Genetic Notes: One
- Gregor Mendel is credited as the "father of genetics"
- he did much of his work during the mid 1800s as a priest in Austria; he was a mathematician and botanist in charge of the monastery garden.
- The monastery was interested in crossbreeding pea plants.
- During his time, scientists thought that traits were blended in offspring similar to mixing the colors white and black to produce grey, but they didn't understand how traits could be expressed white being diluted.
- He selected 7 traits in pea plants to study: seed shape, seed color, pod shape, pod color, plant height, flower color, and flower position.
- By using pea plants, Mendel could control his study of inheritance patterns.
- Pea plants are pure breeding, which means that they produce offspring identical to themselves (they self-pollinate)
- Pea plants are only tall or short, produce yellow or green seeds, or have smooth pods or constricted pods (have traits that appear in only two alternate forms/ either/or traits)
- In his experiments, he cross-pollinated plants with contrasting traits, and observed the offspring; cross is called a monohybrid cross
- in one experiment, he cross-pollinated the tall plant with the short plant; he observed that the all the offspring were all tall and not a combination of tall and short.
- he called the offspring of the parents the first filial; filial is a Latin word meaning "child or offspring"
- then, he allowed the filial generation to self-pollinate to see if the shortness disappeared; he found that they short trait reappeared.
- he found that the filial generation produced a ratio of 3/4 tall plants, and 1/4 short plants in the F2 generation; this ratio is 3:1, and he produced results like this with the other 7 traits he crossed.
- Traits are inherited as distinct units from each parent.
- he concluded that organisms inherit 2 copies of each unit, one from each parent
- Organisms donate a single unit of inheritance in the gametes (sex cells). The two copies separate (segregate) during gamete formation. The conclusion become known as the law of segregation.
- Unit for tallness - dominant, unit for shortness - recessive
- genes are located on the chromosomes.
- Each trait is coded by a separate gene and has a specific location on the a chromosome. The location of a gene on a chromosome is called the locus
- Organisms receive one gene from the father and one from the mother. Each form of gene is called an allele.
- Homozygous genes- YY or yy (pure)
- Heterozygous gene - Yy (hybrid)
- Physical characteristics of an organism - phenotype
- Genes that code for a trait - genotype
- At Cambridge in the 1900s, Reginald C Punnett introduced the Punnett square for predicting possible genotypes from a genetic cross.
- The Punnett square verified Mendel's data.
Discussion Questions
1. Mendel was able to control his experiments with pea plants because Mendel made sure that the pea plants couldn't self pollinate when he cut away the male parts of the flowers. Then, he dusted the female parts of the flower with pollen from different plants.
2. His conclusions were that organisms inherit two copies of each unit, one from each parent, and the other conclusion was that when organisms donate a single unit of inheritance in the gametes, the two copies separate.
3. The Punnett helped verify Mendel's conclusions because they showed that the parents donated separate units.
4. The terms genes, homologous chromosomes, alleles, locus, dominant, and recessive all talk about genes, alleles, and your traits.
5. Zero percent of the offspring will have a white coat color.
2. His conclusions were that organisms inherit two copies of each unit, one from each parent, and the other conclusion was that when organisms donate a single unit of inheritance in the gametes, the two copies separate.
3. The Punnett helped verify Mendel's conclusions because they showed that the parents donated separate units.
4. The terms genes, homologous chromosomes, alleles, locus, dominant, and recessive all talk about genes, alleles, and your traits.
5. Zero percent of the offspring will have a white coat color.