Mendel’s Law of Mendel’s Law of HeredityHeredity

Chapter 10, Section 1Chapter 10, Section 1

The Father of GeneticsThe Father of Genetics

Gregor Mendel’s experiments Gregor Mendel’s experiments founded many of the principles of founded many of the principles of Genetics we use todayGenetics we use today

He was a He was a mathematicianmathematician, he , he studied statisticsstudied statistics

He was a teacherHe was a teacher He was a gardenerHe was a gardener

HeredityHeredity = = characteristics characteristics transmitted transmitted from 2 parents from 2 parents to their to their offspringoffspring

TraitTrait = variant = variant of a certain of a certain characteristic characteristic based on based on geneticsgenetics

Mendel noticed Mendel noticed plant heightplant height, , flower flower positionposition, , pod color & appearancepod color & appearance, , seed color & appearanceseed color & appearance, and , and flower flower colorcolor

GametesGametes = sex cells = sex cells FertilizationFertilization = process of uniting = process of uniting

female gamete & male gametefemale gamete & male gamete ZygoteZygote = fertilized cell = fertilized cell PollinationPollination = transfer of pollen = transfer of pollen

from male reproductive organ to the from male reproductive organ to the female reproductive organfemale reproductive organ

Mendel’s Monohybrid Mendel’s Monohybrid CrossesCrosses

Mendel crossed pea Mendel crossed pea plants, testing one plants, testing one trait at a timetrait at a time

Ex: Flower ColorEx: Flower Color– Mendel crossed a Mendel crossed a

purebred purple purebred purple flower pea with a flower pea with a purebred white purebred white flower peaflower pea

HybridHybrid = offspring = offspring of parents that have of parents that have different forms of a different forms of a traittrait

PurebredPurebred = = produces offspring produces offspring w/ the same trait w/ the same trait when self-fertilized when self-fertilized

P generationP generation = parents = parents F1 generationF1 generation = offspring of the = offspring of the

parent generation, parent generation, first generationfirst generation F2 generationF2 generation = offspring of a F1 = offspring of a F1

mating with another F1, mating with another F1, second second generationgeneration

Dominant & RecessiveDominant & Recessive Offspring get Offspring get two copies of genestwo copies of genes for a trait for a trait

(ONE FROM (ONE FROM MOMMOM, ONE FROM , ONE FROM DAD)DAD), , sometimes one copy dominates over the sometimes one copy dominates over the other copyother copy

TraitTrait = variant of a certain characteristic = variant of a certain characteristic based on geneticsbased on genetics

Genes Genes = found in chromosomes, made of = found in chromosomes, made of DNADNA (they make you like you, they make (they make you like you, they make peas look like peas!)peas look like peas!)

AlleleAllele = alternative versions of a gene = alternative versions of a gene DominantDominant = an allele that = an allele that dominatesdominates over over

the recessive allele; only need one copy to the recessive allele; only need one copy to be expressedbe expressed

RecessiveRecessive = an allele that gets masked if a = an allele that gets masked if a dominant is paired with it; must have two dominant is paired with it; must have two copies to be expressedcopies to be expressed

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

The The recessiverecessive white color was white color was “masked” in the F1 generation by “masked” in the F1 generation by the the dominantdominant purple color, but it purple color, but it reappeared again in the F2 reappeared again in the F2 generationgeneration

Each individual organism will Each individual organism will have have 2 alleles2 alleles for a trait for a trait (remember, one from each (remember, one from each parent)parent)

HomozygousHomozygous = an organism = an organism with 2 with 2 identical allelesidentical alleles for a trait for a trait

HeterozygousHeterozygous = an organism = an organism with 2 with 2 different allelesdifferent alleles for a trait for a trait

Alleles for flower color are Alleles for flower color are represented by letters:represented by letters:

PP = dominant allele for purple = dominant allele for purple flowersflowers

p p = recessive allele for white = recessive allele for white flowersflowers

Be careful, representations are Be careful, representations are case sensitive!!!case sensitive!!!

GenotypeGenotype = allele combination = allele combination PhenotypePhenotype = the way an organism = the way an organism

looks, trait that is expressedlooks, trait that is expressed

What was the genotype of the purple What was the genotype of the purple flower from the P Generation?flower from the P Generation?

PPPP What was the genotype of the white What was the genotype of the white

flower from the P Generation?flower from the P Generation? pppp How do we figure the probability of the How do we figure the probability of the

genotypes of the F1 Generation?genotypes of the F1 Generation? Monohybrid Cross (involves one trait)Monohybrid Cross (involves one trait)

Monohybrid CrossMonohybrid Cross

Test CrossTest Cross

Used to determine an unknown Used to determine an unknown dominant genotype.dominant genotype.– Cross the unknown with a Cross the unknown with a

homozygous recessive and look at homozygous recessive and look at the phenotype results.the phenotype results. 100% dominant means the genotype 100% dominant means the genotype

was homozygous dominantwas homozygous dominant 50% dominant : 50% recessive means 50% dominant : 50% recessive means

the genotype was heterozygousthe genotype was heterozygous

Mendel’s Law of Mendel’s Law of Heredity Cont.Heredity Cont.

Chapter 10, Section 1Chapter 10, Section 1

Law of SegregationLaw of Segregation

Each individual has Each individual has 2 alleles 2 alleles for for each geneeach gene

During During gamete (sex cell) gamete (sex cell) production an individual production an individual separates its pairs of alleles separates its pairs of alleles

Each gamete gets one allele !!!Each gamete gets one allele !!! Alleles pair up again when one Alleles pair up again when one

gamete joins with another gamete joins with another gamete during gamete during fertilizationfertilization

Law of Independent Law of Independent AssortmentAssortment

Genes for different Genes for different traits are inherited traits are inherited independentlyindependently of one of one anotheranother

Ex: Pea plants can be Ex: Pea plants can be tall (T) or short (t)tall (T) or short (t) and and they can also have they can also have purple flowers (P) or purple flowers (P) or white flowers (p)white flowers (p)

Just because a pea Just because a pea plant has the dominant plant has the dominant trait for height trait for height does does notnot mean that it will mean that it will have the dominant trait have the dominant trait for flower color toofor flower color too

Dihybrid CrossesDihybrid Crosses

Round seeds (Round seeds (RR), wrinkled seeds (), wrinkled seeds (rr)) Purple flowers (Purple flowers (PP), white flowers (), white flowers (pp)) An individual whose An individual whose genotypegenotype is is RRPPRRPP

has what has what phenotypephenotype?? Round seeds, purple flowersRound seeds, purple flowers An individual whose An individual whose genotypegenotype is is rrpprrpp

has what has what phenotypephenotype?? Wrinkled seeds, white flowersWrinkled seeds, white flowers An individual whose An individual whose genotypegenotype is is RrPpRrPp

has what has what phenotypephenotype?? Round seeds, purple flowersRound seeds, purple flowers

2 characteristics per cross2 characteristics per cross Punnett Square has 16 boxesPunnett Square has 16 boxes

Method to organize alleles on a Method to organize alleles on a Punnett SquarePunnett Square

FF first first OO outter outter II inner inner LL last last

R= roundR= round r= wrinkledr= wrinkled P= purple flowers P= purple flowers p= white p= white

flowersflowers

Please cross a homozygous round, Please cross a homozygous round, heterozygous purple plant with a heterozygous purple plant with a homozygous wrinkled, heterozygous homozygous wrinkled, heterozygous purple plant.purple plant.