I need. help with question in genetics 6. Using the agouti and agouti viable yel
ID: 64673 • Letter: I
Question
I need. help with question in genetics 6. Using the agouti and agouti viable yellow alleles in mice as an example, discuss the role of diet in coontolling gene activity (transcription)? 7. Using queen/worker bees, the SRY gene and puberty as examples, discuss the role of DNA methylation in coontolling gene activity (transcription)? 8. What are two examples of human tratits that are polygenic? 9. With an example, discuss how Mendelian genes explain continuos variations as is seen with polygenic traits? 10. What is variance and what determines the variance of a polygenic trait? 11. How can genetic and environmental variance be controlled? 12. What role(s) did UVA and UVB/UVC light probably play in the evolution of dark skin, light skin and the tanning reflex? 13. What genes play a role in determining skin color? Eye color? Hair color? 14. Most populations of the world have dark hair and dark eyes. What gene(s) is (are) responsible for blue eyes, blond hair and red hair? 15. With an example, discuss selective breeding. Why is it possible to select a trait by breeding?Explanation / Answer
6.Ans : Epigenetic gene regulation comprises the heritable changes in gene expression that occur in the absence of changes to the DNA sequence itself. Epigenetic mechanisms include chromatin folding and attachment to the nuclear matrix, packaging of DNA around nucleosomes, covalent modifications of histone tails (e.g. acetylation, methylation, phosphorylation), and DNA methylation. The influence of regulatory small RNAs and micro RNAs on gene transcription is also increasingly recognized as a key mechanism of epigenetic gene regulation.The viable yellow agouti (Avy) mouse model, in which coat color variation is correlated to epigenetic marks established early in development, has been used to investigate the impacts of nutritional and environmental influences on the fetal epigenome . The wild-type murine Agouti gene encodes a paracrine signaling molecule that produces either black eumelanin (a) or yellow phaeomelanin (A). Both A and a transcriptions are initiated from a developmentally regulated hair-cycle-specific promoter in exon 2 . Transient A expression in hair follicles during a specific stage of hair growth results in a sub-apical yellow band on each black hair shaft, causing the brown agouti coat color of wild-type mice.2 The Avy metastable epiallele resulted from the insertion of an intracisternal A particle (IAP) murine retrotransposon upstream of the transcription start site of the Agouti gene .2,3 A cryptic promoter in the proximal end of the Avy IAP promotes constitutive ectopic Agouti transcription not only in hair follicles, but throughout all cells, leading to yellow fur, as well as adult-onset obesity, diabetes, and tumorigenesis.4,5 Interestingly, CpG methylation in the Avy IAP correlates inversely with ectopic Agouti expression. The degree of methylation within the 5 IAP long terminal repeat (LTR) varies dramatically among individual isogenic Avy/a mice, causing a wide variation in coat color ranging from yellow (unmethylated) to pseudoagouti (methylated).
7.Ans: The epigenetic process of DNAmethylation represents what is generally considered a more stable and enduring modification to the activity of genes. DNA methylation occurs when cytosine nucleotides within DNA become converted to 5-methylcytosine. This process is mediated by methyltransferases which either promote maintenance.The conversion to 5-methylcytosine does not alter the DNA sequence but does reduce the likelihood that that sequence of DNA will be transcribed.Methylated DNA attracts methyl-binding proteins, such as MeCP2, which further reduce the accessibility of the gene and is associated with transcriptional repression (Fan & Hutnick, 2005). The stability of DNA methylation patterns within the genome permits the stable regulation
of gene expression associated with cellular differentiation.
8.Ans :Polygenic inheritance is when a trait is influenced by more than one gene.
1)Skin color is another polygenic trait for humans and a variety of other animals.
2) Behavioral characteristics of animals are often controlled by multiple gene loci as well, although the environment, in the form of parental care, often influences behavior as well.
9.Ans: The traits have what's called continuous variation, showing a bell curve of values for the phenotype. This is because there are multiple genes that play a role in the phenotype, and each gene could have multiple alleles. This can give a range of possible phenotypes from all the variation that's coming into play here. The more genes or alleles that contribute to the trait, the larger the possible variation can be. polygenic traits can also be quantitative because they have a continuous variation over a range of measurement. Polygenic traits can also be called multifactorial, which applies when there are multiple factors that play a role in a trait.
10.Ans: A polygenic trait usually demonstrates a great deal of phenotypic variability in a population. Some of this variation is genetic, VG, due to the different genotypic classes in the population and to dominance and epistatic effects. Some of the variation is environmental influence on the genes, VE. (There may also be gene-environemntal interaction variance; we will, for now, assume this to be 0). Thus, there are two major components of the total phenotypic variability observed in a sample, and they are additive:
VP (total phenotypic variance) = VG (genetic variance)+ VE(environmental variance)
H = VG/VP
11.Ans:Heritability reflects the fact that all individuals in any species of living things differ in many ways among each other.The variation (~differences) among individuals within a species depends on both genetic and environmental differences.Much of it has a basis in our genes, a fact that is of tremendous evolutionary significance. Other variation is primarily due to environmental influences on our development. For nearly every trait, however, both genes and environment interact to some extent to produce the organism's phenotype.
12.Ans:UVA wavelengths(320-400 nm) are only slightly affected by ozone levels. Most UVA radiation is able to reach the earth's surface and can contribute to tanning, skin aging, eye damage, and immune suppresion.UVB wavelengths(280-320 nm) are strongly affected by ozone levels. Decreases in stratospheric ozone mean that more UVB radiation can reach the earth's surface, causing sunburns, snow blindness and a variety of skin problems including skin cancer .
UVC wavelengths (100-280 nm) are very strongly affected by ozone levels, so that the levels of UVC radiation reaching the earth's surface are relatively small.
The effects of UV radiation on earth's ecosystems are not completely understood. Even isolating the effects of UVA versus UVB is somewhat arbitrary. All UV radiation can be damaging. This knowledge has prompted many manufacturers of sun screen and sunglasses to offer products that protect against both UVA and UVB wavelengths.
13.Ans: MC1R gene provides instructions for making a protein called the melanocortin 1 receptor. This receptor plays an important role in normal pigmentation. The receptor is primarily located on the surface of melanocytes, which are specialized cells that produce a pigment called melanin. Melanin is the substance that gives skin, hair, and eyes their color.Melanocytes make two forms of melanin, eumelanin and pheomelanin
14.Ans: MC1R gene are responsible for blue eyes and blonde hair and red hair because the mutations in the MC1R gene imparts the hair and skin more pheomelanin than eumelanin, causing both red hair and blonde and blue eyes.
15.Ans Humans have used selective breeding long before Darwin's Postulates and the discovery of genetics. Farmers chose cattle with beneficial traits such as larger size or producing more milk, and made them breed; and although they may have known nothing about genes, they knew that the beneficial traits could be heritable. Scientists study these traits and spend a lot of time calculating how heritable these traits can be. The more these traits are expressed in the offspring (i.e. size, milk production, etc), the more heritable these traits are said to be.Hunting is also a form of artificial selection, with the genes that humans "want" (i.e. - the biggest buck with the most points, the largest fish, etc.) being removed from the gene pool, allowing the less "wanted" genes to pass on to the next generation by increasing their odds of mating when compared to the hunted specimens.