ObserviObserving ng

PatternPatterns s in in

InheriteInherited Traitsd TraitsChapter 7Chapter 7

Skin ColorSkin Color

Terms Used in Modern Terms Used in Modern GeneticsGenetics

Heredity- Heredity- characteristics passing from characteristics passing from parents to offspring through genesparents to offspring through genes

GenesGenes Each gene has a specific Each gene has a specific locuslocus on a on a

chromosomechromosome Heterozygous (Aa or Bb)Heterozygous (Aa or Bb) Homomzygous (AA or BB)Homomzygous (AA or BB)

Gregor Mendel

GeneticsGenetics

An allele is An allele is dominantdominant if its effect if its effect masks the effect of a masks the effect of a recessiverecessive allele paired with itallele paired with it

Mendel’s Law of Mendel’s Law of SegregationSegregation

Only one of the Only one of the 2 alleles gets 2 alleles gets put into each put into each gametegamete

Fig. 11-5, p. 172

homozygous dominant parent

homozygous recessive parent

(chromosomes duplicated before

meiosis)

meiosis I

meiosis II

(gametes) (gametes)

fertilization produces heterozygous offspring

Segregation of Alleles at Segregation of Alleles at a Gene Locusa Gene Locus

genotype

phenotype

Construction of a Construction of a Punnett SquarePunnett Square

Punnett squarePunnett square

Dihybrid CrossDihybrid Cross

2 loci 2 loci

AABBAABB x x aabbaabb FF22 phenotype ratio is 9:3:3:1 phenotype ratio is 9:3:3:1

Mendel’s Law Mendel’s Law of Independent of Independent

AssortmentAssortment Mendel’s law ofMendel’s law of independent independent

assortmentassortment One trait does not influence the One trait does not influence the

inheritance of the otherinheritance of the other Exception: linked genesException: linked genes

Fig. 11-9a, p. 175

parent plant homozygous for purple

flowers and long

stems

parent plant homozygous

for white flowers and short stems

AABB aabb

AB x ab

Fig. 11-9b, p. 175

What gametes will they form?

AaBb AaBb AaBb

F1 generation

Fig. 11-9c, p. 175

AB Ab aB ab

AB AABB AABb AaBB AaBb

Ab AABb AAbb AaBb Aabb

aB AaBB AaBb aaBB aaBb

ab AaBb Aabb aaBb aabb

D Out of 16 possible genetic outcomes of this dihybrid cross, 9 will result in plants that are purple-flowered and tall; 3, purple-flowered and short; 3, white-flowered and tall; and 1, white-flowered and short. The ratio of phenotypes of this dihybrid cross is 9:3:3:1.

CodominanceCodominance Two nonidentical alleles of a gene are Two nonidentical alleles of a gene are

both fully expressed in heterozygotes, both fully expressed in heterozygotes, so neither is dominant or recessiveso neither is dominant or recessive

Multiple allele systemsMultiple allele systems

Incomplete DominanceIncomplete Dominance One allele is not fully dominant over its One allele is not fully dominant over its

partnerpartner

EpistasisEpistasis

EpistasisEpistasis Two or more gene products influence a Two or more gene products influence a

traittrait Typically, one gene product suppresses Typically, one gene product suppresses

the effect of anotherthe effect of another

Epistasis in Coat ColorsEpistasis in Coat Colors

PleiotropyPleiotropy

PleiotropyPleiotropy One gene One gene

product product influences two or influences two or more traitsmore traits

Example:Example: Marfan Marfan syndromesyndrome

Genes and the Genes and the EnvironmentEnvironment

Expression of some genes is affected Expression of some genes is affected by environmental factors such as by environmental factors such as temperature, altitude, or chemical temperature, altitude, or chemical exposureexposure