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College Prep Biology Mr. Martino.  Modern genetics began in 1860’s when Mendel discovered fundamental principles of genetics  studied physics, math,

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Presentation on theme: "College Prep Biology Mr. Martino.  Modern genetics began in 1860’s when Mendel discovered fundamental principles of genetics  studied physics, math,"— Presentation transcript:

1 College Prep Biology Mr. Martino

2  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  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  Monohybrid cross: experiment that tracks the inheritance of a single trait  Mendel crossed white flowers with purple and all F 1 (first filial) generation were purple  Then he crossed 2 F 1 ’s and some F 2 ’s were white F 1 ’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  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  Incomplete dominance: causes the appearance of a third phenotype in the hybrid (F 1 generation)  Parental phenotypes reappear in F 2  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  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


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