14. Use a Punnet square to solve a cross between two parents that both have the genotype Yy.
15. What are alleles & what are the two forms?
alleles are two forms of a gene (dominant & recessive)
16. Explain the difference between dominant & recessive alleles.
Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R)
Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r)
17. Using a letter of the alphabet, show how each allele would be represented.
A- dominant a- recessive
18. What is a genotype and write 3 possible genotypes?
Genotype - gene combination for a trait (e.g. RR, Rr, rr)
19. What is a phenotype and write possible phenotypes for your genotypes in question 18?
Phenotype - the physical feature resulting from a genotype (e.g. red, white)
20. Using these alleles, R = red flower and r = yellow flowers; write all possible genotypes & phenotypes.
Genotype of alleles:
R = red flower
r = yellow flower
All genes occur in pairs, so 2 alleles affect a characteristic
Genotypes RR Rr rr
Phenotypes RED RED YELLOW
STOPPING POINT 11/24/09
21. What are homozygous genotypes?
gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure
22. Write a homozygous dominant genotype. RR
23. Write a homozygous recessive genotype. rr
24. What is meant by a heterozygous genotype?
gene combination of one dominant & one recessive allele (e.g. Rr)
25. Write a heterozygous genotype. Rr
26. Heterozygous genotypes are also called _ hybrid____.
27. What two things actually determine an organism's characteristics? Genes and Environment
28. Give 4 reasons that Mendel used garden peas, Pisum sativum, for his experiments.
1) Can be grown in a small area
2) Produce lots of offspring
3) Produce pure plants when allowed to self-pollinate several generations
4) Can be artificially cross-pollinated
29. Name the male and female parts of a flowering plant and explain how pollination occurs.
Pollen contains sperm and is produced by the stamen
Ovary contains eggs and is found inside the flower
30. What is the difference between self and cross pollination?
Pollen carries sperm to the eggs for fertilization
Self-fertilization can occur in the same flower
Cross-fertilization can occur between flowers
31. Explain how Mendel cross pollinated his pea plants.
Mendel hand-pollinated flowers using a paintbrush,
He could snip the stamens to prevent self-pollination, then covered each flower with a cloth bag
He traced traits through the several generations
32. How did Mendel get pure plants?
produced pure strains by allowing the plants to self-pollinate for several generations
33. Name 8 pea plant traits and give the dominant & recessive form of each.
Seed shape --- Round (R) or Wrinkled (r)
Seed Color ---- Yellow (Y) or Green (y)
Pod Shape --- Smooth (S) or wrinkled (s)
Pod Color --- Green (G) or Yellow (g)
Seed Coat Color ---Gray (G) or White (g)
Flower position---Axial (A) or Terminal (a)
Plant Height --- Tall (T) or Short (t)
Flower color --- Purple (P) or white (p)
34. How did Mendel's experimental results compare to the theoretical genotypic ratios? Explain.
The theoretical or expected ratio of plants producing round or wrinkled seeds is 3 round :1 wrinkled
Mendel’s observed ratio was 2.96:1
The discrepancy is due to statistical error
The larger the sample the more nearly the results approximate to the theoretical ratio
35. What does P1 mean? Parental P1 Generation = the parental generation in a breeding experiment.
36. What is the F1 generation? F1 generation = the first-generation offspring in a breeding experiment. (1st filial
From breeding individuals from the P1 generation
37. What is the F2 generation? F2 generation = the second-generation offspring in a breeding experiment. (2nd
From breeding individuals from the F1 generation
38. What results from this cross --- TT x tt? All hybrids (Tt)
39. What results do you get from crossing two hybrids (Tt x Tt)?
you would get the following genotypes TT, Tt, tt
Assuming T represents tall and t represents short; you would get 3 tall and 1 short
40. Show all your work for solving a P1 monohybrid cross for seed shape.
Trait: Seed Shape
Alleles: R – Round r – Wrinkled
Cross: Round seeds x Wrinkled seeds
P1 cross: __RR___ x _ rr __
Genotype __ Rr ____
Phenotype __Round _
G. Ratio _ All alike _
P. Ratio _ All alike _
41. The offspring of the above cross are called the _F1____ generation.
42. Show all your work for solving a F1 monohybrid cross for seed shape.
Trait: Seed Shape
Alleles: R – Round r – Wrinkled
Cross: Round seeds x Round seeds
F1 cross: _ Rr _ x _ Rr _
Genotype: RR, Rr, rr
Phenotype: Round & wrinkled
G. Ratio: 1:2:1
P. Ratio: 3:1
43. Show all your work for solving both F2 monohybrid crosses for seed shape.
Trait: cross 1: Round, Round cross 2: wrinkled round
Alleles: cross 1 RR, Rr cross 2: rr, Rr
F2 cross: __ RR ______ x ___ Rr _____ F2 cross: __ rr ______ x ___ Rr _____
R r R r
RR Rr rr
R Rr r
R RR Rr r Rr rr
Genotype: RR, Rr Genotype: Rr, rr
Phenotype: Round & Wrinkled Phenotype: Round
Ratio: 1:1 G. Ratio: 1:1
Ratio: All alike P. Ratio: 1:1
Complete the following question:
44. __genes_______ are responsible for inherited traits.
45. Phenotype is based on __genotype_____________.
46. Each trait requires _2__ genes, one from each _parent__.
47. State the Law of Dominance and give an example.
In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next
All the offspring will be heterozygous and express only the dominant trait.
RR x rr yields all Rr (round seeds)
3 genotypes yields 3 phenotypes
48. State the Law of Segregation and tell when alleles are "recombined".
During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each
Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the
49. State the Law of Independent assortment & tell what type of crosses show this.
Alleles for different traits are distributed to sex cells (& offspring) independently of one another.
This law can be illustrated using dihybrid crosses.
50. Using the formula 2n where n = the number of heterozygotes, tell how many gametes will be produced by each of the
following allele combinations:
a. RrYy = 22 = 4
b. AaBbCCDd = 23 = 8
c. MmNnOoPPQQRrssTtQq = 26 = 64
51. What are the possible allele combinations in the egg and sperm from the following cross --- RrYy x RrYy.
RY Ry rY ry from egg RY Ry rY ry from sperm
52. Show how to work an F1 dihybrid cross for seed shape & seed color.
Traits: Seed shape & Seed color
Alleles: R round
F1 cross _RrYy _______ x _RrYy _________