1. GENETICS CHAPTER 10

2. GENETICS = THE STUDY OF HEREDITY AND ITS VARIATION. THE FATHER OF GENETICS: GREGOR MENDEL WE HAVE 46 CHROMOSOMES (23 PAIRS) EACH CARRIES A MULTITUDE OF DIFFERENT TRAITS.

3. MENDEL’S WORK Gregor Mendel accomplished most of his work in the MONASTERY in the small country of AUSTRIA. Working with garden peas, he worked with clear-cut characteristics (TRAITS) so they could be easily followed. Each of his chosen traits occurred in alternate forms: WRINKLED and SMOOTH seeds, GREEN and YELLOW color, tall and short, etc.

4. Mendel mated pure (HOMOZYGOUS) individuals, one dominant (TALL PEA PLANTS) the other recessive (SHORT PEA PLANTS) = PARENTS. He called this the P1 generation. P1 F1 The offspring he received from this mating were labeled the F1 generation. Next he mated two F1 individuals and a F2 generation was formed. F2 and

5. GENETIC VOCABULARY  PHENOTYPE = The outward appearance of a characteristic. Brown hair, blue eyes, tongue roller, etc.  GENOTYPE = The genetic makeup of an organism. Tt, rr, etc.  ALLELES = alternate forms of a gene, T and t, each are forms of the same trait.  HOMOZYGOUS = The alleles in a pair are identical. TT, hh, etc.  HETEROZYGOUS = The alleles in a pair are idfferent. Tt, Hh, etc.  HOMOZYGOUS DOMINANT = A genotype of two dominant alleles. HH, TT.  HOMOZYGOUS RECESSIVE = The genotype of two recessive alleles. hh, tt.

6.  PUNNETT SQUARE = A chart used to solve genetic problems.  MONOHYBRID CROSS = When a single trait is crossed. Tt x TT, etc.  DIHYBRID CROSS = When two traits are crossed at the same time. TtRr x TTRR, etc.  TESTCROSS = Mate a homozygous recessive individual with an unknown genotype for that characteristic. Way to determine the genotype of a homozygous individual. Example: BB or Bb x bb  PEDIGREE = A family tree describing the occurrence of heritable characters in parents and offspring across as many generations as possible.

7. HOW ARE TRAITS PASSED FROM PARENT TO OFFSPRING? Traits are transmitted by the CHROMOSOMES which contain genes made of DNA. HOW WAS THIS DISCOVERED? Mendel studied traits with his pea plants. From the results of his experiments Mendel made three conclusions (known as MENDELS GENETIC PRINCIPLES) PRINCIPLE OF DOMINANCE – One gene in a pair may prevent the other from being expressed. PRINCIPLE OF SEGREGATION – Each member of a gene pair separates when the gametes form. PRINCIPLE OF INDEPENDENT ASSORTMENT – As each gamete is formed, the genes are independently given to each gamete.

9. LET’S PRACTICE SOME MONOHYBRID CROSSES A type of insect has either a red or black body, determined by a pair of genes. The dominant allele, R, gives red, and the recessive allele, r, gives black. Cross a heterozygous red insect with a black insect. What are the phenotypic and genotypic ratios of their offspring? To solve the problem follow these steps: 1.Choose the correct genotype letters for each parent. 2.Put one letter above each box on the top of the Punnett square to represent one parent. Put one letter in each box on the side to represent the other parent. 3.Multiply the top and bottom squares together R r r r Rr rr Rr rr

10. 4. Finally determine the genotypic and phenotypic ratios. GENOTYPE = DIFFERENT LETTER COMBINATIONS 2 Rr to 2 rr = 1Rr:1rr OR 50% Rr and 50% rr PHENOTYPE = HOW THEY APPEAR TO US. 2 RED to 2 BLACK = 1 RED: 1 BLACK Or 50% red and 50% black PROBLEM #2 – Some people detect a distinctive taste from the chemical phenylthiocarbamide in low concentrations while others do not detect it at all. The ability to taste PTC is due to the effect of a dominant gene. If a homozygous dominant PTC taster mates with a nontaster, what % of their offspring will be nontasters?

11. CHOOSE THE CORRECT LETTERS TO REPRESENT THE PARENTS (Remember each parent gets two letters): P = TASTER; p = nontaster PARENTS = PP x pp Correctly place the letters for each parent on one side of the Punnett Square. P P p p Multiply each box. Pp Count number of individuals for a particular phenotype – nontaster – divide by 4 = %

12. TEST CROSS HOW DO YOU KNOW IF A DOMINANT TRAIT IS HETEROZYGOUS OR HOMOZYGOUS DOMINANT? By doing a TEST CROSS. Cross the DOMINANT individual with a HOMOZYGOUS RECESSIVE individual. SAMPLE PROBLEM: White hair in rabbits is dominant over black hair? What is the genotype of a white-haired rabbit, if it produces both black and white haired offspring? The mate is black haired.

13. What are the genotypes of the parents? White haired = ___________ or ___________ Black haired = ___________ What are the genotypes of the offspring: ______ and _______ WW Ww ww Ww ww W w w w Wwww Ww ww W W w w All Ww

14. DIHYBRID CROSSES The type of offspring can be determined for two different traits at the ___________________ time by doing a dihybrid cross. Sample Problem: Widow’s peak is a recessive trait. Tongue rolling is a dominant trait. A person that is heterozygous for tongue rolling and heterozygous for no widow’s peak mates with an individual that has a widow’s peak and cannot roll his tongue. What percent of their offspring will be heterozygous for both traits? What percent of the offspring will be widow peaked, tongue rollers?

15. Determine the genotype of each parent. Since there are two traits, how many letters should you have for each parent? _________ Genotypes of parents: _______________ x _______________ Determine the different possibilities of gametes that each parent can pass on. Parent 1 gamete possibilities: Parent 2 gamete possibilities: Put all the different gamete possibilities for Parent 1 in the top boxes of the Punnett Square and all the different gamete possibilities for Parent 2 in the side boxes. Multiply each of the boxes, enter the offspring letters in each box. Count the number of offspring that are heterozygous for each trait. Divide by the total number of boxes in the Punnett Square. This equals your percent. Look at the genotypes and determine which are recessive for both traits. Take this number and divide by the total number of boxes in the Punnet Square. This equals the percent for question #2. WwTt wwtt 4 WT, Wt, wT, wt wt

16. WT Wt wT wt WwTt WwttwwTt wwtt Number of Heterozygous for both traits - _________ Total number of Punnett boxes – ____________ 1 4 % Offspring heterozygous for both traits = 25% (1/4) What % will be widow- peaked, tongue rollers? ¼ = 25%