Genetic Crosses Shows possible outcomes of genes the new generation will have We use: Punnett Squares Visit For 100’s of free powerpoints

Terminology Genotype Phenotype Parent Gamete Offspring dominant recessive allele

Gene control of characteristics All characteristics are controlled by a minimum of 2 genes. These genes give the characteristic a different way of presenting itself. Different genes that control the same feature are called ALLELES

Punnett Square Another method of showing crosses

Gamete genotypes are inserted Parent genotypes are inserted B=black b=white Bb male black bb white female Bb b b What are the crosses Bb bb Bbbb 2 white and 2 black offspring 50:50 chance with these parents

Question 2 black rats are mated, they have 13 offspring. All of which are black, what are the genotypes of the parents The male is re-mated with a white female, the offspring are 6 black and 7 white What were the genotypes of the original parents Rats have 2 coat colors – black B, white b. Both BB BB BUT one could be Bb Female BB Male Bb

7 Mendel’s Laws 1. Law of Dominance 2. Law of Segregation 3. Law of Independent assortment

8 Law of Dominance States that on crossing homozygous organisms for a single pair of contrasting characters, only one character make its appearance in F 1 generation and is the Dominant character.

9 Law of Dominance In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. All the offspring will be heterozygous and express only the dominant trait. RR x rr yields all Rr (round seeds)

10. Law of Segregation The two alleles for each trait separate during gamete formation.

11 Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

12 Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another. Alleles for different traits are distributed to sex cells (& offspring) independently of one another. This law can be illustrated using dihybrid crosses. This law can be illustrated using dihybrid crosses.

13 Dihybrid Cross Traits: Seed shape & Seed color Traits: Seed shape & Seed color Alleles: Alleles: R round r wrinkled Y yellow y green RrYy x RrYy RY Ry rY ry All possible gamete combinations

14 Dihybrid Cross RYRyrYry RYRy rY ry

15 Dihybrid Cross RRYY RRYy RrYY RrYy RRYy RRyy RrYy Rryy RrYY RrYy rrYY rrYy RrYy Rryy rrYy rryy Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio RYRyrYryRY Ry rY ry

16 Dihybrid Cross Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1

17 Question: How many gametes will be produced for the following allele arrangements? Remember: 2 n (n = # of heterozygotes) Remember: 2 n (n = # of heterozygotes) 1.RrYy 1.RrYy 2.AaBbCCDd 2.AaBbCCDd 3.MmNnOoPPQQRrssTtQq 3.MmNnOoPPQQRrssTtQq

18 Answer: 1. RrYy: 2 n = 2 2 = 4 gametes RY Ry rY ry 2. AaBbCCDd: 2 n = 2 3 = 8 gametes ABCD ABCd AbCD AbCd aBCD aBCd abCD abCD 3. MmNnOoPPQQRrssTtQq: 2 n = 2 6 = 64 gametes

19 Summary of Mendel’s laws LAW PARENT CROSS OFFSPRING DOMINANCE TT x tt tall x short 100% Tt tall SEGREGATION Tt x Tt tall x tall 75% tall 25% short INDEPENDENT ASSORTMENT RrGg x RrGg round & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods