Genetics I - Mendelian Genetics & Chromosomal Disorders PDF

Genetics I = Mendelian Genetics & Chromosomal Disorders 6a: Construct an argument based on evidence to support the claim that heritable genetic variations may result from various process such as crossing over during mitosis 6a1: Develop and use models to investigate ho...

Genetics I = Mendelian Genetics & Chromosomal Disorders 6a: Construct an argument based on evidence to support the claim that heritable genetic variations may result from various process such as crossing over during mitosis 6a1: Develop and use models to investigate how genetic variations arise during meiosis (crossing over; nondisjunction) 7b: ask questions and define problems that explain the relationship between Mendel’s laws and role (segregation & independent assortment) & the role of meiosis in reproductive variability. 7c: Construct an explanation regarding how errors in meiosis (non-disjunction) may contribute to certain human genetic disorders resulting from monosomy & trisomy. Genetics: The Science of Gregor Mendel What is genetics? the science of heredity What is heredity? passing of traits from parents to offspring. From Mom & Dad to Child Gregor Mendel (Born in 1822) – Austrian monk who laid important groundwork for understanding biological inheritance. He observed 7 inherited traits in pea plants.  “ The Father of Modern Genetics” Studied offspring from different “matings,” or crosses, of pea plants. He began his research with pea plants that were considered true-breeding. Plants that have the ability to produce offspring identical to themselves, through the use of their own gametes = “Self-Pollination” = true breeding  Most plants reproduce via cross-pollination, the combining of gametes from two separate plants. Mendel DID NOT want to have this extra variable in his research, so he prevented his plants from “self-pollinating” by crossing the pea plants himself. He cross-pollinated plants with different forms of the same trait (i.e. purple x white) to examine offspring. Conclusions… Inheritance is determined by genes. Some alleles (different forms of a gene) are considered Dominant and some are Recessive The Principle of Dominance.  From Mendel’s Research we have 2 Important Laws: 1. Law of Segregation = Offspring inherit two copies of each gene, one from each parent. Two alleles for a trait segregate (separate) when Gametes are formed  From Mendel’s Research we have 2 Important Laws: Law of Independent Assortment = alleles for different genes separate independently of each other during gamete formation, Meiosis. Applying Content I: Laws of Mendel Christian’s hair is brown, but his eye color is blue. Construct an argument using Mendel’s law to explain why Christian’s hair does not match his eye color. Construct an argument that supports why a little girl named Allison would only inherit one set of information on hair color from her mother, rather than 2 sets.  Applying Content I: Laws of Mendel (ANSWERS) Christian’s hair is brown, but his eye color is blue. Construct an argument using Mendel’s law to explain why Christian’s hair does not match his eye color. According to the Law of Independent Assortment, alleles for different genes are separate independently during meiosis. Therefore, hair color does not affect ones eye color, because they are on separate genes. Thus, Christians hair color can be different from his eye color – they are independent of each other. Construct an argument that supports why a little girl named Allison will only inherit one set of information on hair color from her mother, rather than 2 sets. Based on the Law of Segregation, during meiosis each parent has a 50% chance of passing on one of their traits to their offspring. Therefore, Allison will only inherit one set/ half of the info on hair color from her mom (and she will get the other half/ set from her dad). If Allison had 2 sets, she would a mutation that could result in a genetic disorder. So what happens when meiosis goes wrong? The most common error in meiosis occurs when homologous chromosomes fail to separate. This is known as nondisjunction (not coming apart). If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes, and a disorder of chromosome numbers may result. Nondisjunction Nondisjunction causes gametes to have abnormal numbers of chromosomes. Applying Content II: Nondisjunction Complete the models showing what would happen if Nondisjunction nondisjunction took place. Nondisjunction Applying Content II: Nondisjunction (ANSWERS) Complete the models showing what would happen if Nondisjunction nondisjunction took place. Nondisjunction How can we view our chromosomes? To analyze chromosomes, cell biologists photograph cells in mitosis (because the chromosomes are fully condensed and easy to see) Biologists then cut out the chromosomes from the photographs and group them together in pairs A picture of chromosomes arranged in this way is known as a karyotype  The Human Karyotype The chromosomes in this figure are from a typical human body cell, which contains 23 pairs (46 total) chromosomes. Is this a karyotype for a male or female? How do you know? HINT: look at the 23rd pair of chromosomes…  An example of Nondisjunction… If two copies of an autosomal chromosome fail to separate during meiosis, an individual may be born with three copies of a chromosome. This type of nondisjunction is known as trisomy (three bodies). The most common form of trisomy involves 3 copies of chromosome 21 and is called Down syndrome (trisomy 21). Down syndrome produces mild to severe mental retardation, increased susceptibility to many diseases, and a high frequency of birth defects.  Trisomy 21 – Down Syndrome Karyotype showing trisomy 21 – individual has three #21 chromosomes. Child will exhibit facial characteristics of Down syndrome, as well as difficulty processing some information in the brain.  Applying Content II: Chromosomal Disorders A Kayrotype XYY – not characterized by a particular syndrome, but usually are males who are somewhat taller than average; additional amounts of testosterone.  Applying Content II: Chromosomal Disorders B Trisomy 16 – Major Cause of Miscarriage in 1st Trimester Pregnancy  Applying Content II: Chromosomal Disorders C Monosomy X (also known as XO) - individuals are phenotypically female, but their sex organs do not mature at adolescence, and they are sterile. Most have normal intelligence.  Turner’s Syndrome (XO) Symp/Charac Missing or incomplete chromosome of girls; Short, "webbed" neck with folds of skin; Low hairline in the back; Low-set ears; Swollen hands and feet ; infertility Sex-linked Chromosomal Treatments Specific to symptoms  Applying Content II: Chromosomal Disorders D Klinefelter Syndrome – XXY – have male sex organs, but testes are abnormally small and the man is sterile. Often includes breast enlargement and other feminine body characteristics.  Klinefelter’s Syndrome (XXY) ⚫ Symp/Charac XXY male; Abnormal body proportions (long legs, short trunk, shoulder equal to hip size) ; Enlarged breasts; Less than normal amount of pubic, armpit, and facial hair; Small, firm testicles ;Tall height ⚫ Sex-linked Chromosomal ⚫ Treatment Educational services; Physical, speech and occupational therapy; Medical treatments including testosterone replacement