Chapter 12 Inheritance Patterns and Human Genetics

staff.tuhsd.k12.az.us Chapter 12 Inheritance Patterns and Human Genetics

Objectives • Tell the difference between sex chromosomes and autosomes • Define different types of mutations • Evaluate and create pedigree charts

I. Chromosomes • In the early 1990’s a researchers noticed that Drosophiliamelanogaster (fruit flies) had 4 chromosomes • 3 were the same in both males and females and 1 was different house-flies.net exploratorium.edu

2 Types of Chromosomes • Sex chromosomes contain genes that determine the sex of an individual (“X” or “Y”) • Males decide the gender • Autosomes-all the other chromosomes that are not involved in gender determination • Cause about half of all genetic diseases

II. Linked Traits • Pair of genes that are inherited together • They are located in the same chromosome and very close together. graphicshunt.com

Sex-linked Genes and Traits • Refers to a trait that is coded for by an allele on a sex chromosome (X or Y) • More X-linked traits than Y-linked traits because the of the size difference • Males who have an X chromosome that carries a recessive allele will exhibit the sex-linked trait • Females have less of a chance expressing an X linked disease because they have 2 X-chromosomes karakalpak.com

Mutations • Germ-cell – occur in the gametes • Effect the offspring • Somatic-cell – occur in an organisms body cells • Can not be inherited-results in things like leukemia or skin cancer • Lethal – cause death, often before birth • Beneficial – help the organism survive and reproduce photography.nationalgeographic.com

Chromosome Mutations • Change the structure of the chromosome • Deletion and Insertion • Loss of nucleotide bases or an addition of them biology-online.org

A piece of one chromosome breaks off and attaches to a nonhomologous chromosome Inversion Translocation • A piece of the chromosome breaks off and flips around backward http://www.youtube.com/watch?v=XAGxp9j5rtc&feature=related activars.com staff.jccc.net

Nondisjunction • The chromosomes don’t separate during meiosis so one gamete receives 2 copies and the other receives none.

2 Types of Nondisjunction • Trisomy – an extra chromosome in every cell • Most of these disorders make it very difficult for the individual to survive • Trisomy 21-down syndrome • Trisomy 18 &13-normally die before age 1 • Monosomy – absence of 1 chromosome • Typically lethal to embryonic development • Turner’s syndrome cdadc.com

Gene Mutations • Point mutation – change within a single gene • Substitution – one nucleotide replaces another • Frameshift mutation – if some nucleotides are deleted the entire segment of DNA moves down changing the codons for amino acids • Detrimental to the proteins function • Insertion mutation – one or more nucleotides are added which can result in a frameshift mutation

Example of Substitution • Sickle Cell Anemia: only 1 amino acid is substituted to produce the sickle shape • Recessive trait that prohibits Hemoglobin from binding correctly To the red blood cell unitedhealthdirectory.com

Frameshift Mutation • Changing one letter completely alters the codon sequence staff.um.edu.mt

Examples of gene mutations • Substitution: • Original – the fat cat ate the wee rat. • Mutation - The fat hat ate the wee rat. • Insertion: • Original: The fat cat ate the wee rat. • Mutation: The fat cat xlw ate the wee rat. • Frameshift: • Original: The fat cat ate the wee rat. • Mutation: The fat caatet hew eer at.

1. Below is the base sequece for the normal protein for normal hemoglobin and sickle cell: Normal: GGG CTT CTT TTT Sickle: GGG CAT CTT TTT Is this a point or frameshift mutation? Explain. 2. Delete the first H in the following sequence and regroup the letters in groups of three. Does the sentence still make sense? What type of mutation is this THE FAT CAT ATE THE RAT 3. Name 2 chromosome mutations. How are they alike? How are they different? 4. Using the sequence ATT GCA AAG GGT. Give an example of a deletion, insertion, and substitution. Circle the change you have made. 5. What is the difference between sex chromosomes and autosomes?

List of Genetic Disorders – Pick 1 for your project • Thalassemia • Marfan syndrome • Breast Cancer • Hemophilia • Cri du Chat • Polydactyly • Maple Syrup urine disease • Turner Syndrome • Klinefelter's syndrome, • (XXY syndrome) • Super males (XYY) • Patau syndrome • Albinism • Huntington’s Disease • Down’s Syndrome • Cystic Fibrosis • Duchenne muscular dystrophy • Sickle Cell Anemia • Trisomy 18 (Edwards) • Tay-Sachs disease • Color blindness • PKU (Phenylketonuria) • Fragile X syndrome

II. Pedigrees • Diagram that shows how a trait is inherited over several generations http://www.uic.edu/classes/bms/bms655/gfx/pedigree1.gif

Reading Pedigrees • A circle represents a female • A square represents a male • If the circle or square is filled in that means the individual has the trait • Horizontal lines indicate marriage or having children • Vertical lines show offspring

Practice Problems • Is the mom or dad in generation I affected by a trait? • How many offspring are shown in generation II? • How many daughters & sons in generation II? • How many have the trait? • How many offspring does daughter #1 have? • How many have the trait?

Patterns of Inheritance • Autosomal Dominant Traits • Passed on to sons or daughters even if only one parent has the gene • Affected individuals who mate with an unaffected individual have a 50% chance of passing on the gene as long as they are not homozygous for the trait • Can appear in males and females equally

What must the genotype of the parents be to produce a child #7 who is unaffected? • What is the genotype of #9? • What are the genotypes of the 3 children in the third generation?

Recessive Pedigrees • In order to be passed on both parents must have the gene • Traits can be passed on if both parents are “carriers” of the trait • Have the trait but it isn’t expressed because they also have the dominant trait • An individual who is infected may have parents who are not • If both parents are affected, all of their children will be affected

Carriers for Autosomal recessive traits

Recessive Pedigree • If individuals 2 + 3 in generation 3 have more children- will they be affected? • Can Individual #8 in gen. 3 have any unaffected children? • Can individual #9 in gen 3 have affected children?

Sex Linked Traits • Located only the sex chromosomes (X and Y) • More frequently expressed on males than females • Y-linked is male only • X-linked –passed from mother to son • Mainly expressed in males • Daughters are carriers

X-linked Traits • Traits that are on the X chromosome • Males are affected more than females • Color blindness is an X-linked recessive disorder passed from mother to son

X-linked recessive • Evident in males because they only have 1 X chromosome • Women are rarely affected because they have 2 X chromosomes-better chance of not getting it • If the father has the mutated gene all of his daughters will have it

X-linked Dominant • No transmission from father to son • All daughters of the affected male will have it • Only 1 dominant allele is needed for the trait to be expressed • What is the genotype of #2 in generation II?

Genetic Disorders • Diseases that have a genetic basis • Researchers have found that most traits are Polygenic – influenced by several genes • Skin color – combination of 3-6 genes which control the amount of melanin in the skin • Complex characters – influenced by both genes and environment • Height, certain diseases such as breast cancer cosbiology.pbworks.com

Incomplete Dominance • Displaying a trait that is intermediate of the two parents • Wavy hair comes from one parent having straight hair and one parent having curly hair • Red flower and a white flower produce a pink flower doctortee.com

Sex Influenced Trait • Males and females can show different phenotypes even when they share the same genotype Ex: Male pattern baldness – the allele is dominant in males but recessive in females due to the higher testosterone levels in males

Single-Allele Traits • Trait controlled by 1 allele-dominant or recessive • Recessive Examples • Cystic Fibrosis-most common lethal disease • Sickle-cell anemia-blood disorder • Albinism- lack of color pigment in skin, hair, and eyes • Dominant Examples • Huntington’s Disease- degradation of the brain • Polydactly- presence of a sixth digit • Achondroplastic dwarfism-dwarf size

Detecting Genetic disease • Amniocentesis – technique used to detect genetic disorders in a fetus • Chrionic villi sampling – takes some cells derived from the placenta • Treatments depend on the specific disease

Chapter 12 Inheritance Patterns and Human Genetics