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Grade 9 Science Unit #3: Reproduction and Human Development Topic #1 – Genetic information is passed from parent to offspring Lesson Topic 1 Variation and Characteristics 2 Heredity and Genetics 3 Genetics, Technology, Society, and the Environment What you will learn: - Variation can be discrete or continuous. Variation can be affected by heredity and the environment - Heritable characteristics are the traits of an organism that are inherited from the organism’s parents - Non-heritable characteristics are traits that are learned or developed during an organism’s life - The First Nations and Métis ways of understanding heredity include the transmission of personality traits as well as physical traits. - The nucleus of the cell contains DNA which has the genetic information that is required for cells to divide - DNA is packaged in the form of chromosomes - A gene is a segment of DNA that provides information for a characteristic. An allele is a variation of a gene that provides information for a trait - Traits can be dominant or recessive. The combination of alleles from the parents determines which traits the offspring will have. - Genetic conditions are passed down from parent to offspring - Some personal choices and environmental factors can alter a cell’s DNA - Developments in the study of genetics have a major impact on society - Saskatchewan plays a major role in the study of genetics 1. Variation and Characteristics When studying genetics, a characteristic is a feature such as eye colour or wing shape. Characteristics can vary within a species or be the same for the entire species. A trait is a variation of a characteristic. It describes what the characteristic looks like. With the characteristic of eye colour, people could have the trait of blue eye colour versus brown eye colour. Some traits are not visible. Jack pines exhibit variation because some individuals can resist drought better than others. Magpies show variation because some individuals can fly longer distances. Some bacteria of the same species can be more resistant to antibiotics. Heritable and Non-Heritable Characteristics The transmission of characteristics from one generation to the next is called heredity. Examples of heritable characteristics are eye colour, hair type, and skin colour. Non-heritable characteristics cannot be passed on to other generations. An example of non-heritable characteristics include when someone dyes their hair. The Dakota people believe that traits are inherited through a spiritual means. When a woman is pregnant, she looks for a wise relative who leads a healthy lifestyle. This person is present for the delivery of the baby and cleans the baby’s ears, eyes, and mouth. Prayers are said and ceremonies performed for the baby. It is believed that the soft spot on a baby’s head is a point of entry for the baby’s spirit and the baby’s traits and characteristics. Dene people believe that a baby develops its traits when it is conceived. The pregnant woman is encouraged to act and speak in a fashion that would promote desirable traits in her child. She would practise patience, stay calm, and help in her community. The community treats a pregnant woman well to help her maintain a positive frame of mind and to keep her in happy spirits. The Nakawe believe that the behaviour and actions of the parents and relatives in the child’s life impact the baby in the womb. Discrete and Continuous Variation Discrete variation refers to traits that have a defined form. It is the “either/or” form of a characteristic. For example, a particular species of plant may produce only white or purple flower. Continuous variation refers to traits that have a range of forms. The height of a human can be between 1.2m to 2.1m. Variation and the Environment The environment can also affect the traits of an organism. If a plant is placed in a sunny window and the other in a dim closet, they would soon begin to look very different. Soil acidity will cause flowers to change colour in some species of plants. Height is a characteristic that is inherited but it can also be affected by diet. Variations caused by interactions with the environment are usually not passed from parents to offspring. If a child of tall parents does not receive proper nutrition, he or she probably will not be as tall as his or her parents. 2. Heredity and Genetics DNA and the Genetic Code DNA, or deoxyribonucleic acid, is found in the nucleus of a cell. DNA contains all of the genetic information required to develop and function any living organism. DNA was discovered in 1869. In 1944, Oswald Avery and his colleagues confirmed that it was genetic material that would determine how traits were passed from one generation to the next. In 1953, Watson and Crick completed a model of the DNA molecule. The Watson-Crick model of the DNA molecule can be compared to a ladder that has been twisted into a continuous spiral, this shape is known as a double helix. Each “rung” pairs up two of the following four chemicals: guanine, cytosine, adenine, and thymine (or G, C, A, and T for short). Guanine can only pair with cytosine and Adenine can only pair with Thymine. The arrangement of these chemicals forms a code called the genetic code. The diagram to the left shows how DNA is organized in the nucleus of a cell. The length of DNA in one human cell is estimated to be over 6 ft in length when stretched out. DNA is organized into larger structures called chromosomes. In human cells there are 46 chromosomes, or 23 pairs of chromosomes. On each chromosome there are many genes. Genes are the sections of DNA that provide the specific information for development or functioning. Genes provide the information for our bodies to create proteins, hormones, and sugars. Chromosomes are also organized in two sister chromatids. You get one copy from your mother and one copy from your father. These sister chromatids are exact copies of each other. Each pair of chromosomes code for the same genes, but may or may not have the same alleles of each gene. Alleles are various forms of the same type of gene that create our different characteristics. Ex/ There is a specific gene to determine each of the following hair characteristics: colour, straight/curly, thick/thin, course/fine, etc. The different alleles will determine the different forms of the characteristics. Dominant and Recessive Traits Some genes determine the physical traits that differentiate us from one another. Everyone has two copies of each gene. These copies can be the same allele or different alleles. When the alleles are the same, the information that they provide is what is expressed. When the alleles are different, the trait that is expressed is dependent on which of the alleles is dominant. Traits can be described as dominant, recessive or co-dominant. A dominant trait is one that will be expressed when there are two alleles, whereas a recessive trait is one that will not be expressed when there are two alleles. Traits that are codominant are traits that can be expressed at the same time. An example of a co-dominant traits are the gene for blood type, people with type AB blood have both the A gene and B gene. Examples Trait Eye Colour Vision Dominant Brown Farsightedness Normal Hair Dark Non-red Curly Full head of hair Widow’s peak Dimples Unattached earlobes Freckles Broad lips Extra digits Fused digits Short digits Fingers lack 1 joint Limb dwarfing Clubbed thumb Double – jointedness Immunity to poison ivy Normal pigmented skin Normal blood clotting Normal hearing Normal hearing and speaking Facial Features Appendages Other Recessive Grey, green, hazel, blue Normal Nearsightedness, night blindness, colour blindness Blonde, light, red Red Straight Baldness Normal hairline No dimples Attached earlobes No freckles Thin lips Normal number Normal digits Normal digits Normal joints Normal proportions Normal thumb Normal joints Susceptibility to poison ivy Albinism Haemophilia Congenital deafness Deaf mutism How can we explain a two dark haired parents having a blonde haired child? If parents are hybrids and they each have a dark haired allele and a blonde haired allele, there are four combinations that can occur in their children. 1. One dark haired allele from the father and a dark haired allele from the mother. The child will have dark hair 2. One dark hair allele from its mother and a blonde haired allele from the father. The child will have dark hair 3. One dark hair allele from its father and a blonde haired allele from the mother. The child will have dark hair 4. One blonde hair allele from the father and a blonde haired allele from the mother. The child will have blonde hair. A diagram called a Punnett square can be used to predict the results of a particular cross. The diagram of the cross of hybrid people shows all possible combinations of genes in the offspring of the parents. The blond condition is an example of a recessive trait, and the blonde allele is an example of a recessive allele. A recessive trait appears in the offspring of a recessive allele. A recessive trait appears in the offspring only if both inherited alleles are recessive alleles. In contrast, even one dominant allele will cause the dominant trait to appear. Father (Db – dark/blonde alleles) D Mother (Db – dark/blonde alleles) b D DD Db b Db bb 3. Genetics, Technology, Society, and the Environment Biotechnology Biotechnology is a scientific term that describes the use or modification of living things to improve our lives in areas such as medicine, agriculture, and engineering. Although biotechnology has successfully produced most of our world’s crops and livestock, it takes a very long time - many generations of the plants and animals – to produce offspring that consistently have the desired combination of traits. Selective breeding is the process of selecting and breeding individuals with desirable traits to produce offspring that also have these traits. The grains and fruits you ate for breakfast, in addition to many other foods, are probably products of selective breeding. Another place that this is used is with horses. The genes of champion parents are combined with the hope that the offspring will have the prized traits of both parents. Also, since some cultures have used selective breeding while farming for more than 10 000 years, most of our plants no longer resemble the original species from which they were bred. Artificial Reproductive Technology refers to any artificial method of joining a male and a female gamete. Most livestock in Canada are produced by some method of artificial reproduction. With this technology sperm are collected from a chosen male and inserted into many females. Another reproductive technology is in vitro fertilization (IVF). The term in vitro means “in glass”. With this technology, sperm from a male and eggs from a female are collected. In a laboratory, the eggs and sperm are combined in a Petri dish to fertilize the eggs. This produces many more embryos than could be produced naturally. Each embryo is implanted into a different female. If implantation is successful, the females will eventually give birth to the offspring, all of which will be brothers and sisters. Scientists can also determine the sex of the embryos before they are implanted. By choosing only female embryos, dairy farmers can guarantee that all the calves produced will be female. Genetic engineering refers to any technology process that directly alters or changes the DNA of an organism. Genetic engineering is a rapidly developing science and industry, and every new advance increases our ability to control the characteristics of organisms. Most genetic engineering involves a gene from one species being inserted into another species. Bacteria can be genetically engineered to produce medicine, like insulin. Twenty years ago, insulin had to be extracted from the pancreas of cattle, and it was expensive to produce. Now, insulin can be produces quickly and cheaply because most of the world’s supply of insulin comes from genetically engineered bacteria. Another example involves a micro-organism that produces a toxin that is poisonous to many insects. When the DNA containing the instructions for producing this toxin is inserted into the DNA of plants, the plant begins to produce the toxin. When insects eat the plant, they die and growers never need to apply pesticides to the engineered plants. Since 1990’s cotton, corn, and potatoes have been engineered to produce this toxin. Biotechnology and Society Risks in Animals In agriculture, most individuals in a crop or livestock population are extremely genetically similar as a result of generations of selective breeding. Now, scientist and breeders can produce an identical copy of a single animal. The most famous example of this is a sheep named Dolly. Dolly’s cells appeared the same age as her mother’s, even though Dolly was six years younger. One risk is that herds of genetically identical individuals may be far more susceptible to disease than more genetically varied herds. Other problems cattle cloners have reported include numerous examples of unsuccessful pregnancies, birth defects, and deaths among clones. Risk in Plants Most plant crops were produced by selective breeding of wild plants. Weeds are often the wild relatives of crop plants. Some crops have been genetically engineered to resist herbicides, but there have been unforeseen problems. Many crop plants can cross-pollinate with their wild weed relatives. Cases have been reported of genetically engineered canola interbreeding with weeds, and the weeds’ offspring becoming resistant to herbicides. Accidental Changes to DNA Sometimes DNA is accidentally altered or damaged by environmental factors and personal choices. Usually the damaged DNA is detected by the cell, in which case the DNA is repaired or the cell is destroyed. However, if the damage is not detected, normal cell function can be disrupted. Carcinogens Carcinogens are chemicals or toxins that cause cancer. These chemicals can change a cell’s DNA or change the way a cell reproduces, resulting in cells dividing uncontrollably and forming tumours. Smoking cigarettes is extremely dangerous because cigarettes contain thousands of chemicals, many of which are toxic carcinogens. Asbestos is another carcinogen. It was commonly used in building as insulation throughout Canada and the United States starting in 1870s. It is able to resist fire, electrical and chemical damage, so it seemed and excellent building material. Almost one hundred years later it was realized that inhaling the tiny fibres can cause irreparable damage to cells by physically breaking strands of DNA. This can lead to cancer in people who are exposed to asbestos on a regular basis. Pesticides are chemicals that are sprayed onto crops to try to eliminate pests that cause damage to crops. Some pesticides are also carcinogens and many people and animals consume them without realizing. This is done when you drink water that contains small amounts of pesticides, eating food that has not been thoroughly cleaned to remove the chemicals, or by inhaling chemical particles from the air. Sun Exposure Over exposure to the ultraviolet rays from sunlight and from tanning beds is a major cause of skin cancer. Moderate exposure to sunlight is important, since it allows our bodies to produce vitamin D. Over exposure damages DNA, which could result in cancer. Research shows that even a single use of a tanning bed can be extremely damaging and may greatly increase the chance of getting skin cancer. Genetic Conditions Genetic conditions may be passed from parents to their child as a recessive trait. To inherit the condition, offspring would have to inherit a recessive allele from each parent. Genetic conditions can also occur as a result of an error in the copying of DNA during cell reproduction. Changes to a cell’s DNA that cause genetic conditions are usually random, and result from small changes in the order of the chemicals in the DNA Male infertility – when males are unable to produce sperm that are viable or able to fertilize and egg. Approximately 10% of all male infertility cases are recognized as a genetic condition. This type of infertility is a result of a mutation in the DNA. Breast Cancer – mutations in the certain genes can make cells reproduce at an abnormal rate, which can causes tumour to form. Some forms of breast cancer (about 10% of cases) are genetic others are a mutation that forms in the genetic code. Sex-linked Genetic Conditions – Sex chromosomes are the x and y chromosomes. Females have two x chromosomes, while males have one x and one y chromosome. Some genes are located only on the Y chromosome, but many more genes are located exclusively on the x chromosome. Males are more likely to inherit sex-linked genetic disorders because they receive only one x chromosome. If a male inherits an affected x chromosome with a recessive allele, he will automatically display the recessive trait because the Y chromosome does not have the matching gene that could mask the effect of the recessive allele. Where as females have a chance of having the dominant gene on the second x chromosome. Examples of sex-linked genetic conditions include: colour blindness and haemophilia (a disorder in which the blood is unable to clot) Trisomy 21 (Down Syndrome) – occurs in people when there is a third chromosome 21. People with this disorder often have smaller body frames and limbs, large tongues, and large, round eyes. They typically develop more slowly, both physically and mentally. Despite developmental delays, people with trisomy 21 can lead active productive lives. Canadian and Saskatchewan Contributions to the Study of Genetics Scientists in Saskatchewan try to discover the causes for genetic conditions in order to try to prevent them. Once this is done they can test parents to determine if they are at risk of having a baby with certain conditions. Two Saskatchewan scientists contributed to the study of a gene responsible for babies being born without any arms or legs. Now, support and testing is being offered to family members at risk of carrying the gene for this condition. In 1962, a Saskatchewan medical student discovered a gene responsible for causing significant learning disabilities in males. Two Canadian scientists have become internationally recognized for their findings about the effects of radiation on human chromosomes. Another scientist discovered an important cell structure that is only found in female cells, now known as the Barr body. This information in used at the Olympics to determine the gender of athletes if there were concerns that an athlete was attempting to compete in the opposite gender. The gene responsible for causing cystic fibrosis was discovered by a Toronto geneticist and his associates in 1989.