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Mendel’s Law of Heredity

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Presentation on theme: "Mendel’s Law of Heredity"— Presentation transcript:

1 Mendel’s Law of Heredity
Chapter 10, Section 1

2 The Father of Genetics Gregor Mendel’s experiments founded many of the principles of Genetics we use today He was a mathematician, he studied statistics He was a teacher He was a gardener


4 Heredity = characteristics transmitted from 2 parents to their offspring
Trait = variant of a certain characteristic based on genetics


6 Mendel noticed plant height, flower position, pod color & appearance, seed color & appearance, and flower color Gametes = sex cells Fertilization = process of uniting female gamete & male gamete Zygote = fertilized cell Pollination = transfer of pollen from male reproductive organ to the female reproductive organ


8 Mendel’s Monohybrid Crosses
Mendel crossed pea plants, testing one trait at a time Ex: Flower Color Mendel crossed a purebred purple flower pea with a purebred white flower pea Hybrid = offspring of parents that have different forms of a trait Purebred = produces offspring w/ the same trait when self-fertilized

9 F1 generation = offspring of the parent generation, first generation
P generation = parents F1 generation = offspring of the parent generation, first generation F2 generation = offspring of a F1 mating with another F1, second generation Cerval & Savannah cat


11 Dominant & Recessive Offspring get two copies of genes for a trait (ONE FROM MOM, ONE FROM DAD), sometimes one copy dominates over the other copy Trait = variant of a certain characteristic based on genetics Genes = found in chromosomes, made of DNA (they make you like you, they make peas look like peas!) Allele = alternative versions of a gene Dominant = an allele that dominates over the recessive allele; only need one copy to be expressed Recessive = an allele that gets masked if a dominant is paired with it; must have two copies to be expressed


13 What happened to the white flowers in the F1 generation
What happened to the white flowers in the F1 generation? Which color is the dominant color?

14 The recessive white color was “masked” in the F1 generation by the dominant purple color, but it reappeared again in the F2 generation

15 Each individual organism will have 2 alleles for a trait (remember, one from each parent)
Homozygous = an organism with 2 identical alleles for a trait Heterozygous = an organism with 2 different alleles for a trait

16 Alleles for flower color are represented by letters:
P = dominant allele for purple flowers p = recessive allele for white flowers Be careful, representations are case sensitive!!! Genotype = allele combination Phenotype = the way an organism looks, trait that is expressed

17 What was the genotype of the purple flower from the P Generation?
PP What was the genotype of the white flower from the P Generation? pp How do we figure the probability of the genotypes of the F1 Generation? Monohybrid Cross (involves one trait)

18 Monohybrid Cross


20 Test Cross Used to determine an unknown dominant genotype.
Cross the unknown with a homozygous recessive and look at the phenotype results. 100% dominant means the genotype was homozygous dominant 50% dominant : 50% recessive means the genotype was heterozygous

21 Mendel’s Law of Heredity Cont.
Chapter 10, Section 1

22 Law of Segregation Each individual has 2 alleles for each gene
During gamete (sex cell) production an individual separates its pairs of alleles Each gamete gets one allele !!! Alleles pair up again when one gamete joins with another gamete during fertilization

23 Law of Independent Assortment
Genes for different traits are inherited independently of one another Ex: Pea plants can be tall (T) or short (t) and they can also have purple flowers (P) or white flowers (p) Just because a pea plant has the dominant trait for height does not mean that it will have the dominant trait for flower color too

24 Dihybrid Crosses Round seeds (R), wrinkled seeds (r)
Purple flowers (P), white flowers (p) An individual whose genotype is RRPP has what phenotype? Round seeds, purple flowers An individual whose genotype is rrpp has what phenotype? Wrinkled seeds, white flowers An individual whose genotype is RrPp has what phenotype?

25 2 characteristics per cross
Punnett Square has 16 boxes

26 Method to organize alleles on a Punnett Square
F first O outter I inner L last

27 R= round r= wrinkled P= purple flowers p= white flowers Please cross a homozygous round, heterozygous purple plant with a homozygous wrinkled, heterozygous purple plant.



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