Inheritance Patterns & Human Genetics

Inheritance Patterns & Human Genetics Chapter 12

Chromosomes & Inheritance Section 12.1

What makes human males different than females? • Sex chromosomes (X and Y) • Male: XY • Female: XX • Gametes: • Egg: carry only X • Sperm: carry either X or Y

Who Discovered Sex Chromosomes? • Thomas Morgan • Early 1900s • Geneticist, embryologist, evolutionary biologist, Columbia University (USA) • Worked with fruit flies; discovered the role chromosomes play in inheritance

Sex Linkage: • When genes are found on the sex chromosomes • X-linked Genes: genes on the X chromosome • Y-linked Genes: genes on the Y chromosome

Sex Linked Traits • Most sex linked genes are found on the X chromosome • Only genes on the Y chromosome are for male reproductive organ development

Sex Linked Genetic Problems • In flies: R = red eyes, r = white eyes • Gene located on the X chromosome X X X Y

Example 1: • White eye male mates with a red homozygous dominant female • XrY x XRXR Xr Y XRXr XRY XR 100 % red female 0 % white female 100 % red male 0 % white male XRXr XRY XR

Example 2: • Red eye male mates with a red heterozygous female • XRY x XRXr XR Y XRXR XRY XR 100 % red female 0 % white female 50 % red male 50 % white male XRXr XrY Xr

Example 3: • White eye male mates with a red heterozygous female • XrY x XRXr Xr Y XRXr XRY XR 50 % red female 50 % white female 50 % red male 50 % white male XrXr XrY Xr

Linkage Groups • Genes located on the same chromosome and therefore inherited together • Goes against Mendel’s Law of Independent Assortment

How do linked genes get “unlinked”? • Crossing Over • The frequency of crossing over between certain genes is used to make achromosome map

Which two genes have the highest probability of crossing over? The lowest? a A Highest: A & C Lowest: A & B b B c C

Chromosome Map: Diagram of the linear order of genes on a chromosome

Sex Linkage Problems!!!! Use these genotypic symbols for the sex linked trait of red-green color blindness in humans to solve the problems that follow. • "Normal" female = XBXB • Carrier female = XBXb • Color-blind female = XbXb • Normal male = XBY • Color-blind Male = XbY

1) A normal female marries a color blind male. What are the chances that the offspring will be color blind if they are females? What are the chances that the offspring will be color blind if they are males?

2) A color blind female marries a normal male. How many of the female offspring will be carriers of the color blind allele?

3) A man whose mother is color blind marries a woman with normal vision. What is the genotype of the husband? What percent of their offspring can be expected to be color blind? What percentage of their offspring can be expected to be carriers?

How do biologist keep track of inherited traits over generations in a family? • Pedigree (page 241)

Pedigree Key Normal male Marriage Affected male Dead Normal female Affected female Let’s try a pedigree problem!

R = Tongue Roller r = No Tongue Roller John Jones, a tongue roller, marries Jill Smith, a woman that cannot roll her tongue. John and Jill have four children that can each roll their tongue: John Jr., Alice, Lisa, and Sean. John Jr. later marries non-tongue roller Pamela, and they have four children: Jessica, Sherri, Mary, and John III. Sherri and Mary both can roll their tongues, and Jessica and John III are non-tongue rollers. Sean marries Robin, a non-tongue roller. Both Robin’s parents are non-tongue rollers also. Sean and Robin have four children: Nicholas, Harry, Donna, and Sean Jr. Nicholas, Harry and Donna each have the ability to roll their tongues. Sean Jr. cannot.

Human Genetics Section 12.2

Human genetics is not as easy as Mendel’s peas! Many patterns of inheritance

Human Patterns of Inheritance • Single allele trait • Multiple allele trait • Polygenic trait • X-linked trait • Nondisjunction

1. Single Allele Trait • A trait that is controlled by a single allele of a gene • Normal dominant-recessive (Mendel) • Example Genetic Disorders: • Huntington’s Disease (autosomal dominant) • Cystic Fibrosis (autosomal recessive)

2. Multiple Allele Trait • 3 or more alleles of the same gene code for a single trait • Example: ABO Blood Type IA = type A (dominant) IB = type B (dominant) i = type O (recessive)

Blood Type Problems • If a person is type A blood….what is his/her genotype? IAIA or IAi • If a person is type B blood….what is his/her genotype? IBIB or IBi • If a person is type O blood….what is his/her genotype? ii • If a person is type AB blood….what is his/her genotype? IAIB

Blood Types

Blood Type Problems # 1 • A mother gives birth to a type O child. The mother is type A blood. The two potential fathers are type A (father 1) and type AB (father 2). Who’s the daddy?

Blood Type Problems #2 • Pretend that Mark is homozygous for blood type “A” allele, and Mary is type “O”. • What are all the possible blood types of their baby?

3. Polygenic Trait • Trait that is controlled by 2 or more genes • Range of phenotypes • Influenced by environmental factors too • Examples: skin color eye color human height

4. X-Linked Trait • Trait controlled by a gene on the X chromosome • Examples: colorblindness (recessive) hemophilia (recessive)

Hemophilia Pedigree

5. Nondisjunction • The failure of chromosomes to separate during meiosis resulting in one gamete with too many chromosomes and one gamete withtoo few chromosomes Monosomy Trisomy

Trisomy: cell with 3 copies of a chromosome (too many chromosomes) • Monosomy: cell with 1 copy of a chromosome (too few chromosome) • Example Genetic Disorders: Down Syndrome (Tri-21) Klinefelter’s Syndrome (XXY) Turner’s Syndrome (X__)

Blood Typing Lab! • Background Blood is a tissue comprised of 4 components: plasma, red and white blood cells, and platelets. Plasma is a clear straw-colored liquid portion that makes up 55% of the blood. It contains a number of blood-clotting chemicals that help stop bleeding. Red and white blood cells and platelets make up the remaining 45% of the blood. Red blood cells are tiny biconcave discs. Each red blood cell contains the oxygen-binding protein, hemoglobin. Hemoglobin contains 4 iron ions with bind with oxygen and carbon dioxide.

Blood functions principally as a vehicle with transports gases, metabolic waste products and hormones throughout the body. As blood passes through the lungs, oxygen molecules attach to the hemoglobin. As blood passes through the body’s tissues in capillary beds, the hemoglobin releases the oxygen. Carbon dioxide and other waste gases are, in turn, transported by the hemoglobin back to the lungs. Thereafter the process is repeated.

Mutations that Lead to Genetic Disorders: • Mutation: a change in the DNA of an organism • Can involve an entire chromosome or a single nucleotide • Can lead to genetic disorders

Mutation Types • Germ-cell mutation: occurs in the germ cells (gametes) • Does not affect the organism • Does affect the organism’s offspring • Somatic-cell mutation: occurs in the organism’s body cells • Does affect the organism • Does not affect the organism’s offspring • Lethal mutation: causes death, often before birth

Chromosome mutation:change in the structure of a chromosome a.Deletion – loss of a piece of chromosome b.Inversion- segments of chromosome breaks off, flips, and reattaches c.Translocation- piece of chromosome breaks off and attaches to another chromosome d.Nondisjunction- chromosome fails to separate during meiosis

Deletion Inversion Translocation Nondisjunction

5. Gene mutation: involves large segments of DNA or a single nucleotide of DNA a. Point mutation: single nucleotide mutation within a codon (substitution, addition, or deletion) b. Frame shift mutation: cause the misreading of codons during translation thus making the wrong protein (insertion or deletion)

Detecting Human Genetic Disorders • Before Pregnancy: • Genetic Screening • Genetic Counseling • During Pregnancy: • Amniocentesis • Chorionic Villi Sampling • After Birth: • Genetic Screening video

Inheritance Patterns & Human Genetics