Chapter 8 Heredity. Learning Target(s):

Transcription

1 Chapter 8 Heredity copyright cmassengale 1 Learning Target(s): I Can. A) explain the differences between dominant and recessive traits. B) explain the differences between phenotypes and genotypes. 1

2 Why don t you look exactly like your parents? You don t look exactly like your parents because of what is known as heredity. Heredity is the passing of traits from parent to offspring. You may have curly hair while both your parents have straight hair or blue eyes while both of your parents have brown eyes People have investigated this question for a long time. About 150 years ago, Gregor Mendel performed an important experiment which helped find answers to many of our questions. Gregor Mendel ( ) Is credited for the theories that explain how are traits are inherited from generation to generation. copyright cmassengale 4 2

3 Gregor Johann Mendel Was an Austrian monk who studied the inheritance of traits in pea plants. He was also great in Math, which helped him to better understand his research. He developed the laws of inheritance He is known as the Father of Genetics." copyright cmassengale 5 Mendel s Pea Plant Experiments copyright cmassengale 6 3

4 12/10/14 Let s look back for a second: remember that whole Reproduction thing in Flowering Plants???? ò Pollen contains the male sex cell ( sperm). It is Produced by the. Stamen (anther) ò The female sex cells (eggs) is called the. This is located ovule ovary inside of the flower. ò Flowers are able to reproduce with the help of bees and other living organisms. copyright cmassengale 7 Two types of fertilization in Flowering Plants Pollen carries sperm to the eggs for fertilization. Fertilization can occur by: Selfa) pollination can occur in the same flower. b) Cross pollination can occur between two different flowers. 8 4

5 How Mendel Began Mendel produced pure strains of plants by allowing plants to selfpollinate for several generations copyright cmassengale 9 Mendel s experiments From working with these plants, Mendel noticed that the patterns of inherited traits were not always clear. Sometimes traits would appear in one generation and be absent in another generation. In generations afterwards, the trait would reappear again. Mendel noticed this also occurred in other organisms as well, so he wanted to learn more about what caused these patterns To keep his investigation simple, Mendel decided to study plant, since he had already done research on them before. How do you think Mendel s experiment relates to you and your family? 5

6 Mendel studied only one characteristic at a time A characteristic is a feature that has different forms in a population. (ex: hair color) What are some more examples of characteristics a person may have? Any characteristic that can be passed from a parent to his/her offspring are called Traits. These traits can come in different forms such as red hair, brown hair, etc. Trying it all.. Mendel used different plants that had different traits for each of the characteristics he studied. Mendel s First experiment: Mendel used plants that were true-breed to get different traits for each characteristic. (ex: purple flower + white flower) The results: All of the flowers were purple? Are you surprised? What happened to the traits of the White flower? 6

7 Dominant and Recessive.. Mendel noticed that from crossing the plants, one trait was always present and the other seemed to have disappeared. Mendel chose to call these traits: A) Dominant Dominant traits are those that appear or are visible. Recessive traits are those that are hidden. B) Recessive Back to Gregor Mendel Mendel knew that from his experiment there must be two sets of instructions (one given from each parent). We now call these instructions genes. Each parent gives one set of genes to the offspring. The offspring then has two forms of the same gene for every characteristic (one from each parent). 7

8 What s in your genes. B= brown-eyed b= blue-eyed The different forms of a gene (such as dominant or recessive is called an allele. Dominant alleles are represented by a Capital letter. Recessive alleles are represented by a lower-case letter. Quick check: How many genes make up an allele? Where does each gene come from? Scenario: You have freckles. Your mom has rosy cheeks, but dad has freckles also. What is the dominant gene in this example? Now write an example of an allele to represent the freckles and an example to represent the rosy cheeks. Possible Answer: FF= freckles ff= rosy cheeks Ff= freckles 8

9 Genes affect the traits of offspring. An organism s physical appearance is known as its phenotype. ( ex: color of plants: purple or white Shapes : round or wrinkled In humans phenotypes are little more complicated. (Ex: Albinism in humans is even considered a phenotype). copyright cmassengale 17 Describe the phenotype of this flower. Red and Yellow Genes affect the traits of offspring. An organism s genetic make-up appearance is known as its genotype. All genes occur in pairs, so 2 alleles affect a characteristic Possible combinations are: Genotypes RR Rr rr Phenotypes RED RED YELLOW copyright cmassengale 18 9

10 Genotypes Homozygous genotype - gene combination involving 2 dominant or 2 recessive genes Homozygous genotypes are also called purebreed genotypes. (e.g. RR or rr) Heterozygous genotype - gene combination of one dominant & one recessive allele. These are also called hybrid genotypes. (e.g. Rr) copyright cmassengale 19 If T is the allele for tall and t is the allele for short, write the 3 possible genotypes. Ready for the Countdown! 10

11 12/10/14!!! Remember Genotypes represent the genetic makeup of the organism!!! Remember Phenotypes represent the physical appearance What are some words you can use to in the organism Describe the phenotypes in this slide? 11

12 Quickcheck???? What does homozygous mean? Heterozygous? How many of each type is shown here? Learning Target(s): I Can. Use a punnet square to predict possible outcomes when crossing different traits. 12

13 Punnett Squares: What are they and why do we use them? 1) Are used to help solve genetics problems copyright cmassengale 25 2) It organizes all the possible combinations of offspring from particular 25 parents. Y= yellow pea y= green pea

14 Get some practice. Create a Punnet Square to predict the offspring of two plants that produce round seeds. The genotype for each parent is Rr. Round seeds are dominant and wrinkled seeds are recessive. R=round r= wrinkled What will the offspring look like? 27 Practice problem. Trait: Seed Shape Alleles: R Round r Wrinkled Cross: Rr x Rr R r R RR Rr r Rr rr copyright cmassengale 28 What will the offspring look like? What are the Genotypes?: What are the Phenotypes?: What percent is round? Wrinkled? 14

15 Here s your answer. Trait: Seed Shape Alleles: R Round r Wrinkled Cross: Rr x Rr R r R RR Rr r Rr rr copyright cmassengale 29 Three of the offspring are Round and one is wrinkled. What are the Genotype?: RR, rr, Rr What are the Phenotype?: Round & Wrinkled What percent is round? Wrinkled? 75% Round 25% wrinkled Trait: Seed Shape Sample Problem #1 Alleles: R Round r Wrinkled Cross: homozygous Round seeds x Heterozygous Round seeds RR x Rr What are the Genotypes? What is the Phenotype(s)? copyright cmassengale 30 What percent is round? Wrinkled? 15

16 Trait: Seed Shape Sample problem #2: Alleles: R Round r Wrinkled Cross: Wrinkled seeds x Round seeds rr x Rr copyright cmassengale 31 What is the Genotype(s)? What is the Phenotype(s)? What percent is Round? What percent is Wrinkled? More practice: on your notebook paper, predict the offspring of the plants crossed below. T= Tall plants t = short plants Cross 2 Pure Plants TT x tt a) What are your results? copyright cmassengale 32 b) What are your results by Crossing two of the offspring? 16

17 Here s your Answer: How did you do???? Cross 2 Pure Plants TT x tt a) What are your results? All of the Offspring are (Tt) copyright cmassengale 33 b) What are your results by Crossing two of the offspring? 3 Tall & 1 short (TT, Tt, & tt) Nemo has had a small fin ever since he was a baby clown fish. He hopes that one day when he has baby fish of his own, none of them will have a small fin like him. If he marries a clown fish who is purebred for regular-sized fins, is it possible for any of the babies to have small fins? Use a Punnett Square to find your answer. Regular-sized fins: F Small fins: f (1) What are the genotypes of Nemo, the wife, and child? Nemo s Genotype: Wife s Genotype: (2) What is the probability that their children will have a small fin? 17

18 Nemo has had a small fin ever since he was a baby clown fish. He hopes that one day when he has baby fish of his own, none of them will have a small fin like him. If he marries a clown fish who is purebred for regular-sized fins, is it possible for any of the babies to have small fins? Use a Punnett Square to find your answer. Regular-sized fins: F Small fins: f (1) What are the genotypes of the Nemo, wife, and child? Nemo s Genotype: ff Wifes s Genotype: FF f f Child s Genotype: Ff (2) What is the probability that their children will have a small fin? 0% chance F F Ff Ff Ff Ff Objectives: I can: Analyze and interpret a pedigree chart. Explain the differences in genetic disorders and sex-linked traits. 18

19 RECESSIVE GENETIC DISORDERS. Result in the mutation of a recessive genetic gene. Many recessive gene disorders are rare. Examples include: A) Cystic fibrosisin Caucasian- Americans B) Sickle-cell Anemia in African-Americans Genetic Disorders. Cystic fibrosis produces a thick fluid rather than thin to lubricate the lungs and digestion tract. It builds up and makes it hard to breathe. You usually get repeated bacterial respiratory infections. Can be fatal. Sickle cell anemia Occurs when abnormal shaped red blood cells that don t add oxygen to the blood (with hemoglobin). Can also be fatal. 19

20 Other Human Genetic Disorders Of Interest Tay-Sachs Disease Hemophilia Huntington s Disease Muscular Dystrophy Sex-linked Traits Are traits (genes) located on the sex chromosomes Sex chromosomes are X and Y XX genotype for females XY genotype for males Many sex-linked traits carried on X chromosome copyright cmassengale 40 20

21 Sex-linked disorders. Females have two X chromosomes. One is used as a back-up gene in case the other becomes damaged. Males have only one copy of each gene on their one X chromosome. The other gene is a Y chromosome. The genes for certain sexlinked disorders, are carried on the X chromosome. Men are more likely to have sexlinked disorders than women, because the gene is recessive. Color Blindnesss. Color blindness is an example of a sexlinked disorder. People who are color blind have trouble distinguishing between shades of red and green. To help the colorblind, some cities have added shapes to their street lights. 21

22 Hemophilia --Hemophilia is another example of a sex-linked disorder. It prevents blood from clotting, and people with hemophilia bleed for a long time after small cuts. Hemophilia can be fatal!!!! If people worry they might pass a disease to their children, they may seek genetic counseling. Sex-linked Genes Common Examples include: Baldness Hemophilia Color Blindness 22

23 Pedigree Charts A pedigree chart is a tool for tracing a trait through generations of a family. It is used to predict if a person is a carrier of a particular disease (or trait). You can even use a pedigree chart to trace how you inherited your hair color. How to read a pedigree chart. SQUARES= MALES CIRCLES= FEMALES Vertical lines connect children to their parents. A solid square or circle indicates a person has a certain trait. A half-shaded circle indicates a person is a carrier of the trait. Not shaded: they don t have nor carry the recessive trait (homozygous dominant, TT) 23

24 Examine the chart below: Was this a sex-linked trait? copyright cmassengale 47 Yes, In this case the females were only carriers, but a male actually had it copyright cmassengale 48 24

25 Possibilities What if? Both parents are homozygous dominant? - They can t pass the disorder to their children If at least one parent is recessive for the trait? - Their children have to be a carrier for the trait (tt x TT or tt x Tt) Both parents are homozygous recessive? - Their children will be homozygous recessive too