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CHAPTER 7 EXTENDING MENDELIAN GENETICS

CHAPTER 7 EXTENDING MENDELIAN GENETICS. SECTION 1 CHROMOSOMES AND PHENOTYPES. Two copies of each autosomal gene affect phenotype. One copy comes from the Father, the other from the mother ? What cellular process forms gamete cells? (aka haploid cells?)

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CHAPTER 7 EXTENDING MENDELIAN GENETICS

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  1. CHAPTER 7 EXTENDING MENDELIAN GENETICS

  2. SECTION 1 CHROMOSOMES AND PHENOTYPES • Two copies of each autosomal gene affect phenotype. • One copy comes from the Father, the other from the mother • ? What cellular process forms gamete cells? (aka haploid cells?) • Some disorders are caused by recessive alleles. • The Heterozygous form of these conditions are known as CARRIERS because they do not portray the disease, but can pass it on to the next generation.

  3. DISORDERS CAUSED BY ALLELE COMBINATIONS: Recessive ex. Sickle Cell Anemia Dominant ex. Huntington’s disease • Homozygous recessive to have the disease/disorder • The Heterozygous form of these conditions are known as CARRIERS because they do not portray the disease, but can pass it on to the next generation. • less common than recessive disorders. • Since caused by a dominant allele, there is a 50% chance of the next generation having the disease.

  4. SEX LINKED TRAITS • Sex chromosomes = the X and Y • Females = XX, Males = XY • In X-linked traits: • women can be carriers, normal, or affected • males are either affected or not since they have only 1 X • In Y-Linked traits: • Only seen in males, and all the males in a family will be affected from father to son. * The X chromosome is SUPER HUGE as compared to the Y chromosome and must be present in either sex.

  5. X CHROMOSOME INACTIVATION • X chromosome is HUGE, and in cats controls color. • The cells randomly turns one of the X’s off allowing one color to show through. • The Turned off X is called a BARR BODY. • This is how you get calico cats! 

  6. PATTERNS OF INHERITANCE REVIEW: • Incomplete dominance- • occurs when neither of the dominant nor the recessive allele is masked during the heterozygous stage. • The phenotypes seem to BLEND • Codominance- • both alleles of a gene are expressed completely, neither is dominant or recessive. • Polygenic traits- ex skin color, eye color,etc • phenotype that is controled by two or more genes. • Epistasis occures when there is one gene that can mask/ interfere with ALL the rest. Example: Albinism

  7. What term do we use when there is a blending of phenotypes due to the heterozygous genotype? ex white, pink, Red • INCOMPLETE DOMINANCE • What term is used to describe the state where BOTH alleles are expressed completely, where neither is dominant or recessive? • CODOMINANCE • What term is used to describe a trait that is controlled by two or more genes? • POLYGENIC TRAIT POP QUIZ

  8. 4. What do we call the polygenic gene that can mask all the rest? • Epistatic gene 5. What is the term used to describe the X chromosome that has been turned off in female cells? • Barr Body 6. Why are dominant trait disorders less common in a population than recessive trait disorders? • Dominant trait disorders generally cause server damage and death for the creature, generally before it can pass on its genetic information POP QUIZ

  9. Sunlight can cause a person’s hair to become lighter in color. Is this an example of an interaction between genes and the environment? Why or why not? • YES! because phenotype is altered by environment • Give an example of a trait that is considered to be polygenic. • Eye color, skin color, etc POP QUIZ BONUS

  10. HOME WORK Read Chapter 7 sections 3 & 4 pages 209 – 217 Screen notes assignment: Part one Fold your 2 pieces of notebook paper so that each side has 6 boxes. Everytime you come to a BOLD BLUE or BLACK paragraph heading you will do the following. In the LEFT BOX you will write the page number and notes to sum up that section. minimum of 12-15 words! In the RIGHT box you will sketch a picture to illustrate what you wrote in the left box. Something to help you remember it. ***You must have 8 box sets of words & pictures. Part two: Investigation on page 219 #’s 1-4, must show work and use COMPLETE SENTENCES!!!

  11. GENE LINKAGE ,MAPPING, & PEDIGREES chapter 7 sections 3&4

  12. THOMAS HUNT MORGAN AND HIS FRUIT FLYS • Gene linkage was first studied by Morgan in fruit flies because they were easy to raise and had few characteristics to easily study. • He expected the Mendelian 9:3:3:1 ratio but his results did not always follow that. • He observed that some of the triats seemed to be inherited together in four groups…. • we later learned that they only had four chromosomes… • He called these genes LINKED GENES because they were on the same chromosome, and found out that the CHROMOSOMES not the GENES assorted independently during meiosis.

  13. He called these genes LINKED GENES because they were on the same chromosome, and found out that the CHROMOSOMES not the GENES assorted independently during meiosis. • He also concluded that chromosomes must exchange homologous genes during meiosis… CROSSING OVER

  14. LINKAGE MAPS • Are used to estimate distances between genes. • The CLOSER together two genes are, the MORE likely they will be inherited together. • The FARTHER apart two genes are, the LESS likely they will be inherited together. • On a linkage map, one map unit is equal to one cross-over for each 100 offspring, or one % point.

  15. MAP CHALLENGE: USE THE DATA BELOW TO ANSWER THE QUESTIONS • Gene A and B cross over 6.0% of the time. • Gene B and C cross over 12.5 % of the time. • Gene A and C cross over 18.5 percent of the time. • Which two genes are closest together? • Which two genes are farthest apart? • Draw a map showing the location of each gene and its %/ map unit distance from the next. ex. ______A__________B__C_________ 25% 2% so A to C = 27%

  16. PEDIGREES • Human genetics, or any mammal’s genetics follow a set of patterns that can be easily recorded in pedigrees. • A Pedigree is a chart that can help trace the phenotypes and genotypes in a family for a particular trait. • Autosomal traits are easily traced since the traits will follow a Mendelian punnett square. • Sex linked traits leave a distinct pattern that requires the observed to remember if the trait is dominant or recessive, X-linked or Y linked

  17. squares = male circles = females Half filled means carrier Filled means affected I A II B III C Give the Genotypes for IA, IIB, and IIIC

  18. KARYOTYPES • Are pictures of ALL the chromosomes in a cell. • Chemical stains produce a pattern of stains on the chromosomes to help identify them. • Karyotypes can be used to show whole or partial chromosome deletions or additions. • Ex. Downs syndrome is caused by an extra #21 chromosome.

  19. HOMEWORK: Complete the at home investigation on page 219. Answer ALL the Analyze and conclude questions. (1-4)

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