1. Patterns of Inheritance Chapter 9

2. Genetics The science of heredity. A distinct genetic makeup results in a distinct set of physical and behavioral characteristics.  The DNA you get from your parents determine your physical characteristics.

3. History of Genetics – Gregor Mendel Modern genetics began in the 1860’s when a monk named Gregor Mendel experimented with breeding garden peas. With a history in mathematics, his research implemented a great deal of statistics. He stressed that the heritable factors (genes) retain their individuality generation after generation (no blending).

4. History of Genetics – Gregor Mendel He studied pea plants because they had short generation times, they produced large numbers of offspring, and they came in many varieties. Character: flower color, height, seed shape, pod color, etc. Traits (each variant for a character) purple/white flower, tall/short height, round/wrinkled seed, green/yellow pod color.

5. Characters Traits Mendel chose to study 7 characters, each of which occurred in two distinct forms.

6. Mendel’s Experiment He could strictly control mating of pea plants. Pea plants usually self-fertilize –pollen grains (carrying sperm) released from the stamens land on the egg containing carpel of the same flower. He could also cross-fertilize – fertilization of one plant by pollen from a different plant.

7. Cross fertilization

8. Mendel’s Experiment He worked with plants until he was sure they were a true-breed (one that produced offspring all identical to the parent if self- fertilized). Example – parent plant had purple flowers, and if self fertilized it would only produce purple flowered plants generation after generation.

9. Mendel’s Experiment Once he had a true-breed, he then investigated what would happen if he crossed true-breeding varieties with each other. Example – what offspring would result from cross-fertilization of true-breeds?  purple flowers x white flowers This offspring of two different true-breeds is called a hybrid.  (the fertilization is called hybridization, or cross.)

10. Mendel’s Experiment P generation – the true-breeding parental plants. F 1 generation – the hybrid offspring.  (F stands for filial, Latin for “son”) F 2 generation – result self-fertilization of the F 1 plants.

11. Mendel’s Results Mendel tracked and recorded the inheritance of characters, & the results lead him to formulate several ideas about inheritance. Let’s look at his monohybrid-cross (parent plants differ in only 1 character).

12. Mendel’s Results He crossed a true-breed purple flower with a true- breed white flower.  He observed that the F 1 generation were all purple flowers. Self-fertilizing the F 1 generation he found that the F 2 generation had a ratio of 1:3. One white for every three purple.  He concluded that the white trait did not disappear, and that they MUST carry two factors for the flower color character.  He called these alleles – alternative versions of a gene. ** Very important to know this term

14. ** Important Notes To Remember Gene – enough DNA to make 1 protein (which would in turn control 1 trait)  You inherit 23 chromosomes from your mom and 23 from your dad. These 23 chromosomes from each pair up to form homologous chromosomes (on these chromosomes will be hundreds of genes). Allele – the 2 versions of each gene that you receive (1 from each parent)

15. Homologous chromosomes – pairs of chromosomes that are the same size, shape, and carry the same genes (get 1 from mom and 1 from dad)  Alleles reside at the same locus (location) on homologous chromosomes.

16. Terms Mendel use to describe his findings Dominant allele – is always expressed if present. (like a trump card)  PP or Pp ** Note: This does not mean that the dominant allele is better or even more frequent. It simply means that the dominant allele will mask or cover up the recessive allele. Recessive allele – is only expressed if the dominant allele is NOT present.  pp

17. Examples of human traits that are dominant / recessive Tongue rolling Attached earlobes Widows peak Hitchhiker’s thumb

19. Terms Mendel use to describe his findings A homozygous genotype has identical alleles.  PP or pp A heterozygous genotype has two different alleles  Pp

20. Genetic composition & appearance Genotype – organism’s genetic makeup. (Represented by letters – Each letter represents 1 allele ) Phenotype – organism’s physical traits.

21. Genetic composition & appearance Carriers – organisms that are heterozygous, they carry the recessive allele for a trait but phenotypically only the dominant trait is expressed.  Note that being a carrier and being heterozygous are the same thing

22. Types of hybrid crosses Monohybrid cross – the parents differ in only one character.  Green or Yellow seeds. Dihybrid cross – parents differ in two characters.  (Round or Wrinkled) and (Green or Yellow) seeds.

23. Law of Segregation: A sperm or egg carries only one allele for each inherited character.  Because allele pairs separate from each other during the production of gametes. Which stage of meiosis does this occur in? This means you will have a 50% chance of getting either of your parents alleles.

24. Law of Independent Assortment: For Dihybrid Crosses Each pair of alleles segregates independently of other pairs of alleles during gamete formation. (Each trait is inherited independently of one another.)  Which means you could get your mom’s hair color and not get her eye color (or vice versa). The two traits are inherited INDEPENDENTLY of one another.

25. Law of Independent Assortment

26. Punnett Square Punnett squares are used to show the probability of what genotypes the offspring could have.  ** Note – In all of our somatic (body) cells, we have 2 alleles for each chromosome. During meiosis we separate these chromosomes (and thus the alleles) when making our gametes. (Law of segregation) Show this on the Punnett square above

27. Using Punnett Squares Rules: 1. Separate alleles from each parent (it doesn’t matter if mother or father goes on top) 2. Pull the alleles from up top down and the alleles from the side over to show the possibilities of all of the zygotes that could be created from this cross. 3. Each box represents a 25% chance that this particular zygote will be formed. 4. Genotype ratio – Homozygous dominant : Heterozygous : Homozygous recessive 5. Phenotype Ratio – Dominant : Recessive Parents Offspring (zygotes) Alleles

28. Practice Questions Use your whiteboards to answer the following questions. 1. What is meant by the P, F1, and F2 generations? 2. What are genes, alleles, and homologous chromosomes? 3. Difference between homozygous and heterozygous? 4. Difference between genotype and phenotype? 5. Define: Law of segregation, Law of independent assortment 6. Complete the monohybrid cross on the board and give the genotype / phenotype ratios. (We will work on dihybrid crosses tomorrow)

29. Test Cross Used to determine the genotype of a unknown character. Used to verify if organism is in fact a true- breed. B = black. The dominant allele. But, is it BB or Bb? This is unknown.

30. Test Cross Mate organism with unknown genotype, with an organism that has a homozygous recessive genotype. The appearance of the offspring reveals the unknown genotype.