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Review

Review. What is a gamete? Why do we need to know the gamete composition?. Aa 2 1 =2 AaBB 2 1 =2 AaBbCc 2 3 =8 AaBbCC 2 2 =4 We need to know the gamete composition so that we can insert them into the boxes in punnet square e.g # AaBbCc x AaBbCC. Testcross.

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Review

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  1. Review

  2. What is a gamete? Why do we need to know the gamete composition? • Aa 21=2 • AaBB 21=2 • AaBbCc 23=8 • AaBbCC 22=4 We need to know the gamete composition so that we can insert them into the boxes in punnet square e.g # AaBbCc x AaBbCC

  3. Testcross • What is a testcross? • Why do we do testcross? - homozygous recessive alleles

  4. Sex linked • 2 ways to write it, depending on instruction • Eg, assume that PTC is a sex-linked gene. • Ability to taste is dominant XP+/ XP • Inability to taste is recessive XP/ Xp • So, XP+XP+,XP+X , XP+Y are tasters and non-tasters will be XPXP,XPY • Always bear in mind that if they talk about disease, normal means a NONCARRIER XP+XP+,XP+Y

  5. Try this • The gene for eye in flies (Drosophila melanogaster) are sex linked. The gene for red eye is dominant over yellow eye. A red eyed male is mated with yellow eyed female. Diagram the cross is the male is heterozygous.

  6. Try this • The gene for eye in flies (Drosophila melanogaster) are sex linked. While gene gene for wings are autosomal. The gene for red eye is dominant over yellow eye, gene for vestigial wings is dominant over long wing. A red eyed male fly with vestigial wings is mated with yellow eyed female fly with long wings. Diagram the cross is the male is heterozygous.

  7. Map distance and chi-square How do we determine the ratio Green pod, starchy 568 Red pod, wrinkle 525 Green pod wrinkle 154 Red pod, starchy 163 1400 • Recombinant ?? • Ratio ?? • Which one is which ??

  8. Trihybrid cross- determining map distance Parent flies were mated • Black body, purple eyes, vestigial wings • Gray body, red eyes, long wings Producing • Black body, purple eyes, vestigial wings 411 • Gray body, red eyes, long wings 412 • Black body, purple eyes, long wings 60 • Black body, red eyes, long wings 28 • Black body, red eyes, vestigial wings 1 • Gray body, purple eyes, vestigial wings 30 • Gray body, red eyes, vestigial wings 61 • Gray body, purple eyes, long wings 2 b+ pr+ vg+ b pr vg

  9. Calculate the distance between genes • We know that map distance is So, we need to calculate the map distance of • Between body and eye color • Between body and wings • Between eye and wing Recombinant Total X 100

  10. Between body and eye color • Between body and wing • Between eye and wing

  11. But.. The actual distance calculated was 18.4 mu, therefore, this is said to experience rare double crossovers. • Therefore

  12. Single and Double crossovers

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