers Allele for white flowers
Recall…Alleles
Alternative versions of genes account for variations in inherited characters, which are now called alleles
Allele for purple flowers
Locus for flower-color gene
Homologous
pair of
chromosomes
Allele for white flowers

30. For each characteristic,
An organism inherits TWO alleles, one from each parent
A genetic locus is actually represented twice (once on each of the homologues)

31. Mendelian Genetics aka-COMPLETE DOMINANCE
If the 2 alleles at a locus differ (heterozygous)
Then the dominant allele determines organism’s appearance
The recessive allele has no noticeable effect on organism’s appearance (it is hidden)
The 1st allele is “completely dominant” over the 2nd allele

32. Mendelian Genetics COMPLETE DOMINANCE
Ex: Tongue rolling = trait
Tongue roller = dominant (T)
Non-tongue roller = recessive (t)
What is the phenotype of an individual with a genotype TT? tt? Tt?

33. More Genetic Vocabulary
An organism’s phenotype
Is its physical outcome
Ex: Blue eyes, brown hair, etc
An organism’s genotype
Is its genetic makeup
A.k.a.-the allele combination
Ex: aa, Aa, AA

34. Non-Mendelian Genetics INCOMPLETE DOMINANCE
Does not follow Mendel’s pattern…
If 2 alleles at a locus differ (heterozygous)
Then the dominant allele “mixes with” the recessive allele to determines organism’s appearance
The recessive allele is NOT hidden
An “inbetween or mixed” phenotype is the result

35. Non-Mendelian Genetics INCOMPLETE DOMINANCE
Ex: Hair texture = trait
Curly = dominant (H)
Straight = recessive (h)
What would a “mix” of curly and straight be???
What is the phenotype of an individual with a genotype HH? hh? Hh?