college prep biology mr. martino. modern genetics began in 1860’s when mendel discovered...
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CHAPTER 10PATTERNS OF INHERITANCE
College Prep Biology
Mr. 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 F2
Ex. 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