(CHAPTER 4- Brooker Text) Extensions of Mendelian Genetics Dec 4 & 6, 2007 BIO 184 Dr. Tom Peavy.

Slides:



Advertisements
Similar presentations
Beyond Mendel: Exceptions/Additions to Mendel’s Laws
Advertisements

Unit IV : Extension to Mendelian Genetics
How can we explain inheritance patterns that do not follow simple Mendelian genetics? 1. Incomplete Dominance 2. Co-dominance 3. Multiple Alleles.
Simple Mendelian inheritance involves
EXTENSIONS OF MENDELIAN INHERITANCE
Modifications to Mendelian Inheritance I. Allelic, Genic, and Environmental Interactions.
EXTENSIONS OF MENDELIAN GENETICS
Extended mendlian inheritance
3. LETHAL ALLELES Compiled by Siti Sarah Jumali Level 3 Room 14 Ext 2123.
EXTENSIONS OF MENDELIAN INHERITANCE
Beyond Mendalian Genetics What Mendel could not learn from pea plants.
Section 2: Complex Patterns of Inheritance
Mendel and nonmendel Genetics Quarter 3 week 3 Section 12.2 Summary – pages Complex Patterns of Inheritance Patterns of inheritance that are.
Bio 178 Lecture 25 Genetics. Reading Chapter 13 Quiz Material Questions on P Chapter 13 Quizzes on Text Website (
This Powerpoint is hosted on Please visit for 100’s more free powerpoints 1.
2. CODOMINANCE, INCOMPLETE DOMINANCE AND MULTIPLE ALLELES Compiled by Siti Sarah Jumali Level 3 Room 14 Ext 2123.
Recessive Genetic Disorders
Patterns of Inheritance
Unit: Mendelian Genetics. For example: ◦ Some alleles are neither dominant nor recessive. ◦ In most organisms, the majority of genes have more than two.
AP Biology Lecture #27 Exceptions to Mendelian Genetics.
Chapter 4: Modification of Mendelian Ratios Allele *Wild-type allele *Mutant allele Conventional symbols for alleles: recessive allele - initial letter.
CHAPTER 4 : EXTENSIONS OF MENDELIAN GENETICS
State Standard 2C. Using Mendel’s laws, explain the role of meiosis in reproductive variability. 2D. Describe the relationships between changes in DNA.
Incomplete Dominance  Neither allele is dominant over the other  Heterozygous offspring have a phenotype that is somewhere between the two.
Patterns of Heredity Can Be Complex
Extending Mendelian Genetics The relationship between genotype and phenotype is rarely simple.
Chapter 4 Lecture Concepts of Genetics Tenth Edition Extensions of Mendelian Genetics.
CHAPTER BASIC PATTERNS IN HUMAN INHERITANCE Objectives 1.Analyze genetic patterns to determine dominant or recessive inheritance patterns 2.Summarize.
Section 4: Complex Patterns of Heredity
EXTENSIONS OF MENDELIAN INHERITANCE. INTRODUCTION Mendelian inheritance describes inheritance patterns that obey two laws Law of segregation Law of independent.
Heredity, Gene Regulation, and Development I. Mendel's Contributions II. Meiosis and the Chromosomal Theory III. Allelic, Genic, and Environmental Interactions.
1.Tell me all of the possible gamete combinations for a parent with this genotype for two traits: Bb Tt 2. Match the following vocab words with their definitions:
After Mendel Ch. 8 – 3 (con’t) Beyond Dominant And Recessive Alleles Dominant/recessive inheritance is the simplest type of gene interaction What causes.
Incomplete Dominance  Neither allele is dominant over the other  Heterozygous offspring have a phenotype that is somewhere between the two.  Red + White.
Bellringer (Week 3). Bellringer cont. Section 12-2 When Heredity Follows Different Rules.
Lecture 46 – Lecture 47 – Lecture 48 Complex Patterns of Inheritance Ozgur Unal 1.
When the hybrid offspring shows an intermediate phenotype between the two parents. Example: Flower color C R C R = red C W C W = white C R C W = pink.
Chapter 11.2 Pg  When red-flowered snapdragons (RR) are crossed with white-flowered snapdragons (rr) the heterozygous offspring have pink flowers.
COMPLEX PATTERNS OF HEREDITY Polygenic Traits: traits influenced by several genes ex: human eye color, height, weight, hair color.
Non Mendelian Genetics Patterns of inheritance that aren’t simply dominant or recessive.
AP Biology Application of H-W principle  Sickle cell anemia  inherit a mutation in gene coding for hemoglobin  oxygen-carrying blood protein  recessive.
11.1 Basic Patterns of Human Inheritance Complex Inheritance and Human Heredity Chapter 11 Recessive Genetic Disorders  A recessive trait is expressed.
LET’S TAKE SOME NOTES! Mendelian Genetics. Mendel’s Law of Segregation Definition: The idea that, of the two copies of each gene everyone carries, only.
Recessive Genetic Disorders
COMPLEX PATTERNS OF INHERITANCE. Simple Dominant Traits SimpleSimple dominant dominant traits need only 1 allele in order to express phenotype – RR RR.
Complex Inheritance and Human Heredity Cystic Fibrosis  Affects the mucus-producing glands, digestive enzymes, and sweat glands  Chloride ions are not.
Chapter 4: Modification of Mendelian Ratios Allele *Wild-type allele *Mutant allele Conventional symbols for alleles: recessive allele- initial letter.
Bell-ringer 3/3/16 1.What are linked genes? 2.Which two are more likely to always be linked and why? 3.GET OUT YOUR SEX-LINKED PRACTICE or PICK UP YOUR.
Chapter 12 Patterns of Heredity And Human Genetics.
To Mendel and BEYOND!! Mendel was fortunate to use pea plants because each trait that he observed was not only controlled by one set of genes, but there.
Incomplete Dominance Neither allele is dominant over the other
WarmUP In Labrador retrievers, yellow is incompletely dominant to black. The heterozygous phenotype is chocolate. Cross a yellow lab with a chocolate lab.
Incomplete Dominance and Codominance
Section 2: Complex Patterns of Inheritance
WarmUP In Labrador retrievers, yellow is incompletely dominant to black. The heterozygous phenotype is chocolate. Cross a yellow lab with a chocolate lab.
6.1-Beyond Mendel’s Observations of Inheritance
Complex Patterns of Inheritance
5.2 Extending Mendel’s Laws
Complex Patterns of Inheritance (11.2)
Complex Patterns of Inheritance (11.2)
Hardy-Weinberg Part of Chapter 23.
Modifications to Mendelian Inheritance
COMPLEX PATTERNS OF INHERITANCE
Complex Patterns of Inheritance
Gene linkage and polyploidy
DIHYBRID CROSSES A dihybrid cross is a cross of two individuals that differ in two traits due to two different genes on different chromosomes. Mendel designed.
Modifications to Mendelian Inheritance
Genes and Inheritance.
Heredity Patterns of Inheritance.
Presentation transcript:

(CHAPTER 4- Brooker Text) Extensions of Mendelian Genetics Dec 4 & 6, 2007 BIO 184 Dr. Tom Peavy

Lethal Alleles Essential genes are those that are absolutely required for survival –The absence of their protein product leads to a lethal phenotype Nonessential genes are those not absolutely required for survival A lethal allele is one that has the potential to cause the death of an organism –These alleles are typically the result of mutations in essential genes –They are usually inherited in a recessive manner

Some lethal alleles exert their effect later in life =Late age of onset e.g. Huntington disease (progressive degeneration of the nervous system, dementia and early death; onset between yrs old Conditional lethal alleles may kill an organism only when certain environmental conditions prevail –Temperature-sensitive (ts) lethals A developing Drosophila larva may be killed at 30 C But it will survive if grown at 22 C Semilethal alleles –Kill some individuals in a population, not all of them –Environmental factors and other genes may help prevent the detrimental effects of semilethal genes

In a simple dominant/recessive relationship, the recessive allele does not affect the phenotype of the heterozygote –So how can the wild-type phenotype of the heterozygote be explained? There are two possible explanations –1. 50% of the normal protein is enough to accomplish the protein’s cellular function –2. The heterozygote may actually produce more than 50% of the functional protein The normal gene is “up-regulated” to compensate for the lack of function of the defective allele

Figure 4.1

Incomplete Dominance In incomplete dominance the heterozygote exhibits a phenotype that is intermediate between the corresponding homozygotes Example: –Flower color in the four o’clock plant –Two alleles C R = wild-type allele for red flower color C W = allele for white flower color

1:2:1 phenotypic ratio NOT the 3:1 ratio observed in simple Mendelian inheritance In this case, 50% of the C R protein is not sufficient to produce the red phenotype

Example of Lethalilty and Incomplete Dominance Creeper chicken= shortened legs and creep along this is a incomplete dominant trait heterozygotes are Creeper individuals but homozygote condition is lethal What are the phenotypic ratios of the following crosses? Creeper x Normal Creeper x Creeper

Multiple Alleles (3 or more alleles) An interesting example is coat color in rabbits –Four different alleles C (full coat color) c ch (chinchilla pattern of coat color) –Partial defect in pigmentation c h (himalayan pattern of coat color) –Pigmentation in only certain parts of the body c (albino) –Lack of pigmentation –The dominance hierarchy is as follows: C > c ch > c h > c

The himalayan pattern of coat color is an example of a temperature-sensitive conditional allele –The enzyme encoded by this gene is functional only at low temperatures Therefore, dark fur will only occur in cooler areas of the body This is also the case in the Siamese pattern of coat color in cats Refer to Figures 4.4c and 4.5

The ABO blood group provides another example of multiple alleles It is determined by the type of antigen present on the surface of red blood cells –Antigens are substances that are recognized by antibodies produced by the immune system There are three different types of antigens found on red blood (Table 4.3) –Antigen A, which is controlled by allele I A –Antigen B, which is controlled by allele I B –Antigen O, which is controlled by allele i

Allele i is recessive to both I A and I B Alleles I A and I B are codominant –They are both expressed in a heterozygous individual B N-acetyl- galactosamine

For safe blood transfusions to occur, the donor’s blood must be an appropriate match with the recipient’s blood For example, if a type O individual received blood from a type A, type B or type AB blood –Antibodies in the recipient blood will react with antigens in the donated blood cells (= agglutination and clogging)

Overdominance is the phenomenon in which a heterozygote is more vigorous than both of the corresponding homozygotes –It is also called heterozygote advantage Example = Sickle-cell anemia –Autosomal recessive disorder –Affected individuals produce abnormal form of hemoglobin –Two alleles Hb A  Encodes the normal hemoglobin, hemoglobin A Hb S  Encodes the abnormal hemoglobin, hemoglobin S Overdominance

Hb S Hb S individuals have red blood cells that deform into a sickle shape under conditions of low oxygen tension –This has two major ramifications 1. Sickling phenomenon greatly shortens the life span of the red blood cells –Anemia results 2. Odd-shaped cells clump –Partial or complete blocks in capillary circulation –Thus, affected individuals tend to have a shorter life span than unaffected ones

The sickle cell allele has been found at a fairly high frequency in parts of Africa where malaria is found –How come? Malaria is caused by a protozoan, Plasmodium –This parasite undergoes its life cycle in two main parts One inside the Anopheles mosquito The other inside red blood cells –Red blood cells of heterozygotes, are likely to rupture when infected by Plasmodium sp. This prevents the propagation of the parasite Therefore, Hb A Hb S individuals are “better” than –Hb S Hb S, because they do not suffer from sickle cell anemia –Hb A Hb A, because they are more resistant to malaria