1. Class # ____ Genetics Practice Problems

2. Genetics What is heredity/Genetics?
How do you look like your parents, or more like one parent than the other?

3. Martin Sheen
Charlie Sheen
How is it possible to maintain such genetic continuity?
Kirk
Kirk Douglas
Michael
Emilio Estevez

4. History - Gregor Mendel
Augustinian monk lived ( )
Documented a particulate mechanism of inheritance through his experiments with garden peas
Figure 2.2
Gregor Mendel’s monastery garden.
Fig. 2.2

5. Crossing Pea Plants Removed stamens from purple flower1 5 4 3 2
Removed stamens
from purple flower
Transferred sperm-
bearing pollen from
stamens of white
flower to egg-
bearing carpel of
purple flower
Parental
generation
(P)
Pollinated carpel
matured into pod
Carpel
(female)
Stamens
(male)
Planted seeds
from pod
Examined
offspring:
all purple
flowers
First
offspring
(F1)

6. Mendel’s Observations
When Mendel crossed white and purple flowered pea plants all of the offspring were purple
When Mendel crossed the F1 plants, many of the plants had purple flowers, but some had white flowers
A ratio of about three to one, purple to white flowers, in the F2 generation
EXPERIMENT True-breeding purple-flowered pea plants and
white-flowered pea plants were crossed (symbolized by ). The
resulting F1 hybrids were allowed to self-pollinate or were cross-
pollinated with other F1 hybrids. Flower color was then observed
in the F2 generation.
P Generation
(true-breeding
parents)
Purple
flowers
White 
F1 Generation
(hybrids)
All plants had
purple flowers
F2 Generation
RESULTS Both purple-flowered plants and white-
flowered plants appeared in the F2 generation. In Mendel’s
experiment, 705 plants had purple flowers, and 224 had white
flowers, a ratio of about 3 purple : 1 white.

7. Phenotype vs Genotype Figure 14.6 Phenotype Genotype Purple PP3 1 2
Phenotype
Purple
White
Genotype PP
(homozygous) Pp
(heterozygous) pp
Ratio 3:1
Ratio 1:2:1

8. Mendel’s Monohybrid Cross
White
(pp)
Purple
(Pp)
Gametes
Gametes p p P p
Purple
(PP)
Purple
(Pp) P P
Gametes Pp Pp PP Pp
Gametes p P Pp Pp Pp pp
F1 generation
All purple
F2 generation
¾ purple, ¼ white

9. Mendel’s Studied Discrete Traits

10. Mendel Observed The Same Pattern In Characters

11. Genes can be dominant or recessive.
Dominant trait is one which will be expressed if one of the parents has the gene for that trait.
Recessive trait is one that will be expressed only if both parents carry the trait.

12. But, most human traits are NOT simple!
Co-dominance
Incomplete dominance
Humans have 23 pairs of chromosomes for a total of 46.
22 are autosomal
one set determine what sex we are: XX (female) XY (male)
Sex-linked traits
And most traits involve many genes!!
The Human Genome Project has confirmed 19,599 genes, at this point...
Relax, we won’t be getting into that level of complexity in 8th grade! 

13. Simple “Mendelian” – Autosomal Dominant & Recessive
Ability to taste phenylthiocarbamide (dominant)
Ability to smell (bitter almond-like) hydrogen cyanide
Albinism (recessive)
Brachydactyly (shortness of fingers and toes)
Immunity to poison ivy (dominant)
Hitchiker's thumb (recessive)
Wet (dominant) or dry (recessive) earwax

14. Genotype = Full hereditary information
Genotype = Full hereditary information. It describes the genetic contribution from both parents.
Example: Wet ear wax is (dominant) & dry is recessive
Written based on the DOMINANT trait using a letter. W
Dominant wet ear wax gets a capital. W
Recessive dry ear was gets a lower case letter. w
Homozygous = BOTH genes are the same
WW homozygous dominant or ww homozygous recessive
Heterozygous = Genes are different Ww
W for a dominant gene from one parent
w for a recessive gene from the other parent

15. Do Problem Set #1

16. 1. For each genotype, indicate whether it is heterozygous (HE) or homozygous (HO).
AA _HO Bb _ HE Cc _ HE Dd _HE
Ee ff GG HH
Ii Jj kk Ll
Mm nn OO Pp

17. 1. For each genotype, indicate whether it is heterozygous (HE) or homozygous (HO).
AA _HO Bb _ HE Cc _ HE Dd _HE
Ee _HE ff _ HO GG _HO HH _HO
Ii __HE Jj __HE kk _HO Ll _HE
Mm HE nn HO OO HO Pp HE

18. Phenotype = the physical expression of the resulting genetic code
In sneeches, stars are dominant and no stars are recessive.
Genotypes could be:
SS or Ss for stars
What would the genotype for no stars have to be?

19. Do Problem Set # 2

20. Genetic Vocabulary
Phenotype – observable characteristic of an organism
Genotype – pair of alleles present in and individual
Homozygous – two alleles of trait are the same (YY or yy)
Heterozygous – two alleles of trait are different (Yy)
Capitalized traits = dominant phenotypes
Lowercase traits= recessive phenotypes

21. 2. For each of the genotypes below, determine the phenotype.
Purple flowers are dominant to white flowers PP ______purple____________ Pp ______purple_______________ pp _____ white________________
Brown eyes are dominant to blue eyes BB Bb bb
Round seeds are dominant to wrinkled RR Rr rr
Bobtails are recessive (long tails dominant) LL Ll ll

22. 2. For each of the genotypes below, determine the phenotype.
Purple flowers are dominant to white flowers PP ______purple____________ Pp ______purple_______________ pp _____ white________________
Brown eyes are dominant to blue eyes BB _______brown________________ Bb _______brown________________ bb _______blue________________
Round seeds are dominant to wrinkled RR ______round__________________ Rr ______round________________ rr _______wrinkled_______________
Bobtails are recessive (long tails dominant) LL________long________________ Ll _________long__________________ ll _________bobtails_____________

23. 3. For each phenotype, list the genotypes
3. For each phenotype, list the genotypes. (Remember to use the letter of the dominant trait)
Straight hair is dominant to curly. _____SS_____ straight _____Ss_____ straight _____ss_____ curly
Pointed heads are dominant to round heads.

24. 3. For each phenotype, list the genotypes
3. For each phenotype, list the genotypes. (Remember to use the letter of the dominant trait)
Straight hair is dominant to curly. _____SS_____ straight _____Ss_____ straight _____ss_____ curly
Pointed heads are dominant to round heads. ____PP____ pointed ____Pp______ pointed ____pp_______ round

25. Punnett Squares Tool for determining phenotypes from genotypes.
Begin with the genotypes of the parents.
Meiosis splits the chromosome in half to produce 2 gametes:
Dad  2 sperm
Mom  2 eggs
Each has HALF!
Example: Wet & dry ear wax:

26. Mendelian Genetics
Pink (P) flowers are dominant over white flowers (p)
Parental P0 cross
F1 cross
Determine the genotype and phenotype

27. 4. Set up the square for each of the crosses listed below
4. Set up the square for each of the crosses listed below. The trait being studied is round seeds (dominant) and wrinkled seeds (recessive)
Rr x rr What percentage of the offspring will be round?
Rr x Rr  What percentage of the offspring will be round?
RR x Rr  What percentage of the offspring will be round?

28. 4. Set up the square for each of the crosses listed below
4. Set up the square for each of the crosses listed below. The trait being studied is round seeds (dominant) and wrinkled seeds (recessive)
Rr x rr What percentage of the offspring will be round?

29. 4. Set up the square for each of the crosses listed below
4. Set up the square for each of the crosses listed below. The trait being studied is round seeds (dominant) and wrinkled seeds (recessive)
B) Rr x Rr  What percentage of the offspring will be round?
R r
RR Rr
Rr rr R r

30. 4. Set up the square for each of the crosses listed below
4. Set up the square for each of the crosses listed below. The trait being studied is round seeds (dominant) and wrinkled seeds (recessive)
C) RR x Rr  What percentage of the offspring will be round?
R r
RR Rr R

31. Do problems
Show all your work in your Lab Journal.

32. Answer Key
5. A TT (tall) plant is crossed with a tt (short plant). What percentage of the offspring will be tall? 100% 6. A Tt plant is crossed with a Tt plant. What percentage of the offspring will be short? 25% 7. A heterozygous round seeded plant (Rr) is crossed with a homozygous round seeded plant (RR). What percentage of the offspring will be homozygous (RR)? 1/2 or 50% 8. A homozygous round seeded plant is crossed with a homozygous wrinkled seeded plant. What are the genotypes of the parents? RR x rr What percentage of the offspring will also be homozygous? 0 % 9. In pea plants purple flowers are dominant to white flowers. If two white flowered plants are cross, what percentage of their offspring will be white flowered? 100% white 10. A white flowered plant is crossed with a plant that is heterozygous for the trait. What percentage of the offspring will have purple flowers? pp x Pp results in 50% purple