Crosses and Chromosomes Do Now (dihybrid cross) In fruit flies, red eyes are dominant to white, and wings are dominant to no wings Draw a Punnett square representing a cross between two flies heterozygous for both traits. What is the probability of having a white-eyed wingless offspring?

Quiz Review 1: floppy completely dominant to pointy 2: yellow + orange = codominant 3: more common in men = sex-linkage 4: in between phenotype (blend) = incomplete dominance 5: 4 phenotypes = >2 alleles

6: Sex-Linkage X+ Xo X+X+ X+Xo Y X+Y XoY Carrier f. 50% of males will be colorblind 50% of females will be colorblind, 50% will be carriers. No females w/ disease Normal m.

7: multiple alleles G B O GO BO Green + Blue 1:1 green spots:blue OO = no spots No spots

Dihybrid Punnett Square PY Py pY py PY Py pY py PP YY PP Yy Pp YY Pp Yy PP yy Pp yy pp YY pp Yy pp yy

Pedigree

TEST WEDNESDAY COME TO COACH CLASS TOMORROW! TOPICS: CHAPTER 9 Chromosomes, cell reproduction, crosses, + today’s topics (Mendel’s Laws + crossing over) CHAPTER 9

Mendel’s Law of Segregation A pair of factors is segregated (separated) during the formation of gametes (sex cells) Y y For example: 50% Of Gametes 50% Of Gametes

Mendel’s Law of Independent Assortment Factors (alleles) for different characteristics are distributed independently from one another. T T t t Y Y y y For example: 25% Of Gametes 25% Of Gametes 25% Of Gametes 25% Of Gametes

Mendel’s “Laws” of Heredity It is important to note that these “laws” work under certain conditions: Each gene is on a different chromosome The organisms are diploid

It’s all about the Chromosomes In meiosis, the chromosome number is reduced by half (2nn; diploidhaploid) 50% of gametes get one allele, 50% get the other. b b B B

Dihybrid Gametes Pea plant cross: PpYy x PpYy Gametes: reproductive haploid cells (sperm and egg) One individual heterozygous for 2 traits can produce 4 (2n, where n= number of different genes)possible combinations of alleles. PY Py pY py

Dihybrid Punnett Square PY Py pY py PY Py pY py PP YY PP Yy Pp YY Pp Yy PP yy Pp yy pp YY pp Yy pp yy

One More Twist a A crossing over: when two homologous chromosomes exchange material during meiosis, leading to a new combination of alleles B b a A B b

Meiosis and Genetics The 2 alleles a diploid organism has for a trait are located on 2 homologous chromosomes. The separation of these chromosomes during meiosis leads to the 50/50 chance of a gamete having one version or the other. Mendel’s Laws of heredity only work for alleles on different chromosomes. Crossing over creates new combinations of alleles.