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Unformatted text preview: Types of Variation continued s Polygenic inheritance - One trait is affected by many genes
E.g. skin color Additive effect of 3 separately inherited genes on pigmentation in skin. Types of Variation
Genotypes, Phenotypes, and evolution
Polygenic inheritance e.g. height Polygenic inheritance e.g. height Note: males in dark; females in white Types of Variation
is usually complex:
x Environment - The phenotype is influenced by the s Relationship between genotype and phenotype environment
3 E.g. height, PKU 3 "Norm of Reaction" s Relationship between genotype and phenotype is usually complex x Genomic imprinting Types of Variation
s Relationship between genotype and phenotype can be complex:
x Development - Do identical twins have identical fingerprints? s Pedigree Chart- shows the pattern of inheritance for a particular trait See Figures 13.21; 13.22 Does this pedigree represent recessive or dominant inheritance? Chromosomal Theory of Inheritance
s Genes are located on chromosomes.
x 1902- Boveri & Sutton s Autosomes= Humans = 22 pair
x Same genes on both homologues. s Sex chromosomes in humans: Female = XX; Male = XY
x Males determine the gender! x X-linked- Genes carried on X chromosome
3 2000 genes s How it all began- 1900's Thomas Hunt Morgan (Nobel in 1933)
x Looked for a relationship between gender & traits working with fruit fly eye color.
s Morgan found- some traits are inherited as a group:
x Linkage = tendency of genes on the same chromosome to end up together in the same gamete. s Linked genes are inherited together and are close together on the chromosome. x So, Mendel's law of independent assortment applies to genes on different chromosomes. Chromosomal Inheritance
s Sex-linked inheritance
See Figure 15.8a (X- linked) See Fig. 13.23 Transmission of X-linked traits
A B C A = dominant allele a = recessive allele X-linked recessive Genetic disorders:
s 1. Color-blindness X-linked recessive Genetic disorders:
s 1. Color-blindness s 2. Duchenne Muscular Dystrophyx Muscles waste away x 1: 3,500 males born x Lethal by age 20 s 3. Hemophilia- 1:7,000 males 3. See Fig. 13.23 X-linked recessive Genetic disorders:
- Fragile X syndrome Lesch Nyan syndrome Ichthyosis Menkes syndrome Brown teeth Common genetic cause of mental retardation. 1 in 1,500 males; 1 in 2,500 females Caused by duplication mutation. 200+ CGG Remember: Offspring inherit genes, not phenotypes!
s Which alleles end up in a given gamete and later, a new individual?
x 1. Crossing over at Meiosis I x 2. Independent assortment at Meiosis I x 3. Fertilization x 4. Gene mutation x 5. Change in chromosome number or structure Sources of Genetic Variation
s Recombination and independent assortment reshuffle existing variation
s Where does variation come from?
x Errors in repair or synthesis x Damage caused by X-rays or chemicals x Unequal crossing over x Errors in meiosis Mutation s Larger scale chromosome rearrangements Sources of Genetic Variation
s Point mutations- pages 347-349
x Base-pair Substitution
3 1. Silent - Code for same amino acid (neutral) 3 2. Missense - Code for wrong amino acid E.g. Sickle cell anemia THE FAT CAT ATE THE RAT THE FAT CAT ATE THE HAT Sources of Genetic Variation
s Point mutations: mistakes at 1 location on DNA Sources of Genetic Variation
s Point mutations:
x 3. Table 16.3 Nonsense
stop translation THE FAT CAT ATE. Lead to nonfunctional proteins 3 Prematurely x 4. Frameshift 3 Often have major effects 3 Insertion or deletion of a nucleotide 3 THE FAT CAT ATE THE RAT 3 THE ATC ATA TET HER AT- 4 Types of chromosomal mutations/ rearrangements:
s 1. Inversion a segment is excised then reversed and rejoined. See Table 16.4 s 2. Translocation- most often occurs. Transfer or exchange of all or part of one chromosome to a nonhomologous chromosome. Figure 15.13 s 3. Deletion- loss of a chromosomal segment.
(loss of piece of chr.#5) x E.g. Cri du chat syndrome Figure 15.13 s 4. Duplication- repeating a segment of a chromosome more than once in the same chromo.
x E.g. Huntington's disorder (Repeats CAG on #4) Figure 15.13 Sources of Genetic Variation
s Larger scale chromosomal rearrangements
x Deletion - E.g. Some Duchenne's muscular dystrophy x Duplication
3 E.g. Huntington's disease 3 Repetitions of CAG. O.k. if <30 Sources of Genetic Variation
s Larger scale chromosomal rearrangements
x Deletion - E.g. Some Duchenne's muscular dystrophy x Duplication - E.g. Huntington's chorea x Inversion x Translocation 3 E.g. of SRY gene 3 -> XX males Changes in chromosome #
s Monosomy- (2n 1) only 1 type of chromosome s Trisomy- (2n + 1) three of 1 type of chromosome s Polyploid- more than 2 pair of chromosomes
x Plants Disorders from Nondisjunction:
s Most sex chromosome abnormalities occur during meiosis/ gamete formation due to nondisjuction. s E.g.,
x Down syndrome- Trisomy 21 x Turner syndrome- XO x Klinefelter syndrome- XXY x XYY- Jacob syndrome Disorders from Nondisjunction:
x Down syndrome
3 Trisomy 21 x Turner syndrome
3 XO females x Klinefelter syndrome
3 XXY males 3 2 or more X's s Alteration of chromosome number
3 E.g. Down syndrome Turner syndrome Klinefelter syndrome Klinefelter syndrome Jacob syndrome s Genetic Testing before birth: See Figure 14.17 1. 2. Summary
s The relationship between the genotype and the phenotype ranges from simple to very complex.
x Know and be able to give examples of each of the following: x Complete dominance x Recessive inheritance x Incomplete dominance be able to work problems x Codominancex Pleiotropy x Epistasis x Polygenic inheritance x Environmental influence x Genomic imprinting inheritance be able to work blood group problems s Pedigrees know how to interpret s Truly Mendelian inheritance is just a small subset of patterns of inheritance:
x Chromosomal Theory of inheritance
3 Summary X-linked examples and problems s Recombination and independent assortment reshuffle existing variation, creating new combinations of genes. s Sources of Variation
3 - know 4 types and examples Point mutations x Changes in chromosome number or structure
3 Non-disjunction (examples) 3 Karyotypes 3 Examples of human genetic disorders ...
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This note was uploaded on 05/11/2010 for the course BIOLOGY 100 taught by Professor Richard during the Spring '10 term at George Mason.
- Spring '10