1 / 9

Phenotype and Genotype Ratios

Do Now: In a species of fish, the allele for blue scales (B) is dominant to the allele for white scales (b). A blue fish mates with a white fist and produces the following offspring: 88 blue fish and 92 white fish . Is the blue parent heterozygous or homozygous?

luna
Download Presentation

Phenotype and Genotype Ratios

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Do Now: In a species of fish, the allele for blue scales (B) is dominant to the allele for white scales (b). A blue fish mates with a white fist and produces the following offspring: 88 blue fish and 92 white fish . Is the blue parent heterozygous or homozygous? Draw a Punnett square of the cross. Phenotype and Genotype Ratios

  2. Heterozygous! • Since blue (B) is dominant to white (b), the blue fish might be BB or Bb. • If the blue fish was homozygous dominant, all of the offspring would be blue!

  3. Genotype & Phenotype Ratios • Remember those definitions: • Genotype = what alleles an organism has (Aa, etc.) • Phenotype = the characteristic (green seeds, etc.) • A ratio is a relationship between numbers

  4. Heterozygous x Homozygous recessive • Consider the fish cross: • Since 50% of the offspring will be Bb and 50% will be bb (2 squares:2 squares), the genotype ratio will be 1:1 Bb:bb • Since all of the fish are blue, there’s not really a phenotype ratio for this one – just 100% blue.

  5. More Interesting Ratios • When Mendel crossed two heterozygous purple flowered pea plants, he noticed a 3:1 phenotype ratio. In other words, there were 3 times as many purple flowered plants as white flowered plants. • He immediately knew the plants had 2 alleles!

  6. 3:1 Phenotype Ratio • Notice that 3 of the squares represent purple-flowered plants, and 1 represents white flowered plants. • CAUTION: RANDOM BEHAVIOR • In the real world, these ratios might not be perfect, because of chance. You might flip a coin 10 times and get heads 6 and tails 4… • Just remember: 305:98 is just as valid as 300:100

  7. 1:2:1 Genotype Ratio • The previous cross produces 3 different genotypes: PP, Pp, and pp. • Thus, our genotype ratio must also have 3 terms • 1:2:1 PP:Pp:pp

  8. Possible Ratios • There are only a few ratios you will see in monohybrid crosses: • 100% • 1:1 • 3:1 • 1:2:1

  9. Generations • In genetics, the generations of offspring are designated as P (parents), F1 (offspring 1), F2 (offspring 2), etc.

More Related