Genetics

1. the branch of biology that studies the transmission of hereditary information from parents to offspring Genetics

2. Gregor Mendel and his pea plants experiments (1857-1865)

3. Mendel was a monk who was educated--he knew MATH! He also had a lot of free time.As for the peas? Well, they were:* easy to grow * inexpensive* easy to pollinate (either self or cross)* easy to study their TRAITS (characteristics) such as: height, seed pod shape, seed color, seed pod color, seed texture, flower position, and seed shape WHY MENDEL? WHY PEAS?

4. Mendel kept very accurate records for hundreds of individual plants. He used statistical analysis (MATH) to study the traits of different generations. Through his findings, he proposed that the traits were passed on by some kind of hereditary factors (now know to us as DNA).

5. One trait he studied was plant height. Mendel pollinated all tall plants for many generations to get a pure population of tall plants. He also pollinated all short plants to get a pure population of small plants. See picture below...X means to cross(as in cross-pollinate) tall plants X tall plants as well as short plants X short plants He then cross-pollinated a member of the tall pure population with a member of the short pure population... P1 (pure parent generation)P1 TALL PLANT X P1 SHORT PLANT ALL TALL PLANTS F1 (first filial [family] generation) Where did the short trait go? Mendel then crossed two tall members of the F1 generation. F1 TALL PLANT X F1 TALL PLANTTHIS IS CALLED A MONOHYBRID CROSS (hybrids known for one trait) F2 (second filial generation) For every 3 TALL PLANTS there was 1 SHORT PLANT Here's basically what he did

6. So, the short trait did not disappear. It was present in the F1 generation, but IT WAS NOT EXPRESSED (this means it did not show up!) Somehow, it was expressed (visible) in the F2 generation.

7. because the tall trait showed up more than short, Mendel call this trait DOMINANT the short trait, because it seemed 'weaker' than the tall trait, was called RECESSIVE After this discovery...well, um...NOBODY CARED! Later on, when scientists studies meiosis in Drosophila (genus name for fruit flies), they linked together Mendel's factors with the chromosomes in gametes Mendel's Principal of Dominance

8. Mendel's factors are now called GENES • genes are segments of chromosomes (DNA) that code for a characteristic • these characteristics can be: • physical traits (can be seen like eye color, hair color, height, etc.) • chemicals produced in the body (like for hormones or enzymes)

9. genes are lined up on chromosomes in a certain order, like beads on a string homologous (similar) chromosomes have the same order of genes...HOWEVER.. these chromosomes might have the different forms of a gene ex. trait=eye color can be blue, black, brown, hazel, green, etc. these different forms of a gene are called alleles in simple patterns of inheritance, there are 2 different forms of a gene (alleles), where one is dominant and one is recessive DOMINANT IS SHOWN BY CAPITAL LETTERS recessive is shown by lowercase letters ex. in Mendel's peas T = tall t = short

10. diploid (having 2 sets of chromosomes) organisms have 2 copies of genes, one on each chromosome they have • the 2 copies can be the same--HOMOZYGOUS, like TT (homozygous dominant) or tt (homozygous recessive) • the 2 copies can be different--HETEROZYGOUSTt (heterozygous)

11. phenotype: what the appearance of an organism is (how it looks) ph = physical genotype: what the genetic makeup of an organism is (what genes it has) gen = genes genotype can be: homozygous dominant----------> TTheterozygous (a hybrid--a mix)---> Tthomozygous recessive----------> tt recessive phenotypes can only be expressed (show up) when there are 2 copies of a recessive gene present at the same time...if a dominant gene was there, then that would be expressed, hiding the recessive gene! Notice that what the organism looks like and the kind of genes it has are two separate ways to classify an organism

12. when gametes are formed during meiosis (DIPLOID to HAPLOID) the homologous chromosomes (which contain the many different genes) separate randomly • this is called SEGREGATION Mendel's Principle of Segregation and Recombination

13. if the organism has a homozygous (the same) genotype for a given trait (TT or tt), then all gametes will also have that trait TT <----diploid----> ttmeiosisT or T <----haploid----> t or t if the organism has a heterozygous (not the same) genotype for a given trait (Tt), then half of the gametes will have one trait, and the other half will have the other trait Tt <----diploidmeiosisT or t <----haploid when the haploid gametes fuse during fertilization, the diploid number of chromosomes is restored this can result in a new combination of genes this is called RECOMBINATION

14. P1 (pure parent generation) cross was: TTXtt F1 (first filial generation) cross was TtXTt F2 (second filial generation) offspring had genotypes of TT, Tt, tT, and tt Let's look back at Mendel's first few pea plant crosses

15. For the F2 generation what is the PHENOTYPIC RATIO? 3 tall : 1 short For the F2 generation, what is the GENOTYPIC RATIO? 1 homozygous dominant : 2 heterozygous : 1 homozygous recessive PHENOTYPE DOES NOT ALWAYS EQUAL GENOTYPE! Now, compare the different phenotypes (physical appearance) and genotypes (genetic makeup).

16. to show segregation (separation of genes/chromosomes) and recombination (during fertilization), we use Punnett Squares

17. Problem: A homozygous tall pea plant is crossed with a short pea plant. (Remember, tall is dominant over short for pea plants!) What would the expected genotypes (the genotypic ratio) and phenotypes (the phenotypic ratio) of their offspring? Punnett Square Method

18. T = tallt = short STEP 1: set up the key that will show how each allele (form of a gene) will be shown

19. TT x tttall homozygous parent & short parent * remember, to be short, it has to have both short alleles! STEP 2: set up the parents that will be crossed; use the information from the word problem itself

20. STEP 3: do the Punnett square; that is, put one parent on the top and the other parent on the left of the square...then from a blank box, take the allele on the top and the allele from the left and fill them in

21. GENOTYPIC RATIO: PHENOTYPIC RATIO: STEP 4: show the results (ratios) of the cross

22. Use a Punnett square to show the offspring of a cross between two pea plants that are heterozygous for height (Tt). Give the phenotype and genotypes of the offspring. (That is, what is the phenotypic and genotypic ratios!) Use a Punnett square to show the offspring of a cross between a pea plant that is homozygous tall and one that is heterozygous. Give the phenotypes and genotypes of the offspring. Use a Punnett square to show the offspring of a cross between a pea plant that is heterozygous tall and one that is homozygous recessive for height. Give the phenotypes and genotypes of the offspring. TRY THESE PUNNETT SQUARE PROBLEMS

23. when one allele (form of a gene) is partially dominant over the other it is a blending of the alleles ex. Four O'clock Flowers (key below) R = red RW = pink W = white Incomplete Dominance

24. 4) Use a Punnett square to show the offspring of a cross between a red Four O'clock flower and one that is heterozygous. Give the phenotypes and genotypes of the offspring. 5) Use a Punnett square to show the offspring of a cross between a homozygous white Four O'clock flower and one that is heterozygous pink. Give the phenotypes and genotypes of the offspring More practice problems

25. this time, both the alleles are expressed, but they are not blended together in humans, this is like hair texture and blood groups ex. cattle coat color (key below) R = red RW = roan (where both red and white are expressed) W = white Codominance

26. 6) Use a Punnett square to show the offspring of a cross between a homozygous white fur cattle and one that is roan. Give the phenotypes and genotypes of the offspring. More practice problems

27. when there are more than 2 alleles for a gene in human blood types there 3 possible alleles for the ABO blood typing system IA = A antigen IB = B antigen i = no antigen both IA and IB are dominant over i but, both IA and IB are codominant with each other (that means, they are both expressed equally) Multiple Alleles

29. 7) Four newborn babies in the delivery room of the hospital at the same time were mixed up by the nurse who attached the wristbands. The blood types of the four babies were known to be AB, O, A, and B. How did the doctors find out which baby belonged to which set of parents? Carry out all possible crosses to determine which baby belongs to which set of parents. (HINT: You may not have to use all the Punnett squares!) Parents #1 had blood types O and AB Blood type of baby: _______ Parents #2 had blood types AB and B Blood type of baby: _______ Parents #3 had blood types O and O Blood type of baby: _______ Parents #4 had blood types O and A Blood type of baby: _______ 8) If a heterozygous A person and a homozygous B person have children, can they have an A type baby? More practice problems

30. most diploid organisms have 2 different types of chromosomes autosomes- contains genes on regular 'body chromosomes‘ sex chromosomes- contains genes for sex differences (male-female) humans have 22 pairs of autosomes and 1 pair of sex-chromosomes XX = female XY = male women (XX) always pass an X chromosome; men can pass an X or a Y (a 50%-50% chance) this is determined during the random selection process during the production of gametes (meiosis) besides the sex characteristics, there are also other traits on these chromosomes ex. hemophiliacolor blindness Sex-Linked Genes

32. Thomas Hunt Morgan (the fruit fly guy) noticed that some traits are inherited more frequently in males than females these were found to be recessive alleles found on the X chromosome because the Y chromosome is actually smaller than the X chromosome, men only have one copy of certain genes... so...if the X chromosome has a recessive allele, that will be expressed because that is all that is there! (key below) X= normal X chromosome X*=carrier X chromosome Y= normal Y chromosome

33. 9) Use a Punnett square to show the offspring of a cross between a woman with normal vision and a color blind male. Give the phenotypes and genotypes of the offspring including the sex of the children. Can any of them be color-blind? 10) Use a Punnett square to show the offspring of a cross between woman who carries the hemophilia gene and a man who is a hemophiliac. Give the phenotypes and genotypes of the offspring. Can any of their daughters be a hemophiliac? More practice problems

34. A pedigree is a diagram of family relationships that uses symbols to represent people and lines to represent genetic relationships. These diagrams make it easier to visualize relationships within families, particularly large extended families. Pedigrees are often used to determine the mode of inheritance (dominant, recessive, etc.) of genetic diseases. If the purpose of a pedigree is to analyze the pattern of inheritance of a particular trait, it is customary to shade in the symbol of all individuals that possess this trait. Pedigree’s

35. In a pedigree, squares represent males and circles represent females. Horizontal lines connecting a male and female represent mating. Vertical lines extending downward from a couple represent their children. Subsequent generations are therefore written underneath the parental generations and the oldest individuals are found at the top of the pedigree.

36. The Ultimate Pedigree Challenge Is it possible for someone to be his own ‘grandpa’? This story is a clever song written by Dwight Latham and Moe Jaffe (1947, General Music Publishing Company, Inc.). Listen and attempt to draw a pedigree chart of this man’s family. He’s his Own Grandpa?

37. The Answer… Maybe Widow Dad Red-haired Daughter 23 yr old