Understanding Genetic Inheritance and Cross-Fertilization in Garden Peas

1. Fig. 10-1a, p.152

2. ATP ATP Fig. 10-1b, p.152

3. p.153

4. Fig. 10-2, p.154

5. carpel stamen a Garden pea flower, cut in half. Sperm form in pollen grains, which originate in male floral parts (stamens). Eggs develop, fertilization takes place, and seeds mature in female floral parts (carpels). b Pollen from a plant that breeds true for purple flowers is brushed onto a floral bud of a plant that breeds true for white flowers. The white flower had its stamens snipped off. This is one way to assure cross-fertilization of plants. c Later, seeds develop inside pods of the cross-fertilized plant. An embryo within each seed develops into a mature pea plant. d Each new plant’s flower color is indirect but observable evidence that hereditary material has been transmitted from the parent plants. Fig. 10-3, p.154

6. a A pair of homologous chromosomes, both unduplicated. In most species, one is inherited from a female parent and its partner from a male parent. b A gene locus (plural, loci), the location for a specific gene on a chromosome. Alleles are at corresponding loci on a pair of homologous chromosomes c A pair of alleles may be identical or not. Alleles are represented in the text by letters such as D or d. d Three pairs of genes (at three loci on this pair of homologous chromosomes); same thing as three pairs of alleles. Fig. 10-4, p.155

7. Homozygous dominant parent Homozygous recessive parent (chromosomes duplicated before meiosis) meiosis I meiosis II (gametes) (gametes) fertilization produces heterozygous offspring Fig. 10-5, p.156

8. Trait Studied Dominant Form Recessive Form F2 Dominant-to-Recessive Ratio Seed shape 5,474 round 1,850 wrinkled 2.98:1 Seed color 6,022 yellow 2,001 green 3.01:1 Pod shape 2.95:1 882 inflated 299 wrinkled Pod color 428 green 152 yellow 2.82:1 Flower color 705 purple 224 white 3.15:1 Flower position 3.14:1 651 long stem 207 at tip Stem length 2.84:1 277 dwarf 787 tall Fig. 10-6, p.156

9. female gametes a a a a A A A A A A A Aa Aa A AA male gametes a a a aa a Aa aa Aa aa aa Aa a From left to right, step-by-step construction of a Punnett square. Circles signify gametes. A stands for a dominant allele and a for a recessive allele at the same gene locus. Offspring genotypes are indicated inside the squares. Fig. 10-7a, p.157

10. F1 offspring aa True-breeding homozygous recessive parent plant a a Aa Aa Aa Aa A AA A Aa Aa True-breeding homozygous dominant parent plant Aa Aa b Cross between two plants that breed true for different forms of a trait. Fig. 10-7b, p.157

11. F2 offspring Aa Heterozygous F1 offspring a A Aa AA A AA Aa Aa a Aa aa Heterozygous F1 offspring Aa aa c Cross between heterozygous F1 offspring. Fig. 10-7c, p.157

12. A a AA (dominant) AA A Aa the expected phenotypic ratio of 3:1 (dominant) Aa (dominant) Aa a Aa aa aa (recessive) p.165

13. Meiosis, gamete formation in true-breeding parent plants parent homozygous dominant for purple flowers, tall stems parent homozygous recessive for white flowers, short stems Gametes at fertilization Possible genotypes resulting from a cross between two F1 plants: meiosis, gamete formation meiosis, gamete formation All F1 plants are AaBb heterozygotes with purple flowers and tall stems. Fig. 10-9, p.159

14. AA BB or or Genotypes: AO AB BO OO Phenotypes (Blood type): A AB B O Fig. 10-10, p.160

15. homozygous parent (RR) homozygous parent (rr) heterozygous F1 offspring (Rr) x Cross two of the F1 plants, and the F2 offspring will show three phenotypes in a 1:2:1 ratio: RR Rr Rr rr Fig. 10-11, p.160

16. EB Eb eB eb EEBB black EEBb black EeBB black EeBb black EB EEBb black EEbb chocolate EeBb black Eebb chocolate Eb EeBB black EeBb black eeBB yellow eeBb yellow eB eeBb yellow eebb yellow EeBb black Eebb chocolate eb Fig. 10-13, p.161

17. Fig. 10-16, p.163

18. p.164

19. This red graph line of the range of variation for a trait in a population plots out as a bell-shaped curve. Such curves indicate continuous variation in a population. Number of individuals with a measurable value for the trait Range of values for the trait Fig. 10-19a, p.164

20. Fig. 10-19c, p.164

21. Fig. 10-20a-b, p.166