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Chapter 12 Patterns of Heredity and Human Genetics Chapter 12.1 Scientific Terms 1. 2. 3. Pedigree Carrier Fetus 1. What is a pedigree? How do you make one? Pedigree graphic representation of genetic inheritance - looks like a “family tree” It is made of a set of symbols that identify: - male or female - the trait being studied - the relationships between the members 2. Describe how you would analyze a pedigree. Why are these useful? Pedigrees show “carriers”, which are heterozygous individuals You can follow a trait through generations by looking at a pedigree Helpful for knowing the possibility of genetic disorders, or any recessive trait 3. Describe what “simple recessive heredity” refers to. Describe the three recessive disorders that the book discusses. 1. 2. 3. Genetic disorders caused by a homozygous recessive situation (rr or tt, etc) Cystic fibrosis 1 in 28 white Americans carry the recessive allele (Rr) - 1 in 2500 white kids born with it Tay-Sachs common in Amish people and Jewish people from eastern Europe Phenylketonuria common in descendants of Norway and Sweden 4. Describe what “simple dominant heredity” refers to. Overview the several dominant traits that the book discusses. A trait is inherited with at least one dominant allele (RR or Rr) Tongue rolling Free hanging ear lobes Hitchhiker’s thumb Almond shaped eyes Full lips Hair on middle section of fingers Huntington’s disease Section Assessment Answer questions (1-4) on page 314. Chapter 12.2 Scientific Terms 1. 2. 3. 4. 5. Incomplete dominance Codominant allele Multiple allele Autosome Sex chromosome 5. Describe the concept of “incomplete dominance” and describe an example. When the phenotype of the heterozygote is a blending of the two homozygotes Ex: If a red flower (RR) is crossed with a white flower (R’R’), the resulting offspring are heterozygotes (RR’) which look pink 6. Describe the concept of codominance. Show an example. Codominant alleles cause the phenotypes of both homozygotes to be produced in the heterozygote Both alleles are expressed equally, not combined When a black chicken is crossed with a white chicken, the offspring are NOT gray, they are black and white 7. Describe the concept of multiple phenotypes from multiple alleles. Describe the book’s example. It is common for more than 2 alleles to control one trait Traits controlled by more than 2 alleles have “multiple alleles” In pigeons, a single gene that controls feather color has 3 alleles Ex: BA makes red feathers B makes blue feathers b makes chocolate colored feathers 8. What is the difference between autosomes and sex chromosomes? How do the sex chromosomes affect sex-linked inheritance? Can you think of any sex-linked traits in humans? Autosomes the 22 pairs of homologous chromosomes besides the sex chromosomes Sex chromosomes the 2 chromosomes that determine the sex of an individual Sex-linked traits traits controlled by genes located on the sex chromosomes - the Y chromosome has no corresponding allele to some traits on the X chromosome Ex: color blindness, male pattern baldness Review… write answers with SAQs 1. A blue fish and a yellow fish have all green babies! What inheritance pattern does fish color follow? 2. A red cow and a white cow have red & white calves. What inheritance pattern does this follow? 3. What is a chart of chromosomes called? 4. What is II-2’s genotype? 5. What is most likely II-1’s genotype? Types of Inheritance… 1. 2. 3. 4. 5. 6. 7. 8. Complete dominance Incomplete dominance Codominance Multiple Alleles Sex Determination Sex-linked inheritance Polygenic inheritance Environmental Influences Chapter 12.2 & 3 Terms 1. 2. 3. Sex-linked trait Polygenic inheritance Karyotype *Turn in terms sheet* 9. Describe what polygenic inheritance is and describe an example. It is the inheritance pattern of a trait that is controlled by two or more genes Ex: skin color (AABBCC) - the CAPITAL letters are darkness - the lowercase letters are lightness AABBCC AaBbCc aabbcc AAbbCc very dark medium very light medium 10. How does the environment influence genetic expression? Describe the influence of the external and internal environments. The genetic makeup at fertilization is the potential Many factors can influence how the gene is expressed (internal and external factors) External temperature, nutrition, light, chemicals, infections - Ex: tree leaves, height Internal male vs female due to hormones and structural differences - Ex: horn size, male baldness, peacock feathers 11. Describe what disorder exhibits codominance in humans, and why this is actually an advantage. Sickle-cell anemia Most common in African-Americans and white Americans from the Mediterranean About 1 in 12 are heterozygous (RR’) and produce both normal RBCs and sickle ones Advantage in malaria 12. Describe how multiple alleles govern human blood types, and why this is important to know. ABO blood group Determined by the presence or absence of surface proteins on RBCs Three alleles for the “I” trait IA, IB, i Section Assessment Answer questions (1-4) on page 322 Turn in your Ch 12.2 sheet Types of Inheritance… 1. 2. 3. 4. 5. 6. 7. 8. Complete dominance Incomplete dominance Codominance Multiple Alleles Sex Determination Sex-linked inheritance Polygenic inheritance Environmental Influences 13. Describe the two sex-linked traits talked about in your book. Why do males usually get these disorders? 1. 2. Red-Green color blindness - caused by two recessive alleles at two gene sites on the X chromosome Hemophilia - problem with blood clotting - 1 in 10,000 males - 1 in 100,000,000 females - inherited on X chromosome from mother carriers - treated with blood transfusions and Factor VIII (a blood clotting enzyme) 14. Describe how skin color is considered polygenic inheritance. There aren’t just light and dark people, there are intermediates also Ex: light person + dark person = medium people medium + medium = dark, medium, light The “AABBCC” idea from before 15. What happens when there are changes in the chromosome numbers in humans? Many abnormal phenotypes result from changes in chromosome numbers Missing information Too much information Usually results in disorders 16. How do scientists figure out if someone has an unusual number of autosomes? Normal: 23 pairs (46 chromosomes) 22 pair are autosomes; 1 pair are sex If unusual autosome number, can have 47 or more chromosomes A “karyotype” is a chart of chromosome pairs from an individual’s cells 17. What happens when an individual has an extra chromosome 21? Usually disorders of chromosome number cause problems so severe the fetus dies Down syndrome the only autosomal trisomy where the individual survives into adulthood (1 in 700 births) It is a trisomy of chromosome 21 Higher incidence in mothers over 40 years 18. Describe the abnormalities that occur when there is an unusual number of sex chromosomes. The 2 sex chromosomes XX if female and XY if male An X chromosome can be missing and be XO An X may be extra and be XXY or XXX An extra Y could be added and have XYY There is not enough information in the Y to have no X at all YO won’t happen MiniQuiz Which inheritance pattern is exhibited by the following: Red flowers + white flowers = pink flowers Red, blue, and chocolate pigeon feathers Black chicken + white chicken = checkered chicken Red-green colorblindness & hemophilia Cystic fibrosis & Tay-Sachs disease Section assessment Answer questions (1-4) on page 329 The End!