Genetics PowerPoint PDF

GENETICS Copyright © Amy Brown Science GENETICS ….the science that studies how genes are transmitted from one generation to the next. Copyright © Amy Brown Science Genes and Chromosomes Chromosomes are contained in the _______ nucleus of the cell. Chromosomes are made of: Gene: A segment of DNA that controls a hereditary trait. Chromosome: A long chain of genes. Trait: The characteristics that an organism has, such as hair color, eye color, height, or skin color. Alleles: Diﬀerent versions of a gene that produce dis;nguishable traits in oﬀspring. Two ______ alleles must be present in order for a trait to appear in the ________. each parent to the offspring One allele is provided by __________ offspring. When __________ fertilization of sperm and egg occurs, the new offspring will have _______ 2 alleles for each gene. The Contributions of Gregor Mendel Gregor Mendel was an Austrian monk who was born in 1822. He is known as the Father of Genetics. He discovered three laws of genetics that would forever change biology. He conducted a series of experiments in a quiet monastery garden. Mendel spent 14 years growing and experimen;ng with the pea plants grown in his garden. St. Thomas Augustinian Abbey where Mendel lived and worked. Mendel gave us the three basic laws of inheritance which are still used today: Ø The Law of Dominance and Recessiveness Ø The Principle of Segregation Ø The Principle of Independent Assortment Mendel's great contribution was to demonstrate that inherited characteristics are carried by genes. Mendel chose the garden pea for his experiments. It was a good choice because: 1. They were readily available. 2. They were easy to grow. 3. They grew rapidly. The sexual structures of the flower are completely enclosed within the petals. There would be no accidental cross-pollination between plants. Before we learn about Mendel’s experiments, let’s review the basics of sexual reproduc:on in ﬂowering plants. Flowers contain both male and female reproductive structures. Pistil The female part of the flower, the pistil produces ________. egg cells _____, Stamen The male part of the flower, the stamen produces ______. pollen _______, sperm cells Pollen contains ___________. Pollen Stamen Pistil Sperm cells When the pollen is delivered to the pistil, the sperm travels to the egg cell, and the result is __________. fertilization Egg Fertilization produces … … a tiny embryo, which is enclosed inside a seed. Mendel’s Use of Pea Plants for Genetics Experiments Pea flowers are normally _____________. self-pollinating Since the male and female reproductive structures are relatively enclosed inside the flower, the sperm of the flower will fertilize the egg of the same flower. The resulting embryos will have the same ____________ characteris=cs as the parent plant. Even though sexual reproduction has occurred, there is just __________. one parent Mendel knew that these pea plants were “____________.” This means that if they true breeding are allowed to ___________, self-pollinate they would produce offspring ___________________. identical to themselves For example: If allowed to self-pollinate, tall plants would always produce tall plants ________. Plants with yellow seeds would always produce yellow seeds offspring with ___________. These true breeding plants were the cornerstone of Mendel’s experiments. Mendel’s Work Mendel wanted to produce _____ seeds by joining the egg and sperm from _________________. two different plants To do this, he had to first prevent the possibility of _____________. self-pollination Tall Pea Plant Dwarf Pea Plant Mendel cut away the stamens, the male reproductive parts of the flower, and then dusted the remaining female structure with pollen from a different plant. This is known as cross-pollination and produces ______________ different offspring from two ________ parents. Now Mendel could easily crossbreed plants and experiment with different characteristics. Mendel’s Experiments Essen%al Vocabulary needed for Gene%cs Can you roll your tongue? Round Seed Wrinkled Seed 1. Trait: A specific characteristic that varies from one individual to another. Mendel focused on seven _____ traits found in pea plants. Each of these traits had only two contrasting variants. For example: Pea plants were either tall or dwarf. Seeds were either round or wrinkled. Seed color was either yellow or green. Essen=al Vocabulary: 2. Alleles: Do you have dimples? 3. 4. 5. 6. Different versions of a gene that produce distinguishable traits in offspring P generation: Parental generation F1 generation: First generation of offspring F2 generation: Second generation of offspring Hybrids: The offspring of parents with different traits Mendel crossed true-breeding tall plants with true-breeding dwarf plants. Tall plants x dwarf plants à Produces only tall offspring Tall Pea Plant Dwarf Pea Plant 1. The F1 hybrids were all tall. 2. All of the offspring had the appearance of only one of the parents. 3. The trait of the other parent seemed to have disappeared. Mendel thought that the dwarf trait had been lost. Mendel’s Conclusions: Biological inheritance is determined by “______ factors ” that are passed from one generaIon to the next. Today, we know these factors to be ______. genes Each of the traits that Mendel observed in the pea plants was controlled by ________ one gene two contrasting forms that occurred in ___________________. For example: The gene for the height of pea plants occurs in a tall form and in a ______ dwarf form. ____ alleles The different forms of a gene are called ______. dominant Mendel realized that some alleles are __________ over other alleles. Principal of Dominance and Recessiveness: Some alleles are dominant, and others are recessive. A dominant allele can cover up or mask a recessive allele. Dominant allele: If the dominant allele is present in an oﬀspring, the dominant trait will show up in the oﬀspring. Recessive allele: This trait will show up in the oﬀspring only if the dominant allele is not present. Copyright © Amy Brown Science In Mendel’s experiments, the allele for tall pea plants was dominant over the allele for dwarf pea plants. The Principal of Segregation Mendel had another question: Had the dwarf trait (recessive allele) disappeared, or was it still present in the F1 offspring? Mendel allowed the _________ hybrid tall offspring from the first generation to ___________. self-pollinate F1 Tall x F1 Tall à Produces oﬀspring that are ¾ tall and ¼ dwarf 1. He found that ¾ of the offspring were tall and ¼ of the offspring were dwarf. F1 Tall Pea Plant allowed to self-pollinate F1 Tall Pea Plant allowed to self-pollinate F2 Offspring 2.Evidently the F1 "tall" offspring must have been carrying the dwarf trait, but it had been hidden. 3.The dwarf trait had been passed down to the offspring, and it reappeared in the ____________. F2 generation Why did the recessive allele seem to disappear in the F1 generation and then reappear in the F2 generation? Mendel realized that organisms have two alleles for every ____. trait _________ These two alleles are inherited, one from each ______. parent If the oﬀspring receives a dominant allele from one parent, that dominant trait will ______ appear in the oﬀspring. Recessive traits show up in the oﬀspring only if the oﬀspring receives … recessive alleles from both parents. If a parent has two alleles for a trait, how does the parent pass only one allele to the offspring? Today, we know that the answer to this lies in the type of cell division known as _______, meiosis the formation of ________. gametes Gametes are sex cells or egg and sperm cells. The capital letter, T, represents a dominant allele. The lower-case letter, t, represents a recessive allele. During meiosis, the DNA is _________ replicated and then separated into _________. 4 gametes Each gamete has ____ half the number of chromosomes as the parent cell. In this way, a parent passes one allele for each gene to their offspring. Mendel’s Principle of Segregation Mendel’s Principle of Segregation says that every individual carries two alleles for each trait. These two alleles separate or segregate during the formation of the egg and sperm cells. Homozygous or Heterozygous? An offspring will inherit two alleles for a trait, one allele from each parent. The combination of alleles received by the offspring may be either homozygous or heterozygous. Homozygous means that … … the two alleles are the same: TT or tt T T Homozygous t t Homozygous T t Heterozygous Heterozygous means that … … the two alleles are different: Tt Genotypes and Phenotypes A phenotype is the … … physical characteristics of an organism or what the organism looks like. Genotypes A genotype is the … … genetic makeup of an organism. Phenotype: One flower is purple, and one flower is red. For example, in Mendel’s pea plants, the tall allele was dominant over the dwarf allele: Genotype TT Tt tt Phenotype Tall plant Tall plant Dwarf plant Using Probability and Punnett Squares to Work Genetics Problems If we know the geneIc makeup of parents, what type of oﬀspring might they produce? What is the probability of producing diﬀerent types of oﬀspring? Probability: The likelihood that a particular event will occur. Using Probability and Punnett Squares to Work Genetics Problems A a a a Punnett Square 1. A Punnett square is a diagram showing the ________________ allele combina=ons that might result from a genetic cross between two parents. 2. The ______ alleles of the first parent will be placed across the ___ top of the square. 3. The ______ alleles of the second parent will be placed along the _______ left side of the square. Using Probability and PunneR Squares to Work Gene;cs Problems A a a a Monohybrid Cross: 4. The possible gene combina;ons offspring will be placed of the ________ ________________. inside the squares 5. LeRers will represent the ______. alleles 6. A capital leRer represents a dominant allele. _________ 7. A lower-case leRer represents a ________ recessive allele. one trait or characteristic is being A cross in which only ______________________ considered. boxes Monohybrid crosses use Punnett squares consisting of 4 _______. Practice Problem #1 Mendel began his experiments using true-breeding parents. He soon discovered that the tall trait was dominant over the dwarf trait. Cross a true-breeding tall pea plant to a true-breeding dwarf pea plant. What is the genotype of the ﬁrst parent? TT What is the genotype of the second parent? tt Place the alleles of the first parent on the top of the square. Place the alleles for the second parent on the left of the square. T T Tt Tt t Tt Tt t Fill in the squares to show all the possible combinations of alleles that the offspring might inherit. Use this table to show all possible genotypes and phenotypes of the offspring, and the probabilities of each. 4⁄4 Tt 4⁄4 tall Practice Problem #2 T In the above problem, none of the offspring will show the dwarf trait. As we learned earlier, Mendel wondered what had happened to the dwarf trait. He allowed the F1 generation to self-pollinate. Show this cross using the Punnett square below. What is the genotype of each parent? t T TT Tt t Tt % 1/4 TT 2/4 Tt 1/4 tt Tt x Tt ¾ Tall ¼ dwarf Practice Problem #3 Having dimples is dominant over the absence of dimples. Cross a heterozygous dimpled man with a woman who does not have dimples. Show all work in the Punnett square and summarize your findings in the table. Dd What is the genotype of the woman? dd What is the genotype of the man? D d d Dd dd d Dd dd 2/4 Dd 2/4 dd 2/4 dimples 2/4 no dimples Normal skin is dominant over albino skin. A woman who has normal skin, but whose father was albino, marries a heterozygous, normal skinned man. What type of oﬀspring might they expect? Practice Problem #4 What is the genotype of the woman? Aa A What is the genotype of the man? a A AA Aa a Aa aa 1/4 AA 2/4 Aa 1/4 aa Aa ¾ Normal ¼ albino Practice Problem #4 How many different genotypes are possible among the offspring? 3 How many different phenotypes are possible among the offspring? 2 What is the probability of getting homozygous offspring? 2/4 What is the probability of getting heterozygous offspring? 2/4 What is the probability of getting normal offspring? 3/4 What is the probability of getting albino offspring? 1/4 Practice Problem #5 In dogs, the allele for short hair (B) is dominant over the allele for long hair (b). Two short haired dogs have a litter of puppies. Some of the puppies have short hair and some of the puppies have long hair. What are the genotypes of the parents? Bb and Bb B b B BB Bb b Bb bb 1/4 BB 2/4 Bb 1/4 bb ¾ short hair ¼ long hair Practice Problem #5 If the litter of puppies contained 12 pups, how many would you expect to have short hair? ¾ of the 12 should have short hair. ¾ of 12 = 9 pups How many would you expect to have long hair? ¼ of the 12 should have long hair. ¼ of 12 = 3 pups The Principal of Independent Assortment Mendel needed to answer one more quesJon. When alleles are being segregated during gamete formaJon, does the segregaJon of one pair of alleles have any eﬀect on the segregaJon of a diﬀerent pair of alleles? In other words, does the gene that determines if a pea plant is tall or dwarf have any eﬀect on the gene for seed color? Mendel designed a second set of experiments to follow two different genes as they passed from parent to offspring. This is known as a … … two-factor cross or a dihybrid cross. One parent had peas that were round and yellow. The second parent had peas that were wrinkled and green. The round and yellow traits are dominant. First, Mendel crossed true-breeding parents. Round, yellow peas RRYY X Wrinkled, green peas rryy All F1 oﬀspring produced round, yellow peas. If round and yellow are dominant, what is the genotype of all of the F1 oﬀspring? RrYy When the first generation was allowed to self-pollinate (RrYy x RrYy), it resulted in the production of 556 seeds: Ø 315 round, yellow (dominant, dominant) Ø 105 round, green (dominant, recessive) Ø 104 wrinkled, yellow (recessive, dominant) Ø 32 wrinkled, green (recessive, recessive) This meant that the alleles for seed shape had segregated independently of the alleles for seed color. The alleles for one trait had ___________ no inﬂuence on the alleles of another trait. This is known as independent assortment _____________________. The Principle of Independent Assortment states that … … when gametes are formed, the alleles of a gene for one trait segregate independently of the alleles of a gene for another trait. NOTE: This is assuming that the two genes are located on separate nonhomologous chromosomes and are not linked on the same chromosome. Using a Punnett square for a two-factor or dihybrid cross ü A dihybrid cross considers two traits at the same time. ü When two traits are being considered, the Punnett square will need 16 squares. ü Each parent will pass one allele of each gene pair to the offspring. Given the following parental genotypes, what alleles could each parent pass to their offspring? If the parent was AaBb: AB, Ab, aB, ab If the parent was Aabb: Ab, Ab, ab, ab If the parent was aaBb: aB, ab, aB, ab If the parent was AABB: AB, AB, AB, AB Use the following Punnett square to illustrate Mendel’s experiments True-breeding Round and Yellow (RRYY) x True-breeding wrinkled and green (rryy) RY True breeding Round, yellow seed (RRYY) RY RY RY ry RrYy RrYy RrYy RrYy ry RrYy RrYy RrYy RrYy ry RrYy RrYy RrYy RrYy True breeding Wrinkled, green seed (rryy) ry RrYy RrYy RrYy RrYy 16/16 RrYy 16/16 Round, yellow seeds If the oﬀspring from the above cross are allowed to self-pollinate: Round and Yellow x Round and Yellow RrYy x RrYy RY Ry rY Practice Problem ry RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy 1/16 RRYY 2/16 RRYy 1/16 RRyy 2/16 RrYY 4/16 RrYy 2/16 Rryy 1/16 rrYY 2/16 rrYy 1/16 rryy Round,yellow 9/16 Round, green 3/16 Wrinkled, Yellow 3/16 Wrinkled, green 1/16 Right handedness (R) is dominant over left handedness (r). The ability to roll your tongue (T) is dominant over the inability to roll your tongue (t). What oﬀspring might be expected from a cross involving the following parents: RRR x RRTt Rt Rt Rt Practice Problem Rt RT RRTt RRTt RRTt RRTt Rt RRtt RRtt RRtt RRtt RT RRTt RRTt RRTt RRTt 8/16 RRTt Rt RRtt RRR RRR RRR 8/16 RRR 8/16 Right-handed, tongue roller 8/16 Right-handed, nonroller Practice Problem A woman, who is right handed and a tongue roller, has a father who is left handed and cannot roll his tongue. She marries a heterozygous right handed, tongue rolling man. What possible offspring might they expect? What is the genotype of the woman? RrTt What is the genotype of the man? RrTt RT 1/16 RRTT 2/16 RRTt 1/16 RR4 2/16 RrTT 4/16 RrTt 2/16 Rr4 1/16 rrTT 2/16 rrTt 1/16 rr4 9/16 Right handed tongue rollers 3/16 right handed nonrollers 3/16 le< handed tongue rollers 1/16 le< handed nonrollers Rt rT rt RT RRTT RRTt RrTT RrTt Rt RRTt RRtt RrTt Rrtt rT RrTT RrTt rrTT rrTt rt RrTt rrtt Rrtt rrTt A Summary of Mendel’s Principles Mendel’s principles form the basis of modern gene;cs. Mendel’s principles include the following: 1. The inheritance of traits is determined by individual units known as genes. 2. Genes are passed from parent to offspring. 3. Each gene has two or more forms called alleles. 4. Some alleles are dominant, while other alleles are recessive. A Summary of Mendel’s Principles two alleles for a 5. Each parent has __________ particular trait that they inherited from their parents. one allele to their offspring They will pass _________ when the alleles are segregated into gametes ______________________. 6. The alleles for one trait segregate independently of the alleles for another trait, when the genes are located on separate, nonhomologous chromosomes. Today we know that there are exceptions to the principles set forth by Gregor Mendel. These exceptions include the following: 1. Some alleles are neither dominant nor recessive. 2. The majority of genes have more than 2 alleles. 3. Some traits are controlled by more than one gene. Genes and the Environment Gene expression is the result of the interaction of genetic potential with the environment. A seedling may have the geneHc capacity to be green, to ﬂower, and to fruit, but it will never do these things if it is kept in the dark. A tree may never grow tall if the soil is poor and no water is available. In other words, the presence of the gene is not all that is required for the expression of a trait. The gene must be present along with the proper environmental condi;ons. Examples: Primrose plants that are red ﬂowered at room temperature are white ﬂowered when raised at hoRer temperatures. Himalayan rabbits are white at high temperatures and black at low temperatures. Snowshoe rabbits are white at low temperatures and brown at high temperatures. Snowshoe Rabbits The phenotype of any organism is the result of interaction between genes and the environment. Incomplete Dominance or Nondominance not controlled by Some traits are ____________ dominant and recessive alleles. _____________________ In some cases, the offspring will in between have a phenotype __________ the phenotypes of the parents. In radishes, a pure-breeding white radish plant crossed with a purebreeding red radish plant produces plants with purple radishes. The phenotypes of the parents blend or mix together appear to ___________ in the phenotype of the offspring ________. Incomplete Dominance This is known as incomplete dominance. Alleles are neither dominant nor recessive. The alleles blend together in the offspring. For example: In some flowers, such as snapdragons and four o'clocks, a homozygous red _______________ flower crossed with a ________________ homozygous white flower yields a heterozygous pink ________________ flower. Since there is no recessive allele, use only capital ______ letters. For example: A red flower would be ___, RR and white flower would be WW and the ____, heterozygous pink hybrid RW would be ___. In eggplants, a pure-breeding white eggplant crossed with a purebreeding purple eggplant produces eggplants with a violet color. What type of offspring might be produced by two pink flowering plants? What are the genotypes of the parents? Practice Problem RW and RW 1/4 RR 1/4 Red 2/4 RW 2/4 Pink 1/4 WW 1/4 White R W R RR RW W RW WW e c i t c Pra m e l b o r P In a certain plant, flower color shows incomplete dominance, but the stem length shows dominance. The allele for long stem is dominant over the allele for short stem. Cross a heterozygous long-stemmed red plant with a short-stemmed pink plant. What is the genotype of the first parent? LlRR What is the genotype of the second parent? llRW LR lR lR lR LlRR LlRR llRR llRR lW LlRW lR LR LlRW llRW llRW LlRR LlRR llRR llRR lW LlRW LlRW llRW llRW 4/16 LlRR 4/16 LlRW 4/16 llRR 4/16 llRW 4/16 Long, red 4/16 Long, pink 4/16 short, red 4/16 short, pink Codominance In codominance … … neither allele is dominant or recessive, nor do the alleles blend together in the phenotype of the offspring. Both codominant alleles contribute to the phenotype of the offspring. Both _________ dominant alleles are apparent in the phenotype of the heterozygous offspring. ____________ Codominance in Human Blood Types In humans, four blood types are possible: A, B, AB, and O three alleles that determine There are ___________ blood type. A and B alleles are ___________ codominant The _______ O blood is recessive and the allele for _________________. These three alleles are written as follows: IA, IB, and i. Alleles IA and IB are codominant, and the allele “i” is recessive. Blood Genotypes and Phenotypes Genotypes Phenotypes IA IA IA i IB IB IB i IA IB ii Type A blood Type A blood Type B blood Type B blood Type AB blood Type O blood What types of offspring might be expected if one parent has type AB blood and the other parent is heterozygous for type A blood? What is the genotype of the first parent? IA IB Practice Problem What is the genotype of the second parent? IA i IA IB IA IA IA IA IB i IA i IB i ¼ ¼ ¼ ¼ IA IA IA IB IA i IB i 2/4 Type A blood 1/4 Type AB blood 1/4 Type B blood A man and a woman have four children. Each child has a different blood type. What are the genotypes of the parents and the four children? What are the genotypes of the parents? IA i and IB i. What are the genotypes of the four children? The type O child is ii. The type AB child is IA IB. The type A child is IA i. The type B child is IB i. Blood Type and Rh Factor Another component of our blood type is the Rh factor. Some people have Rh positive blood and others have Rh negative blood. The Rh factor is determined by one gene with two alleles. The allele for Rh positive is dominant over the allele for Rh negative. Let’s use “R” to represent the positive allele and “r” to represent the negative allele. A woman whose blood type is AB negative marries a man with blood type O positive. The man’s mother had blood that was A negative. Practice Problem What is the genotype of the woman? IA IB rr What is the genotype of the man? ii Rr What is the genotype of the man’s mother? IA i rr IAr IAr IBr IBr iR IAi Rr IAi Rr IBi Rr IBi Rr ir IAi rr IAi rr IBi rr IBi rr 4/16 IAi rr iR IAi IAi IBi IBi 4/16 IBi Rr ir Rr IAi rr Rr IAi rr Rr IBi rr Rr IBi rr 4/16 IAi Rr 4/16 IBi rr 4/16 Type A Rh positive 4/16 Type A Rh negative 4/16 Type B Rh positive 4/16 Type B Rh negative Mul;ple Alleles more than two alleles Many genes have ___________________. Genes with three or more alleles are said to have multiple alleles “______________.” In genetics problems with multiple alleles, there are three __________________ or more alleles for the trait. This does not mean that an individual will have more than two alleles for a given trait. “Multiple alleles” means that there are three or more alleles for a trait in a population. The best example for multiple alleles involves coat color in rabbits. Coat color in rabbits is determined by a single gene that has at least four different alleles. These four alleles demonstrate a “dominance hierarchy” in which some alleles are dominant over others. The four alleles for coat color in rabbits in order of dominance are as follows: Allele Phenotype C Full color ( oJen called wild type or agouK) cch Light gray or Chinchilla ch Albino with black extremiKes or Himalayan c Albino These alleles are listed in order of their dominance. What would be the possible genotypes of each of these rabbits? CC, Ccch, Cch, Cc Full color: ________________ Full Color cchcch, cchch, cchc Chinchilla: _______________ hch, chc Himalayan: c________ cc Albino: ___ Albino Himalayan Chinchilla Practice Problem C What types of offspring could be produced by a full color rabbit that had a genotype of C cch that was bred with a Himalayan rabbit that was ch c? cch ch C ch cch ch c Cc cch c ¼ C ch ¼ cch ch ¼ Cc ¼ cch c 2/4 Full color 2/4 chinchilla Polygenic Inheritance In polygenic inheritance, the determination of a given characteristic is the result of the … … interaction of many genes. Some traits, such as size, height, shape, weight, color, metabolic rate, and behavior are not determined by one pair of alleles. These traits are the cumulaJve result of the combined eﬀects of many genes. This is known as polygenic inheritance. A trait affected by a number of genes (polygenes) does not show a clear difference between groups of individuals. Instead, it shows a graduation of small differences. Many normal human traits are thought to be polygenic. Examples include hair color, eye color, weight, height, and skin color. Chromosomes Gene Linkage Independent Assortment states that when Mendel’s Principle of ______________________ gametes are formed, the alleles of a gene for one trait segregate independently of the alleles of a gene for another trait. for genes that are We now know that this principle is true only ____________ nonhomologous chromosomes located on separate ___________________________. A B If Gene A and Gene B are located on separate nonhomologous chromosomes, they will assort into gametes independently of one another. A B Independent assortment cannot occur if Gene A and Gene B are linked together on the same chromosome. Chromosomes Gene Linkage A chromosome is a group of ___________. linked genes chromosomes During meiosis, it is the _____________ that assort independently in gametes, not genes the individual ______. As luck would have it, most of the traits Mendel studied in pea plants are located on separate chromosomes. Chromosomes Gene Linkage Does this mean that two genes located on the same chromosome are forever linked together? The answer is no. Remember that “____________” crossing-over sometimes occurs during meiosis. Crossing-over is the process in which homologous chromosomes may exchange portions of their chromatids. This produces new combinations of genes and contributes to genetic diversity. Sex Determination Human cells contain _______ 23 pairs of chromosomes. There are 22 pairs of __________ autosomes and one pair of ________________. sex chromosomes In males and females, all of the pairs of chromosomes are the same except one pair. The pairs that are the same in both males and females are called autosomes. Autosomes are all of the chromosomes within a cell except for the sex chromosomes. One pair differs between males and females. sex chromosomes This pair is called the ________________. The sex chromosomes differ in structure contain genes that determine the and _____________ ____ sex of the individual. Females have 2 copies of a large X chromosome. Males have one X and one small Y chromosome. There are many genes found on the X chromosome. The Y chromosome appears to contain only a few genes. Since the X and Y chromosomes determine the sex of an individual, all genes found on these chromosomes are said to be sex-linked _________. More than 100 sex-linked genetic disorders have now been associated with the X chromosome. Sex-linked traits in humans include … … colorblindness, hemophilia, and muscular dystrophy. recessive alleles. These are caused by _________ Since males have only one copy of the X chromosome, they will have the disorder if they inherit just one copy of the allele. Females must inherit __________ two copies of the allele, one on each of X chromosomes, in order for the trait to appear in the their ___ offspring. Therefore, sex linked genetic disorders are much more common in ______ males than ________. females Colorblindness in Humans The table below summarizes the possible genotypes and phenotypes. Genotype Phenotype XCXC Normal vision female XCXc Normal vision female, but a carrier of the colorblind allele XcXc Colorblind female XCY Normal vision male XcY Colorblind male Hemophilia in Humans The table below summarizes the possible genotypes and phenotypes. Genotype XHXH Phenotype Normal blood clolng female XHXh Normal clotting female, but a carrier of hemophilia XhXh Hemophiliac female XHY Normal blood clotting male XhY Hemophiliac male Eye Color in Fruit Flies Sex-linked traits were discovered in the early 1900’s in the lab of Thomas Hunt Morgan. It was discovered that the gene for eye color in fruit Clies was carried on the X chromosome. In fruit Clies, the allele for red eyes is dominant over the allele for white eyes. Genotype Phenotype XRXR Red-eyed female XRXr Red-eyed female XrXr White-eyed female XRY Red-eyed male XrY White-eyed male A normal woman, whose father had hemophilia, married a normal man. What is the chance of hemophilia in their children? Practice Problem What is the genotype of the woman’s father? XhY What is the genotype of the woman? XHXh What is the genotype of the man? XHY XH XH XHXH Y XHY Xh XHXh XhY 1/4 1/4 1/4 1/4 XHXH 2/4 Normal cloSng XHXh female H X Y 1/4 Normal XhY cloSng male 1/4 Hemophiliac male The gene for colorblindness is carried on the X chromosome and is recessive. A man, whose father was colorblind, has a colorblind daughter. 1. Is this man colorblind? How do you know? Yes. The colorblind daughter had to get one allele for colorblindness from each parent. This would require her father to be colorblind. Practice Problem 2. Where did the man get his allele for colorblindness? A man gets his allele for colorblindness from his mother. He gets his Y chromosome from his father. 3. Must the fathers of all colorblind girls be colorblind? Explain. Yes. For a girl to be colorblind, she must inherit the colorblind allele from each parent. A. A pedigree chart shows … … relationships within a family. B. Squares represent males and circles represent females. C. A shaded circle or square indicates that a person has the trait being considered. The following table shows three generations of guinea pigs. In guinea pigs, rough coat (R) is dominant over smooth coat (r). Shaded individuals have smooth coat. What is the genotype of each individual on the table below? Practice Problem rr Rr RR or Rr* Rr Rr Rr Rr Rr Rr rr Rr / RR There is no way to know! rr Rr / RR rr There is no way to know! * #2 is most likely RR since no offspring have smooth coat.) The following pedigree table is for colorblindness. Colorblindness is a sex-linked trait. Shaded individuals have colorblindness. Determine the genotype of each of the following family members. XB Xb XB Xb Xb Y XB Xb Xb Y Xb Y XBY Xb Xb XB Xb XBY Practice Problem XB Y XB Xb XB XB XB Xb XB Xb XB XB Mutations Normally genes are copied accurately during DNA replication ______________. Occasionally there is an error when a gene is not copied correctly or chromosomes do not _________________, segregate properly _________________. These mistakes are called _________. mutations Mutations are changes … … in the nucleotide-base sequence of a gene or DNA molecule. Germ-Cell Mutations and Somatic-Cell Mutations Germ-cell mutations occur in an organism’s ________. gametes do not aﬀect the organism itself. These mutations ____________ These mutations are very important, however, because they can passed along to future offspring be ___________________________. Somatic-cell mutations occur in the _________ body cells of an organism. These mutations _________ can affect the organism. For example: Some skin cancers and leukemias are the result of somatic-cell mutations. These mutations are not inherited by offspring. The Importance of Mutations 1. Mutations range from lethal to beneficial. However, most mutations are neutral and have little or no effect. 2. Some mutations cause such ________________ dramatic changes that normal cell functions are _________ disrupted and may genetic disorder result in a ______________. 3. Some mutations may actually be _________. beneficial The mutation may cause a change in the _________ phenotype of the organism that better suited for its makes it ____________ environment. 4. Those organisms that are better suited are more likely to survive, reproduce, and pass these favorable traits on to their offspring. Natural Selection This is the mechanism of _______________. Types of Muta;ons 1. Mutations can involve an entire ____________ chromosome or a single ______________. DNA nucleotide 2. Gene mutation: A gene mutation produces a change within a single gene. It involves the substitution, addition, or removal of a single nucleotide along the DNA strand. Usually, a gene mutation results in a certain amino acid being left out of a protein. The proper protein is not formed. These “point mutations” will be studied in more detail when you learn about DNA, RNA, and Protein Synthesis. 3. Chromosome mutations produce changes in the whole chromosome. 1. A chromosome mutation involves either a change in the ________ structure of a chromosome, or the gain or loss of ___________________. an entire chromosome 2. Chromosome mutations have a much more drastic ___________ effect on the organism than gene mutations because they involve the _________________ entire chromosome rather than just ________. one gene 3. Types of chromosome mutations include: Deletion, inversion, translocation, and nondisjunction. Deletion: The loss of a piece of chromosome due to breakage. Inversion: A segment of chromosome breaks off, flips around, and reattaches to the same chromosome. Translocation: A piece of one chromosome breaks off and reattaches to a nonhomologous chromosome. Nondisjunction a) In nondisjunction the members of a pair of homologous chromosomes do not move apart properly during meiosis I, or sister chromatids fail to separate during meiosis II. b) The result is that one gamete receives two of the same type of chromosome and another gamete receives no copy. The other chromosomes are usually distributed normally. Nondisjunction c) If either of these gametes is then fertilized by a normal gamete, the zygote will have an abnormal chromosome number for that one particular chromosome. One zygote will have an extra chromosome, and the other zygote will be missing a chromosome. d) If the organism survives, it usually has a set of symptoms caused by an abnormal dose of the genes associated with the extra or missing chromosome. An example is Down Syndrome. “Crossing Over” It should be noted that “crossing over” during meiosis is not a chromosome mutation. In crossing over, the order of the genes on a chromosome is not altered. The chromatids break at exactly corresponding points. There is no loss or gain of genetic information, and they always rejoin to a homologous chromosome. This is a source of genetic variation, but it is not considered a mutation. GeneAc Disorders A genetic disorder is an inherited disease or disorder that is caused by a mutation in a gene or by a chromosomal defect. Genetic disorders can be caused by inheriting autosomal ________ recessive alleles, autosomal _________ dominant alleles, or alleles linked on the sex _______________. chromosomes Some genetic disorders are caused when chromosomes fail to separate correctly during meiosis. Huntington’s Disease 1. Huntington’s disease is caused by inheriting a single dominant allele. It develops when the affected person reaches the age of 30 to 40 years. 2. Symptoms include: Forgetfulness, muscle spasms, severe mental illness, and finally, death. Cystic Fibrosis 1. This disease is caused by a recessive allele on autosomal chromosome 7. 2. Two recessive alleles must be inherited to cause the disease. People with one copy of the normal dominant allele are unaffected. 3. Those suffering from this disease have … … digestive problems and produce a thick, heavy mucus that clogs the lungs and airways. Duchenne Muscular Dystrophy 1. This is a sex-linked disorder caused by a defective version of the gene that codes for a muscle protein. 2. This disease results in … … the progressive weakening and loss of skeletal muscle tissue. Down Syndrome 1. Down Syndrome is caused when autosomal chromosome 21 fails to separate during meiosis. It results in an extra chromosome 21 in each cell of the body. 2. Symptoms: Short, stocky body, thick neck and tongue, mental retardation, and heart defects. 3. Most cases are the result of nondisjunction. When the gamete is formed, it has 2 copies of chromosome #21 instead of one. When fertilized, the resulting embryo then has three copies. 4. The older the mother, the greater the probability of nondisjunction occurring. 5. This affects 1 out of every 800 children born in the USA. Nondisjunction of the Sex Chromosomes 1. Klinefelter’s Syndrome is the result of a male receiving an extra X chromosome. They are XXY. It occurs once in every 2000 births. The male has sex organs, but they are not functional. 2. Turner’s syndrome occurs in females. The female inherits a single X chromosome. This occurs once in 5000 births. They appear to be female, but the sex organs never develop during puberty. They are sterile. Human disorders are also caused by chromosomal translocation. This is the attachment of a fragment from one chromosome to another nonhomologous chromosome. Chromosomal translocations have been implicated in certain cancers, and a small fraction of the people with Down Syndrome are the result of the translocation of chromosome #21 to another nonhomologous chromosome. Created by Amy Brown Copyright © Amy Brown Science All rights reserved by author. This document is for your classroom use only. This document may not be electronically distributed or posted to a public web site, except for permitted use in password-protected Google Drive, Google Classroom, or Microsoft OneDrive. http://www.teacherspayteachers.com/Store/Amy-Brown-Science Clipart Credits: Adobe Photo Deposit Photo

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