# Announcements  Discussion sections meet next week (T, W, TH) -check the web page for the room (some have changed)  HW1 is due Monday in lecture (know.

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Announcements  Discussion sections meet next week (T, W, TH) -check the web page for the room (some have changed)  HW1 is due Monday in lecture (know who your TA is)  Any questions about logistics??

cleft chins Caleb Fishman Miller Scott Miller Review of basic Mendelian inheritance 1.Given that I do not have a cleft chin, which trait is dominant? 2. What is Caleb’s genotype? 3. What information would we need to calculate the probability that the new baby has a cleft chin?

Review of basic Mendelian inheritance 1.Given that I do not have a cleft chin, which trait is dominant? This is a bit of a trick question. It is most likely (and true) that cleft is dominant, but from this information you can’t be totally sure. 2. What is Caleb’s genotype? Cc, if cleft allele is C. 3. What information would we need to calculate the probability that the new baby has a cleft chin? What is Scott’s genotype?? How would we figure that out?

Review of basic Mendelian inheritance 4.Assuming that Scott is a heterozygote and cleft is dominant, what is the probability that the new baby will have a cleft chin? Use a Punnett square or simple math...

Learning Goals Understand Mendel’s 3 rd principle  Independent assortment Use Punnett square and forked-line diagram to predict the inheritance of trait combinations Understand a test cross

TRAIT VARIANTS Flower colorPurple White Flower positionAxial Terminal Seed color Yellow Green Seed shapeRound Wrinkled Pod shape Inflated Constricted Pod color Height TallDwarf Yellow Green

Experimental Protocol (1) Develop parental lines (P) by self-breeding individuals until they are true breeding. (2) Create first-generation progeny (F 1 ) by mating parental lines with alternative phenotypes (e.g., tall x dwarf). (3) Create second-generation progeny (F 2 ) by self-fertilizing F 1 ’s.

PHENOTYPE P generation TTtt F 1 generation 100% tall progeny (hybrids) Cross-fertilization Self-fertilization F 2 generation GENOTYPE 100% Tt (tall) 25% TT 50% Tt 25% tt (tall) (dwarf) 25% dwarf 75% tall

Mendel’s Principles, so far 1. Dominance: In a heterozygote, one allele may conceal another. 2. Segregation: In a heterozygote, two different alleles segregate from each other with equal probability during the formation of gametes. What happens if we consider two traits simultaneously?

TRAIT VARIANTS Flower colorPurple White Flower positionAxial Terminal Seed color Yellow Green Seed shapeRound Wrinkled Pod shape Inflated Constricted Pod color Height TallDwarf Yellow Green

R R r r Round Wrinkled RR Rr rr 3 round : 1 wrinkled

Y Y y y Yellow Green YYYy yy 3 yellow : 1 green

Yellow X Green YY yy Yellow (Yy) Yellow (YY, Yy) 6,022 Green (yy) 2,000 Round X Wrinkled RR rr Round (Rr) Round (RR, Rr) 5,474 Wrinkled (rr) 1,850

Dihybrid cross - seed color and seed texture F 1 hybrid seed gametes? YRyr YYRR yyrr YyRr ??? 2 possiblities: complete linkage or independent assortment

RRYYrryy RY ry round, yellow wrinkled, green round, yellow Gametes Complete linkage: only parental combinations RrYy

RRYYrryy RrYy RY Ry rY ry round, yellow wrinkled, green round, yellow Gametes Independent assortment: all combinations possible

RrYy R r R r Y Y y y RY Ry rY ry Fork Diagram 25%

RrYy x Independent assortment predictions: Dihybrid F 2 phenotypes RYRyrYry RY Ry rY ry RrYy RRYY RRYy RrYYRRYy RrYyRrYY RRyyRrYy Rryy RrYy rrYY rrYy rryy 9 round, yellow 3 round, green 3 wrinkled, yellow 1 wrinkled, green

RRYYrryy RrYy (self-fertilize) round, yellow wrinkled, yellow round, green green, wrinkled round, yellow wrinkled, green round, yellow 315 101 108 32 9:3:3:1 Mendel’s Data

Mendel’s Principles 1. Dominance: In a heterozygote, one allele may conceal another. 2. Segregation: In a heterozygote, two different alleles segregate from each other during the formation of gametes. 3. Independent Assortment: The alleles of different genes (or loci) segregate (or assort) independently of each other.

The forked-line method can be used to predict the outcome of an intercross involving three independently assorting genes in peas. TtYyRr x TtYyRr

Use of a test cross Tall Dwarf TT or Tt tt

TT or Tt How would you determine if the genotype of this phenotypically tall plant is TT or Tt?

TT or Tt X tt 100% tall (Tt) 50% Tall (Tt) or dwarf (tt) Test cross

TY ty TytYty Tall, yellowTall, green Dwarf, yellow Dwarf, green TtYyTtyyttYyttyy Dihybrid test cross ttyy x TtYy 25% 25%

Mendelian laws of segregation: mechanism 1: Alleles at a single gene segregate into the gametes at random (1:1 ratio) 2: Alleles at unlinked genes assort independently, so all combinations are equally likely. Both of these laws result from how homologous chromosomes line up in metaphase of Meiosis I.

Why is independent assortment important??

How many chromosomally unique gametes can one person make? LOTS!!!!

Next: Video clip for HW 1 ? ?

Independent assortment of chromosomes Meiosis I metaphase Meiosis II metaphase A’A’ A A’BAB’ B’B’ B A’A’ A B’B’ B ABA’B ’ A’BAB’ gametes A B A’A’ B’B’ parental

Independent assortment of chromosomes Meiosis I metaphase Meiosis II metaphase A’A’ A A’BAB’ B’B’ B A’A’ A B’B’ B ABA’B ’ A’BAB’ gametes A B A’A’ B’B’ parental nonparental

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