Genetics Origin and Theory Gregor Mendel

Pea Plant Characters and Traits Wrinkled Short Character Trait

Mendel ’ s Experiments Began with monohybrid crosses Crosses that involve organisms that are different in only one trait Ex- tall pea plant with a short plant (P1)

3 steps…

1 st step… Allow self-pollination for several generations Result: true-breeding P generation (parent generation) Purple flowers plants will only produce purple flowered offspring

2 nd step…. Cross-pollination of P generation Result: F 1 generation (first filial generation) All same trait

…3 rd step Self-pollination of F 1 generation Result: F 2 generation (second filial generation) Some purple, Some white

His data

Mendel’s Hypotheses 1. For each inherited character, an individual has two copies of the gene-one from each parent. 2. There are alternative versions of genes: alleles 3. When two different alleles occur together, one of them may be completely expressed (dominant ) while the other may have no observable effect on the organism’s appearance (recessive) 4. When gametes are formed, the alleles for each gene separate independently of the other (law of independent assortment

Monohybrid cross- plant height Two traits (alleles)  tall and short Dominant trait: tall Recessive trait: short In genetics problems we generally assign a letter to each trait with the upper case being the dominant and lower being the recessive allele. Ex. Height T = Tall & t = short

Monohybrid cross Example of a Monohybrid Cross with seed shape Create a visual of Mendel’s Experiment with plant height.

F 2 Generation From this cross his 2 nd generation were. 2 nd generation 75% tall and 25% short (F2) Why was the short gene apparent in the 2 nd and not in the 1 st Generation of offspring?

Tt TTtt Fertilization

Back to his hypotheses From this experiment Mendel concluded that for each gene we carry there are two factors called Alleles. One allele from each homologous chromosome One from Mom and one from Dad

Mendel Cont. This brought up the terms recessive and dominant For a recessive trait to show both alleles must be recessive. For a dominant trait to show only one dominant allele needs to be present  Can be a carrier if you have one dominant and one recessive (carrier for recessive) – The recessive trait does not show.

Passing on the Trait When gametes (sex cells) are formed only one of the alleles is passed on from each parent The allele combination that the child receives is called the genotype. (Tt) Genotype= genomic composition The genotype may be homozygous or heterozygous  homozygous have the same alleles (TT, tt)  Heterozygous have different alleles (Tt) The trait that physically appears is the phenotype (tall or short)

Write out the genotype for pea height ex for…. Homozygous dominant, homozygous recessive, and heterozygous

Punnett squares The Punnett square is a diagram that is used to predict an outcome of a particular cross or breeding experiment. Named after Regi Punnett Is a summary of every possible combination Draw the punnett squares for the height example

Mendel ’ s Laws Law of Segregation: Gene pairs separate when gametes form. Alleles separate during meiosis Alleles are found on the homologous chromosomes so when they separate the Gene Pairs separate.

Mendel ’ s Law Law of Independent Assortment: Gene pairs segregate into gametes randomly and independently of each other regardless of how they are connected in the organism. Note: they have to be on different chromosomes. These allele pairs are then randomly united at fertilization.fertilization

YyPpYyPp Independent Assortment YPYPYpYp yPyPypyp Y = Yellow y = green P = Purple p = White

Review What is an allele? What is a phenotype? What is a genotype? Define dominant and recessive based upon allele presence. Explain Law of Segregation Explain Law of Independent Assortment.