Human Inheritance and Genetic DisordersPolydactyly Progeria Hypertrichosis Hemophelia Down Syndrome Sickle Cell Anaemia
Warm-up: Below is an actual photo of a persons full set of chromosomes. Use the picturebelow to answer the following questions in your notebook: How many chromosomes does each human have? How any chromosomes does the person below have? What might have caused this extra chromosome? (Hint: It happens during meiosis) How do you predict this might affect the person?
Human InheritanceReview: Every living thing (organism) is controlled by its DNA, which is tightly bound in strands called chromosomes inside the nucleus of each cell. Each individual trait (characteristic) of an organism is controlled by a gene which is a part of a chromosome. Each gene is controlled by two allelles; one from mother, one from father. Allelles are patterns of DNA that tell the body how to make certain amino acids which form proteins. Proteins control how an organism looks and functions.
Human Inheritance Some traits are controlled by just one gene, two alleles. A widows peak for example. Multiple alleles are three or four forms of a gene that code for a single trait. Our blood type is an example: Still other traits are controlled by multiple genes. Skin type, eye color, hair color and many others are controlled by multiple genes.
Sex Chromosomes Sex Chromosomes are 1 pair of the 23 pairs of chromosomes in the body. Sex Chromosomes carry the genes that makes a person male or female, but also carry genes which determine other traits.
Sex Chromosomes The Y chromosome (male) is much smaller than than the X chromosome. Because the X is bigger, it carries a lot more genetic information than the Y Sex-Linked Genes have alleles that pass from parent to child on a sex chromosome.
Sex-Linked Genes A common sex-linked gene is colorblindness.
Is anyone unable to see the image in this circle? If so, you have red-green colorblindness! This is a sex-linked recessive trait.
Sex-Linked Genes This punnet square shows sex-linked genes for colorblindness. Only the X chromosome carries the gene, so if a male gets a recessive Xc and a Y, he automatically has the disease. Females, however, can be carriers of the disorder with one dominant XC and one recessive Xc, but only have the disorder if she has both recessive: Xc Xc A carrier is a person who has one recessive and one dominant allele for the trait.
Environment Environmental factors also determine how genes are expressed. A person can have genes to be really tall, but if they do not have proper nutrition, they will not reach their optimal height. A person can even have genes which wire the brain to be good at making music, but if they never try to play an instrument, they will never know. This is why everyone should try everything at least once; you could end up being really great at anything!
Genetic Disorders A Genetic Disorder is an abnormal condition that a person inherits through their genes. Genetic disorders can be caused by either changes in the DNA, or an extra, or a missing chromosome.
Types of Genetic Disorders Cystic Fibrosis is where the body produces abnormally thick mucus in the lungs. It is caused by a recessive allele on one chromosome. The recessive allele is a mutation where strands of DNA are deleted.
Types of Genetic Disorders Sickle Cell Disease is where a persons blood cells are shaped differently. The sickle shape of blood causes it to clot in vessels and cause blockage and carries less oxygen. The allele for the disease is codominant with the normal allele. A person with one recessive and one dominant allele will produce half normal blood cells, half sickle. A person with two recessive alleles will produce only sickle cells. Normal RBC Sickle-Cell RBC
Types of Genetic Disorders Hemophilia prevents blood clotting. It is a recessive sex-linked disorder, found on the X sex chromosome. It is dangerous because even small wounds can cause unnecessary bleeding and even death through blood loss.
Types of Genetic Disorders Down Syndrome is a form of mental retardation and physical abnormalities. It is caused by a duplicate 21st chromosome. Instead of two, they have three 21st chromosomes. This occurs when the chromosomes fail to seperate during meiosis.
Pedigrees A Pedigree is a chart or “family tree” which maps genetic disorders in a family.
Pedigrees Below is a sample of a pedigree from a family which carries hemophilia.
Karyotypes A Karyotype is a picture of all the chromosomes in a cell. Modern scientists can take a blood sample from an unborn child to an adult, create a karyotype by seperating chromosomes, and be able to determine if any genetic disorders are present. A couple who wishes to have children can receive genetic counseling where a doctor looks at both parents karyotypes to see if any disorders will pass to offspring.