HUMAN GENETICS AND MUTATIONS MODERN GENETICS Regents Biology

HUMAN GENETICS AND MUTATIONS (MODERN GENETICS) Regents Biology

OBJECTIVES Upon completion of this unit students will be able to: 1. State the chromosome theory. 2. Explain why the male determines the sex of offspring. 3. Describe the work that T. H. Morgan and W. S. Sutton did. 4. Explain why Drosophila flies were ideal for early genetic research. 5. Describe what a sex-linked trait is and give examples. 6. Using Punnett Squares predict the probability of having a child with a sex- linked trait when given the genotype and or phenotype of the parents. 7. Explain gene linkage and how it is related to crossing-over. 8. Explain multiple-gene inheritance. 9. Define mutation. 10. Differentiate chromosomal and gene mutations. 11. Understand that for a mutation to be passed on to offspring, it must be present in the gametes (sex cells) of the parent organism. 12. List and briefly describe the FOUR types of gene mutations. 13. Recognize that gene mutations are usually recessive genetic conditions. 14. Give examples of genetic diseases caused by gene mutations. 15. Using Punnett Squares predict the probability of having a child with a gene mutation when given the genotype and or phenotype of the parents. 16. Identify and describe the SIX examples of chromosomal mutations. 17. Give examples of genetic diseases caused by chromosomal mutations. 18. Explain some of the difficulties that arise in studying human genetics. 19. Briefly describe what genetic counseling is. 20. Recognize a pedigree chart and identify its purpose. 21. Describe the processes of amniocentesis and chorionic villus sampling and how they can be used to diagnose some human genetic disorders. 22. Construct a karyotype and explain how it can be used to diagnose some human genetic disorders. 23. Identify the FOUR types of breeding and explain the reasons why breeding is done. 24. Understand that the environment plays a role in how certain genes are expressed and give an example. 25. Recall and understand that each gene carries a separate piece of information that codes for a particular trait (protein), and relate this to genetic mutations.

KEY WORDS 1. 2. 3. 4. 5. addition amniocentesis chorionic villus sampling chromosomal mutation deletion 6. Down Syndrome 7. gene mutation 8. inversion 9. karyotyping 10. multiple-gene inheritance 11. mutation 12. sex chromosomes 13. sex-linked trait 14. sickle-cell disease (anemia) 15. translocation (in genetics)

INTRODUCTION We have already learned that genes are made up of DNA molecules, which are the simplest building blocks of heredity. They are grouped together in specific patterns within a person's chromosomes, forming the unique "blueprint" for every physical and biological characteristic of that person. Humans have 46 chromosomes, arranged in pairs in every living cell of our bodies. When the egg and sperm join at conception, half of each chromosomal pair is inherited from each parent. This newly formed combination of chromosomes then copies itself again and again during fetal growth and development, passing identical genetic information to each new cell in the growing fetus. Current science suggests that human chromosomes carry about 30, 000 genes. An error in just one gene (and in some instances, even the alteration of a single piece of DNA) can sometimes be the cause for a serious medical condition. Some diseases, such as Huntington's disease (a degenerative nerve disease) and Marfan syndrome (a connective tissue disorder), can be inherited from just one parent. Most disorders cannot occur unless both the mother and father pass along the gene. Some of these are cystic fibrosis, sickle cell anemia, and Tay-Sachs disease. Other diseases, such as Down syndrome, are not inherited. In general, they result from an error (mutation) in the cell division process during conception or fetal development. Still others, such as achondroplasia (the most common form of dwarfism), may either be inherited or the result of a genetic mutation. Unlike your parents, you have the option of genetic testing. These tests identify the likelihood of passing certain genetic diseases or disorders (those caused by a defect in the genes, the tiny, DNA -containing units of heredity that determine the characteristics and functioning of the entire body) to your children LIKE 10 YEARS FROM NOW, RIGHT? !? !. Some of the more familiar genetic disorders are Down syndrome, cystic fibrosis, sickle cell anemia, and Tay-Sachs disease (a fatal disease affecting the central nervous system). If your history suggests that genetic testing would be helpful, you may be referred to a genetic counselor. Or you might decide to seek out genetic counseling yourself. We’ll talk about the ethics involved in our next unit…. .

I. THE CHROMOSOME THEORY • This theory states that THE ALLELES ARE CARRIED ON CHROMOSOMES (THE GENES ARE ON THE CHROMOSOMES) A L L E CHROMOSOME L E S • W. S. SUTTON did the initial research on genes and chromosomes, but the substantial evidence to support Sutton’s hypothesis was obtained by T. H. MORGAN; Sutton’s hypothesis led to Morgan’s theory http: //images. google. com/imgres? imgurl=http: //www. blackwellpublishing. com/korfgenetics/jpg/300_96 dpi/Fig 47. jpg&imgrefurl=http: //www. blackwellpublishing. com/korfgenetics/figure. asp%3 Fchap%3 D 04%26 fig%3 DFig 47&h=363&w=500&sz=31&hl=en&start=1&tbnid=V 0 Re. Dri 8 Ih. GS 5 M: &tbnh=94&tbnw=130&prev=/images%3 Fq%3 Dalleles%2 Bon%2 Bchromosomes%26 gbv%3 D 2%26 hl%3 Den%26 client%3 Dfirefox-a%26 rls%3 Dorg. mozilla: en. US: official%26 sa%3 DG

II. SEXES AND CHROMOSOMES • HUMANS have 23 pairs of chromosomes in the body (46 total) • 22 of these are called AUTOSOMES and the 23 rd pair contains the SEX CHROMOSOMES • The sex chromosomes are the X AND Y chromosomes: Each egg cell from meiosis receives one X chromosome Two types of sperm cells are produced from meiosis, X and Y X X XX = female X XY = male Y • In humans, the SPERM of the male (X or Y) determines the sex of the offspring

• Example: Do the following cross:

III. T. H. MORGAN • T. H. Morgan worked with Drosophila (fruit flies) to study genetics and was very successful • Why Drosophila? 1. SMALL IN SIZE 2. EASY TO RAISE 3. PRODUCES MANY OFFSPRING 4. LIFE CYCLE IS SHORT AND MANY GENERATIONS CAN BE STUDIED IN A SHORT TIME 5. ONLY HAVE 8 CHROMOSOMES http: //images. google. com/imgres? imgurl=http: //bp 0. blogger. com/_l. GP 8 b 6 RWv. YI/Ruamajc. Ka. NI/AAAAAN 4/LQdd. Al. S 2 jb 0/s 320/Drosophila_melanogaster__side_%252528 aka%252529. jpg&imgrefurl=http: //orbitalteapot. blogspot. com/2007/09/culturaldrosophila. html&h=248&w=320&sz=13&hl=en&start=34&tbnid=_Tpyv. EY_N 2 P_2 M: &tbnh=91&tbnw=118&prev=/images%3 Fq%3 Ddrosophila%26 start%3 D 20%26 g bv%3 D 2%26 ndsp%3 D 20%26 hl%3 Den%26 client%3 Dfirefox-a%26 rls%3 Dorg. mozilla: en-US: official%26 sa%3 DN

IV. SEX-LINKED TRAITS • The normal eye color for Drosophila is RED • One day, T. H. Morgan noticed a WHITE-EYED male fly appear in one of the generations • What he did: 1.

V. SEX-LINKED TRAITS IN HUMANS • Defective allele – ABNORMAL ALLELE THAT CAUSES GENETIC DISEASES Examples: hemophilia, muscular dystrophy (MD), color and night blindness • Color blindness – cannot see RED or GREEN and is more common in MALES; females can be CARRIERS Examples using color blindness XB = normal allele Xb = recessive allele for color blindness Example 1

VI. GENE LINKAGE • Every organism has THOUSANDS of genes (gene for eye color, etc. ) • Every organism has a certain number of chromosomes in each BODY cell (humans have 46) • Therefore, MANY GENES MUST BE PRESENT ON EACH CHROMOSOME • Genes located on the same chromosome are said to be LINKED because they are inherited together • If two (or more) genes are linked they DO NOT obey the law of INDEPENDENT ASSORTMENT http: //scienceblogs. com/gnxp/2007/01/basic_concepts_linkage_disequi. php

VII. CROSSING-OVER • Crossing over occurs during PROPHASE I of meiosis I • As a result of crossing-over, the gametes have DIFFERENT gene linkages than the parent cells • Genes that are far apart on the same chromosome will become separated more often than those close together http: //www. phschool. com/science/biology_place/labbench/lab 3/images/crossovr. gif

VIII. MULTIPLE GENE INHERITANCE • Traits that vary in a continuous manner (like height and skin color) between two extremes ARE NOT controlled by the alleles of a single gene; they are affected by the alleles of two or more DIFFERENT genes IX. MUTATIONS • Mutation: CHANGE IN DNA • Factors in the environment that cause mutations are called MUTAGENS (e. g. , asbestos, UV rays) • Mutations may also be passed on from parent to offspring. For a mutation to be inherited in a sexually reproducing organism, it MUST be present IN THE DNA OF THE GAMETE; THE MUTATION MUST OCCUR IN THE REPRODUCTIVE CELLS • Inherited mutations are usually RECESSIVE • Mutations are likely to result in the production of LOW OR NONFUNCTIONING PROTEINS, AND SOME CAN BE FATAL

• Types of mutations: 1. Gene mutation – CHANGE IN THE SEQUENCES OF BASES ON A GENE 2. Chromosomal mutation – CHANGE IN THE ENTIRE CHROMOSOME STRUCTURE OR NUMBER 1. GENE MUTATIONS • Gene mutations are a change in the base sequence of a gene. In turn, this will affect the PROTEIN that is produced from that gene. • Mutation in a SEX CELL (GAMETE) can be passed on to future generations • Gene mutations can occur at RANDOM and are typically called point mutations

DISEASES ASSOCIATED WITH GENE MUTATIONS: • Phenylketonuria (PKU) – ENZYME THAT BREAKS DOWN THE AMINO ACID PHENYLALANINE IS ABSENT; RESULTS IN BRAIN DAMAGE/MENTAL RETARDATION) • Sickle-Cell Anemia – ABNORMAL RED BLOOD CELLS; RESULTS IN OXYGEN DEFICIENCY • Tay-Sachs Disease – ENZYME TO BREAK DOWN LIPIDS IN THE BRAIN IS ABSENT; RESULTS IN TOO MANY LIPID CELLS IN THE BRAIN DEATH How can you get it?

TYPES OF GENE MUTATIONS 1. ADDITION • An entire base is ADDED TO the base sequence of a gene • RESULT: CODONS CHANGE LOW OR NON-FUNCTIONING PROTEIN 2. DELETION • An entire base is MISSING FROM the base sequence of a gene • RESULT: CODONS CHANGE LOW OR NON-FUNCTIONING PROTEIN 3. SUBSTITUTION • One base is SUBSTITUTED FOR another • RESULT: CHANGES ONE CODON LOW OR NONFUNCTIONING PROTEIN 4. INVERSION • A group of bases are removed and then put back in REVERSE order • RESULT: CODONS CHANGE LOW OR NON-FUNCTIONING PROTEIN

2. CHROMOSOMAL MUTATIONS A. Change in chromosome structure o Usually occurs during meiosis 1. ADDITION – GENES ARE REPEATED ON A CHROMOSOME (ADDED) 2. DELETION – CHROMOSOME SEGMENT BREAKS OFF 3. TRANSLOCATION – TRANSFER OF A CHROMOSOME SEGMENT TO A NONHOMOLOGOUS CHROMOSOME 4. INVERSION – A PIECE OF CHROMOSOME IS ROTATED SO THAT THE GENES ARE REVERSED

B. Change in chromosome number (NONDISJUNCTION) o Chromosomes that normally separate during meiosis remain together, which means that AN EXTRA CHROMOSOME MAY BE PRESENT OR ABSENT o DISEASES ASSOCIATED WITH NONDISJUNCTION: 1. Down Syndrome – EXTRA CHROMOSOME ON 21 ST PAIR; RESULTS IN MENTAL RETARDATION 2. Turner’s Syndrome – ONLY ONE X CHROMOSOME ON 23 RD PAIR; RESULTS IN A SEXUALLY UNDERDEVELOPED FEMALE 3. Klinefelter’s Syndrome – TWO X’S AND ONE Y (XXY) ON THE 23 RD PAIR; RESULTS IN A MALE THAT APPEARS NORMAL WITH UNDERDEVELOPED SEX ORGANS

o POLYPLOIDY • Found in PLANTS • Cells have a multiple of the normal chromosome number (2 n, 5 n, 6 n, etc. ) • Occurs when CHROMOSOMES FAIL TO SEPARATE NORMALLY • Polyploids are usually much LARGER than normal http: //www. bbc. co. uk/scotland/education/bitesize/higher/img/biology/genetics_adaptation/mutations/10 polyploid_formation. gif

X. HUMAN GENETIC DISEASES A. Problems with Studying Human Heredity: 1. LONG LIFE SPAN (HARD TO ANALYZE GENERATIONS) 2. SMALL NUMBER OF OFFSPRING 3. IMPOSSIBLE TO CONTROL EXPERIMENTS • We use PEDIGREE CHARTS to analyze the inheritance of genetic traits; these are commonly used to track sex-linked traits (Color blindness, Muscular Dystrophy, Hemophilia) but are also used to track autosomal genetic diseases (PKU, Huntington’s, Tay-Sachs, Cystic Fibrosis)

XI. GENETIC COUNSELING • Available so that parents can find out if THEY ARE CARRIERS FOR GENETIC DISEASES • Amniocentesis – NEEDLE PROCEDURE PERFORMED ON PREGNANT WOMEN TO TEST THE DNA OF THE BABY • Chorionic villus sampling – The chorion of the placenta is removed for genetic analysis • Karyotyping – is when a picture of the chromosomes is taken and compared to a normal human karyotype to DIAGNOSE AN INDIVIDUAL (OR NOT) WITH A GENETIC DISEASE

XII. BREEDING • There are 4 types of breeding: 1. SELECTION – CHOOSING OF ANIMALS AND PLANTS WITH THE MOST DESIRABLE TRAITS FOR MATING (aka – SELECTIVE BREEDING) 2. INBREEDING - MATING OF GENTICALLY CLOSE INDIVIDUALS TO OBTAIN DESIRED RESULTS (BROTHER/SISTER, MOTHER/SON, FATHER/DAUGHTER, etc. ) • Increases the number of homozygous genes • May bring out unwanted effects 3. OUTBREEDING – MATING OF INDIVIDUALS NOT CLOSELY RELATED • Brings new beneficial alleles • “Hybrid vigor” = hybrid offspring are superior to the parents (ex. mule) 4. MUTATIONS • Plant mutations that once occurred and then deemed as useful are perpetuated by vegetative propagation (ASEXUAL reproduction)

XIII. ENVIRONMENT AND HEREDITY • The ENVIRONMENT plays a role in how certain genes are expressed • Example: the Himalayan rabbit change in temp.

XIV. THE MOLECULAR BASIS FOR MUTATIONS • You are such good students that you remember that: ·DNA MAKES RNA WHICH MAKES PROTEINS. ·PROTEINS ARE SO VERY IMPORTANT! Our structures are MOSTLY PROTEINS, enzymes are PROTEINS (and we know that next to NOTHING happens without those). ·SO, if a mutation is a change in DNA, then the DNA is all messed up! And If the DNA is messed up, the PROTEINS that are created from them will be too!!! Wow-wee!!!