BIOL 1140 Intro to Genetics & Monohybrid Crosses Fall 2024 PDF

BIOL 1140: Ch 23 Intro to Genetics & Monohybrid Crosses Prof. Susan Cordova (Tappen)  Genetics: what is it? What is genetics? – “Genetics is the study of heredity, the process in which a parent passes certain genes onto their children.” ( http://www.nlm.n...

BIOL 1140: Ch 23 Intro to Genetics & Monohybrid Crosses Prof. Susan Cordova (Tappen)  Genetics: what is it? What is genetics? – “Genetics is the study of heredity, the process in which a parent passes certain genes onto their children.” ( http://www.nlm.nih.gov/medlineplus/ency/article/002048.htm) What does that mean? – Children inherit their biological parents’ genes that express specific traits, such as physical characteristics, natural talents, and genetic disorders.  Review... Humans have 46 chromosomes total in each somatic cell (2N=46) We inherited 23 chromosomes from Mom (egg), and 23 chromosomes from Dad (sperm) These “homologous”(same) chromosomes pair up as tetrads at the start of Meiosis I. This diagram of all 46 chromosomes in their homologous pairs (their tetrads) is called a: _________________________________ Recall that these chromosomes are long strands of DNA that carry genes that code for various RNA and protein  Human Genome Project International scientific research project 1990-2003 Generated the very first sequence of the human genome Found ~21,000 genes Mapped out locations of specific genes & found over 3 million genetic variations  Important Definitions to Start _____________________________________________________ = pair of chromosomes that have similar size, staining pattern, centromere location, and genes; inherit 1 from Mom + 1 from Dad. ___________ = segment of DNA that codes for a specific product (usually a protein) ___________ = physical location of a gene on the chromosome – its like an “address” – often given as combinations of numbers and letters _______________ = alternate forms (versions) of a gene; – You inherit 1 from Mom, and 1 from Dad. _______________________ ______________________ = alleles are the same = alleles are different (code for the same (code for different trait) traits) __________________________ allele = determines the phenotype; only need 1 to express it – Does NOT necessarily mean that it is more common in the population! __________________________ allele = is masked by the dominant allele; need 2 to express it – Does NOT necessarily mean that it is less common in the population! ___________________________= the genetic make-up of an individual, presented by letters _____________________= the observable expression of a trait, presented by words – Examples: height, brown hair, blood type, blue eyes, widow’s peak, sickle cell disease, etc.)  Genetic or Inherited Diseases Recessive Allele Diseases – Must have 2 recessive alleles to exhibit full disease characteristics – Many have heterozygous parents who don’t really show symptoms but are “carriers” of the recessive allele – Examples: Cystic Fibrosis, Sickle Cell Anemia, etc. – Chances of having the disease increases if close relatives mate = Inbreeding People in isolated areas Dog breeding Endangered animals Dominant Allele Diseases – Only need 1 allele to express the disease – Examples: Huntington’s Disease, Achondroplasia, Duchenne’s Muscular Dystrophy, etc. – If 2nd allele also codes for the disease, result could possibly be fatal (miscarriage or early death)  More Definitions… ____________________ Ratio = statistical chance that an offspring will have a genotype ____________________ Ratio = statistical chance that an offspring will have a phenotype NOTE: Be careful here – don’t use the following terms when reporting these ratios: “Heterozygous” or “Homozygous” is NOT a phenotype “Dominant” or “Recessive” is NOT a phenotype Just saying “Normal” – Normal for what exactly? What’s the trait? May need to be more specific! Just saying “Disease” – What disease exactly? Definitely needs to be more specific! ____________________ cross = tracking the inheritance of one trait ____________________ cross = tracking the inheritance of two traits found on different chromosomes  Cystic Fibrosis Autosomal Recessive Allele Disease – need both alleles to have CF gene in order to express the disease CFTR gene (Cystic Fibrosis Transmembrane Regulator) on Chromosome 7 – codes for membrane protein that transports chloride ions out of the cell Defective protein leads to build-up of sticky mucus in pancreas, lungs, digestive tract, etc. Causes poor absorption of nutrients, chronic bronchitis, recurrent bacterial infections Life expectancy can be ~26 yrs, ~44 yrs, ~61 yrs 1 in 2,500 births – mostly Caucasian – ~30,000 in US currently affected Locus Example for CFTR gene: Cystic Fibrosis Symptoms Cystic Fibrosis Chloride Transporter Protein  Cystic Fibrosis (CF) Phenotypes: Normal Normal Cystic *Is a carrier of fibrosis (CF) CF though Genotype: CC Cc cc Alleles:  Sickle Cell Anemia/Disease (SCD): Autosomal Recessive allele disease Point mutation causes defect in hemoglobin gene on chromosome 11 (Locus is 11p15.5) Sickled blood cells – Clumps can block small blood vessels  “sickle crises” can last hours to days & require hospitalization – Also can cause bone pain (osteonecrosis), organ damage, arthritis, headaches, jaundice, coldness in hands & feet (poor circulation) – Are fragile & die quickly  anemia – Anemia, Can’t carry O2 well  fatigue, dizziness, fainting, shortness of breath Affects ~100,000 in US – 1 of every ~365 Black or African-American births have SCD – 1 of every 16,300 Hispanic-American births Sickle Cell Mutation Changes Amino Acid Polar, so Hydrophi lic R group Hydrophob ic R group HBB protein is 146 amino acids long HBB gene found on chromosome 11  Sickle Allele & Pleiotropy Pleiotropy = ‘many affects’, ability of a single gene to have multiple phenotypic effects (that are seemingly unrelated) Sickle trait actually gives that person protection against malaria (parasite spread by mosquitos)  Sickle Cell Anemia Phenotype: Normal Sickle Cell Sickle Cell blood trait anemia/disease Genotype: AA Aa aa Alleles:  MONOHYBRID CROSSES: Punnett Square=chart used to predict the genotypes and phenotypes of offspring A a A a How to Read A Punnett Square to Give Genotypic and Phenotypic Ratios: A a All ratios must add up A AA Aa to 1! All percentages must add up to 100%! a Aa aa Genotypic Ratios: Phenotypic Ratios:  Genetics Problem Example: Juan (CC) and Juanita (cc) are expecting a baby. They are worried that the baby will suffer from Cystic fibrosis like Juanita does. What are the chances of that happening? Give both the genotypic and phenotypic ratios for this cross.  Genetics Problem Example: Ross is heterozygous for Sickle cell, while Rachel has sickle cell anemia. Give both the genotypic and phenotypic ratios for this cross. What are the chances that their child will have normal hemoglobin?  Achondroplasia: Dominant allele disorder Achondroplasia is D, Normal/Avg Height is d Affects ability of cartilage to form bone during development Causes shorter arms/legs, enlarged head, but average torso Is just one cause of ‘dwarfism’ Occurs 1 in ~15-25,000 people NOTE: DD (homozygous dominant) is fatal before age of 1  Huntington’s Disease: Autosomal Dominant allele disease (H) Slow, progressive brain deterioration – Targets basal ganglia Motor symptoms Cognitive impairment Personality & mood disturbances Symptoms typically begin ~30-55 yrs No cure (currently) Affects ~4-8 per 100,000 people in US Average age of death is ~50-57 years old Locus: near tip of chromosome 4  Mutated gene for Huntington’s Disease, Huntingtin protein (Htt) has more than 36 CAG Con’t repeats CAG codes for glutamine Htt is large cytoplasmic protein found in many tissues but is most active in the brain Believed to be involved in many processes, including cell signaling, transporting of materials, mitochondrial & ribosomal functions, cellular adhesion, homeostasis, protecting cell from apoptosis, regulating gene expression, etc.  Genetics Problem Example: Georgette was just diagnosed with Huntington’s Disease, and genetic testing showed she is heterozygous. Her husband Liam was also tested and is homozygous normal. They have 3 children already: James, Jorge’, & Jimena. What are the chances that James will develop Huntington’s Disease? What are the chances that Jorge’ will? What about Jimena?  Genetics Problem Example: Both Marcie and John are achondroplasia dwarfs. Marcie is pregnant. Give the genotypic and phenotypic ratios for this cross. What are the chances for them to have a child of normal/average height?  Test Crosses Commonly needed or used with animal & plant breeders What if you don’t know the complete genotype of one of the parents who is showing a dominant trait? Test Cross – mating between: – Known Parent that’s Homozygous recessive Ex: aa AND – Unknown Parent who is Homozygous OR Heterozygous dominant Ex: A__ Having multiple offspring (like litters or seeds) can reveal the genotype of the unknown dominant parent  Example: Test Cross for Guinea Pigs Short hair is dominant – S Long hair is recessive – s Mom Guinea Pig has long hair, so must be ss Dad Guinea Pig has short hair, so could be SS or Ss?  Example: Test Cross for Guinea Pigs Mom Guinea Pig is ss (Heterozgous Recessive) Dad Guinea Pig has short hair, so could be SS or Ss? What would be difference in offspring if the mom is SS vs Ss? – Do the Punnett squares! ALL of the offspring had short hair, so what is the most likely genotype of the mom? Why are test crosses not done with humans?  Genetics Problem Example: Jack and Jill are Yorkshire terriers that are being used for breeding purposes. Jill has rough hair and Jack has silky hair. The allele for rough hair (R) is dominant over the allele for silky hair (r). It is unknown whether Jill is heterozygous or homozygous, but in their first litter, about half the offspring had rough hair and half had silky hair. What are Jill and Jack’s genotypes? What kind of cross is being described?