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Bell Work: A royal blue betta fish mates with a green betta fish. What is the phenotypic ratio of their offspring? Look in your notes under incomplete dominance. Boy or Girl?? • The genes on chromosomes determine the sex of a baby. • Sex chromosomes are the only pair of chromosomes that do not always match… • Females (XX) Males (XY) • Females only have X’s so all eggs contain only one X • (remember gametes or sex cells have half the number of chromosomes) • Males have 2 different sex chromosomes so ½ will be Y’s and the other half of the sperm will be X’s. • Therefore, it is the sperm that determine the sex of the baby.. 1 XChromosome Inactivation Since males have one ___ and one ___, they express all of Y X the _______________ on both chromosomes. genes Even if males have all ___________________ genes, they will recessive still be ___________________. expressed In females (_______) one of the XX _________________________ is turned off, this is X-chromosomes _________________________________. X-chromosome inactivation Because one Xchromosome is randomly turned off, females are a ____________________ of two types of cells. One mixture type with an active Xchromosome from ___________ and mom one with an active Xchromosome from __________. dad Examples: _________________________________________________ Tortioseshell and calico cats ___________ Female calico cats have white fur and alleles for black and orange fur that are expressed randomly in some cells. Since males have only 1 X chromosome they can have black or orange. SexLinked Traits • Sexlinked traits are traits that are passed from parent to child on a sex chromosome • (ALLELES ARE CONNECTED TO THE XCHROMOSOME OR THE YCHROMOSOME) • Can still have dominant and recessive alleles • Some traits occur more often in one sex than the other 2 SexLinked Genes cont. • If a trait is carried on the xchromosome and they guy receives that xchromosome • He inherits that trait • Example: red/green colorblindness, more males than females have this • Xchromosome recessive trait • dangerous because you can not see the colors of traffic signals. • Common colorblindness testchart • Carriera person who has one recessive allele for a trait and one dominant allele. • Sexlinked traits can be hidden on carriers and passed on to the offspring. • In the case of sexlinked traits, only females can be carriers. (If a male has the trait…he’s got the disease) 3 REMINDER: Sex-Linked Traits ARE TRAITS EXPRESSED FROM A GENE LOCATED ON A SEX CHROMOSOME; (ALLELES ARE CONNECTED TO THE X CHROMOSOME OR THE YCHROMOSOME) Examples: Hemophilia (blood disease) and colorblindness Practice Problems: The human blood clotting disorder is a recessive trait (must receive both recessive alleles to express trait) which is found on the X chromosome. XH XH and XH Xh = females without hemophilia Xh Xh = female with hemophilia XH Y = male without hemophilia Xh Y = male with hemophilia 4 1. A woman who is heterozygous for hemophilia mates with a male without hemophilia. What % of female offspring will be a carrier for hemophilia (heterozygous) and describe the phenotypes of the boy offspring. % female offspring carriers: ______________ male offspring phenotypes: ______________ 2. A woman who is a carrier mates with a male with hemophilia. Will any girls have hemophilia? 5 Complete Practice Problems 3 and 4 Below is a chart listing some alien sexlinked characteristics. Use the chart to solve the genetics problems below. • A male with yellow eyes mates with a redeyed female. What is the chance that this couple will have a baby boy with red eyes? Probability of baby boy having red eyes: _______ % • A female, heterozygous for the body color trait mates with a pink male. What is the chance that these aliens will give birth to a purpleskinned girls? Purpleskinned Girl: _______ % 6 Genetic Disorder • An abnormal condition that a person inherits through genes or chromosomes • caused by mutations or changes in a person’s DNA • Mutations can occur during meiosis or can be passed from parent to child through an alreadyexisting mutation. • Mutationa sudden change in characteristics What’s the difference between a treatment and a cure? • A cure eliminates the symptoms and the disease. • A treatment controls the symptoms without eliminating the disease. 7 Cystic Fibrosis • A genetic disorder that causes thick mucus to build up in a person’s lungs and intestines making it hard to breathe. • Bacteria grow in mucus and can cause infection/lung damage • Mucus makes digestion in intestines difficult • Affects the whole body, oftentimes leads to an early death • Avg. life span is 37.4 years • Other symptoms include: poor growth and poor weight gain despite a normal food intake, accumulation of thick, sticky mucus, frequent chest infections and coughing, and sinus infections. • Can be diagnosed using a genetic test, even before birth • Recessive • Most common in people from Northern Europe • Currently no cure exists but treatments exists • for lung infections: medications, breathing treatments • Sometimes lung transplants are also necessary • physical therapy is available to help break down the mucus • Important for them to stay active 8 Sickle Cell Anemia • Genetic disorder that affects the blood • Shape of cells always serves a purpose • RBC are usually disc shape so that they can move easily through the vessels in your body • Sickle cell anemia patients have sickle or halfmoon shape RBC causing them to get stuck in narrow blood vessels. • The mutation that causes the disorder affects the production of an important protein called hemoglobin • Carries oxygen to all parts of your body • Oxygen levels are very low in people who have sickle cell anemia. • It is a codominant allele with the normal one. • African ancestry is most common place for disease (1 in 12 are carriers). • Pain, weakness, and lack of oxygen are all symptoms. • A person with two sickle cell traits will have the disease, • person with one allele will be a carrier and produce ½ sickle cells, ½ normal and generally they do not have any health issues. • No cure but given drugs to help with pain and prevent blockage in blood vessels. 9 Huntington’s Disease • Lethal genetic disorder by a rare dominant allele in which certain parts of the brain start to break down. • This causes uncontrolled movements, emotional disturbance, lack of concentration, eventually they have trouble feeding themselves and swallowing • Onset doesn’t usually occur until 3050 years old • there is no way to stop or reverse the course of HD • Medications do exist to help with muscle control and emotional problems Inheritance of Huntington’s • We now have a test that can be done to determine whether or not you have the allele • The disease runs in families • passed from parent to child through a mutation in the normal gene. • Each child of an HD parent has a 5050 chance of inheriting the HD gene. • If a child does not inherit the HD gene, he or she will not develop the disease and cannot pass it to subsequent generations 10 Hemophilia • Genetic disorder in which a person’s blood clots very slowly or not at all • they lack the proteins necessary for clotting • Could bleed to death from a minor cut or scrape • Doesn’t bleed at a faster rate, just for longer periods of time • Recessive allele on xchromosome (sexlinked) • more common in males than females • Can lead normal lives but advised to avoid contact sports and other activities that could cause internal injuries Down Syndrome • A genetic disorder in which a person’s cells have an extra copy of chromosome 21 • Can see this by doing an amniocentesis or looking at baby when born • An error occurs during meiosis • chromosomes fail to separate • Occurs when mothers are older when they have kids • People with this genetic disorder have a distinctive physical appearance (flattened face, upward slanted eyes) and some degree of mental retardation, heart defects are also common but most can be treated, infertile. • Physical genetic limitations of Down syndrome cannot be overcome, but education and proper care will improve quality of life. 11 Friday, December 9 Bell Work: A woman who has hemophilia marries a man without hemophilia. What is the probability that their children will have hemophilia? 12 Diagnosing Genetic Disorders • Years ago Dr.’s relied on pedigrees and punnett squares to help predict whether a child might have a genetic disorder • Today doctors use tools such as amniocentesis and karyotypes to help determine genetic disorders. • Amniocentesisa long needle is inserted into the mother’s belly to remove a small amount of fluid that surrounds the developing baby…why? • Because cells from the baby will be found there and then they use that to make a karyotype Karyotype • karyotype a picture of all the chromosomes in a cell • arranged in pairs by length and location of the centromeres • Reveals whether a baby has the right number of chromosomes (would show genetic disorders) • you can also tell whether it is a boy/girl 13 Karyotyping Activity Diagnosis…analyzing karyotypes and determining the sex and the disease. Genetic Counseling • A couple with a concern about genetic disorders may turn to a genetic counselor for advice. • Agerelated • Family history • Genetic counselors might run tests to see if the parents are carriers for a particular genetic disorder. 14 Pedigrees • To study patterns of inheritance in humans you would need to trace the inheritance of traits through many generations in a number of families • An important tool that geneticists use to trace the inheritance of traits in humans is a pedigree • Pedigree a chart or “family tree” that tracks which members of a family have a particular trait. • You can use pedigrees for any kind of trait…including sexlinked. Pedigrees Continued… understanding the symbols Scientists use a bunch of symbols that help us to simplify the actual ‘charts’. 15 More pedigree symbols Pedigree symbols cont. • The generations are identified in sequence by Roman numerals • Each individual is also given a number to make conversations and studies easier to understand 16 Practice with A6: Interpreting Information in a Pedigree 17 18 19 20 Pedigree miniproject their own family already designed family 21