Fundamentals of Genetics

Genetics- Terms to know Genetics- studies how characteristics are transmitted from parent to offspring Trait- genetically determined variant of a characteristic (pink or white)

Gregor Mendel (1822-1884) Old monk who studied peas (Pisum sativum)

Mendel’s Pea Plants- Characteristics Mendel observed 7 different characteristics of pea plants, each with 2 different traits Plant height Traits: tall or short Flower position along stem Traits: axial or terminal Flower color Traits: Purple or white

Mendel’s Pea Plants- Characteristics Mendel observed 7 different characteristics of pea plants, each with 2 different traits Pod color Traits: green or yellow Pod appearance Traits: inflated or constricted Seed texture Traits: Round or wrinkled Seed color Traits: Yellow or green

Mendel’s Garden Peas- Terms Pollination- when male pollen (from anthers) is transferred to female reproductive parts (stigma) of a flower (sexual reproduction in plants)

Mendel’s Garden Peas- Terms Self-pollination- male pollen of a flower is transferred to female stigma of flowers on the same plant Common in pea plants Cross pollination- transfer of male pollen to a stigma of a different plant

Mendel’s Garden Peas- Terms Self-pollination- male pollen of a flower is transferred to female stigma of flowers on the same plant Common in pea plants Cross pollination- transfer of male pollen to a stigma of a different plant

Mendel’s Garden Peas- Terms To control his study, Mendel had to prevent self- pollination sometimes. To cross- pollinate, he would manually transfer pollen from one plant to another then cut off the anthers of the flowers.

Mendel’s Garden Peas- Terms True-breeding- plants that always produce offspring with a certain trait when self-pollinated Ex. A plant with purple flowers that always produces offspring with purple flowers when self-pollinated Produced by self-pollinating plants for many generations until all offspring share the same trait

Mendel’s Garden Peas- Terms P generation- parent generation F1 generation- first generation of offspring (generation after P) F2 generation- second generation of offspring (generation after F1)

Mendel’s Experiments Self-pollinated plants until they were true-breeding Seeds that always produce purple flowers Seeds that always produce white flowers Cross-pollinated true- breeding plants (P generation) with contrasting traits Purple flowers X white flowers Observed offspring (F1 generation) All purple Self-pollinated F1 Purple X Purple Observed F2 3 purple:1 white ratio

Mendel’s Conclusions Keep in mind… no one knew what genes were. Mendel hypothesized that there were alleles in the pea plants that controlled traits He called them factors We now call them alleles Since each characteristic had two traits, Mendel believed that each allele came in pairs.

Modern Genetics Molecular genetics- study of the structure and function of chromosomes and genes Gene- segment of DNA on a chromosome that controls a particular heredity of a trait Occur in pairs Allele- each of two or more alternative forms of a gene Represented by letters Capital letters = dominant alleles P = purple flowers Lower case letters = recessive alleles p = white flowers

Mendel’s Conclusions Recessive and Dominant Traits . Recessive and Dominant Traits One allele in a pair prevents the other from having an effect Dominant allele- masked the allele for the other trait in a pair Recessive allele- allele that is masked by a dominant allele

Gamete- sex cell with ½ the number of chromosomes as parent. Has one allele for each trait. Formed during meiosis

Mendel’s Conclusions Law of Segregation . Law of Segregation Paired alleles separate during the formation of gametes When two gametes combine, offspring have tow alleles for each characteristic

Just because you have one trait, doesn’t mean you have another. Mendel’s Conclusions . Law of Independent Assortment alleles separate independently of one another during the formation of gametes alleles for individual characteristics are not connected For example, tall (dominant) plants do not always have purple (dominant) flowers Just because you have one trait, doesn’t mean you have another.

Phenotype- what the organisms looks like Genotype- what alleles the organisms has Letters depict the alleles Genotype PP = phenotype purple Genotype Pp = phenotype purple Genotype pp = phenotype white

Homozygous- when both alleles are the same Aka. Purebred Heterozygous- when both alleles are different Aka. hybrid