Genetics: the Scientific Study of Inheritance Mendelian Genetics

Gregory Mendel: Father of Genetics 1860’s people supported one of two notions Blending theory of Inheritance Pangenesis The work of Gregory Mendel would refute both!

Gregory Mendel: Father of Genetics Austrian Monk (1822-84) Studied how traits were passed from one generation to another Used pea plants since: Express contrasting traits (tall/short, smooth/wrinkled) Easy to grow and control reproduction Self pollination or cross-pollination (pollen from one plant to pistil of another plant)

Gregory Mendel: Father of Genetics First Experiment: Used Pure bred Tall and Pure Bred Short Cross-pollinated them, harvested seeds and planted them First Generation plants (F1), were ALL tall He repeated with several contrasting traits, each time the F1 showed only one trait

Contrasting Traits in pea plants Page 156, fig 6.5 Conclusion: Law of Dominance: Traits shown in the F1 generation were Dominant and traits that were masked were Recessive Dominant traits: capital letters, eg T for tall Recessive traits: lower case letter, eg t for short

Some others, see handout

Recall: You have two copies of each chromosome One Maternal and one Paternal copy of each of the 22 chrom. Thus for any gene located on the maternal chromosome 1, you have a copy of it on the paternal chromosome 1!

A Couple Key Terms Gene: specific packets of DNA, units of inheritance, passed from one generation to another. All genes have 2 forms called alleles. Allele: one form of a gene for a specific trait. E.g. blue vs brown eyes Phenotype: Observable trait, what we see Genotype: types of alleles present; e.g. TT, Tt produce tall plant, tt short plant

Gregory Mendel: Father of Genetics Second Experiment: Allowed self pollination of Tall F1 generation plants to see if traits were lost forever or not being expressed F2 generation had 75% tall and 25% short Phenotypic Ratio of 3:1; 3 tall: 1 short

Gregory Mendel: Father of Genetics His Hypothesis Contrasting traits caused by internal ‘factors’ (known as genes) Each offspring inherits 2 types of factors, now known as alleles

Gregory Mendel: Father of Genetics If purebred, plant inherits 2 identical copies, said to be Homozygous: genotype with identical alleles, e.g. TT (tall) or tt (short) Hybrid plants inherit 2 contrasting traits, said to be Heterozygous: genotypes with different alleles, e.g. Tt These plants will appear tall since tall is dominant

Gregory Mendel: Father of Genetics Mendel’s First Law: The Law of Segregation An individual contains genes in pairs. These pairs segregate and are distributed into different sex cells. Each parent can only contribute one member of a pair to offspring

SUMMARY Terms to know: Gregory Mendel: Gene Alleles Genotype Phenotype Homozygous Heterozygous Dominant Recessive Gregory Mendel: Father of Genetics Law of Dominance Law of Segregation

Let’s have a look at how Mendel did this! Monohybrid Crosses: A cross involving a single trait, e.g. Height, thus only one pair of alleles Punnett Square: A chart used by geneticists to show the possible combinations of alleles in offspring . Helps organize results of a cross between individuals.

Using a Punnett Square Determine the Dominant and Recessive trait Write down genotypes of the parents List possible gametes each parent produces Complete the Punnett square