1. Mendelian Genetics
Gregor Mendel –

2. Asexual Reproduction
Bacteria can reproduce as often as every 12 minutes – and may go through 120 generations in one day
Thus capable of producing 6 x 1035 offspring per day
Bacteria often produce 1 mutation per 1000 replications of DNA
So for fast-growing species, mutation is a good way to respond to a changing environment

3. Why Sex?
John
Maynard
Smith

4. Sexual reproduction leads to genetic variation via:
Independent assortment during meiosis
Crossing over during meiosis
Random mixing of gametes (sperm and egg)

5. Independent Assortment

6. Nonsister chromatids held together during synapsis
Prophase I of meiosis
Nonsister chromatids held together during synapsis
Pair of homologs
Chiasma
Centromere
TEM
Anaphase I
Figure The results of crossing over during meiosis.
Anaphase II
Daughter cells
Recombinant chromosomes

7. The random nature of fertilization adds to the genetic variation arising from meiosis.
Any sperm can fuse with any egg.
A zygote produced by a mating of a woman and man has a unique genetic identity.
An ovum is one of approximately 8,388,608 possible chromosome combinations (223).
The successful sperm represents one of 8,388,608 different possibilities (223).
The resulting zygote is composed of 1 in 70 trillion (223 x 223) possible combinations of chromosomes.
Crossing over adds even more variation to this.

8. Mendelian Genetics
Gregor Mendel –

9. Two possible types of inheritance
One possible explanation of heredity is a “blending” hypothesis
The idea that genetic material contributed by two parents mixes in a manner analogous to the way blue and yellow paints blend to make green
An alternative to the blending model is the “particulate” hypothesis of inheritance: the gene idea
Parents pass on discrete heritable units, later known as genes

10. Mendel’s time Today
Mendel’s garden at Brunn (Brno) Monastery

11. Some genetic vocabulary
Character: a heritable feature, such as flower color
Trait: a variant of a character, such as purple or white flowers
Garden Pea

12. Flower Structure

13. Parental generation (P)
TECHNIQUE 1 2
Parental generation (P)
Stamens 3
Carpel 4
Figure 14.2 RESEARCH METHOD: Crossing Pea Plants
RESULTS 5
First filial generation offspring (F1)

14. In Mendel’s Experiments:
Mendel chose to track
Only those characters that varied in an “either-or” manner
Mendel also made sure that
He started his experiments with varieties that were “true-breeding”
In a typical breeding experiment
Mendel mated two contrasting, true-breeding varieties, a process called hybridization

15. Breeding Terminology The true-breeding parents
Are called the P (parental) generation
The hybrid offspring of the P generation
Are called the F1 (filial) generation
When F1 individuals self-pollinate
The F2 generation is produced

16. (true-breeding parents)
EXPERIMENT
P Generation
(true-breeding parents)
Purple flowers
White flowers
Figure 14.3 INQUIRY: When F1 hybrid pea plants self- or cross-pollinate, which traits appear in the F2 generation?

17. (true-breeding parents) F1 Generation (hybrids)
EXPERIMENT
P Generation
(true-breeding parents)
Purple flowers
White flowers
F1 Generation (hybrids)
All plants had purple flowers
Self- or cross-pollination
Figure 14.3 INQUIRY: When F1 hybrid pea plants self- or cross-pollinate, which traits appear in the F2 generation?

18. (true-breeding parents) Purple flowers White flowers
EXPERIMENT
P Generation
(true-breeding parents)
Purple flowers
White flowers
F1 Generation (hybrids)
All plants had purple flowers
Self- or cross-pollination
Figure 14.3 INQUIRY: When F1 hybrid pea plants self- or cross-pollinate, which traits appear in the F2 generation?
F2 Generation
705 purple- flowered plants
224 white flowered plants

19. Table 14.1 The Results of Mendel’s F1 Crosses for Seven Characters in Pea Plants

20. Mendel developed a hypothesis to explain his results that consisted of four ideas
Alternative versions of genes (different alleles) account for variations in inherited characters
For each character, an organism inherits two alleles, one from each parent
If two alleles differ, then one, the dominant allele, is fully expressed in the organism’s appearance. The other, recessive allele has no effect on a hybrid organism’s appearance
The two alleles for each character segregate (separate) during gamete formation

22. Law of Segregation P Generation Appearance: Purple flowers
White flowers
Genetic makeup: PP pp
Gametes: P p
Figure 14.5 Mendel’s law of segregation.

23. Law of Segregation P Generation Appearance: Purple flowers
White flowers
Genetic makeup: PP pp
Gametes: P p
F1 Generation
Appearance:
Purple flowers
Genetic makeup: Pp
Gametes:
1/2 P
1/2 p
Figure 14.5 Mendel’s law of segregation.

24. Law of Segregation P Generation Appearance: Purple flowers
White flowers
Genetic makeup: PP pp
Gametes: P p
F1 Generation
Appearance:
Purple flowers
Genetic makeup: Pp
Gametes:
1/2 P
1/2 p
Sperm from F1 (Pp) plant
F2 Generation P p
Figure 14.5 Mendel’s law of segregation. P
Eggs from F1 (Pp) plant PP Pp p Pp pp 3
: 1

25. PP (homozygous) Pp (heterozygous) Pp (heterozygous) pp (homozygous)
Phenotype
Genotype
Purple
PP (homozygous) 1 3
Pp (heterozygous)
Purple 2
Pp (heterozygous)
Purple
Figure 14.6 Phenotype versus genotype.
pp (homozygous) 1
White 1
Ratio 3:1
Ratio 1:2:1

26. Test cross TECHNIQUE Dominant phenotype, unknown genotype: PP or Pp?
Recessive phenotype, known genotype: pp
Predictions
If purple-flowered parent is PP or
If purple-flowered parent is Pp
Sperm
Sperm p p p p P P Pp Pp Pp Pp
Eggs
Eggs
Figure 14.7 RESEARCH METHOD: The Testcross P p Pp Pp pp pp
RESULTS or
All offspring purple
1/2 offspring purple and 1/2 offspring white

28. Hypothesis of dependent assortment
EXPERIMENT
YYRR
P Generation
yyrr
Gametes YR yr
F1 Generation
YyRr
Predictions
Hypothesis of dependent assortment
Hypothesis of independent assortment
Sperm
Predicted offspring of F2 generation or
1/4 YR
1/4 Yr
1/4 yR
1/4 yr
Sperm
1/2 YR
1/2 yr
1/4 YR
YYRR
YYRr
YyRR
YyRr
1/2 YR
YYRR
YyRr
1/4 Yr
Eggs
YYRr
YYrr
YyRr
Yyrr
1/2
Eggs
Figure 14.8 INQUIRY: Do the alleles for one character assort into gametes dependently or independently of the alleles for a different character? yr
YyRr
yyrr
1/4 yR
YyRR
YyRr
yyRR
yyRr
3/4
1/4
1/4 yr
Phenotypic ratio 3:1
YyRr
Yyrr
yyRr
yyrr
9/16
3/16
3/16
1/16
Phenotypic ratio 9:3:3:1
RESULTS
315
108
101 32
Phenotypic ratio approximately 9:3:3:1

29. Segregation of alleles into eggs Segregation of alleles into spermRr  Rr
Segregation of alleles into eggs
Segregation of alleles into sperm
Sperm
1/2 R
1/2 r R R
1/2 R R r
Figure 14.9 Segregation of alleles and fertilization as chance events.
1/4
1/4
Eggs r r R r
1/2 r
1/4
1/4

30. Probability of YYRR  1/4 (probability of YY)  1/4 (RR)  1/16
1/8
Figure 14.UN01

31. Probability of YYRR  1/4 (probability of YY)  1/4 (RR)  1/16
1/8
Figure 14.UN01
Probability of yyrr = ?
A. 1/8 B. 1/16 C. 1/32

32. Probability of YYRR  1/4 (probability of YY)  1/4 (RR)  1/16
1/8
Figure 14.UN01
Probability of YYrr = ?
A. ¼ B. 1/8 C. 1/16

33. Probability of YYRR  1/4 (probability of YY)  1/4 (RR)  1/16
1/8
Figure 14.UN01
Probability of YxRr = ?
(x can be Y or y)
A. ½ B. 3/4 C. 3/8 D. 1/16

34. 1/4 (probability of pp)  1/2 (yy)  1/2 (Rr)  1/16 ppYyrr
1/4  1/2  1/2
 1/16
Ppyyrr
1/2  1/2  1/2
 2/16
PPyyrr
1/4  1/2  1/2
 1/16
ppyyrr
1/4  1/2  1/2
 1/16
Chance of at least two recessive traits
Figure 14.UN02
 6/16 or 3/8