KEY CONCEPT 6.3, 6.4, & 6.5 Mendel’s research showed that traits are inherited as discrete (individual) units.

Mendel laid the groundwork for genetics. Traits are distinguishing characteristics that are inherited. (eye color, hair color) Genetics is the study of biological inheritance patterns and variation. Gregor Mendel showed that traits are inherited as discrete units. Like different colored marbles mixed together that can still be picked out separately.

Mendel crossed many pea plants and observed these seven traits Mendel crossed many pea plants and observed these seven traits. His results led to important conclusions (more on that later)

The same gene can have many versions. A gene is a piece of DNA that directs a cell to make a certain protein. Each gene has a locus, a specific position on a pair of homologous chromosomes.

Each parent donates one allele for every gene. An allele is any alternative form of a gene occurring at a specific locus on a chromosome. (gene=pea shape, alleles= wrinkled or smooth) Each parent donates one allele for every gene. -Genotype: The genetic makeup of a specific set of genes -Phenotype: The physical characteristics of an individual – what you actually SEE -Homozygous(purebred) describes two alleles that are the same at a specific locus. Ex: (RR or rr) Heterozygous (Hybrid) describes two alleles that are different at a specific locus.Ex: (Rr)

Alleles can be represented using letters. A dominant allele is expressed as a phenotype (visible trait) when at least one allele is dominant. A recessive allele is expressed as a phenotype (visible trait) only when two copies are present. Dominant alleles are represented by uppercase letters; recessive alleles by lowercase letters. https://www.youtube.com/watch?v=i-0rSv6oxSY

Mendel used pollen to fertilize selected pea plants (Ex Mendel used pollen to fertilize selected pea plants (Ex.: Purple Flowers X White Flowers) He crossed the P (parent) generation to produce F1 (first filial or first set of offspring) generation. He interrupted the self-pollination process in the plants by removing male flower parts. Mendel controlled the fertilization of his pea plants by removing the male parts, or stamens. He then fertilized the female part, or pistil, with pollen from a different pea plant.

Skip to: Mendel then allowed the resulting plants to self-pollinate. Among the F1 generation, all plants had purple flowers – this is the phenotype (describes physical traits, what we can see) F1 plants are all heterozygous this is the genotype (describes the internal makeup of the genes, what we cannot see).

Back to: Punnett squares illustrate genetic crosses. The Punnett square is a grid system for predicting all possible genotypes resulting from a cross. The axes represent the possible gametes of each parent. The boxes show the possible genotypes of the offspring. The Punnett square yields the ratio of possible genotypes and phenotypes.

A monohybrid cross involves one trait. Monohybrid crosses examine the inheritance of only one specific trait. (let’s do this one from Mendel’s experiment as an example).

Phenotype (Offspring): 100% Purple flowers Genotype (Offspring): 100% Heterozygous

Among the F2 generation (when the F1 generation is crossed with themselves), some plants had purple flowers and some had white Let’s do this cross and see how he got these results.

F2 Results: (Answer) Phenotype: 75% Purple, 25% White (3:1 Purple:White) Genotype: 25% Homozygous Dominant (FF) 50% Heterozygous (Ff) 25% Homozygous Recessive (ff) Ratio: 1:2:1 Homo Dom: Hetero: Homo Rec ¼ Ho Do, ¼ Ho Rec, 2/4 Hetero

Practice: Ff x ff What words would you use to describe the P generation (parents)? What would the phenotype and genotype be of the F1 generation? Phenotype: 50% Purple, 50% White Genotype: 50% Heterozygous, 50% Homozygous Recessive

Both homozygous dominant and heterozygous genotypes yield a dominant phenotype Ex: FF and Ff are both purple The only combination that shows the recessive phenotype is when homozygous recessive is the genotype Ex: ff is white

Mendel drew three important conclusions. 1. Traits are inherited as discrete units. 2. Organisms inherit two copies of each gene, one from each parent. 3. The two copies segregate during gamete formation. The last two conclusions are called the law of segregation. purple white

http://ed.ted.com/lessons/how-mendel-s-pea-plants-helped-us-understand-genetics-hortensia-jimenez-diaz