Class # ____ Genetics Practice Problems

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

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

History - Gregor Mendel Augustinian monk lived (1822-1884) Documented a particulate mechanism of inheritance through his experiments with garden peas Figure 2.2 Gregor Mendel’s monastery garden. Fig. 2.2

Crossing Pea Plants Removed stamens from purple flower 1 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)

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.

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

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

Mendel’s Studied Discrete Traits

Mendel Observed The Same Pattern In Characters

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.

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! 

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

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

Do Problem Set #1

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

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

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?

Do Problem Set # 2

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

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

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_____________

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.

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

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:

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

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?

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?

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

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

Do problems 5 - 10 Show all your work in your Lab Journal.

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