Mendel’s Law of Heredity Chapter 10, Section 1

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

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

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

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

P generation = parents P generation = parents F1 generation = offspring of the parent generation, first generation F1 generation = offspring of the parent generation, first generation F2 generation = offspring of a F1 mating with another F1, second generation F2 generation = offspring of a F1 mating with another F1, second generation

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 Offspring get two copies of genes for a trait (ONE FROM MOM, ONE FROM DAD), sometimes one copy dominates over the other copy Allele = alternative forms of a gene Allele = alternative forms of a gene Dominant = an allele that dominates over the recessive allele Dominant = an allele that dominates over the recessive allele Recessive = an allele that gets masked if a dominant is paired with it Recessive = an allele that gets masked if a dominant is paired with it

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

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

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

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

What was the genotype of the purebred purple flower from the P Generation? What was the genotype of the purebred purple flower from the P Generation? PP – homozygous dominant PP – homozygous dominant What was the genotype of the purebred white flower from the P Generation? What was the genotype of the purebred white flower from the P Generation? pp – homozygous recessive pp – homozygous recessive How do we figure the probability of the genotypes of the F1 Generation? How do we figure the probability of the genotypes of the F1 Generation? Monohybrid Cross (involves one trait) – Punnett Square Monohybrid Cross (involves one trait) – Punnett Square

Monohybrid Cross

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

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

Law of Independent Assortment Genes for different traits are inherited independently of one another 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) 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 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

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

2 characteristics per cross 2 characteristics per cross Punnett Square has 16 boxes Punnett Square has 16 boxes

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