Inheritance - Mendel

1. Inheritance - Mendel • the transfer of characteristics (traits) from one generation to another • your inherited characteristics (traits) are determined by the genes located on your chromosomes

2. Gene • a short segment of a chromosome coding for one trait

3. Homologous chromosomes: • chromosomes are found in pairs • in humans, there are 46 chromosomes, made up of 23 pairs of homologous chromosomes • a pair of chromosomes consists of two homologous chromosomes which look alike and carry genes for the same traits • you receive one homologous chromosome of the pair from each parent, therefore you receive 2 genes for each trait

4. Phenotype • This term is used to describe the physical or visible appearance of an individual as determined by the gene combination you inherit from your parents. • Example: in the case of eye colour, having brown eyes is the phenotype and is dominant

5. Genotype • the gene combination that produces the trait • these genes may be the same or different • genotypes are represented by upper and/or lower case letters e.g. Bb • there are three possibilities for genotypes for a single trait. • e.g. BB or Bb or bb

6. Allele • alternate forms of a gene • same location on a each chromosome of pair • affects the same trait but differently • alleles are different forms of a gene that carry different instructions • eg. Brown eyes or blue eyes

8. Dominant Trait/Allele • Characteristic that is always expressed its gene is present • only one dominant allele needs to be present for the dominant trait to be expressed • an upper case letter designates a dominant allele • eg. Tall is dominant. It is represented with a “T”

9. Recessive Trait/Allele • Characteristic that is only expressed when two genes for that trait are present • two recessive alleles need to be present for a recessive trait to be expressed • if a dominant allele is present it “masks” the recessive allele • eg: Short is recessive. It is represented with a • “t”

10. Homozygous Genotype • “homo” means the “same” • the condition where both alleles for a trait are the same • there are two conditions for homozygous genotype: • homozygous recessive genotype “aa” • homozygous dominant genotype “AA”

11. Heterozygous Genotype • “hetero” means “different” • the condition where both alleles for a trait are different • the genetic information inherited for a trait from both parents is different • example: heterozygous genotype “Aa”

12. Summary (example eye colour)

13. Activity • Introduction to Variability • Worksheet • Compile your own personal profile, and then combine it with the other members in the group. • Ratio for group • Ratio for class

15. Tuesday…

16. Mendel’s Experiment • Crossed two purebred parents (One tall and one short) • All offspring were tall!! Mendel concluded that some traits were ___________ and some traits were ___________.

17. Principal of dominance • When individuals with contrasting traits are crossed, the offspring (F1 generation) will express only the dominant trait. Parents: Tall x Short F1 (Offspring): Tall Tall Tall Tall

18. What happened next?? • Mendel crossed F1 generation. • F1: Tall plants x Tall plants • F2 (Offspring of F1): Tall Tall Tall Short • F2 generation = 3:1 ratio

19. Law of Segregation • Each F1 parent starts with two hereditary factors (alleles); one is dominant and one is recessive • Each parent contributes only one factor (allele) • Each offspring inherits one factor (allele) from each parent • If the dominant factor (allele) is present it will be expressed. • If the recessive factor (allele) is present it will only be expressed if only recessive factors are present.

20. Monohybrid Cross • Mendel crossed two purebred plants • TT – tall plant • Tt – short plant • Monohybrid cross – only one trait is being tested

21. PunnettSquares • Punnett Square • Is a grid system resembling a checkerboard, used in computing possible results of various genetic combinations • Simply stated, it is a way of representing the possible combinations of genes when an egg and sperm unite in fertilization

22. Predicting genotype and phenotype possibilities using Punnett Squares  Characteristic hair texture – • Dominant allele (gene) is curly hair - C. • Recessive allele (gene) is straight hair - c • Mother • Phenotype – straight hair • Genotype- homozygous recessive - cc • Father • Phenotype – curly hair • Genotype – homozygous dominant – CC

23. Punnett Square All of their children will have curly hair. They all have a different genotype from their parents.

24. Fig. 18.5

25. Fig. 18.6

26. Fig. 18.13

27. Fig. 18.14

28. Homework…. Bikini Bottom Genetics – Monohybrid Crosses Due tomorrow (Wednesday) – Will be marked and recorded.

29. Wednesday – Dihybrid Crosses and Sex Linkage

30. What happened when Mendel crossed two pea plants that different in TWO traits? In his second experiment Mendel crossed a pea plant with round/yellow (RRYY) seeds with a pea plant with wrinkled/greed seed (rryy). What genotypes resulted? What phenotypes resulted? Genotype: RrYy F1 - Generation Ratio 100% Phenotype: Round/Yellow Ratio 100%

31. Crossing F1(RrYy) x F1(RrYy) Genotype: RRYY RRYy Rryy RrYY RrYy rrYY rrYy rryy Ratio: 1 2 2 2 4 1 2 1 Phenotype: Round/Yellow Round/Green Wrinkled/Yellow Wrinkled/Green Ratio: 9 3 3 1 F2 - Generation What genotypes resulted? What phenotypes resulted?

32. Law of Independent Assortment • The inheritance of alleles for one trait ________ (does/does not) affect the inheritance of alleles for another trait.