Genetics: Genes and Chromosomes - Essay Example

GENETICS Lecturer’s TAQ Genes and chromosomes A gene is a part or a portion of the DNA. A gene contains instructions that are coded for making and responding to the body needs especially body proteins. In the human body, there are about 25,000 genes. However, many genetic disorders are bound to arise with poor functioning of the genes. Each gene codes for a specific protein in the body by specifying the order that the amino acids needs to be joined together. The function of the DNA in the body is carrying genetic code of information that determines the characteristics of a living thing but it is the function of the genes to carry that genetic code. Genes are the basics of genetics (Nadeau & Dudley 2011, 1015). Genes are packed in bundles referred to as chromosomes. They are threadlike structures that are located inside the nucleus of a living being. For a human being, there are 23 pairs of chromosomes meaning that there are a total of 46 chromosomes (De Koning & Haley 2005, 386). Of these pairs of chromosomes, 1 pair is the sex chromosomes that determines the sex of an individual and their body characteristics. The other pair of chromosomes is referred to as autosomal chromosomes and their function is to determine the rest of the body make up. Word count 205 TAQ 2 Question 1 - Mendel’s rules of inheritance Gregor Mendel is referred to as the father of genetics due to his study of the inheritance in pea plants. A gene contains an allel that is inherited from both parents i.e. tongue roller and non-tongue roller are alleles for the ability to roll the tongue and more than two allels can exist for any specific gene but only two of them will be found in an individual. Allels may be similar or different and if they are identical for a gene are referred to as a homozygous. If the organism has two different alleles for a gene, it is a heterozygous. He hypothesized that these allels separate randomly during gametes production i.e. an egg and a sperm that will carry only one allel for the inherited trait. When they unit each gamete will contribute its allele restoring the paired condition of the offspring (Moore 2001, 21). This is referred to as the law of segregation. He also found out that each individual pair of alleles will separate independently of the other pair of alleles during the process of gamete formation and referred this as the law of independent assortment. He also described that if the two allels of an inherited pair are different (heterozygous), only one will determine the organism’s appearance and will be referred to as the dominant allele while the other one is the recessive allele. He referred this as the law of dominance and case letters are used to represent dominant and recessive alleles. In the initial experimental sets, he concentrated on the pattern of inheritance on a single pair of contrasting characters. The pattern of inheritance involving a pair of contrasting characters is referred to as monohybrid inheritance. An example of monohybrid inheritance Step Parent 1 Parent 2 Phenotype Heterozygous non tongue-roller Heterozygous tongue roller Genotype Rr Rr Gametes produced R or r R or r Possible offspring R r R RR Rr r Rr rr Phenotype of all offspring’s 3 tongue-roller 1 non tongue-rollers In the law of independent assortment, he described the outcome of two characters crosses or the di-hybrid crosses that involved additional characters. He stated that alleles assort independently into gametes. An example of a di-hybrid crosses Step Parent 1 Parent 2 Phenotype Homozygous tongue roller and PTC taster Heterozygous tongue roller and PTC taster Genotype RRaa AaRr Gametes produced All Ra AR, Ar, aR, ar Possible offspring AR Ar aR ar Ra RRAa RrAa RRaa Rraa Phenotype Tongue roller and PTC taster Tongue roller and PTC taster Tongue roller and non-PTC taster Tongue roller and non-PTC taster Word count 250 Question 2 In human, there is a gene that controls tongue rolling allowing people with the muscles to do so will those without the muscle cannot role their tongues as the gene is expressed as a dominant or recessive gene. The questions address results of a homozygous non tongue-roller (rr) and a heterozygous roller (Rr). We will use R for the dominant gene and r for the recessive gene of a non-roller. Step Parent 1 Parent 2 Phenotype Homozygous non tongue-roller Heterozygous tongue roller Genotype rr Rr Gametes produced r or r R or r Possible offspring r r R Rr Rr r rr rr Phenotype of all offspring’s 2 tongue-roller 2 non tongue-rollers From the punnett diagram, half of the offspring’s will be homozygous non tongue-rollers while the other half will be heterozygous tongue rollers. Therefore, only two of the offspring’s will possess the characteristic of tongue rolling while the other two will not. The ratio will be 2/4 Rr (roller): 2/4 rr (non-roller) a 50: 50 chance probability. Word count 115 Question 3 Some people have the ability of tasting phenylthiocarbonate (PTC) while others cannot because of their genetics. The ability to taste PTC is a dominant trait. The questions address results of offspring’s between two heterozygous parents possessing the traits. We will use A for the dominant gene and a for the recessive gene. Step Parent 1 Parent 2 Phenotype Heterozygous PTC-taster Heterozygous PTC-taster Genotype Aa Aa Gametes produced A or a A or a Possible offspring A a A AA Aa a Aa aa Phenotype 75 percent will be PTC tasters 25 percent non-PTC tasters From the punnett diagram, 75 percent chance of the offspring would produce a child who could taste PTC while 25 percent chance that the couple would not produce a child that could taste PTC. The ratio will be ¾ with the ability (Aa, Aa, AA): ¼(aa) without ability. Word count 100 Question 4 The question addresses the results of a couple where the woman has a homozygous tongue-roller (RR) and a non- PTC- taster genes (aa) marries a heterozygous tongue roller (Rr) and heterozygous PTC taster (Aa) and decide to have many child as many as 16 children. Step Parent 1 Parent 2 Phenotype Homozygous tongue roller and PTC taster Heterozygous tongue roller and PTC taster Genotype RRaa AaRr Gametes produced All Ra AR, Ar, aR, ar Possible offspring AR Ar aR ar Ra RRAa RrAa RRaa Rraa Phenotype Tongue roller and PTC taster Tongue roller and PTC taster Tongue roller and non-PTC taster Tongue roller and non-PTC taster From the punnett table all the children will be tongue rollers from 4 results with two being homozygous tongue rollers and two being heterogynous tongue rollers. On the other hand, from 4 results two offspring’s will have the ability of tasting PTC while the rest two will have no ability. From the results half of the offspring will be tongue rollers RR (homozygous) and PTC taster’s Aa (heterozygous) while the other half will be tongue rollers Rr (heterozygous) and non –PTC- taster’s aa (homozygous). The results are a total representation of the other four groups that are likely to be as a result. Therefore, half of the 16 children that is 8 will be tongue rollers RR (homozygous) and PTC taster’s Aa (heterozygous) while the other 8 will be tongue rollers Rr (heterozygous) and non –PTC- taster’s aa (homozygous). Word count 170 Question 5 The question addresses the results of a couple where the woman has a heterozygous tongue-roller (Rr) and a PTC- taster heterozygous genes (Aa) marries a heterozygous tongue roller (Rr) and heterozygous PTC taster (Aa) and shows the off springs that may result. Step Parent 1 Parent 2 Phenotype Tongue roller and PTC taster Tongue roller and PTC taster Genotype Rr, Aa Rr, Aa Gametes produced AR, Ar, aR, ar AR, Ar, aR, ar Possible offspring AR Ar Ra ar AR AARR AARr AaRR AaRr Ar AARr AArr AaRr Aarr Ra AaRR AaRr aaRR aaRr ar AaRr Aarr aaRr aarr Phenotype Tongue rollers and PTC taster 9 out of 16 Tongue roller and non-PTC taster 3 out of 16 Non- tongue roller and PTC taster 3 out of 16 Non- tongue roller and non PTC taster 1out of 16 From the results, ¾ will have the ability of rolling their tongue while half will not, ¾ will have the ability of tasting PTC will ¼ will not. Word count 145 TAQ 3 Question 1 – Genetic linkage and its importance in genetic characteristics transmission Genetic linkage is phenomena were genes tend to stay proximal to each other on the same chromosome during inheritance through generations without any separation. Genetic linkage is important as it enables the linked genes to be inherited together during the process of meiosis. An example is the linkage between factor III of the clotting gene and factor V that are both located on the same chromosomes. If the two are not linked then an abnormality is bound to arise. Genes whose loci are nearer to each other will likely be separated on different chromatids during the process of chromosomal crossing over and are genetically linked i.e. there is a lower chance of a swap occurring between them and are more likely to be inherited together. According to Mendel, the strength of the linkage between genes is inversely proportional to the distance between the two genes and will show a higher frequency of crossing over if the distance between them is higher (Brown T 2010,85). On the other hand, unlinked genes are those found on different chromosomes and they show independent assortment. However, the linked genes will not show independent assortment as describe by Mendel in the laws of inheritance but are inherited as a block producing only parental type of progeny. Word count 208 Question 2 – how gender or sex is determined Sex determination system is a biologically based system that determines the sexual characteristics of organisms. Most living organisms have two sexes; however, there are hermaphrodites who have both sexes. There are some organisms species that are only one sex as a result of the parthenogenesis acting on the female reproduction that take place without fertilization. Thus, sex determination is genetically based as females and males have different alleles or genes that specify their sexual characteristics. In animals, it results from chromosomal differences that come from the genes combination. For a human being, there are 23 pairs of chromosomes meaning that there are a total of 46 chromosomes (Short et al. 2013, 103). Of these pairs of chromosomes, one pair is the sex chromosomes that determine the sex of an individual and their body characteristics. Humans use the XY sex system to determine the sex types. In females, they have two X chromosomes although one is inactive (XX) while the males have an X and Y chromosome (XY). In the Y chromosome there is a region called the SRY that contains a gene that triggers embryonic development of the male characteristics. Word count- 200 Question 3 – crossing over and the role it plays in transfer of genetic information It is a process where the homologous chromosomes exchange content or parts with each other in the meiotic phase of division. During the time, the chromosome is formed by two sister chromatids and crossing over will take place on none sister chromatids of two different chromosomes. The exchange of the genetic content also occurs between the sisters chromatids but such an exchange has no significance for the genetic recombination process. In the prophase phase of meiosis, homologous chromosomes come together in a process called synapsis and chromosomal sections are exchanged. The resulting chromosomes as a result are neither paternal nor maternal and contain genes of both parents. This occurs only in meiosis. Crossing over is important as it enables genetic diversity of the genetic materials between the two patterns where mew cells are created containing characteristics of both parents. As a result of this, there is a difference that results between off springs of two parents. However, the frequency of crossing over will be determined by the distance between the linked genes. These linked genes will be transferred every time crossing over takes place and it is impossible to divide them. Thus, crossing over will occur just on places between the linked groups of genes (Nadeau & Dudley 2011, 1015). Word count 205 TAQ 4 Continuous and discontinuous variation Variation refers to the differences that exist between members of the same species. Two types of variation exists continuous and discontinuous variation. Continuous variation is also referred to as quantitative entails a range from differences that are observed in many characteristics in a population. There is no clear cut between any two things. Examples of continuous variation are weight, height, foot sizes that are bound to vary between different individuals. It results from two factors i.e. genetic inheritance and environmental effect such as disease and availability of food and climatic changes (Schlichting 2007, 372). On the other hand, discontinuous variation also referred to as qualitative variation is defined as differences in characteristics that are observed in the population but presents with clear-cut differences, i.e. distinct entities result. An example is the blood groups A, B, AB and O as an individual only has the above blood groups. Another example is gender that is either female or male, ability of rolling the tongue and eye color. It only results from inheritance. Word count 165 TAQ 5 Question 1 – Mutation Mutation is a permanent change that occurs on the DNA sequence genes. However, changes that occur on the non-coding sections of the DNA do not affect function. Mutations results from external or endogenous factors as well as errors in the cellular machinery. Mutagens are chemical or physical agents that induce the mutations in the cell’s DNA (Kumar & Subramanian 2002,123). External factors include radiation effect, smoking and sunlight that can induce mutation. Endogenous factors are errors in DNA replication causing genetic changes. Moreover, mutations can also be inherited from the parent. These mutations are referred to as hereditary mutations and presents throughout the individual’s life. Word count 103 Question 2 - Describe de novo mutations and provide one example De novo mutations are mutations that occur in an egg or a sperm cell. The mutation can also occur just after fertilization has taken place and is referred to as new de novo mutation. The kind of mutation explains genetic disorders in which an affected presents with no mutation cells and has no family history of the resulting disorder resulting from mutation. However, the rate of these kinds of mutations is high among those individuals who have genetic diseases especially sporadic conditions such as autism and intellectual disability. The mutations that results to sporadic diseases are usually disruptive to gene functioning and affects important areas of developmental genes. The kind of mutation explains why advanced parental age increases the risk that a child will develop autism disease thus; they have been associated to become more common with age (Lynch 2010, 350). Couples are advised to get children early to avoid such complications. Word count 150 Question 3 – describe mosaicism and provide one example Mosaicism is a term used for describing the presence of more than cell type in a person. It is a situation where different cells on the same individual contain different arrangements or numbers. It is referred as mosaicism because the cells of the body are similar to tiles of a mosaic design similar to a mosaic art piece where each tile is different. Just like the body cells in the condition they are of different colors and shapes. It is explained in percentage and results when mutation arises early in development. It can be germ line to affect the egg or sperm or somatic affecting other cells or a combination. An example of such a condition is Down syndrome (Nadeau & Dudley 2011, 1016). The individual has extra cells apart from the 46 pairs of chromosomes. Most of the individuals with down syndrome have trisomy 21 that results in an extra number 21 chromosome in every cell of the individuals body. However, other individuals have Tran’s- locational Down syndrome where the extra chromosome is attached to another chromosome. Word count 170 Question 4- describe polymorphism and provide one example At times, some genetic changes in the genetic composition of an individual are not common and are rare in the population with little percentage. Polymorphism occurs in more than one percent of the population and due to their occurrence, they are common enough to be to be considered as normal DNA variations. They are responsible for the many differences among the individual’s hair color, blood type as well as eye color differences. Many of the polymorphism disorders and effects have no negative effects on an individual’s health while other influence the risk of developing other types of disorders on the individual. Single nucleotide polymorphism (SNPs) is a common type of genetic variation among people where each SNP represents a difference in DNA building block. Examples include genes for sickle cell diseases and thalassemia. Such genes are believed to offer an advantage on malaria for the affected persons. Word count 150 TAQ 6 Protein synthesis It is a process where cells construct proteins and the RNA and DNA are usually involved. The enzymes in the nucleus of the cell stat the process of protein synthesis y unwinding the DNA sections that are needed for the formation of the RNA. The RNA then forms a DNA copy that is sent to other cell areas to help in bringing together different amino acids to form proteins. Proteins are very essential for the normal functioning of the body (Shimizu et al. 2005, 303). Processes involved Transcription and Translation Transcription- the DNA is untwisted by dna helixase enzyme and it splits into two as the hydrogen bonds have been broken between the base pairs. The mRNA is made with complimentary base pairs similar to the DNA replication. The mRNA then leaves the nucleus through the nucleus pores. Translation- it occurs in the cytoplasm and requires ribosomes. A small subunit of the ribosome attaches at the bottom of the mRNA strand while a large ribosomal unit is attached to the top of the messenger RNA. Synthesis then begins and for it to start, the first codon base triplet needs to be methionine (AUG). Anticodons on the tRNA with an amino acid go in to the larger ribosomal unit to match with the codon. The first anticodon needs to be AUC as it is complementary with AUG. the second anticodon then comes along. Before the tRNA leaves the ribosome polymerase creates a peptide bond between the amino acids then it leaves the ribosome leaving the amino acid behind and the process is repeated until it reaches a stop (Kim & Kim 2009, 4). The amino acid chain is then released into the cytoplasm as a protein as the ribosome and messenger RNA separate. Word count 280 References Brown T, A., 2010. Introduction of DNA into Living Cells. In Gene Cloning & DNA Analysis: An Introduction. pp. 72–87. Kim, H.C. & Kim, D.M., 2009. Methods for energizing cell-free protein synthesis. Journal of Bioscience and Bioengineering, 108, pp.1–4. De Koning, D.J. & Haley, C.S., 2005. Genetical genomics in humans and model organisms. Trends in Genetics, 21, pp.377–381. Kumar, S. & Subramanian, S., 2002. Mutation rates in mammalian genomes. Proceedings of the National Academy of Sciences of the United States of America, 99, pp.803–808. Lynch, M., 2010. Evolution of the mutation rate. Trends in Genetics, 26, pp.345–352. Moore, R., 2001. The “Rediscovery” of Mendel’s Work. Bioscene, 27, pp.13–24. Nadeau, J.H. & Dudley, A.M., 2011. Genetics. Systems genetics. Science (New York, N.Y.), 331, pp.1015–1016. SCHLICHTING, C.D., 2007. Variation: A Central Concept in Biology. BioScience, 57, p.372. Shimizu, Y., Kanamori, T. & Ueda, T., 2005. Protein synthesis by pure translation systems. Methods, 36, pp.299–304. Short, S.E., Yang, Y.C. & Jenkins, T.M., 2013. Sex, gender, genetics, and health. American Journal of Public Health, 103. Read More