Mendel’s TheoryMendel’s Theory

Mendel: The man, the Mendel: The man, the myth , the legendmyth , the legend

Mendel’s HypothesesMendel’s Hypotheses Mendel found that there are two Mendel found that there are two

separate “heritable factors” for each separate “heritable factors” for each traittrait AllelesAlleles

Mendel’s Findings in Modern Mendel’s Findings in Modern TermsTerms

Dominant allelesDominant alleles

Recessive alleles Recessive alleles

HomozygousHomozygous

HeterozygousHeterozygous

GenotypeGenotype

PhenotypePhenotype

Laws of HeredityLaws of Heredity

Law of SegregationLaw of Segregation The two alleles for a trait segregate The two alleles for a trait segregate

when gametes are formedwhen gametes are formed Law of Independent AssortmentLaw of Independent Assortment

Found that inheritance of one trait does Found that inheritance of one trait does not influence inheritance of any other not influence inheritance of any other traittrait

Punnett SquaresPunnett Squares

A diagram that A diagram that predicts the predicts the expected outcome expected outcome of a genetic crossof a genetic cross

The cross of a long-stem (LL or Ll) The cross of a long-stem (LL or Ll) and short-stem (ll) plants involves a and short-stem (ll) plants involves a single pair of alternate single pair of alternate characteristics. Give the genotype characteristics. Give the genotype and phenotype ratios of the F1 and phenotype ratios of the F1 generation when a homozygous long-generation when a homozygous long-stem plant is crossed with a short stem plant is crossed with a short stem plant.stem plant.

Cross plants from the F1 generation Cross plants from the F1 generation in the above problem and determine in the above problem and determine the genotype and phenotype ratios the genotype and phenotype ratios of the F2 generation.of the F2 generation.

ProblemProblem In pea plants, inflated pods are dominant to In pea plants, inflated pods are dominant to

constricted pods. Show the cross between a constricted pods. Show the cross between a true-breeding inflated pod plant with a true-true-breeding inflated pod plant with a true-breeding constricted pod plant. What are breeding constricted pod plant. What are the expected phenotypes and in what the expected phenotypes and in what proportion?proportion?

ProblemProblem In goats, a recessive gene causes the goats In goats, a recessive gene causes the goats

to "faint" when they are startled. A farmer to "faint" when they are startled. A farmer breeds two goats (that have never fainted) breeds two goats (that have never fainted) and their first offspring faints two days after and their first offspring faints two days after its birth. What must the parent's genotypes its birth. What must the parent's genotypes have been? Show the cross to prove it.have been? Show the cross to prove it.

Determining Unknown Determining Unknown GenotypesGenotypes

Perform a test crossPerform a test cross An organism with an unknown genotype An organism with an unknown genotype

is crossed with a homozygous recessive is crossed with a homozygous recessive individualindividual

ExampleExample

A pea plant with A pea plant with yellow seeds has yellow seeds has an unknown an unknown genotype. It is genotype. It is crossed with a crossed with a plant with green plant with green seeds.seeds.

YyYy YyYy

YyYy YyYy

YyYy yyyy

YyYy yyyy

Y Y

y

y

Y y

y

y

Dihybrid ProblemDihybrid Problem

In peas, the allele for tall (T) plants is In peas, the allele for tall (T) plants is dominant to the allele for dwarf (t) plants and dominant to the allele for dwarf (t) plants and the allele for round (R) peas is dominant to the allele for round (R) peas is dominant to that for wrinkled (r) peas.that for wrinkled (r) peas.

Find both phenotypic for the results of the Find both phenotypic for the results of the following cross:following cross:

TtRrTtRr xx TtRrTtRr

Dominant or Recessive?Dominant or Recessive?

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Family GeneticsFamily Genetics