Chapter 9

1. Genetics Chapter 9

2. The Standards • 2c. Students know how random chromosome segregation explains the probability that a particular allele will be in a gamete. • 3b. Students know the genetic basis for Mendel's laws of segregation and independent assortment.

3. Gregor Mendel • Heredity: transmission of characteristics from parents to offspring • Gregor Mendel: Austrian monk Father of genetics, studied peas • Genetics: field of biology devoted to understanding how characteristics are transmitted from parents to offspring 1822-1884

4. Mendel examined peas for heritable traits • It has many traits, which take on 2 clearly different forms that are easy to tell apart. Table 9-1 • Traits: particular forms of one characteristic

5. Why the Garden Pea • Crosses between flowers can easily be controlled because the male and female parts are enclosed within the same flower. • Self-fertilization – fertilization of a flower by the male part of the same flower. • Cross- pollination – transfer of pollen to a different flower • The plant is small, grows easily, matures quickly, and produces many offspring, allowing for faster collection of data.

7. Characteristic: Seed Shape Seed Color Flower Color Pod Color Traits: Wrinkled or round Yellow or green Purple or white Green or yellow Characteristics vs. Traits

8. Mendel’s Experiments • Mendel experimented by controlling how pea plants reproduced • Observed that traits could be expressed as simple ratios. • Mendel’s first crosses were monohybrid crosses. • Monohybrid cross – cross that involves one pair of contrasting traits. Ex. Purple and white flowers.

9. 1st: Allowed each pea to self-pollinate for several generations. He grew plants that were pure for each trait. This led to the formation of strains. • To ensure that each variety was true-breeding for a particular trait. • True-breeding plants were used as parental generation (P generation)- first individuals to be crossed in a breeding experiment.

10. 2nd: Cross-pollinate two P generation plants with contrasting traits, producing offspring (F1 generation), record how many F1 plants express each trait. • He took flowers from different strains and crossed them. These plants were the P1Generation(parents) • Cross: to mate • This cross produced offspring plants called the F1 generation P1 F1

11. 3rd: He allowed the F1 generation to self-pollinate to produce offspring (F2 generation) • F2 could self-pollinate to produced F3, F3 produce F4 and so on … to infinity

13. Mendel’s Results • All plants from F1 showed only one form of the trait. • Pure wrinkled vs. Pure round: all F1 seeds were round • BUT wrinkled seeds reappeared in the F2 generation Round Wrinkled

14. When the F1 generation was allowed to self-pollinate the missing trait reappeared in some of the F2 generation. • The F2 generation produced a ratio of 705 to 224 purple flowers to white flowers. • A 3:1 ratio was discovered for each of the 7 traits studied

15. Mendel’s 4 Conclusions • There was something in the pea plant that controlled the characteristics he observed -He called these controlling things “Factors” • There must be a pair of “factors” controlling each trait • One factor would come from each parent • One “factor” in the pair may prevent the other from having an effect

16. Recessive and Dominant Traits • Dominant: A factor that covers or masks another factor • Recessive: A factor that is covered or masked when paired with a dominant factor

17. Chromosomes and Genes • We now know a little more and can explain some of Mendel’s observations • Gene: A segment of DNA on a chromosome that controls a particular hereditary trait • What Mendel called “factors” we now call Alleles • Allele: alternative form of a gene, one is dominant and one is recessive

18. In genetics, alleles are represented by letters • Capital letters represent dominant alleles B = dominant allele for black hair • Lower-case letters represent recessive alleles b = recessive allele that will yield brown hair

19. Mendel’s Findings • Homozygous – the two alleles for a particular gene are the same. • AA – homozygous dominant • aa – homozygous recessive • Only way to see the recessive trait • Heterozygous – the two alleles for a particular gene are different. • Aa – will typically display the dominant characteristic.

20. Mendel’s Findings • Genotype – the set of alleles that an individual carries. • Phenotype – the physical appearance of a trait, determined by which alleles are present. • Just because you know the phenotype does not mean you know the genotype.

21. Law of Segregation • Paired factors separate during the formation of gametes • Each gamete receives 1 factor from each pair • When 2 gametes combine offspring would have 2 factors controlling each trait

23. Law of Independent Assortment • Factors for different characteristics are distributed to gametes independently

24. Independent Assortment and Gene Location • The law of independent assortment applies most accurately to genes located on separate chromosomes • It is a poor predictor for combinations of genes that are on the same chromosome

25. Self Check • What is genetics? • What is a pure strain? • Define “dominant” and “recessive.” • What are Mendel’s two laws and what do they state? • During what process does segregation occur? • What is a gene?