Mendel’s Legacy - PowerPoint PPT Presentation

Mendel’s Legacy

Genetics

• Father of genetics
• Researched heredity looking at traits or genetically determined variant of a characteristic.
• Pea plant

• Pollination
• Self-pollination occurs when pollen is transferred from the anthers of a flower to the stigma of either that flower or another flower on the same plant.
• Cross-pollination occurs between flowers of two plants

Monohybrid cross

• Cross for only one trait
• Legend:
• Trait (pea plant height)
• P1 – Parents
• F1 – First filial (son or daughter) generation
• F2 – Second filial generation

• Factors controlled the characteristics/ traits observed
• i.e. Plant height, flower color, etc.
• A pair of factors must control each trait
• Dominant
• The factor that is observed
• Recessive
• The factor that is masked by the dominant factor

• Law of Segregation states that a pair of factors is segregated, or separated, during the formation of gametes
• Law of Independent Assortment states that factors separate independently of one another during the formation of gametes.

• Each organism has two factors for each trait called genes
• Two alleles for shortness, two alleles for tallness
• Alleles are alternative forms for genes
• Alleles are found on different copies of a chromosome (one from mom, one from dad)

• Genotype
• Gene combination of an organism
• Tt, RR
• Phenotype
• The way an organism looks
• Tt – tall plant
• RR – round pea

• Two alleles for the trait are the same
• RR, rr
• Heterozygous
• Two alleles for the trait are different
• Rr

Probability = number of times an event is expected to happen/number of times an event could happen

F2 generation:

Dominant trait (yellow seeds) = 6,022

Recessive traits (green seeds)= 2,001

Total # plants produced= 8,023

6,022/8,023=0.75

2,001/8,023=0.25

There is a 75% probability the dominant trait of yellow seeds will occur

• Only one characteristic is tracked
• Genotypic ratio
• Phenotypic ratio
• Testcross- identify an individual of unknown genotype

• Used to predict the probable distribution of inherited traits in the offspring

• Complete dominance- one allele is completely dominant over another allele
• Incomplete dominance- a phenotype in between that of the dominant and recessive traits
• Codominance-both alleles for a gene are expressed in a heterozygous offspring

• Track two traits