Genetics DNA contains the genetic code for the production of. A gene is a part of DNA, which has enough bases to make for many different proteins. These specific proteins made by a gene decide the of an organism. The traits of that organism can then be passed on to, or by their offspring. The study of the inheritance of traits is called. Who is Gregor Mendel? Mendel can be called the of genetics because he made the principles of genetics that we still use today! Mendel s most important work was the research and experiments that he did by studying. These experiments helped him explain how were passed from one generation to the next. Where are these genes? Each gene controls something different, and it has a specific location on a DNA molecule. A DNA molecule that is curled or coiled up is called a, which may have more than a thousand genes on it. Your chromosomes are in the of the cell. Each species of organism has a different number of chromosomes. Every chromosome carries genes for different traits. Humans have chromosomes in a somatic cell (body cell) and in a gamete (sex cell). In body cells, chromosomes are in. The pictures below are of a. This is a picture of a test that shows human chromosomes that have been cut out and arranged in their pairs. Academy Biology 1
Who cares about the pairs? Mendel s research showed that there are two factors that control a trait or characteristic. He concluded that at the end of, when the gametes are produced, each sperm or egg cell has only one factor instead of two. When the gametes combine during, the offspring will then have the two factors controlling each specific trait. We now call these factors, chromosomes. One chromosome is from the mom and the other chromosome of the pair is from the dad. The pair of factors is separated during meiosis. Mendel named this process of separating the Law of. Humans have pairs of chromosomes in every cell. One characteristic of humans that can be found by looking at a karyotype is the of the baby. The first 22 pairs of chromosomes in a male and a female are the same; they are called or body chromosomes. The 23 rd pair isn t really a pair so it is labeled differently. This last two chromosomes are called the. These chromosomes decide the gender or sex of the organism. They also carry for other characteristics. The sex chromosome of the female is the chromosome. A human female has two X chromosomes in each cell. The sex chromosome only found in males is the chromosome. A human male has one chromosome and one chromosome in each cell. Look at the karyotypes from page 1. What is the sex of person A? how do you know?. What is the sex of person B? how do you know?. Academy Biology 2
Are more chromosomes better? It would be easy to think that having an extra chromosome or two would make a superhuman, but this in not true. Extra chromosomes, damaged chromosomes and missing chromosomes almost always cause. A karyotype can be used to find some genetic disorders that a developing baby, or may have. Doctors will use cells taken from a developing baby to see if the baby has the correct number of chromosomes. This is done with a test called. If there are too many, too few, or damaged chromosomes, then that means that there must have been a mistake in when the are formed. If the number of chromosomes is wrong, then the did not separate correctly Meiosis. The phase of meiosis when this separation happens is called. This kind of mistake in which a tetrad does not separate is called. If an egg like this (with the mutation) is fertilized, the mother may miscarry the baby or the baby may die in the first year. If the baby is born, it will have a genetic disorder. The kind of genetic disorder is determined by how many chromosomes have a mistake and which ones have the mistake. What could happen to the baby? Here are some of the possible disorders that are caused by these types of mistakes. Read the descriptions and fill in the chart below. Cri Du Chat Syndrome: This disorder results in severe mental and physical retardation. This means that the child has trouble learning and they have physical difficulties. The affected people make sounds like a cat; that is the reason for the name cri du chat, which is French for cry of the cat. A missing part of chromosome five causes this; the amount of the chromosome that is missing determines how bad the effects are. Down Syndrome: Non-disjunction in the 21 st pair of chromosomes in one of the gametes causes an extra 21 st chromosome. This causes mental retardation (trouble learning). A person born with this genetic disorder has very serious physical and mental disabilities. They may have small, round heads, shorter bodies and almond shaped eyes. They can get other diseases very easily and they do not live as long as most people. This is found in about 3 of every 2000 births. Klinefelter Syndrome: A person with this disorder has an extra sex chromosome. Non-disjunction in either the egg or the sperm causes the fertilized egg to have two X chromosomes and one Y chromosome. The Y chromosome makes this person a male. A person with this karyotype has internal male sex organs, but they are not fully developed and cannot produce sperm. They also develop a few female characteristics, such as enlarged breasts. They have above-average height (usually over 6 ft tall) and below- normal intelligence; they may even be mentally retarded (have trouble learning). Turner Syndrome: A person with this disorder is missing one of the sex chromosomes. Non-disjunction in the egg or sperm causes the fertilized egg to have only one X chromosome. There is no second sex chromosome. This baby will be a female, but her ovaries will not develop and she will be unable to have children. She will have some physical problem like being very short. Her mental abilities may also be inhibited, which means she will have trouble learning. Academy Biology 3
Read the descriptions from the previous page to fill in this chart. Karyotype What is the sex or gender of the person? What disorder does this person have? Academy Biology 4
What is the probability of having a boy or a girl? Many times in genetics, we can make guesses about whether or not a parent will give a certain trait to their children. To do this we use a tool called a. This is a way to show all of the possible combinations of genes from the and and chances for certain combinations happen. Meiosis produces egg in a woman and sperm in a man. Gametes have the number of chromosomes that any body cell has. The gametes then will also only have one sex chromosome. What are the possible sex chromosomes that a woman can give? or What are the possible sex chromosomes that a man can give? or An example of an empty Punnett Square is below. Follow the directions to predict (guess) how likely it is to have a boy or girl. Dad s sex chromosomes Mom s sex chromosomes 1. The sides of a Punnett Square are for what chromosomes the gametes could have. In this case, we are looking at sex chromosomes. Write in the sex chromosomes that the mother can give on the top and those from the father on the side. 2. Copy the letters from the top of the square into each of the boxes below it. 3. Copy the letters from the sides of the square into each of the boxes next to it. 4. Each of the boxes now shows a possible combination of the egg and sperm. Within all 4 boxes is every possible combination of these two parents. What are the possible combinations of sex chromosomes? How many times does each occur? How likely is it for any woman and man to have a make child? How likely is it for any woman and man to have a female child? If a woman has a baby boy, what are the chances of her having another baby boy? Explain. Academy Biology 5
How do certain traits get passed on? Non-sex chromosomes are called. Every regular body cell has paired (in two) autosomal chromosomes. Every sex cell has one of the paired autosomal chromosomes. The offspring receives one copy of each autosomal chromosome from each. The two autosomal chromosomes that make the pair are called chromosomes. Homologous chromosomes are the same size and shape and carry genes for the same traits. The picture below is a pair of homologous human autosomal chromosomes. The different kinds of genes that are possible for each trait are called. Every trait of an organism is decided by at least two alleles. If a trait is decided by more than two alleles, it is called. Alleles are represented by a letter. Capital letters represent alleles and lower case letters represent alleles. The trait for a dominant allele will cover or mask a trait for a. The genes of an organism make up its. We write the letters of the alleles to show this. Look at the chromosomes in the picture above. The genotype for the trait showing of this person is. Both of these alleles are. If both of the alleles are the same, for example two dominant (GG) or two recessive (gg), the genotype is called. If the alleles are different (Gg) the genotype is called, When you have a heterozygous genotype, you are a for the recessive trait. This person s genotype is. The way that an organism looks is called its. If B represents the trait for brown eyes, and b represents the trait for blue eyes, what is the phenotype of this person? Academy Biology 6
1. 2. 3. 1. 2. 3. 4. 5. 6. List the genotypes of each of the plants: 1. 2. 3. 4. 5. 6. List the phenotypes of each of the plants: 1. 2. 3. 4. 5. 6. Describe the genotype of each of the plants using the following terms: Homozygous, Heterozygous If it is Homozygous, write whether it is Dominant or Recessive 1. 2. 3. 4. 5. 6. If plants 1 and 3 reproduced, what would be the possible genotypes and phenotypes of the offspring? - Start by completing this Punnett Square. Possible genotypes Possible phenotypes Academy Biology 7
A B C D E F Follow the directions provided. To fill in the chart, you will have to make some Punnett Squares. Use the space at the bottom of the page to make them. A B C D E F Academy Biology 8
Name: Date: Period: Punnett Square Problems Write the possible genotypes and the genotypic ratios (fractions) each Punnett Square below. Academy Biology 9
Use Punnett Squares to help you predict (guess) the genotypes and phenotypes from each of the crosses shown below. Complete each section of the chart. Cross Genotypes of parents Phenotypes of Parents Punnett Square Genotypic Ratios Phenotypic Ratios Green (GG) peas X Yellow (gg) peas Green (Gg) peas X Yellow (gg) peas Green (Gg) peas X Green (Gg) peas Green (GG) peas X Green (GG) peas Green (GG) peas X Yellow (gg) peas Academy Biology 10
Are some traits more common in boys than girls? Like autosomes, the sex chromosomes also carry genes for certain traits. The figure below shows some of the traits that are controlled by the on the sex chromosomes. Label the sex chromosomes as either male or female. How many genes decide whether or not a female has dry skin? How many genes decide whether or not a male has dry skin? The Y chromosome does not have ALL of the genes that the X chromosome has. In autosomes, recessive genes are needed for the recessive trait to show. This is different in sex chromosomes. One sex-linked trait shown above is color blindness. This trait is on an X of the sex chromosome. We write X c for recessive or X C for dominant. We use the X to show that it is found on the X sex chromosome. The dominant trait is normal color vision and the recessive trait is red-green color blindness. In order for a female to be colorblind, she must have the genotype In order for a male to be colorblind, he must have the genotype.. Academy Biology 11
Let s look at muscular dystrophy, another recessive sex-linked disorder, weakens and destroys muscle tissue. You are a genetic counselor and you have to tell each of these couples the chance that they will have children with this disorder. Figure out the probability (chance of this happening) using Punnett squares. SHOW YOUR WORK! Remember- THERE IS NO GENE FOR THIS TRAIT ON THE Y CHROMOSOME. 1.) Healthy father and homozygous dominant mother 2.) Father with MD and heterozygous mother 3.) Healthy father and mother with MD 4.) Healthy father and heterozygous mother 5.) Father with MD and mother with MD 6.) Father with MD and homozygous dominant mother Couple # 1. Punnett square Genotypic ratios (fractions) Phenotypic ratios (fractions) 2. 3. 4. 5. 6. Who has a bigger chance of having a recessive sex-linked genetic disorder, a male or female? Why? Academy Biology 12
How do we know if we could pass a trait to our children? When Mendel did his studies on genetics, he cross-pollinated (mixed) different pea plants. Using a green pea plant and a yellow (gg) plant, he could find out the genotype of a yellow pea plant. Since a green pea plant could have a genotype of or, how could he use this figure out the genotype of a yellow pea plant? The study of human genetics is different, we can t do a test-cross and as many experiments as we can with plants or small animals. When geneticists mate (reproduce) fruit flies, they control which ones mate with others. We cannot do this with humans. The study of human genetics depends a lot on the study of the family history of disorders and traits. A is a diagram, which shows how a particular trait is passed through a family from one to the next. Some of the symbols that are used in a pedigree chart are: Pedigree I looks at the dimples trait through three generations of a family. 1. What do the Roman Numerals stand for? 2. What symbols do we use for marriage and mating? 3. What symbol do we use for children? 4. What do the numbers stand for? Academy Biology 13
5. The genes for dimples are on autosomes. Are dimples a dominant or recessive trait? How can you tell? Even though Jane and Joe Smith have dimples, their daughter, Clarissa, does not. Joe s dad has dimples, but his mother and sister Grace do not. Jane s dad, Mr. Renaldo, her brother Jorge, and her sister Emily do not have dimples, but her mother does. 6. Write the name of each person in the pedigree below. I-1. II-2. I-2. II-3. I-3. II-4. I-4. II-5. II-1. III-1. Think about the pedigree below that shows cystic fibrosis, a recessive autosomal disorder. How many generations does this pedigree represent? What does it mean if the shape is half colored in? Is the gene for cystic fibrosis dominant or recessive? How can you tell? Write in the genotypes of the family members in the pedigree. Who married a homozygous dominant person? In which generation does the first case of cystic fibrosis appear? Who was born with it? Academy Biology 14
Complete the pedigree chart exercise below. The man and woman in the first step (first generation) of the pedigree chart are both red-green colorblind. Remember that red-green colorblindness is a recessive trait carried on the X sex-chromosome. All of the people who marry into this family are NOT colorblind and are NOT carriers for being colorblind. 1. You must decide what the symbols of the chart will be. Write all of the symbols in a key (box) under the chart. 2. Complete the pedigree chart below. Use the symbols you made in the key to show the genotype of each of the family members. You will need to do Punnett squares to figure out these genotypes. Show the Punnett squares in the space below the chart. Academy Biology 15
Are all genes that decide traits either dominant or recessive? Certain traits like freckles or dimples are caused by dominant alleles. Only one parent has to have the dominant allele, because there only needs to be dominant gene for the trait to show. Draw a Punnett square below to show what kind of alleles the parents must have to make a child with more than five fingers per hand. Five fingers on a hand is a recessive trait. Explain how this shows what the parents genotypes must be. Some traits are neither totally nor totally. When this happens, When this happens, the trait does not follow the usual Law of Dominance. We call this. If there is one dominant and one recessive gene, then usually only the gene is seen. Incomplete dominance will not show either trait. In incomplete dominance, the phenotype of the organism is a mixture of both of the genes. Because neither trait is recessive, both alleles are written as capital letters. Try the examples below. Academy Biology 16
When there are two dominant genes, and the phenotype is a mixture of the two dominant traits, it is called. There are other cases in which both traits show because they are both dominant, but the traits do not mix together. This is called. Sickle-cell anemia is a dangerous genetic disorder. Red blood cells carry through your body. The shape of sickle red blood cells is different from the shape of normal red blood cells. The sickle cells do not carry enough oxygen to body parts. Their shape also makes it difficult for them to move through blood vessels, which causes. R is the gene for round (regular) cell shape and R is the gene for sickle cell shape. Put checkmarks in the table to show the cell shape that goes with each genotype listed. What are the genotypes from the chart above? 1.) 3.) 4.) What are the phenotypes shown in the chart above? 1.) 2.) 3.) When genes are codominant, what do you notice about the phenotype of the organism? The genes for human blood type are also codominant. Complete the chart with the possible genes that a person with each of the following blood types could have. Blood Type A B O AB Possible genes Or Or Which of the blood types show regular dominance? How do you know? What blood types show codominance? How do you know? What possible blood types could a child have if the parents blood types were A and B? Use a separate sheet of paper to show all of the possible Punnett squares. Academy Biology 17
Baby Mix Up Four newborn babies are born in the hospital at the same time. Clumsy Clara the nurse ran was about to give each of the babies a wristband with that child s name on it, but she dropped the wristbands and they got out of order. She looked at the charts with the blood types of all four babies and their parents. Please help her figure out which baby belongs to which family. The baby s blood types are luckily all different. There is one baby with each: Baby A = blood type A Baby B = blood type B Baby C = blood type AB Baby D = blood type O The parents blood types are as follows: The Gonzalez parents: blood types O and O The Johnson parents: blood types O and A The Rogers parents: blood types AB and B The Smith parents: blood types O and AB Show your Punnett Squares below. Write the last name of each baby below. Baby A is a. Baby B is a. Baby C is a. Baby D is a. Academy Biology 18
If every gamete has half of the chromosomes, why are siblings so different? Mendel s research also showed that offspring could get one trait without necessarily getting another. For example, some children may have brown hair and blue eyes, or they may have brown hair and brown eyes. He concluded that the alleles (genes) for different traits are not always connected. The Law of Independent Assortment says that alleles for different traits are separated into gametes. That means that they do not go together; they go one by one. The phase of Meiosis when crossing over occurs is called. This is when changes can happen in the genes or alleles of each gamete. How likely is it for a person to have TWO TRAITS? So far, we have only done crosses for one trait at a time. For instance whether or not the child will be able to roll his tongue. This is called a cross. What if someone is interested in finding out the chances for their child to have two traits like brown hair and brown eyes? We would have to do a Punnett Square to show all of the possible genotypes. This gets a little more complicated. A cross with two traits is called a cross and a cross for three traits is called a tri-hybrid cross. Let s pretend to mate a pair of hamsters. What are the possible genotypes and phenotypes of the following cross? Black fur (B) is dominant over brown fur (b). Short fur (A) is dominant over long fur (a). Rough coat (R) is dominant over smooth coat (r). Gene Information Heterozygous black and heterozygous short fur X heterozygous black and heterozygous short fur Genotypes of Parents: X Gamete Possibilities: Punnett Square: X Genotype & Phenotype Ratios: Academy Biology 19