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QUIZ Name___________________ Meiosis 1. End result 1n or 2n? 2. Daughter cells Distinct or identical? 3. Chiasmata? Yes or no? 4. # of divisions 5. Purpose Growth or germ cells? Mitosis QUIZ Name___________________ Meiosis 1. End result 1n or 2n? 2. Daughter cells Distinct or identical? 3. Chiasmata? Yes or no? 4. # of divisions 5. Purpose Growth or germ cells? Mitosis 1n 2n distinct identical Yes No 2 1 Germ cells Growth Chapter 10 Observable Patterns of Inheritance •Attached or detached earlobes depends on a single _____ •A gene has two molecular forms (______) •Inherit one form each _______ •Dominant allele specifies detached earlobes Earlobe Variation • You inherited one allele for this gene from each parent • _______ allele specifies detached earlobes • __________ allele specifies attached lobes Early Ideas About Heredity How are traits transmitted? • _______________ theory– Genetic material mixes much like yellow and blue paint makes ____ Problem: – Would expect variation to ________ – Yet variation in traits _______ Gregor Mendel • Strong background in plant breeding and mathematics- __________ • Using pea plants, found indirect but observable evidence of how parents transmit ____to offspring The Garden Pea Plant •Self-pollinating •______________ (different alleles not normally introduced) •Can be experimentally ____________ What is a gene? • Units of information about specific ____ • Passed from _________ to offspring • Each has a specific location (_____) on a chromosome What is an allele? •Different ________________ of a gene •Arise by _____________ •Dominant allele ___________ a recessive allele that is paired with it Vocabulary • _____________ - An organism with two _______ alleles for a character (e.g. AA or aa) • ___________- An organism with two ____________ alleles for a character (e.g. Aa) • ________ - A description of an organism’s ______ • ________ - A description of its ______________ •Example- For flower color in peas, both PP and Pp plants have the same phenotype (purple) but different genotypes (homozygous and heterozygous). Mendel cross-pollinated peas _________________ _________________ P1 x P2 F1 The F2 generation revealed two principles of heredity: 1. _____________________ F1 x F1 2._______________________ _________________ F2 Mendel’s Monohybrid Cross Results F2 plants showed dominant-torecessive ratio that averaged 3:1 5,474 round 1,850 wrinkled 6,022 yellow 2,001 green 882 inflated 299 wrinkled 428 green 152 yellow 705 purple 224 white 651 long stem 207 at tip 787 tall 277 dwarf Mendel’s Law of Segregation 1. An individual inherits a unit of information (_______) about a trait from each parent 2. During gamete formation, the alleles _________ from each other 1. Law of segregation • A ________________ predicts the results of a genetic cross between individuals of known genotype. Purple White PP x pp Call the dominant allele “P” Call the recessive allele “p” All Pp F1 Purple Pp x Pp P P Predicts 75% purple: 25% white Or 3:1 ratio F2 p p Dihybrid Cross • Experimental cross between individuals that are homozygous for different versions of two traits purple flowers, tall TRUEBREEDING PARENTS: AABB GAMETES: AB x AB white flowers, dwarf aabb ab ab AaBb F1 HYBRID OFFSPRING: All purple-flowered, tall Phenotypic Ratios in F2 AaBb X AaBb Four Phenotypes: – Tall, purple-flowered (9/16) – Tall, white-flowered (3/16) – Dwarf, purple-flowered (3/16) – Dwarf, white-flowered (1/16) 9:3:3:1 is magic ratio in dihybrid cross Explanation of Mendel’s Dihybrid Results If the two traits are coded for by genes on separate chromosomes, sixteen gamete combinations are possible 1/4 AB 1/4 Ab 1/4 aB 1/4 ab 1/4 AB 1/4 Ab 1/4 aB 1/4 ab 1/16 1/16 1/16 1/16 AABB AABb AaBB AaBb 1/16 1/16 1/16 1/16 AABb AAbb AaBb Aabb 1/16 1/16 1/16 1/16 AaBB AaBb aaBB aaBb 1/16 1/16 1/16 1/16 AaBb Aabb aaBb aabb Law of independent assortment Metaphase I A A a a B B b b OR A A a a b b B B Metaphase II: Gametes: A A a a A A a a B B b b b b B B B A B A 1/4 AB b a b a 1/4 ab b A b A 1/4 Ab B a B a 1/4 aB •two “units” for the first trait were to be assorted into gametes ____________ of the two “units” for the other trait Impact of Mendel’s Work • Mendel presented his results in ____ • Paper received _______________ • Mendel discontinued his experiments in 1871 • Paper rediscovered in ______ and finally appreciated Dominance Relations • _____________dominance • ____________ dominance – Heterozygote phenotype is somewhere ___________that of two homozyotes • _________________ – Non-identical alleles specify two ______________ that are both expressed in ________________ Examples of recessive disorders 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 2. Tay-Sachs disease – 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 Ashkenazic Jews (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. __________________ Dominance Flower Color in Snapdragons: Pink-flowered plant X Pink-flowered plant (heterozygote) (heterozygote) White-, pink-, and red-flowered plants in a 1:2:1 ratio Pink flowers have one normal and one ____________allele Codominance Genetics of ABO Blood Types: ______Alleles • Gene that controls ABO type codes for enzyme that dictates structure of a glycolipid on blood cells • Two alleles (IA and IB) are ________ when paired • Third allele (i) is _________ to others • Type A - IAIA or Iai • Type B - IBIB or IBi • Type AB - IAIB • Type O - ii ABO and Transfusions • Recipient’s immune system will attack blood cells that have an unfamiliar glycolipid on surface • Type __ is universal donor because it has neither type A nor type B glycolipid Pleitropy • Alleles at a ______ locus may have effects on _______________ traits • Classic example is the effects of the mutant allele at the _______________ that gives rise to sickle-cell anemia •HbS homozygotes produce only the ___________hemoglobin; suffer from sickle-cell anemia At low ___ levels, cells with only HbS hemoglobin “sickle” and stick together- clog __________•Eye disease, infection, heart disease Fig. 10.12, p. 161 Albinism •________ production is completely blocked •Homozygous recessive at the gene locus that codes for _____ Human Variation • Some human traits occur as a few ________types – Attached or detached earlobes – Many genetic disorders • Other traits show continuous variation – ________ – Weight – Eye color (line of bell-shaped curve indicates continuous variation in population) Range of values for the trait Number of individuals with some value of the trait Number of individuals with some value of the trait Describing Continuous Variation Range of values for the trait Temperature Effects on Phenotype • Himalayan rabbits are Homozygous for an allele that specifies a heatsensitive version of an enzyme in melaninproducing pathway • Melanin is produced in cooler areas of body