Non Mendelian Genetics Chapter 14 Mendel and the

Non. Mendelian Genetics Chapter 14: Mendel and the Gene Idea

Complex patterns of inheritance The relationship between genotype and phenotype is rarely as simple as in Mendelian inheritance (controlled by dominant and recessive paired alleles) Principles of apply to more complex patterns of inheritance Inheritance may deviate from simple Mendelian patterns in the following situations: Alleles are A gene has A gene produces

Incomplete dominance In complete dominance, heterozygous and homozygous dominant individuals have the With incomplete dominance, the phenotype of the heterozygous is This intermediate occurs because

Incomplete Dominance If you cross a white flower with a red flower that exhibit incomplete dominance the first generation (heterozygotes) will be If you cross two of those heterozygotes you will get

Incomplete dominance genetic problems We can still use the Punnett Square to solve problems involving incomplete dominance. The trick is to recognize when you are dealing with a question involving incomplete dominance. There are two steps to this: 
 1) Notice that the offspring is showing a 3 rd phenotype. The parents each have one, and the offspring are different from the parents. 
 2) Notice that the trait in the offspring is a blend (mixing) of the parental traits.

Incomplete Dominance Questions 1. A cross between a black bird & a white bird produces offspring that are grey. The color of birds is determined by just two alleles. a) What are the genotypes of the parent birds in the original cross? 
 b) What is/are the genotype(s) of the grey offspring? 
 c) What would be the phenotypic ratios of offspring produced by two grey birds?

Incomplete Dominance Questions 2. The color of fruit for plant "X" is determined by two alleles. When two plants with orange fruits are crossed the following phenotypic ratios are present in the offspring: 25% red fruit, 50% orange fruit, 25% yellow fruit. What are the genotypes of the parent orange-fruited plants?

Codominance In codominance, two dominant alleles affect the phenotype Codominant alleles cause the phenotypes of in heterozygote individuals. In codominance For example, red cows crossed with white will generate roan cows. Roan refers to cows that have

Codominance The genetic gist to codominance is pretty much the same as incomplete dominance. A hybrid organism shows a --- not the usual "dominant" one & not the "recessive" one. With incomplete dominance we get a blending of the dominant & recessive traits so that the third phenotype is something in the middle (red x white = pink). In codominance, the "recessive" & "dominant" traits red x white ---> red & white spotted

Codominance Punnett Squares Some texts use letters & superscripts when dealing with codominance. Let’s use "F" for the flower color allele. 
FR = allele for red flowers 
FW = allele for white flowers red x white -------> red & white spotted flowers FRFR x FWFW ----> 100% FRFW The symbols you choose to use don't matter, in the end you end up with hybrid organisms, and rather than one trait (allele) dominating the other, both traits appear together in the phenotype.

Codominance Questions 1. Predict the phenotypic ratios of offspring when a homozygous white cow is crossed with a roan bull. 2. A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur together). 
 a) What pattern of inheritance does this illustrate? Why? b) What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?

Multiple Alleles It is common for Traits controlled by more than two alleles are said to have A diploid individual can possess

Multiple Alleles The number of alleles for any particular trait is not limited to four, there are instances in which more than 100 alleles are known to exist for a single trait

Multiple Alleles & Blood Types Multiple Alleles govern blood type Human blood types are determined by the As the determinant of blood type the gene I has IA allele produces IB allele produces i produces

Importance of Blood Typing Incompatible blood types could clump together, causing death. Disputed parentage Example: If a child has type AB blood and its mother has type A, a man with type O blood could not be the father. Why?

Blood Typing Practice 1. A woman with Type O blood and a man who is Type AB have are expecting a child. What are the possible blood types of the kid? • 2. What are the possible blood types of a child who's parents are both heterozygous for "B" blood type? • 3. What are the chances of a woman with Type AB and a man with Type A having a child with Type O? • 4. A test was done to determine the biological father of a child. The child's blood Type is A and the mother's is B. Man #1 has a blood type of O, & Man #2 has blood type AB. Which man is the biological father? 1.

Pleiotropy Most genes have For example, pleiotropic alleles are responsible for the , such as cystic fibrosis and sickle-cell disease In the garden pea, gene for flower color also affects color of seed coat

Epistasis In epistasis, a gene at one locus For example, in mice and many other mammals, coat color depends on One gene determines the (B for black and b for brown) The other gene (C for color and c for no color) determines whether Dominance = Epistasis =

Polygenic inheritance poly = “many” ; genic = “genes” contributes to a phenotype Effects of dominant alleles are More dominant genes = Number of dominant determines are polygenic traits Many disorders may be polygenic

Skin color example If skin color was related to 3 gene pairs Dominant gene A, B or C to a, b or c So # of dominant genes determines AABBCC = Aa. Bb. Cc = aabbcc = 2 heterozygotes (Aa. Bb. Cc) could have a child with any pigment range

Environmental Influences Genes are also influenced by Temperature and Siamese cats The darker colors on the extremities are due to a Gene that codes for production of the pigment in the Siamese cat only functions Many diseases, , have both genetic and environmental components

Pedigree A pedigree is a family tree that describes the Inheritance patterns of particular traits can be Can also be used to make predictions Many genetic disorders are inherited in a Recessively inherited disorders show up only in individuals Carriers are heterozygous individuals who

Pedigree Symbols

Albinism is a recessive condition characterized by a If a recessive allele that causes a disease is rare, then the chance of two carriers meeting and mating is Consanguineous matings (i. e. , matings between close relatives) Most societies and cultures have laws or taboos against

Cystic Fibrosis Recessive condition Cystic fibrosis is the most common , striking one out of every The cystic fibrosis allele results in defective or absent Symptoms include in some internal organs and of nutrients in the small intestine

Sickle-cell disease Recessive condition Sickle-cell disease affects one out of The disease is caused by the substitution of a in the hemoglobin protein in red blood cells Symptoms include

Dominant Genetic Diseases Some human disorders are caused by dominant alleles Dominant alleles that cause a lethal disease are Achondroplasia is a form of Huntington’s disease is a The disease has no obvious phenotypic effects until the individual is about 35 to 40 years of age

Genetic Tests F There are many genetic diseases that exist (way beyond the scope of what we will discuss) F Genetic counselors can provide information to prospective parents concerned about a F Using family histories, genetic counselors help couples determine the F For a growing number of diseases, tests are available that

Amniocentesis In amniocentesis, a long thin needle is used to remove The amniotic fluid contains , which can be tested for genetic diseases The DNA from fetal cells is

Chorionic Villus Sampling In chorionic villus sampling (CVS), a sample of the chorionic villus The chorionic villus cells contain the , making them fetal cells The DNA from fetal cells is

Karyotypes are prepared, which determines:

Other Genetic Tests Other techniques, such as ultrasound and fetoscopy, allow fetal health to be Some genetic disorders can be detected at birth by simple tests that are now routinely performed in most hospitals in the US

Review Questions 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Name 3 examples of when inheritance patterns may not follow Mendelian rules. Explain, identify, and solve genetics problems involving incomplete dominance, codominance, & multiple alleles. Complete genetics problems involving blood types. Explain, differentiate between, and complete nontraditional genetics problems involving pleiotropy, epistasis, and polygenic inheritance. Explain the effect of the environment on the expression of our genes. Define and analyze a pedigree in order to answer inheritance questions. Identify the most common pedigree symbols. Identify the inheritance patterns and major characteristics of the following genetic conditions: albinism, cystic fibrosis, sickle-cell disease, achondroplasia, & Huntington’s disease. Explain the purpose, benefits, and risks of genetic testing. Differentiate between amniocentesis and chorionic villus sampling. Explain the purpose and use of a karyotype. List 3 pieces of information that can be obtained from a karyotype.