Unit 7 Genetics

Pedigrees and Karyotypes Day 7 Pedigrees and Karyotypes

Pedigrees- family tree A pedigree is a chart of the genetic history of a family over several generations Genetic counselors use the to predict the possible occurrence of certain genetic diseases being passed to the next generation http://www.schooltube.com/video/c188ce8266b54a18992b/

How to read a pedigree chart Colored in- affected by disease/ trait Not colored in- not affected Half colored in- carriers of trait

How to read a pedigree chart Roman numerals show generations Numbers assign an individual to a generation

Interpreting a Pedigree Chart Determine if the pedigree chart shows an autosomal oR X-linked disease. If most of the males in the pedigree are affected the disorder is X-linked If it is a 50/50 ratio between men and women the disorder is autosomal When interpreting a pedigree chart of a family with a disease like muscular dystrophy, it is important to consider two steps. The first is to determine if the disorder is autosomal or X-linked. If the disorder is X-linked most of the males will have the disorder because the Y-chromosome cannot mask the affects of an affected X-chromosome. A female can have the disorder, but it would be a very low percentage. For a female to be affected, she would have had to receive an affected gene from the mother and the father. This means that the father would have the disorder and the mother was a carrier. In an autosomal disorder, the disorder is not found on the X or Y chromosome. It is found on the other 22 chromosomes in the human body. This means that men and women have an equal chance of having the disorder. The mother and father can be homozygous dominant, heterozygous, and homozygous recessive. If a person is homozygous dominant, the person has two of the same dominant genes. For example if someone is homozygous dominant for being tall it may be represented as TT. Capital letter always represent a dominant gene. If a person is heterozygous, this person would have a dominant trait and a recessive trait. It may be represent as Tt. The dominant gene will mask the recessive gene, so the person is still tall. If a person is homozygous recessive, the person has two of the same recessive genes. For example if someone is homozygous recessive for height, it may be represented as tt. The tt would mean the person is short.

Example of Pedigree Charts Is it autosomal or X-linked? Take a minute and try to decide if this slide is autosomal or X-linked.

Interpreting a Pedigree Chart Determine whether the disorder is dominant or recessive. If the disorder is dominant, one of the parents must have the disorder If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous The second step is to determine if the disorder is dominant or recessive. It is important to find out if a disorder is dominant or recessive. For example, Huntington’s disease is a dominant disorder. If you have only one dominant gene you will have Huntington’s disease, which is a lethal disorder. The disorder does not show up until a person is in their middle ages such as 45. It will quickly decrease their motor skills and the brain will begin to deteriorate. If a disorder is dominant, one parent must have the disorder (either homozygous dominant (TT) or heterozygous recessive (Tt). Both parents do not have to have the disorder. One parent might not have the disorder or be a carrier. If a disease is dominant, it does not skip a generation unless one parent is heterozygous dominant (Tt) and the other parent is homozygous recessive (tt). In this case the child has a chance of not receiving the dominant gene. If the disorder is recessive, a parent does not have to have the disorder, but could still pass it to their offspring. This would happen when a parent is heterozygous recessive (Tt) and passes on the recessive (t) gene. This means this disorder can skip generations. An example of a recessive disorder would be sickle cell anemia.

Example of Pedigree Charts Dominant or Recessive?

Examples of Pedigree Charts Dominant or Recessive?

Autosomal Dominant aa Aa aa Aa aa Aa aa Aa or AA Aa aa aa Aa Aa Autosomal or Sex-linked? ____________________ Is this dominant or recessive? ____________________ Assign genotypes to the pedigree to show the inheritance pattern Dominant

Sex-linked Recessive XBY XBXb XbY XBXb XBY XBXb XBXb XbY XBY XbY XBXb Autosomal or Sex-linked? ____________________ Is this dominant or recessive? ____________________ Assign genotypes to the pedigree to show the inheritance pattern Fill in what you know first! Recessive

Karyotypes Different # for different species Full set= 2N= Diploid N= # pairs 1 pair from mother 1 pair from father Humans= 23 pairs or 46 total Homologous chromosomes are the sets of each pair

Autosomes & Sex Chromosomes Sex Chromosomes= Pair #23 XX (female) or XY (male)

Some genetic disorders are detectable before birth Screening through Ultrasound Blood work Chorionic villi sampling (10-13 weeks) Amniocentesis (16-20 weeks)- withdraw amniotic fluid, grow fetal cells on plate

Amniocentesis Cells (from blood, amniotic fluid, etc.) are grown in vitro (in a cell culture dish) to increase their number Cell division is the arrested in metaphase with colchicine (prevents mitotic spindle from forming) Cells are centrifuged and lysed to release chromosomes Chromosomes are stained, photographed, and grouped by size and banding patterns

Mutations Definition: Change in genetic makeup. (Point and frame shift mutations have already been discussed.) Nondisjunction: failure of homologous chromosomes to separate properly during anaphase of meiosis 1 or 2. This results in either more (trisomy) or less (monosomy) chromosomes in a gamete than normal…

Nondisjunction www.biostudio.com/d_%20Meiotic%20Nondisj unction%20Meiosis%20I.htm www.biostudio.com/d_%20Meiotic%20Nondisjunction %20Meiosis%20II.htm

Examples of Nondisjunction Down’s Syndrome (Trisomy 21) Kleinfelter’s Syndrome (XXY) Turner’s Syndrome- (XO) One X chromosome missing

Down’s Syndrome Trisomy 21 extra chromosome 21 Poor muscle tone, flat face profile, short neck, heart and respiratory problems

Kleinfelter’s Syndrome XXY- Male with extra X chromosome tall, sterile, tendency to mental retardation

Turner’s Syndrome XO- missing one X chromosome Sterile, delayed puberty, heart defect, learning disabilities, short stature Turner’s Syndrome

XYY Syndrome Extra Y chromosome Tall mall, acne, angers quickly, sometimes below normal intelligence

Metafemale XXX- one extra X chromosome Healthy, fertile, tall, menstrual irregularities

Edward Syndrome Trisomy 18 Ear deformities, heart defects, spasticity, and other damage, almost every organ affected Do not usually live past 3 months

Patau Syndrome Trisomy 13 Eye, brain, and circulation defects, cleft palate Do not live past 3 months

Changes in chromosomes structure Translocation- chromosome abnormality caused by rearrangement of parts between non-homologous chromosomes Addition- A chromosome segment breaks off of one and attaches to another homologous chromosome Deletion- A chromosome segment breaks off of one and does not reattach Inversion- A chromosome segment breaks off one and attaches upside down to the other

Achondroplasia One form of dwarfism Results in the slow growth of bone; normal intelligence

Cri-du-chat Syndrome Missing portion of the 5th chromosome The cry of the cat is caused by larynx development. Respiratory problems, small head, heart, and muscles, mental retardation

Polygenic Traits Phenotype is influenced by more than one gene Traits that display a continuous distribution, such as height or skin color, are polygenic