JOURNAL : EOCT BIOLOGY QUESTIONS 1.In Mendel’s experiment with a single trait, the trait that disappeared in the first generation and reappeared in the next generation is called the a.Homozygous trait b.Dominant trait c.Recessive trait d.Heterozygous trait 2.In fruit flies, the gray body color is (G) is dominant to the ebony body color (g). What is the genotypic ratio of the offspring of a heterozygous gray female and an ebony male? a.25% Gg, 75% gg b.50%Gg, 50% gg c.75% gray, 25% ebony d.100% gray

When is a trait said to display incomplete dominance? When the heterozygote has a phenotype intermediate between the phenotypes of two homozygotes

What is codominance? The phenotype of the heterozygote is not intermediate between the phenotypes of the homozygotes; rather, the heterozygote expresses both homozygote phenotypes simultaneously

In chickens, black feather color (BB) is codominant to white feather color (WW). Both feather colors show up in a checkered pattern in the heterozygous individual (BW). Cross a checkered chicken with a checkered chicken. __________ X ________ In horses, gray horses (GG) are codominant to white horses (WW). The heterozygous horses(GW) is an appaloosa horse (a white horse with gray spots on the rump and loins). Cross a white horse with an appaloosa horse. ________ X ________ Genotypic Ratios: Phenotypic Ratios: Genotypic ratios: Phenotypic ratios:

What is a test cross? A cross that is made in which one individual of unknown genotype is crossed with another individual with a homozygous recessive genotype Ex. TTx tt = all tall (Tt) Recessive will not appear Tt x tt = 50% of offspring will show recessive trait (tt), 50% heterozygous (Tt)

What is a backcross? When a cross made between an F1 genotype and either of the parental genotypes Ex. Tt x tt or Tt x TT

Law of Dominance: The trait that is observed when two alleles are present Ex. Pp - purple

Law of Segregation Alleles segregate (separate) during the formation of gametes and one allele goes into each gamete

Which law was formulated as a result of Mendel’s dihybrid crosses? LAW OF INDEPENDENT ASSORTMENT: Alleles at different loci separate independently of one another

12 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 copyright cmassengale

13 Dihybrid Cross copyright cmassengale 9:3:3:1 9 round yellow 3 wrinkled yellow 3 round green 1 wrinkled green

APRIL 10, 2012 EQ: HOW ARE SEX-LINKED TRAITS & MULTIPLE ALLELES PASSED FROM ONE GENERATION TO THE NEXT? WARM-UP: WHAT DID YOU DO DURING YOUR SPRING BREAK?

*When several genes affect a character/trait

I A, I B, i

*1/700 births * *Individuals contain 3 copies of chromosome 21 * * characteristic facial features, heart defects, & leukemia *caused by nondisjunction of chromosomes during anaphase

*Missing a sex chromosome

Caused by a gene located on either an X or Y chromosome. Ex. Colorblindness & Hemophilia

22 Sex-linked Trait Problem Example: Eye color in fruit flies (red-eyed male) x (white-eyed female) X R Y x X r X r Remember: the Y chromosome in males does not carry traits. RR = red eyed Rr = red eyed rr = white eyed XY = male XX = female XRXR XrXr XrXr Y copyright cmassengale

STANDARD SYMBOLS USED IN PEDIGREES: