1. Chapter 10 Patterns 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. 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

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