Genetics Introduction

Genetics The study of heredity - the transmission of characteristics from parents to offspring The study of heredity - the transmission of characteristics from parents to offspring * Gregor Mendel * Gregor Mendel ( ) ( ) –First person to scientifically attempt to discover the laws of heredity Mendel’s work went unrecognized until 16 yrs after his death…

Gregor Mendel( )

Experimental Design Step 1 - Allowed plants to self-pollinate to ensure plants were true-breeding for a particular trait. Step 1 - Allowed plants to self-pollinate to ensure plants were true-breeding for a particular trait. –All the offspring the same (a purebred) –Called his parental purebreds the P generation Did you know?? Peas have “complete” flowers – both male and female parts. Some plant’s flowers are called “imperfect” – have either male or female parts but not both

Experimental Design Step 2 – Cross- pollinated two different purebred P generation flowers Step 2 – Cross- pollinated two different purebred P generation flowers 1 st generation offspring are called F 1 1 st generation offspring are called F 1 Step 3 – Allowed F 1 to self pollinate Step 3 – Allowed F 1 to self pollinate 2 nd generation are F 2 2 nd generation are F 2 F stands for filial means offspring

Repeated experiment with 7 different characteristics

Discovered some traits were dominant and some recessive Dominant – a trait that is expressed when it is homozygous or heterozygous. (PP or Pp) Dominant – a trait that is expressed when it is homozygous or heterozygous. (PP or Pp) Recessive – does not turn up in the F1 generation (pp) Recessive – does not turn up in the F1 generation (pp)

Homozygous verses Heterozygous Homozygous- organism has two genes for the same trait that are alike (PP or pp) Homozygous- organism has two genes for the same trait that are alike (PP or pp) Heterozygous- the two genes for a trait are different (Pp) Heterozygous- the two genes for a trait are different (Pp) PP pp Pp

Genotype verses Phenotype Genotype-What the genes actually say- gene combination in an organism (alleles) Genotype-What the genes actually say- gene combination in an organism (alleles) ex: GG, Gg or gg ex: GG, Gg or gg Phenotype - physical appearance Phenotype - physical appearance ex: purple or white ex: purple or white

Law of Dominance When parents with contrasting genes (alleles) for traits are crossed, the effect of one gene is often seen in the offspring. Dominant-Capital Letter-When present, this gene is expressed. It masks the recessive trait. Recessive-Lower case letter-Masked by dominant trait.

Punnett Squares A format that simplifies our understanding of how genes are transmitted to offspring.

Examples of Punnett Squares TT is Tall, Tt is Tall, and tt is short Short pea plants crossed with short pea plants. t t t t tt t t GENOTYPE: 100 % tt PHENOTYPE: 100% short

Another Example of Punnett Squares TT is Tall, Tt is Tall, and tt is short Pure Breeding Tall with Pure Breeding Tall T T T T TT TT GENOTYPE: 100 % TT PHENOTYPE: 100 % Tall

Another Example of Punnett Squares TT is Tall, Tt is Tall, and tt is short Heterozygous Tall with Heterozygous Tall TTtTt TtTtt T T t t GENOTYPE: 25% TT 50% Tt 25% tt PHENOTYPE: 75% Tall 25% Short

Another Example of Punnett Squares TT is Tall, Tt is Tall, and tt is short Heterozygous Tall with homozygous short TtTtt TtTtt T t t t GENOTYPE: 50% Tt 50% tt PHENOTYPE: 50% Tall 50% Short

Dihybrid Cross Challenge A dihybrid cross involves two alleles per trait for two traits, for a total of four alleles A dihybrid cross involves two alleles per trait for two traits, for a total of four alleles

Dihybrid Cross A dihybrid cross involves two alleles per trait for two traits, for a total of four alleles A dihybrid cross involves two alleles per trait for two traits, for a total of four alleles What are the phenotypes for this dihybrid cross?

Note: this 9:3:3:1 ratio is typical for parents that are both heterozygous individuals for the traits.