Chapter 10 Patterns of Inheritance

1. Chapter 10Patterns of Inheritance College Prep Biology Mr. Martino

2. 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

3. 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

4. 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

5. 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

6. Mendel also developed the Principle of Dominance • certain traits are masked (recessive) by others (dominant)

7. 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

8. 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

9. Dihybrid Cross: genetic cross showing the inheritance of two traits with two contrasting forms • Dominant and recessive

10. 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

11. 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

12. 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

13. 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