1. Ch.11-2 Applying Mendel’s Principles
Genetics

2. POINT > Review Mendel’s first crosses
POINT > Describe dominant and recessive alleles
POINT > Describe homozygous and heterozygous genotypes
POINT > Distinguish between genotype and phenotype
POINT > Use Punnett Squares to predict genotypes and phenotypes

3. POINT > Review Mendel’s first crosses
Looking back at Mendel’s pea plants…
Parental plants (P) were all purebred x
First generation (F1) offspring
all showed dominant allele

4. POINT > Review Mendel’s first crosses
Looking back at Mendel’s pea plants…
Second generation (F2) offspring showed both dominant & recessive alleles

5. POINT > Review Mendel’s first crosses
6022 =
3.01
2001
Looking back at Mendel’s F2 pea plants...
Trait
Dominant
Recessive
Ratio
Seed Color
6022 Yellow
2001 Green
3.01 : 1
Seed Shape
5474 Round
1850 Wrinkled
2.96 : 1
Flower Color
705 Purple
224 White
3.15 : 1
Pod Color
428 Green
152 Yellow
2.82 : 1
Plant Height
787 Tall
277 Short
2.84 : 1

6. POINT > Describe dominant and recessive alleles
Alleles are represented by a single letter, usually the first letter of the dominant allele
Dominant alleles  Uppercase letter
Recessive alleles  Lowercase letter

7. POINT > Describe dominant and recessive alleles
Example from Mendels peas:
Dominant alleles  yellow seeds = Y
Recessive alleles  green seeds = y

8. POINT > Describe homozygous and heterozygous genotypes
An organism is homozygous for a trait if it has two identical alleles Ex. both alleles code for: Yellow seeds – YY (homozygous dominant) Green seeds – yy (homozygous recessive)

9. POINT > Describe homozygous and heterozygous genotypes
An organism is heterozygous for a trait if it has two different alleles Ex. Alleles codes for: One yellow, one green – Yy

10. WB CHECK:
In pea plants, the allele for purple flowers is dominant (P) and the allele for white flowers is recessive (p). A plant with alleles pp would be a) homozygous dominant and have purple flowers b) homozygous recessive and have purple flowers c) homozygous dominant and have white flowers d) homozygous recessive and have white flowers e) heterozygous and have purple flowers f) heterozygous and have white flowers

11. WB CHECK:
A pea plant with alleles Pp would be a) homozygous dominant and have purple flowers b) homozygous recessive and have purple flowers c) heterozygous and have purple and white flowers d) heterozygous and have purple flowers e) heterozygous and have white flowers

12. POINT > Distinguish between genotype and phenotype
The genotype is the genetic makeup of the alleles for a specific gene
Indicated by writing both alleles:
YY Yy yy

13. POINT > Distinguish between genotype and phenotype
The phenotype is the physical expression of a trait Indicated by writing the name of expressed allele: Yellow Yellow Green

14. WB CHECK:
A pea plant with alleles P and p would be a) genotype = Pp phenotype = white flowers b) genotype = purple flowers phenotype = Pp c) genotype = Pp phenotype = purple flowers d) genotype = white flowers phenotype = Pp

15. We can predict the results of a cross if we know the genotypes of the parents…

16. POINT > Use Punnett Squares to predict genotypes and phenotypes
A Punnett Square is a diagram that shows the mathematical probability of genotypes & phenotypes

17. POINT > Use Punnett Squares to predict genotypes and phenotypes
Parent 1
The two axes represent the two parents
The boxes represent offspring
Pa r en t 2

18. Meiosis of a plant heterozygous for seed color:

19. Meiosis of a plant heterozygous for seed color:

20. Meiosis of a plant heterozygous for seed color:

21. y Y
50%
50% y Y Y y

22. We can use meiosis & a Punnett square to show why Mendel’s first cross for pea color resulted as it did:

23. POINT > Use Punnett Squares to predict genotypes and phenotypesX
Mendel’s first cross:
Alleles
Yellow (Y)
Yellow (Y)
Green (y)
Green (y)

24. POINT > Use Punnett Squares to predict genotypes and phenotypes
Mendel’s first cross:
Yellow (Y)
Yellow (Y) Y Y
Green (y) Y Y
Green (y)

25. POINT > Use Punnett Squares to predict genotypes and phenotypes
Mendel’s first cross:
Yellow (Y)
Yellow (Y) Y y Y y
Green (y) Y y Y y
Green (y)

26. POINT > Use Punnett Squares to predict genotypes and phenotypes
Mendel’s first cross:
Yellow (Y)
Yellow (Y) Y y Y y
Green (y) Y y Y y y
Green (y) Y

27. POINT > Use Punnett Squares to predict genotypes and phenotypes
100% Yy
Yellow (Y)
Yellow (Y)
Ratio 4 : 0 Y y Y y
Green (y)
Phenotype
100% Yellow
Ratio 4 : 0 Y y Y y
Green (y)

28. What about Mendel’s second cross
What about Mendel’s second cross? How would a Punnett square show the results of the self-pollinating F1 generation?

29. POINT > Use Punnett Squares to predict genotypes and phenotypes
Mendel’s second cross
Genotype:
25% YY
50% Yy
25% yy Y y
Ratio 1 : 2 : 1 Y Y Y y Y
Phenotype:
75% Yellow
25% Green
Ratio 3 : 1 Y y y y y

30. WB CHECK:
Determine both the genotype & phenotype ratios using a Punnett Square:
A pea plant homozygous dominant for seed color is crossed with a pea plant heterozygous for seed color
Yellow = dominant (Y), green = recessive (y)

31. WB CHECK:
Determine both the genotypic & phenotypic ratios.
Cross a pea plant homozygous recessive for flower color to a pea plant heterozygous for flower color
Purple = dominant (P) , white = recessive (p)

32. WB CHECK:
Determine both the genotypic & phenotypic ratios.
Cross a fruit fly heterozygous for wing shape to another fruit fly heterozygous for the same trait
Curly = dominant (C), Straight = recessive (c)

33. Homework: Read pages Assess #1-3 page 318 Karyotype exercise pages Workbook pages 163-4