CHAPTER 10PATTERNS OF INHERITANCE

College Prep BiologyMr. Martino

10.1 MENDEL

Modern genetics began in 1860’s when Mendel discovered fundamental principles of geneticsstudied physics, math, and

chemistry at U. of ViennaLived and worked in an abbey in

Brunn, Austria Was very accurate and

mathematically rigorous Worked with peas

Garden peas were a fortunate choiceEasy to growTrue breedingRapid growth and

reproduction InexpensiveRequired little spaceAble to control repro.Several contrasting traits (he

used 7)None of the traits were

linked on same chromosomes

IMPORTANT TERMS Genes: units of hereditary information with specific

loci (locations) on chromosomes Alleles: all the different molecular forms of the same

gene True-breeding: (true/pure) identical alleles for a

specific trait in the pair Hybrid: (heterozygous) alleles of the pair are different Homozygous: pair of alleles are identical (purebred) Heterozygous: pair of alleles are different (hybrid) Dominant: allele of the pair that masks the second

allele Recessive: allele of the pair that gets hidden by the

dominant Phenotype: expressed (observed) traits Genotype: actual genetic (genes) makeup

10.2 PRINCIPLE OF SEGREGATION

Monohybrid cross: experiment that tracks the inheritance of a single traitMendel crossed white flowers

with purple and all F1 (first filial) generation were purple

Then he crossed 2 F1’s and some F2’s were white F1’s must carry 2 genes

Principle of Segregation: pairs of genes separate during meiosis; fertilization pairs them (homologs)Applies to all sexually

reproducing organisms

Mendel also

developed the Principle of Dominance certain traits

are masked (recessive) by others (dominant)

Punnett square: tool used to

predict and calculate the probability outcomes

Probability: the chance that each outcome of a given event can occur

Testcross: a mating between an individual of unknown genotype with a homozygous recessiveUsed to determine genotype of the

unknown

PRINCIPLE OF INDEPENDENT ASSORTMENT

Mendel wondered if traits were inherited together or if each characteristic was inherited independentlyHe crossed two traits together – and each one was

inherited separatelyResults led to Principle of Independent

Assortment: each pair of alleles segregates independently during gamete formation

A conventional dihybrid cross (two heterozygous parents) results in a 9:3:3:1 phenotypic ratio

Dihybrid Cross: genetic cross showing the inheritance of two traits with two contrasting formsDominant and

recessive

10.3 DOMINANCE RELATIONS

Incomplete dominance: causes the appearance of a third phenotype in the hybrid (F1 generation)Parental phenotypes

reappear in F2Ex. Pink snapdragons,

hypercholesterolemia, sickle-cell anemia, blue chickens

Multiple alleles: when genes have more than 2 allelesPeople only inherit 1pair

Ex. Human blood types Codominance: two alleles

are expressed, sharing dominanceEx. A and B blood types, roan

coats, checkered chickens

Polygenic inheritance

(continuous variation): two or more pairs of genes determine genotypeVary in a population along

a continuumEx. Skin color, hair color,

eye color, heightOne pair of heterozygotes

can produce a wide range of skin pigmentation

ENVIRONMENTAL EFFECTS ON PHENOTYPE

Occasionally, environment causes variations in phenotypeEx. Himalayan rabbits &

cats and Siamese catsHeat causes production of

an enzyme needed to form melanin (skin pigment)

Fur growing in warmer body areas is lighter than fur of cooler regions

Hydrangea flowers change color based upon soil acidity