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Gregory Johann Mendel 1822- 1884 Austrian monk Experimented with pea plants He thought that ‘heritable factors’ (genes) retained their individuality generation.

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Presentation on theme: "Gregory Johann Mendel 1822- 1884 Austrian monk Experimented with pea plants He thought that ‘heritable factors’ (genes) retained their individuality generation."— Presentation transcript:

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2 Gregory Johann Mendel Austrian monk Experimented with pea plants He thought that ‘heritable factors’ (genes) retained their individuality generation after generation

3 Terms to Know and Use Gene - a heritable feature: i.e. flower color coded for on a chromosome Trait - variant for a gene: i.e. a purple flower, determined by alleles Dominant trait - expressed over recessive trait when both are present Recessive trait - not expressed when the dominant trait is present

4 Allele - a variation of a gene responsible for different traits, often expressed as A or a Locus - location of a gene,or allele, on a chromosome Chromosome - strand of DNA that codes for genes Haploid - one copy of a chromosome Diploid - two copies of a chromosome Gamete - a spermatozoa or oocyte (egg) cell, they are haploid

5 Zygote – diploid, fertilized egg (2N) Genotype - the type of alleles on a chromosome: genetic makeup Phenotype - the physical result of a genotype ex. blue eyes Hybrid – an organism with two different alleles

6 Garden Pea Experiments Mendel disagreed with the “Blending Theory” of inheritance. Started with34 kinds peas

7 Pea Characteristics Trait on the left is dominant. Trait on the right is recessive. DominantRecessive

8 Mendel Determined that Alleles Separate During Meiosis Parents: Assume Round is S and the other form is s. Punnett Square used to predict the Genotype of Offspring SS SSs Smooth Ss Smooth sSs Smooth ss Smooth So, cross purebred smooth peas with a plant having the recessive wrinkled form of the peas and see the result No Blend as expected!

9 Mendel’s Hypotheses 1.There are alternate forms of ‘genes’ = alleles 2.For each trait, organisms have 2 genes, one from mom & one from dad 3.Sperm and egg each carry 1 allele/trait because alleles separate 4.Dominant alleles mask the effects or recessive alleles

10 AA A A AA Father contributes: Mother contributes: or Pure Breds Crosses – have all dominant traits

11 aa A A AaAa AaAa AaAa AaAa Father contributes: Mother contributes: or Pure Bred Dominant Father breeds with Pure Bred Recessive Mother

12 Purebred Dominant + Purebred Recessive a Hybrid ----> Aa

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14 Describing Alleles Properly Aa means the critter is HETEROZYGOUS It has two different alleles: A & a The critter is not a purebred but a hybrid AA or aa means the critter has the same two alleles, so it is HOMOZYGOUS

15 Test Cross

16 Mendel's Laws of Inheritance 1.Genes produce traits (characteristics) 2.Law of Segregation alleles are separated during meiosis into different eggs/sperm 3.Law of Independent Assortment suggested that other alleles do not influence how other alleles come together (how they assort) (demonstrated with a “dihybrid cross”)


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