Today: Mendelian Genetics Discussion/Notes

Transcription

1 Monday, March 28, 2016 LT: I can describe the molecular process by which organisms pass on physical and behavioral traits to offspring Entry Task: What is heredity? Today: Mendelian Genetics Discussion/Notes

2 RARE DOMINANT TRAITS Why would these dominant traits be rare? Huntington s Disease Marfan Syndrome Dwarfism Extra digits & fused digits

3 COMMON RECESSIVE TRAITS Why would these recessive traits become common? Type O blood about 46% of humans Little body hair Normal blood pressure Normal vision

4 Mendelian Genetics The study of how traits are passed from generation to generation

5 HISTORY OF GENETICS Gregor Mendel (b. 1822) Considered the Father of Genetics. Priest Studied science and mathematics at the University of Vienna Worked in monastery and taught high school In charge of monastery garden began studies of pea plant traits and inheritance

6 ESSENTIAL VOCABULARY FOR GENETICS! Gene sequence of DNA that codes for a protein and thus determines a trait Genetic Trait specific characteristics determined by genes and passed from parents to offspring. Allele - different forms of a gene; can be dominant or recessive Dominant in a relationship between 2 alleles of the same gene, the dominant is expressed over the recessive. Recessive - form only seen when the dominant allele is not present. Phenotype physical or expressed trait Ex eye color, genetic disorder (Cystic Fibrosis) Genotype Genetic makeup, allele combination for a trait

7 VOCABULARY CONTINUED Homozygous 2 identical alleles for a trait Heterozygous 2 different alleles for a trait Hybrid offspring of parents that are homozygous dom. & homozygous rec. for a trait. Review Diploid cells (2n) - contain two complete sets of inherited chromosomes (hence two sets of genes). Homologous Chromosomes - pairs of chromosomes in which one comes from the male parent and one from the female parent. Haploid cells (n) - refers to a cell that contains only a single set of chromosomes (hence one set of genes). Gametes - sex cells (haploid).

8 Mendel s Pea Plant Observations Peas have different variations for traits Height:tall/short, Seed and pod color: green/yellow, Flower color: purple/white Seed shape:round/wrinkled Mendel cross pollinated true-breeding plants with different form of trait. Observation: When given two forms for a trait, one will dominate the other (is seen). The other factor he called recessive (not seen).

9 MENDELIAN INHERITANCE During sex cell formation (what s the process?), the alleles for each gene separate (segregate), so that each gamete receives one allele for each gene. At fertilization, the alleles combine again in the new offspring, which receives two alleles for each trait one from each parent.

10 Mendel s Experimental Results P cross Tall (TT) X Short (tt) F1 Tt Tt The offspring, Tt, are all tall plants (hybrids)

11 MENDEL S EXPERIMENTAL RESULTS F1 Cross Tt Tt F2 Cross TT Tt Tt tt

12 MENDEL S RESULTS. WHAT PATTERN IS SHOWN IN THE F1 AND F2 RESULTS? P1 Parents F1 Offspring F1 Cross F2 Offspring Tall X short All tall Tall X tall 302 tall short Yellow X green seeds All yellow seeds Yellow X yellow 313 yellow green Yellow X green pods All green pods Green X green 298 green + 99 yellow Round X wrinkled seeds All round seeds Round X round 301 round + 97 wrinkled

13 PROBABILITY Mendel realized that his results could be explained mathematically. The alleles combine according to the Laws of Probability! What is probability?

14 FIRST LAW OF PROBABILITY What is the chance of flipping a coin and getting heads? If you flip a coin 5 times and each time you get heads, what is the chance that the next toss will produce heads? Rule of Independent Events: Past events have no influence on future events. 1 outcome out of 2 possibilities = 1/2

15 SECOND LAW OF PROBABILITY What is the chance of flipping a coin two or three times in a row and having it be heads every time? The Rule of Multiplication: The chance that two or more independent events will occur together is equal to the product of the probabilities of each individual event. ½ X ½ = ¼ ½ X ½ X ½ = 1/8

16 EXIT TASK 1. In genetics, what does dominant refer to? 2. What is genetic prevalence? 3. Why are some dominant traits rare and some recessive traits common?

17 Tuesday, March 29, 2016 LT: I can describe the molecular process by which organisms pass on physical and behavioral traits to offspring Entry Task: During which phase of meiosis do alleles for a trait get separated from each other and segregated into different daughter cells? Today: Finish Mendelian Genetics Discussion/Notes Punnet Square Worksheet (#1-11)

18 THIRD LAW OF PROBABILITY What is the chance of flipping two coins and getting heads on one and tails on the other? The Rule of Addition: The chance of an event occurring when that event can occur two or more different ways is equal to the sum of the probabilities of each individual event. This can happen in 2 ways: 1. Coin #1 heads (1/2) X Coin #2 tails (1/2) = ¼ 2. Coin #1 tails (1/2) X Coin #2 heads (1/2) = ¼ Therefore ¼ + ¼ = 1/2

19 Solving Hybrid Cross Problems Punnett Squares used to predict the percentages of genotypes and phenotypes of crosses Ex. Widows Peak X Straightline Widows Peak is dominant = W Straightline is recessive = w Homozygous Widows Peak = WW Homozygous Straightline = ww Heterozygous Widows Peak = Ww

20 What will the genotypes and phenotypes be of a cross of true-breeding (homozygous) parents? WW X ww (P = 1 st Parents) F1 = First Offspring Genotypes: Phenotypes:

21 What will the genotypes and phenotypes be of a cross of heterozygous parents? Ww X Ww (F1 = 1 st Offspring) F2 = 2nd Offspring Genotypes Phenotypes

22 Punnett Square Show the Laws of Probability! 1 st Law ½ chance for each W w W 2 nd Law ½ X ½ = ¼ WW Ww w Ww ww 3 rd Law ½ X ½ + ½ X ½ = ½

23 Punnett Square Practice Use a Punnett Square to determine the phenotype and genotype ratios of a cross between: Bb X bb Dominant = Curly hair

24 Result of Punnett Square Genotypes: Phenotypes:

25 DIHYBRID CROSSES TESTS HOW TWO DIFFERENT TRAITS ARE INHERITED TOGETHER Led to Principle of Independent Assortment - genes for different traits usually segregate into gametes independently of one another.

26 TWO-FACTOR CROSS What are the probable outcomes of a cross between two heterozygous tall, heterozygous green pod plants? How do we represent the parents? T Random Alignment: Possible arrangements of homologous chromosomes at Metaphase 1 Meiosis produces the following gametes because of random alignment: TG, tg, Tg, tg

27 TtGg x TtGg March 28, 2016

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29 EXIT TASK: Cross a heterozygous, dimpled father with a homozygous recessive, nondimpled mother. Give the possible genotypes and phenotypes of the offspring. March 28, 2016

30 Wednesday, March 30, 2016 LT: I can describe the molecular process by which organisms pass on physical and behavioral traits to offspring Entry Task: We know that the process of Meiosis produces unique sex cells that leads to the variation we see within species. What other process that we have been simulating with Punnett Squares contributes to genetic variation within species? Today: Genetics of Reebops

31 EXIT TASK: How many allele combinations can be made when 2 traits assort into gametes?

32 Thursday, March 31, 2016 LT: I can describe the molecular process by which organisms pass on physical and behavioral traits to offspring Entry Task: Give a possible explanation for why our Reebops could have 3 different nose colors? Remember, the QQ genotype produced a red nose, the qq genotype produced a yellow nose and the Qq produced an orange nose. Today: Genetics of Reebops

33 EXIT TASK: Cross a recessive no dimple, no widow's peak mother with a homozygous dimpled, heterozygous widow's peak father. March 28, 2016

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35 Beyond Dominant and Recessive Alleles Incomplete Dominance Cases in which one allele is not completely dominant over another. The heterozygous phenotype is somewhere in between the two homozygous phenotypes. Ex. Four o clock plants: Homozygous are white or red Heterozygous are pink Reebops: Homozygous are red or yellow Heterozygous are orange

36 Cross 2 Pink Plants March 28, 2016

37 Beyond Dominant and Recessive Alleles Codominance Both alleles contribute to the phenotype of the organism. Ex. Hair color in cattle: Homozygous are red or white Heterozygous are roan (pinkish brown) a mixture of red and white hairs Ex. Feathers in chickens: Homozygous are black or white Heterozygous are speckled a mixture of black and white feathers

38 ABO Blood Group Blood type is an example of a trait with multiple alleles: A, B, O A and B are co-dominant, O is recessive Type O is the Universal Donor all blood types can receive type O blood. Type AB is the Universal Recipient can receive blood from all other blood types.

39 Genotypes & Phenotypes Genotype AA or AO BB or BO AB OO Phenotype Type A Type B Type AB Type O

40 Practice: 1. What is the probable genotype ratio among children born to an AO mother and an AB father? One parent has type A blood and the other has type B. What are their genotypes if they produced children who were: 2. All AB 3. ½ AB and ½ A 4. ¼ AB, ¼ A, ¼ B and ¼ O March 28, 2016

41 The Rh Group Named for Rhesus monkey where factor was discovered Single gene with 2 alleles: positive and negative Rh+ allele is dominant Rh- allele is recessive

42 Sex-linked Genes Genes located on chromosomes that determine sex of organism X and Y Many on X chromosome bigger than Y Over 100 sex-linked genetic disorders on X Most affect males more than females. Why? Males have 1 X chromosome. Thus, all x-linked alleles are expressed in males, even if they are recessive. Fathers with recessive allele pass it to their daughters, who in turn pass it to their sons.

43 Examples of Sex-linked Traits Color-blindness Recessive, 3 genes on X chromosome Hemophilia Recessive, 2 genes on X chromosome, a recessive allele for either gene can produce the phenotype. Blood doesn t clot. Duchenne Muscular Dystrophy Recessive, 1 gene on X chromosome. Muscle wasting disease

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45 In sex-linked Punnett Squares we show the X and Y chromosomes with the alleles for the trait we are looking at as superscripts. Ex: X H X h - heterozygous mother X H Y - dominant father (note: father only has 1 allele for an x-linked trait!)

46 Punnett Square Practice with Sex-linked Inheritance 1. Cross a normal (non carrier) mother with a colorblind father. Give phenotype and genotype ratios of their male and female offspring. 2. A normal woman whose father had hemophilia married a hemophiliac man. Give the phenotype and genotype ratios of their sons and daughters.

47 Beyond Dominant and Recessive Alleles Polygenic Traits Traits controlled by two or more genes. Ex. 1. Three genes control eye color in fruit flies. Different combinations of alleles for these genes produce different eye colors. Ex. 2. Skin color in humans is probably controlled by more than four genes. Ex. 3. Eye color in humans