Mendelian GeneticsMendelian GeneticsChapter 6.3 & 6.4Chapter 6.3 & 6.4

Gregor MendelGregor Mendel Gregor Mendel: Father of genetics, Gregor Mendel: Father of genetics,

studied pea plants.studied pea plants.

Genetics:Genetics: study of hereditystudy of heredity Heredity:Heredity: transmission of genetic transmission of genetic

characteristics from parents to offspringcharacteristics from parents to offspring Trait:Trait: a characteristic controlled by genes a characteristic controlled by genes

Ex) Ex) tongue roller, hair color, eye color, etc.tongue roller, hair color, eye color, etc.

1822-18841822-1884

Recessive and Dominant TraitsRecessive and Dominant Traits

Dominant:Dominant: A trait that A trait that covers or masks another trait.covers or masks another trait.

Recessive:Recessive: A trait that is A trait that is covered or masked when covered or masked when paired with a dominant trait.paired with a dominant trait.

Chromosomes and GenesChromosomes and Genes Gene:Gene: A segment of DNA A segment of DNA

on a chromosome that on a chromosome that controls a particular trait.controls a particular trait.

Allele:Allele: alternative form alternative form of a gene, one is of a gene, one is dominant and one dominant and one is recessive.is recessive. An individualAn individual inherits 2 alleles forinherits 2 alleles for every gene – 1 from every gene – 1 from mom and 1 from dadmom and 1 from dad

In genetics, alleles are In genetics, alleles are represented by letters.represented by letters.

Dominant allelesDominant alleles: represented : represented with a capital letterwith a capital letter Example: F = dominant alleleExample: F = dominant allele

for purple flowersfor purple flowers Recessive allelesRecessive alleles: represented : represented

with a lower case letterwith a lower case letter Example: f = recessive allele that Example: f = recessive allele that

will yield white flowerswill yield white flowers

F f

Homologous chromosomes

Different alleles for the same gene

MendelMendel’’s Lawss Laws Law of SegregationLaw of Segregation:: during gamete formation during gamete formation

(MEIOSIS) pairs of alleles separate and are (MEIOSIS) pairs of alleles separate and are randomly united during fertilizationrandomly united during fertilization Offspring receives 1 allele from each parentOffspring receives 1 allele from each parent

Segregation happens

here during Anaphase 1

MendelMendel’’s Laws Conts Laws Cont’’dd Law of Independent Assortment:Law of Independent Assortment: allele pairs allele pairs

separate independently of one another during separate independently of one another during gamete formation. gamete formation.

This law would be violated, for example, if the “G" allele was always associated with the “Y" allele (and thus eliminating the possibility of Gy and gY gametes).

O

R

Chapter 6.4 & 6.5Chapter 6.4 & 6.5

Genotype and PhenotypeGenotype and Phenotype Genotype:Genotype: the genetic makeup the genetic makeup

of an organismof an organismConsists of 2 alleles Consists of 2 alleles inherited from parentsinherited from parents

Phenotype:Phenotype: the physical the physical appearance of an organism appearance of an organism resulting from genotyperesulting from genotype

Genotype and PhenotypeGenotype and Phenotype

Genotype:Genotype: FFFF FfFf ffff

Phenotype:Phenotype:

Purple flowersPurple flowers

Purple flowersPurple flowers

White flowersWhite flowers

F = allele for purple flowers (dominant) f = allele for white flowers (recessive)

Homozygous:Homozygous: both alleles are alike both alleles are alikeHomozygous Dominant: Homozygous Dominant: has 2 has 2 dominant alleles (FF)dominant alleles (FF)

Homozygous Recessive: Homozygous Recessive: has 2 has 2 recessive alleles (ff)recessive alleles (ff)

Heterozygous:Heterozygous: each allele differs (Ff) each allele differs (Ff)Heterozygous organisms usually Heterozygous organisms usually display the dominant phenotypedisplay the dominant phenotype

Always write capital letter first!Always write capital letter first!

Monohybrid CrossesMonohybrid Crosses

Monohybrid Cross:Monohybrid Cross: a cross a cross that involves 1 pair of that involves 1 pair of contrasting traitscontrasting traits

We use diagrams called We use diagrams called Punnett square to predict Punnett square to predict offspring traits.offspring traits.

Create a Create a box & add box & add parent parent genotypesgenotypes

Fill in potential Fill in potential offspring offspring genotypes. genotypes.

Offsp

ring

Genotypic and Phenotypic RatiosGenotypic and Phenotypic Ratios Genotypic Ratio:Genotypic Ratio: ratio of genotypes that ratio of genotypes that

will appear in the offspringwill appear in the offspringExpressed in order from Expressed in order from Most Most

Dominant Dominant to to Most RecessiveMost Recessive 1 RR : 2 Rr : 1 rr1 RR : 2 Rr : 1 rr

Phenotypic Ratio:Phenotypic Ratio: ratio of phenotypes that ratio of phenotypes that will appear in the offspringwill appear in the offspring

Also expressed in order from Also expressed in order from Most Most Dominant Dominant to to Most RecessiveMost Recessive

3 Red : 1 white3 Red : 1 white