Intro to Genetics

1. Intro to Genetics Why do we look the way we do?

2. We already know that if you look carefully at all 46 chromosomes, you would see that there are _________(1 of each pair comes from mom and the other from dad). • That means there are actually two chromosomes with instructions for each kind of trait (such as freckles, nose shape, etc.) 2 pairs What is in our DNA?

3. Genes • __________are segments of DNA or the places on the chromosomes that code for specific traits such as height, eye color, etc. -Each chromosome is made up of hundreds to thousands of genes we inherit from our parents. What is in our DNA?

4. Sometimes the two chromosomes in a pair don’t have the same instructions. The instructions from mom may be different from the ones you inherit from your dad. • Look at the chromosomes on the left: ___traits have been identified in which the mom and dad have passed down different forms of the same gene (called alleles) -Alleles are the result of differences in the G’s, C’s, A’s, and T’s in that stretch of DNA 7 Do your mom and dad look the same? –Probably not

5. Gregor Mendel • _________________(1822-1884) was an Austrian monk that taught high school science and tended the garden of the monastery. • While he was not considered well known scientist of his time, today he is considered to be the father of modern genetics. How do we know this?

6. Geneticsis the branch of biology that studies _________or the passing of traits from parents to offspring. • It took approximately ___________for Mendel to gather enough data to report his theories of heredity. heredity 8 years What is heredity?

7. Using many generations (over 25,000 ____________he was able to show how traits could be passed from parents to offspring, even traits that couldn’t be seen on the parent. • _____- Parental Generation • _____- 1st generation of offspring • _____- 2nd generation of offspring pea plants P1 F1 F2 How do we know this?

8. Mendel looked at the color of the flowers on his pea plants, the shape of the pea pods, and several other traits of the plants. • Mendel drew two conclusions from his experiments: 1. Inheritance is determined by traits that are passed from one generation to the next. 2. Some forms of a trait are dominant and others are recessive. What did Mendel say?

9. We don’t show both of the traits we got from our parents, instead one shows up over the other. • The ____________allele is the trait that will show up even when paired with a different allele. • The _____________allele is a trait that can be hidden or masked when it is paired with a dominant allele. dominant recessive If our parents give us two different versions of a trait, which one will show up?

10. Genotype-the genetic makeup of a trait represented by letters (FF, Ff, or ff; BB, Bb, or bb). Two letters should be used (one given by each parent). -A capital letter is used to represent a dominant allele. -A lower case letter is used to represent a dominant allele. *Your genotype is the genes you have. How do we know what alleles we have?

11. Phenotype- the appearance of a trait (freckles or no freckles, brown hair or blond hair). *Your phenotype is your physical appearance. How do we know what alleles we have?

12. Homozygous- when the pair of alleles are identical or the same form. -Examples: TT or tt; -remember: homo= same • Heterozygous- a pair of alleles that are not the same form… one is dominant and the other is recessive. -Example: Tt -Remember: hetero= different How do we know what alleles we have?

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15. How likely is it that a trait is passed on to the offspring?

16. Probabilityis the likelihood that an event will occur. • So if we know the genetic makeup of the mom and dad, we should be able to figure out if it is probable (how likely) and/or possible (could it) for them to pass down certain traits. How do we know if a trait will be passed to a child?

17. We will use a box called a Punnet Squareto determine the probability that specific traits will be passed down from parent to offspring. How do we know if a trait will be passed to a child?

18. Monohybrid cross- a cross that involves one pair of contrasting traits. E e (Dad’s genotype) (Mom’s genotype) E e EE Ee Ee ee How do we know if a trait will be passed to a child?

19. Dihybridcross- a cross that involves two pairs of contrasting traits. A a B b a a b b How do we know if a trait will be passed on?

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21. And more Awesome biology jokes… More Mendelian Genetics

22. A TEST CROSS is used to determine the unknown genotype of a specific organism. • In most cases, if you have an organism that is showing the Dominanttrait, you can not tell if they are homozygous or heterozygous by looking at them. How do we know what an organism’s genotype is?

23. It is possible to determine their genotype by crossing (breeding) the unknown with an individual that is homozygous recessive. By looking at their offspring you can usually determine the genotype of the unknown parent. How do we know an organism’s genotype?

24. What is the only genotype that we know for sure when we see the phenotype? Homozygous Recessive. If you show the recessive phenotype, your genotype has be two lowercase letters. Let’s look at why this works: E E E e Half of the offspring have dominant phenotype, half have recessive phenotype e e All offspring show dominant phenotype Ee Ee Ee Ee e e Ee ee Ee ee How do we now an organism’s genotype?

25. In tulips, red is dominant over white. When you see a red flower you can’t be sure if the flower is homozygous red (RR) or heterozygous red (Rr). To determine this you can cross it with a plant that produces white (rr) flowers (homozygous recessive) & observe the color of the offspring. Possibility #1: Red (R?) x White (rr) If most offspring have red flowers and several have white flowers… Then the unknown MUST BE Rr (it is not possible for it to be RR) Possibility #2: Red (R?) x white (rr) If ALL offspring have red flowers there are no white flowers… The unknown parent is MOST LIKELY RR R r R R r r r r Example (pg. 7) Rr rr Rr rr Rr Rr Rr Rr

26. In dogs, there is a hereditary deafness caused by a recessive gene, “d.” A kennel owner has a male dog that she wants to use for breeding purposes if possible. -The dog can hear, so the owner knows his genotype is either DD or Dd. -If the dog’s genotype is Dd, the owner does not wish to spend the money to use him for breeding. -The only way to be certain is to breed the dog with a deaf female (dd) and observe the offspring that they produce. 1. If the male dog is DD what is the probability that he would pass on the allele for deafness? 0% 2. If the male dog is Dd what is the probability that he would pass on the allele for deafness? 50% 3. Since the female is dd what is the probability that she would pass on the allele for deafness? 100% Sample Test Cross (pg. 7)

27. Since we do not know what the genotype of the male is, we will complete both punnett squares below to show the possible outcome of the test cross: Assume the male is DD: Assume the male is Dd: D D D d Dd d Dd d dd Dd d Dd d dd Dd Dd 4. If he is DD, what percentage of the puppies would be expected to have normal hearing? deaf? 5. If he is Dd, what percentage of the puppies would be expected to have normal hearing? deaf? 100% 0% 50% 50% Sample Test Cross (pg. 7) If any of the puppies are deaf, the male’s genotype MUST BE _______; but assuming a litter of at least about 4 to 5 puppies or more, if they can all hear, his genotype is MOST LIKELY __________. Dd DD

28. Sometimes instead of just comparing a single trait (like we have been with the four box punnett square) – we may want to see the results of two or more different traits, at the same time. • Example: AAbbCC x aaBBcc … Can you tell what genotype their offspring would have? What if we want to know about more than one trait?

29. To help you understand this we will use the following example: Your two prize show dogs accidentally mate and now the female is expecting a litter. Both are purebreds, but each has two distinct differences from one another. • The male has black fur and a black nose. The female has white fur with a pink nose. Since you know their pedigree, you are certain that at they are homozygous for both traits BBNN • Dad’s Genotype= ______________ • Mom’s Genotype= ______________ bbnn What if we want to know about more than one trait?

30. Since each parent will only pass down one allele for each trait then: • Their offspring’s genotype must be: • Their offspring’s phenotype must be: • Several years later, two of their offspring mate and are expecting a litter of puppies. We want to know ‘what percentage of their puppies are expected to have black fur & a pink nose?’ • There are two ways that this question can be solved BbNn Black fur, black nose What if we want to know about more than one trait?

31. Method # 1– Set up 2 four-box Punnett squares to answer this question; one for each trait. • According to the problem, two of their offspring, which are heterozygous for fur color and heterozygous for nose color, produce a litter of puppies. • What percentage of their puppies are expected to have black fur & a pink nose? In box #2 we’ll cross the trait for nose color. In box #1 we’ll cross the trait for fur color. Nnx Nn Bb x Bb ___ / 4 = NN ___ / 4 = Nn ___ / 4 = nn ___ / 4 = black nose ___ / 4 = pink nose 1 ___ / 4 = BB ___ / 4 = Bb ___ / 4 = bb ___ / 4 = black fur ___ / 4 = white fur B b 2 1 N 3 1 n Now, circle the phenotypes black fur & pink nose. Write the fractions from each one below: _____ puppies are expected to have black fur; ____ puppies are expected to have a pink nose. 3 1

32. To figure out how many are expected to have black fur with a pink nose, use the above fractions &: •multiply the top numbers with one another; •then multiply the bottom numbers together. _______ X _______ = _______ with black fur & a pink nose 3 1 4 4 16 Method 1 continued

33. Set up a 16 box punnett square, called a dihybridcross. This shows two traits being crossed at the same time. The 16 box punnett square is already set up below to show the results of crossing these two hybrid puppies. What are the genotypes of the parents? BbNn x BbNn ? ? ? ? ? Method 2 How do we know what will go here?

34. We’re going to use the FOIL method to get the letters that we’ll use in our cross. • First • Outer • Inner • Last • Our genotype is BbNn, so for the first pair of letters, we’ll take the FIRST letter for each trait: BN • Next, we’ll take the OUTER letters for each trait: Bn • Next, we’ll take the INNERletters for each trait: bN Method 2 continued • Finally, we’ll take the LAST letters for each trait: bn

35. Now we know what to put for each row and column and we can fill in the punnet square… bN bn BN Bn BN BBNN BBNn BbNN BbNn BBNn BbNn BBnn Bbnn BbNn BbNN bbNN bbNn Bbnn BbNn bbNn bbnn •Fill in the two missing boxes (use the other boxes to figure out the pattern of your letters) •Circle the boxes that have the genotypes for black fur AND a pink nose. •What fraction of the boxes did you circle? ____ out of ____ boxes = _____ 3 16 3/16 Method 2 continued The result is the fraction of puppies that are expected to have both traits. Your answer should be the same as the one you found on the previous page.