Chapter 10 Patterns of Inheritance College Prep Biology Mr. Martino

10.1 Mendel Modern genetics began in 1860’s when Mendel discovered fundamental principles of genetics studied physics, math, and chemistry at U. of Vienna Lived and worked in an abbey in Brunn, Austria Was very accurate and mathematically rigorous Worked with peas

Garden peas were a fortunate choice Easy to grow True breeding Rapid growth and reproduction Inexpensive Required little space Able 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 trait Mendel 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)

Probability: the chance that each outcome of a given event can occur 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 recessive Used to determine genotype of the unknown

Principle of Independent Assortment Mendel wondered if traits were inherited together or if each characteristic was inherited independently He crossed two traits together – and each one was inherited separately Results 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 forms Dominant 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 alleles People only inherit 1pair Ex. Human blood types Codominance: two alleles are expressed, sharing dominance Ex. A and B blood types, roan coats, checkered chickens

Polygenic inheritance (continuous variation): two or more pairs of genes determine genotype Vary in a population along a continuum Ex. Skin color, hair color, eye color, height One pair of heterozygotes can produce a wide range of skin pigmentation

Environmental Effects on Phenotype Occasionally, environment causes variations in phenotype Ex. Himalayan rabbits & cats and Siamese cats Heat 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