Genetics Week Five
Genetics Week Five BIO310
Virginia Commonwealth University
Popular in Genetics
Popular in BIO
This 6 page Class Notes was uploaded by Jayda Abrams on Monday September 26, 2016. The Class Notes belongs to BIO310 at Virginia Commonwealth University taught by Dr. Wu in Fall 2016. Since its upload, it has received 18 views. For similar materials see Genetics in BIO at Virginia Commonwealth University.
Reviews for Genetics Week Five
Report this Material
What is Karma?
Karma is the currency of StudySoup.
Date Created: 09/26/16
Genetics Week Five Notes 9/26/2016 Information from the Power Point = Red Verbal information = Purple Chapter 4 Continued 4.9 Complementation Analysis Complementation analysis is used to see if things complement each other. Any trait may be controlled with two separate genes to give one look/phenotype. Complementation analysis Screens number of individual mutations resulting in same phenotype Can predict total number of genes determining a trait Complementation group- All mutations present in any single gene ***Figure 4-11*** 4.10 Expression of a Single Gene Gene- Pieces of DNA. How long is it? – Length depends on the gene, different genes have different lengths The test/ analysis is to see if the phenotype is controlled by one gene or many. Pleiotropy- Expression of single gene has multiple phenotypic effects. (One gene has multiple effects. Example: A disease causing stomach pain and muscle pain do not have the same phenotype) Example: Porphyria variegata – Autosomal disorder – Toxic buildup of porphyrins in body – Numerous phenotypic effects Abdominal pain Muscular weakness Vision issues Example: Marfan syndrome – Single autosomal dominant mutation in gene that encodes protein fibrillin results in multiple phenotypic effects 4.11 X Linkage Is a gene on an X chromosome or not? The sex of the male or the female does not matter! The sex of plants and animals are determined by X and Y chromosomes. Example: Drosophila and humans – Males: XY – Females: XX The X chromosomes contains genes that effect phenotype. The Y chromosome only contains genetic information that determines if something is male or not. Non Reciprocal- Cannot switch the sex and get the same results. Males only need one recessive gene to have a mutation but females need two. This is called X- Linked genetics. Colorblindness- Colorblindness is due to the X-linked recessive allele b, while the X-linked dominant allele B leads to full color vision. Colorblindness in humans is on the X chromosomes. What happens when a female is colorblind?- The male offspring will be colorblind. Female offspring will not. Why? Males must carry one X chromosome to be colorblind and it is automatically passed down from mom because both of her X chromosomes have the colorblindness gene. X-linkage - Genes present on X chromosome exhibit patterns of inheritance however they are different from autosomal genes. Y chromosome- Relatively inert genetically, Male-specific genes found on human Y chromosomes, and lacks copies of genes found on X chromosomes. Some X linked traits include: Fabry’s Diseases, Hemophilia A, Hemophilia B, Ichthyosis and muscular dystrophy. Lethal X-linked recessive disorders – Observed only in males, not in females – Females can only be heterozygous carriers who do not develop the disorders Example: Duchenne muscular dystrophy – Onset prior to age 6 – Lethal around age 20 – Occurs only in males, not in females 4.12 Sex Limited and Sex Influenced Traits “Not everything is expressed. We do not see males with breast and females with mustaches even though we all have the same genes. The genes that are expressed are dependent on the sex. This occurs in other animals like chickens and changes how they look. A phenotype is limited to a sex.” Balding in men occurs more often than bolding than women. This is because balding is sex limited. Women will only show balding if they are homozygote dominant Allele B behaves dominant in males and recessive in females. In BB genotype in females, phenotype is less pronounced. 4.13 Genetic Background and The Environment Phenotypic expression of trait – Influenced by environment and organisms exist in diverse environmental conditions – Influenced by genotype Gene products function within cell in various ways Genetic background: Position effect – Physical location of gene influences expression – Translocation or inversion events modify expression – Gene relocated to condensed or genetically inert chromosome (heterochromatin) – Depends on the gene Temperatures can effect which genes are expressed. Temperature is useful when studying bacteria viruses. Dr. Wu’s research found that replication could occur at room temperature at (30˚C), however when it was raised to 40˚C, everything shut down. Nutrition can also affect how genes are expressed: Nutritional mutations – Prevent synthesis of nutrient molecules in microbes – Auxotrophs (microbe) – Phenotype expressed or not depending upon diet Example: People with obesity have the same genes, but they are impacted differently due to their nutrition. Henylketonuria – Loss of enzyme to metabolize amino acid phenylalanine – Severe problems unless low-Phe diet Galactosemia- Cannot metabolize galactose Lactose intolerance- Cannot metabolize lactose Onset of Genetic Expression Tay-Sachs disease Lesch-Nyhan syndrome Inherited autosomal recessive Inherited X-linked recessive Lethal lipid-metabolism disease Purine salvage enzyme defect (HPRTase) (hexosaminidase A) Normal for about 6 months Baby normal for a few months, dies by X linked recessive disease characterized age 3 by abnormal nuc acid metabolism, leading to the accumulation of uric acid in blood and tissues, mr, palsy,self mutilation of the lips and fingers. Duchene muscular dystrophy (DMD) Huntington disease X-linked recessive disorder Variable age of onset in humans Diagnosis at 3–5 years old, fatal by Autosomal dominant disorder age 20 Affects frontal lobes of cerebral cortex X linked disorder related to muscle Progressive cell death – brain wasting deterioration Age range 30–50 years old Genetic anticipation- Genetic disease has earlier onset and increased severity with each succeeding generation Example: Myotonic dystrophy (DM1) – Adult muscular dystrophy – Autosomal dominant – Increased severity and earlier onset with successive generations of inheritance Genomic (parental) imprinting Sometimes it matters if the same gene comes from mom or dad. – Selective gene silencing impacts phenotypic expression – Silencing depends on parental origin of genes – Silencing occurs in early development – Regions of chromosome imprinted on one homolog but not the other Imprint- genetic phenotype result of DNA modification and not a mutation. The CT from mom and the CT from dad are not the same. Imprints are modifications! What type of modification? The addition of a methyl. Imprint will then be inherited by the next generation. Epigenetic changes- Modifications that will change genetics because of imprints and not because of mutation. With an epigenetic change there is no change in the sequence and the only difference is the addition of the methyl. With a mutation there is a physical change in the base pairs. Silencing impacts phenotypic expression but it doesn’t change the gene. If you have cytosine you are subject to epigenetic changes. This change does not guarantee that the gene will be expressed. Genomic imprinting is an epigenetic process that involves methylation and histone modifications. Histones: Histone binds DNA together and makes it look like a chromosome. Histones bind DNA and make chromatin. Histones are proteins and sugars are subject to modification (ex: glycoprotein) Histone modification- Adds different sugar groups. The binding of DNA will be tighter or looser. Which is better? Looser. If it is too tight expression can no occur and expression occurs best when everything is relaxed. This is a type of epigenetic change. DNA methylation – Involved in mechanism of imprinting and epigenetic effects – Methyl groups (CH )3added to 5 carbon – High levels of methylation inhibit gene activity – Active genes are undermethylated – Demethylation- if a gene is not methylated and doesn’t get expressed. Something is being blocked. DNA sequencing only gives information about DNA and does not give information about epigenetics.