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 traitb. Dominant traitc. Recessive traitd. 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% ggb. 50%Gg, 50% ggc. 75% gray, 25% ebonyd. 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 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.  

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

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Summary of Mendel’s laws

LAWPARENT CROSS

OFFSPRING

DOMINANCE TT x tt tall x short

100% Tt tall

SEGREGATIONTt 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

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Dihybrid Cross

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9:3:3:1

9 round yellow3 wrinkled yellow3 round green1 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?

BEYOND MENDELIAN

HEREDITY

POLYGENIC TRAITS*When several genes affect a character/trait

MULTIPLE ALLELESGenes that have 3 or more possible alleles

IA, IB, 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

SEX-LINKED TRAITS

Caused by a gene located on either an X or Y chromosome.

Ex. Colorblindness & Hemophilia

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Sex-linked Trait Problem• Example: Eye color in fruit flies• (red-eyed male) x (white-eyed female)

XRY x XrXr

• Remember: the Y chromosome in males does not carry traits.

• RR = red eyed• Rr = red eyed• rr = white eyed• XY = male• XX = female

XR

Xr Xr

Y

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STANDARD SYMBOLS USED IN PEDIGREES: