CHAPTER 14 MENDEL AND THE GENE IDEA

1. CHAPTER 14 MENDEL AND THE GENE IDEA How are traits transmitted? One theory- The ____________ hypothesis- Genetic material mixes much like yellow and blue paint makes green Another theory- The _______________ hypothesis- Parents pass on discrete heritable units - genes - that retain their separate identities in offspring.

2. Gregory Mendel is the father of genetics entered Augustinian monastery in Czech republic in 1843 University of Vienna from 1851 to 1853 Influenced by a mathematician and a botanist to study variation in plants Around 1857, Mendel began breeding garden peas in a monastery to study inheritance 1. Mendel brought an experimental and quantitative approach to genetics • Advantages of pea plants – • many varieties with distinct heritable features (characters) • Mendel had strict control over which plants mated with which.

3. 1. Law of segregation Mendel cross-pollinated peas P1 x P2 _________________ The F2 generation revealed two principles of heredity: 1. _____________________ 2._______________________ _________________ F1 F1 x F1 _________________ F2 1. __________________two alleles for a character are packaged into separate gametes Evidence F1 F2 purple x white all purple white + purple 224 705 = 1 to 3 ratio

4. Mendel reasoned that the purple flower is a _____________trait and the white flower is a_________________trait. The plant colors were not “blended” 1. Law of segregation Mendel also found the same 3:1 ratio in other crosses (e.g wrinkled and smooth seeds)

5. Mendel developed a hypothesis to explain these results that consisted of ________related ideas. 1. Alternative version of genes (______________) account for variations in inherited characters. Example: The purple-flower allele and white-flower allele are two DNA variations at the flower-color locus. 1. Law of segregation Locus for flower color Fig. 14.4 2. For each ___________, an organism inherits twoalleles, one from each parent. • E.g. a purple-flower allele from one parent and a white-flower allele from the other.

6. 3. If two alleles differ, the_______________, is fully expressed in the organism’s appearance. 1. Law of segregation • The ________________, has no noticeable effect on the organism’s appearance. • E.g. white-flower allele is recessive. • 4. The two alleles for each character ___________ (separate) during gamete production. • If different alleles are present, then 50% of the gametes will receive one allele and 50% will receive the other. • The separation of alleles into separate gametes is summarized as Mendel’s ____________________

7. A ________________ predicts the results of a genetic cross between individuals of known genotype. 1. Law of segregation Purple White Call the dominant allele “P” Call the recessive allele “p” PP x pp All Pp Purple F1 Pp x Pp F2 Predicts 75% purple: 25% white Or 3:1 ratio

8. Vocabulary ______________- An organism with two ________ alleles for a character _______________- An organism with two ________ alleles for a character __________- A description of an organism’s _____ ___________- A description of its genetic makeup 1. Law of segregation • Example- For flower color in peas, both PP and Pp plants have the same phenotype (purple) but different genotypes (homozygous and heterozygous).

9. This law comes from Mendel’s observing inheritance of ______ different characters 2. Law of independent assortment What about the law of independent assortment??Law of _________ ___________each pair of alleles segregates into gametes independently Color and shape • The allele for yellow seeds (Y) is dominant to the allele for green seeds (y). • The allele for round seeds (R) is dominant to the allele for wrinkled seeds (r). So what happens when we cross YYRR x yyrr?? Known as a ______________

10. Predict- two characters are transmitted from parents to offspring as a__________. The Y and R alleles and y and r alleles stay together. 2. Law of independent assortment • Thus, ________ the F1 to be yellow, round seeds (YyRr) and F2 to be 3:1 (yellow/round:green/wrinkled • But ________ four classes of gametes (________________) produced in equal amounts. 9 • These combinations produce four distinct phenotypes in a ___________ ratio. 3 3 1 Fig. 14.8

11. Mendelian inheritance reflects rule of __________. • Each toss of a coin is an independent event, just like the distribution of alleles into gametes. • Like a coin toss, each ovum from a heterozygous parent has a _____ chance of carrying the dominant allele and a _____ chance of carrying the recessive allele. • The probability that two coins tossed at the same time will land heads up is 1/2 x 1/2 = 1/4. • Similarly, the probability that a heterozygous pea plant (Pp) will produce a white-flowered offspring (pp) is ______________.

12. Predicting phenotypes in dihybrid crosses- The multiplication rule. What is the probability that an F2 plant will have a YYRR genotype from a heterozygous parent (YyRr) = 1/4 (YR ovum) x 1/4 (YR sperm)= 1/16 Y y R r Yy Rr YY RR Y R yy rr Yy Rr y r ¼ YY X ¼ RR = 1/16

13. What are the chances of having a grandchild with the muscular dystrophy (a recessive disease)? Given: Grandparents are RR and rr, where “r” is the disease allele. Their grandson has married a carrier. Grandparents Parents R R R r Rr Rr Rr RR r R Rr rr Rr Rr r r F1 (Parents)- no disease F2 - ¼ with disease

14. 2. The relationship between genotype and phenotype is ___________________ • Mendel’s peas were relatively simple genetically. • Each character is controlled by a____________________. • Each gene has only_________________, one of which is completely dominant to the other. Fig. 14.10 red white Many alleles show_____________________– heterozygotes show a distinct intermediate phenotype, not seen in homozygotes. pink F1 Others show _______________ in which both alleles affect the phenotype red F2 e.g. Two genes encode distinct proteins on blood cells responsible for blood-typing pink white

15. Dominance/recessiveness relationships have three important points. 1. They range from_____________________, to incomplete dominance, to codominance. 2. They reflect the mechanisms by which specific alleles are expressed in the phenotype and _________ involve the ability of one allele to subdue another at the level of DNA. 3. They do not determine or correlate with the relative abundance of alleles in a population.

16. The genes covered so far affect _________ phenotypic character. Most genes are_____________, affecting more than one phenotypic character. Example: A single mutation can contribute to diabetes, eye disease, gangrene infections, and heart disease.

17. Phenotype depends on ______________________. A single tree has leaves that vary in size, shape, and greenness, depending on exposure to wind and sun. For humans, nutrition influences height, exercise alters build, sun-tanning darkens the skin, and experience improves performance on______________________. Even identical twins, genetic equals, accumulate phenotypic differences as a result of their unique experiences. The relative importance of genes and the environment in influencing human characteristics is a very old and hotly contested debate.

18. A ______________emphasis on single genes and single phenotypic characters presents an _____________ perspective on heredity and variation. A more comprehensive theory of Mendelian genetics must view organisms______________.

19. In a_____________________, information about the presence/absence of a particular phenotypic trait is collected from as many individuals in a family as possible and______________________. The distribution of these characters is then mapped on the ____________________. 3. Pedigree analysis reveals Mendelian patterns in human inheritance

20. Example-the occurrence of widows peak (W) is ______________ to a straight hairline (w). A pedigree can help us understand the past and to predict the future. Grandparents Parents Kids • If the kids lacks a widow’s peak, but both parents have widow’s peaks, then her parents must be ____________ for that gene Fig. 14.14 The chance of having a widow’s peak is (1/2 [WW] + 1/4 [Ww]) = _______

21. Thousands of genetic disorders, including disabling or deadly hereditary diseases, are inherited as simple __________________________. From mild (albinism) to life-threatening (cystic fibrosis). 4. Many human disorders follow Mendelian patterns of inheritance • __________________ may have no clear phenotypic effects, they are carriers who may transmit a recessive allele to their offspring. • Most people with ____________________are born to • ______________with normal phenotypes. • Two carriers have a 1/4 chance of having a child with the • disorder, 1/2 chance of a carrier, and 1/4 free.

22. 1. _________________-one of every 2,500 whites of European descent. One in 25 whites is a _____________. The normal allele codes for a membrane protein that transports Cl- between cells and the environment. If these channels are defective or absent, there are abnormally high extracellular levels of chloride that causes the mucus coats of certain cells to become thicker and stickier than normal. This mucus build-up in the pancreas, lungs, digestive tract, and elsewhere favors bacterial infections. Without treatment, affected children die before five, but with treatment can live past their late 20’s. Examples of recessive disorders

23. 2. ___________________________ Caused by a dysfunctional enzyme that fails to break down specific brain lipids. Symptoms- seizures, blindness, and degeneration of motor and mental performance a few months after birth. Child dies after a few years. Among ____________________(those from central Europe) this disease occurs in one of 3,600 births, about 100 times greater than the incidence among non-Jews or Mediterranean (Sephardic) Jews. Examples of recessive disorders

24. Examples of recessive disorders Figure not in text 3. ___________________ • The most common inherited disease among blacks (1:400 African Americans) • Cause- substitution of a single amino acid in hemoglobin. • Effects- sickle-cell hemoglobin crystallizes into long rods. • This deforms red blood cells into a sickle shape. A pleiotropic disease • Multiple problems

25. Why does sickle cell disease remain in the population? Individuals with one sickle-cell allele have increased resistance to malaria (whereas those with normal alleles die) Its relatively high frequency in African Americans is a vestige of their African roots. Examples of recessive disorders

26. Relatively unlikely that two carriers of the same rare harmful allele will meet and mate. However, ___________________matings, those between close relatives, increase the risk. These individuals who share a recent common ancestor are more likely to carry the same recessive alleles. Example- _______________in royal British lineages Most societies and cultures have laws or taboos forbidding marriages between close relatives. Examples of recessive disorders Why is incest genetically dangerous?

27. 1. __________________, a form of dwarfism, has an incidence of one case in 10,000 people. Heterozygous individuals have the dwarf phenotype. Those who are not achodroplastic dwarfs, 99.99% of the population are homozygous recessive for this trait. Lethal dominant alleles are much less common than lethal recessives Why? because if a lethal dominant kills an offspring Examples of ____________disorders • One example -__________________________, a degenerative disease of the nervous system that is fatal.] • The ________________________________has no obvious phenotypic effect until an individuals is about 35 to 45 years old.

28. Many disorders normally involve multiple genes- these are called _________________ Multifactorial disorders include heart disease, diabetes, cancer, alcoholism, and certain mental illnesses, such a schizophrenia and manic-depressive disorder. The genetic component is typically polygenic.

29. 5. Technology is providing new tools for genetic testing and counseling • Most children with recessive disorders are born to parents with a normal phenotype. • A ________ to assessing risk is identifying if prospective parents are carriers of the recessive trait. • However, issues of confidentiality, discrimination, and adequate information and counseling arise.

30. Consider a hypothetical couple, John and Carol, who are planning to have their first child. In both of their families’ histories a recessive lethal disorder is present and both John and Carol had brothers who died of the disease. While neither John and Carol nor their parents have the disease, their parents must have been carriers (Aa x Aa). John and Carol each have a 2/3 chance of being carriers and a 1/3 chance of being homozygous dominant. The probability that their first child will have the disease = 2/3 (chance that John is a carrier) x 2/3 (chance that Carol is a carrier) x 1/4 (chance that the offspring of two carriers is homozygous recessive) = 1/9. A hypothetical case

31. If their first child is born with the disease, we know that John and Carol’s genotype must be Aa and they both are carriers. The chance that their next child will also have the disease is 1/4.

32. In utero testing for a disorder. 1. ____________- beginning at the 14th to 16th week of pregnancy to assess the presence of a specific disease. Fig. 14.17a • Fetal cells extracted from amniotic fluid are cultured and ____________. • 2. _____________________- performed as early as the eighth to tenth week of pregnancy. • Extracts a sample of fetal tissue from the chrionic villi of the placenta are karyotyped. Fig. 14.17b

33. Other techniques-_________________________ allow fetal health to be assessed visually in utero. usually reserved for cases in which the risk of a genetic disorder or other type of birth defect is relatively great. If fetal tests reveal a serious disorder, the parents face the difficult choice of terminating the pregnancy or preparing to care for a child with a genetic disorder.

34. Some genetic tests can be detected at birth by simple tests that are now routinely performed in hospitals. One test can detect the presence of a recessively inherited disorder, _______________________ This disorder occurs in one in 10,000 to 15,000 births. Accumulate the amino acid phenylalanine in the blood to toxic levels. Leads to mental retardation. If the disorder is detected, a special diet low in phenyalalanine usually promotes __________ development.