Ch. 1 Mendel's Principles of Heredity

Gene

a region of DNA that encodes a protein or RNA, basic units of heredity

• underline formation of every heritable trait

  • Single Change = easy to study = EX: sickle cell anemia

  • Complex interactions = hair type, skin color, height

Heredity

the way that genes transmit traits from parents to offspring

Mendel

1st scientist to combine data collection, analysis, and theory to understand heredity = foundation of genetics

• apperance + disapperance of traits through numbers

Artificial Selection + problem

1st applied genetic technique, to control mating by choice of parents for the next generation

• Problem: results were unpredictable

The homunculus (misleading theory of inheritance)

Inherited features of offspring are contributed mainly by only one parent; many microscopists thought they saw a fully formed, miniature fetus in the sperm head

• Real: sperm cell is contributor to genetic info

Blended Inheritance (misleading theory of inheritance)

Parental traits become mixed and changed in the offspring

• Real: sometimes only one gene is visible (ex: skin color)

3 Critical Questions about selective breeding

1. What is inherited?

2. How is it inherited?

3. What is the role of chance in heredity?

Mendel’s paper/experiment

• “Experiments in plant hybrids” (1866)

• Pea plants used to see what traits would show up + how often it showed up

3 Benefits of using pea plants

1. The time between generations is relatively short

2. Can obtain large numbers of offspring in each generation

3. Antagonistic pairs: visibly different traits (white vs. purple flowers) rather than continuous traits (height, skin color)

Pure-breeding

the plant will always make more offspring identical to itself when self-fertilized over many generations

• Difference in one traits: seed color; 3:1 ratio

Alleles

Alternative forms of a single gene

• monohybrid: indiv w/ 2 diff alleles for single trait

Mendel’s 2 major results

1. Each hybrid resembles only one of the parents (disproved the blended inheritance theory)

2. Performed reciprocal crosses (switching traits of male and female parents) and observed the same results. (disproved the theory that traits were transmitted via a single parent)

Mendel’s law of segregation

The two alleles for each trait separate during gamete formation

Diploid Zygote (Yy)

Two gametes, one from each parent, unite at random at fertilization

Phenotype vs Genotype

Pheno: observable characteristic (e.g. yellow or green pea seeds)

Geno: a pair/composition of alleles in an individual (e.g. YY or Yy)