Inheritance Patterns & Human Genetics

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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?. - PowerPoint PPT Presentation

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Human Genetics

Inheritance Patterns & Human GeneticsChapter 12Chromosomes & InheritanceSection 12.1What makes human males different than females?Sex chromosomes (X and Y)Male: XYFemale: XX

Gametes:Egg: carry only XSperm: carry either X or Y

Who Discovered Sex Chromosomes?Thomas MorganEarly 1900sGeneticist, 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 ProblemsIn flies: R = red eyes, r = white eyesGene located on the X chromosomeXXYXExample 1:White eye male mates with a red homozygous dominant female

XrY x XRXRXRXrXRYXRXrXRYXrYXRXR100 % red female 0 % white female

100 % red male 0 % white maleExample 2:Red eye male mates with a red heterozygous female

XRY x XRXrXRXRXRYXRXrXrYXRYXRXr100 % red female 0 % white female

50 % red male 50 % white maleExample 3:White eye male mates with a red heterozygous female

XrY x XRXrXRXrXRYXrXrXrYXrYXRXr 50 % red female 50 % white female

50 % red male 50 % white maleLinkage GroupsGenes located on the same chromosome and therefore inherited togetherGoes against Mendels Law of Independent Assortment

How do linked genes get unlinked?Crossing Over

The frequency of crossing over between certain genes is used to make a chromosome map

Which two genes have the highest probability of crossing over? The lowest?ABCabcHighest: A & CLowest: A & BChromosome 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 = XBXBCarrier female = XBXbColor-blind female = XbXb Normal male = XBYColor-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 KeyNormal maleAffected maleNormal femaleAffected femaleMarriageDeadLets try a pedigree problem!

R = Tongue Roller r = No Tongue RollerJohn 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 Robins 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 GeneticsSection 12.2Human genetics is not as easy as Mendels peas!Many patterns of inheritance

Human Patterns of InheritanceSingle allele traitMultiple allele traitPolygenic traitX-linked traitNondisjunction1. Single Allele TraitA trait that is controlled by a single allele of a gene

Normal dominant-recessive (Mendel)

Example Genetic Disorders:Huntingtons Disease (autosomal dominant)Cystic Fibrosis (autosomal recessive)

2. Multiple Allele Trait3 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 ProblemsIf a person is type A blood.what is his/her genotype?IAIA or IAiIf a person is type B blood.what is his/her genotype?IBIB or IBiIf a person is type O blood.what is his/her genotype?iiIf a person is type AB blood.what is his/her genotype?IAIBBlood TypesBlood Type (Phenotype)GenotypeCan donate blood to:Can receive blood from:OiiA,B,AB and O(universal donor)OABIAIBABA,B,AB and O(universal receiver)AIAIA or IAiAB, AO,ABIBIB or IBiAB,BO,BBlood Type Problems # 1A 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). Whos the daddy?

Blood Type Problems #2Pretend 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 TraitTrait that is controlled by 2 or more genes

Range of phenotypesInfluenced by environmental factors too

Examples: skin coloreye colorhuman height

4. X-Linked TraitTrait controlled by a gene on the X chromosome

Examples:colorblindness (recessive)hemophilia (recessive)

Hemophilia Pedigree5. NondisjunctionThe failure of chromosomes to separate during meiosis resulting in one gamete with too many chromosomes and one gamete with too few chromosomes

TrisomyMonosomyTrisomy: 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)Klinefelters Syndrome (XXY)Turners Syndrome (X__)Blood Typing Lab!BackgroundBlood 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 bodys 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 TypesGerm-cell mutation: occurs in the germ cells (gametes) Does not affect the organismDoes affect the organisms offspring

Somatic-cell mutation: occurs in the organisms body cellsDoes affect the organismDoes not affect the organisms offspring

Lethal mutation: causes death, often before birthChromosome mutation: change in the structure of a chromosomea. Deletion loss of a piece of chromosome b. Inversion- segments of chromosome breaks off, flips, and reattachesc. Translocation- piece of chromosome breaks off and attaches to another chromosomed. Nondisjunction- chromosome fails to separate during meiosis

DeletionInversionNondisjunctionTranslocation5. 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 DisordersBefore Pregnancy:Genetic ScreeningGenetic Counseling

During Pregnancy:AmniocentesisChorionic Villi Sampling

After Birth:Genetic Screeningvideo

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