Patterns of Inheritance and Genetic Concepts PDF

8/27/24, 8:27 PM Platform | Study Fetch Patterns of Inheritance and Genetic Concepts (00:00:25 - 00:02:26) Genotypes and Phenotypes Genotype is the genetic code an organism has, including both alleles from each parent P...

8/27/24, 8:27 PM Platform | Study Fetch Patterns of Inheritance and Genetic Concepts (00:00:25 - 00:02:26) Genotypes and Phenotypes Genotype is the genetic code an organism has, including both alleles from each parent Phenotype is the actual physical appearance or expression of the genotype Homozygous vs. Heterozygous Homozygous means having two alleles of the same type Heterozygous means having two different alleles, typically inherited from different parents Penetrance and Expressivity Penetrance is the proportion of individuals who have the phenotype associated with a genotype Incomplete penetrance is when some individuals with the genotype do not express the phenotype Expressivity is the extent or intensity to which a given genotype is expressed as the phenotype Incomplete Dominance vs. Codominance Incomplete dominance is when two alleles blend together, producing an intermediate phenotype Codominance is when multiple alleles are expressed independently, without one being dominant Epistasis Epistasis is when one gene can suppress the expression of another gene Pleiotropy vs. Polygenic Inheritance Pleiotropy is when one gene affects multiple traits Polygenic inheritance is when multiple genes affect one trait, like height Proto-oncogenes vs. Tumor Suppressor Genes Proto-oncogenes are genes that can become cancer-causing oncogenes with a mutation Tumor suppressor genes have a different mechanism for causing cancer when mutated Mendel's Laws and Genetic Crosses (00:00:13 - 00:00:41) Lesson Overview 1. Patterns of inheritance 2. Mendel's laws and genetic crosses 3. Linked genes https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce6bf3e81bb65113fe36b1/document?go=note 1/6 8/27/24, 8:27 PM Platform | Study Fetch Mendel's Laws Mendel's laws describe how traits are passed from parents to offspring Linked Genes (00:00:41 - 00:01:21) Linkage and Crossing Over Linked genes are genes that are physically close together on the same chromosome Crossing over during meiosis can separate linked genes into different gametes Oncogenes and Tumor Suppressors (00:05:03 - 00:05:24) RSS is a protein that causes cells to divide Each person has two copies of the RSS gene, one from each parent If one of the RSS genes is overactive, it can cause all the cells to start dividing uncontrollably (00:05:24 - 00:05:34) Tumor suppressors are things that slow down cell division or induce apoptosis (programmed cell death) Typically, you need mutations in both copies of a tumor suppressor gene to induce cancer (00:05:34 - 00:05:52) If you lose one copy of a tumor suppressor gene, the other copy can still suppress cell division and prevent tumor formation But if you lose the other copy, you'll start to have uncontrolled growth (00:06:07 - 00:06:21) Haploinsufficiency means that one copy of the wild-type gene is insufficient Haplosufficency means that one copy of the wild-type gene is sufficient Mendel's Laws (00:06:36 - 00:06:46)Mendel's First Law: The Law of Dominance A dominant allele will mask a recessive allele (00:06:46 - 00:07:12) In a heterozygote, the dominant allele will mask the recessive allele If two heterozygotes are crossed, you can get the recessive phenotype in the offspring (00:07:12 - 00:07:23)Mendel's Second Law: The Law of Segregation During gamete formation, homologous gene copies will separate (00:07:23 - 00:07:52) Each parent contributes one copy of each gene to the offspring https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce6bf3e81bb65113fe36b1/document?go=note 2/6 8/27/24, 8:27 PM Platform | Study Fetch The offspring only receives one allele for each trait from the assortment of alleles the parents had (00:08:02 - 00:08:34)Mendel's Third Law: The Law of Independent Assortment Alleles of different genes get sorted into gametes independently of each other This is complicated by the concept of linkage, where genes that are close together on a chromosome are more likely to be inherited together (00:08:46 - 00:09:01)Summary of Mendel's Laws: Law of Dominance: Dominant alleles mask recessive alleles Law of Segregation: Homologous gene copies segregate during gamete formation Law of Independent Assortment: Alleles of different genes sort independently into gametes Non-Disjunction (00:09:22 - 00:09:35) Non-disjunction occurs when two chromosomes fail to separate properly during cell division (anaphase) This can lead to cells with the wrong number of chromosomes Non-Disjunction and Genetic Disorders (00:09:45 - 00:09:55) Normally, chromosomes would separate and form two complete, different nuclei. In the case of non-disjunction, something fails, such as the spindle or the chromosomes failing to break apart. This results in a cell ending up with two copies of the same chromosome. (00:09:55 - 00:10:09) Non-disjunction can occur in two different places: during meiosis I and meiosis II. Both result in errors, but the outcomes are different. (00:10:09 - 00:10:21) In non-disjunction during meiosis I, the sister chromatids will separate normally, but the chromosomes (copies) go together and split. This results in more errors because it's happening earlier in the process. (00:10:21 - 00:10:36) In non-disjunction during meiosis II, the sister chromatids don't separate, leading to two copies of the same allele. This is different from meiosis I, where the copies could be of different alleles. (00:10:36 - 00:10:54) Most questions will just require knowing that non-disjunction can occur during meiosis and usually results in multiple copies of the same chromosome. There are some rare cases, like chromosome fragments or fusions, that can also lead to abnormal chromosome numbers. (00:10:54 - 00:11:21) Triploid chromosomes can occur due to non-disjunction or the fusion of a chromosome onto another. Down syndrome is a result of non-disjunction, typically during meiosis, leading to trisomy 21. Turner syndrome is caused by having only one X chromosome. Kleinfelter syndrome is caused by having two X chromosomes and a Y chromosome. https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce6bf3e81bb65113fe36b1/document?go=note 3/6 8/27/24, 8:27 PM Platform | Study Fetch (00:11:21 - 00:12:00) Genetic disorders like Down syndrome, Turner syndrome, and Kleinfelter syndrome are caused by having an abnormal number of chromosomes. Down syndrome is trisomy 21, Turner syndrome is monosomy X, and Kleinfelter syndrome is XXY. (00:12:00 - 00:12:37) Kleinfelter syndrome results in a somewhat typical male, but they often have difficulty conceiving and may develop breast tissue. Kleinfelter syndrome is typically discovered when a male is having trouble conceiving with a partner. (00:12:37 - 00:13:18) The extra X chromosome in Kleinfelter syndrome significantly reduces the amount of sperm produced, making it difficult for them to conceive. (00:13:18 - 00:13:44) Mnemonic for remembering genetic disorders: Turner is X chromosome monosomy Down syndrome is trisomy 21 Kleinfelter is sex chromosome trisomy XXY (00:13:44 - 00:14:03) Punnett squares and pedigrees are used to observe the patterns of inheritance for genetic disorders. Mendel's Laws and Genetic Inheritance Parental Generation and True Breeding (00:14:03 - 00:14:23) The parental generation is the first generation in a genetic cross True breeding refers to organisms that always produce the same type of offspring, indicating they are homozygous True breeding organisms can be either dominant homozygous or recessive homozygous F1 Generation and Heterozygotes (00:14:23 - 00:14:50) Crossing a homozygous dominant and a homozygous recessive true breeding organism results in an F1 generation of all heterozygotes Heterozygotes have one dominant and one recessive allele F2 Generation and Phenotypic Ratios (00:14:50 - 00:15:57) The F2 generation is the offspring of the F1 heterozygotes The phenotypic ratio in the F2 generation is: https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce6bf3e81bb65113fe36b1/document?go=note 4/6 8/27/24, 8:27 PM Platform | Study Fetch 1 homozygous dominant: 2 heterozygotes: 1 homozygous recessive This 1:2:1 ratio is an important concept to memorize Dihybrid Crosses (00:16:07 - 00:17:25) Dihybrid crosses involve the inheritance of two separate genes The phenotypic ratio in the F2 generation of a dihybrid cross is: 9 with both dominant traits: 3 with one dominant, one recessive: 3 with one recessive, one dominant: 1 with both recessive traits This 9:3:3:1 ratio should also be memorized Pedigree Analysis (00:17:36 - 00:18:18) Pedigree analysis is used to track the inheritance of autosomal dominant traits Squares represent males, circles represent females Affected individuals are typically shown in red or another distinct color Key Concepts: True breeding and homozygosity Phenotypic ratios in F1 (1:0) and F2 (1:2:1) generations Dihybrid crosses and the 9:3:3:1 phenotypic ratio Pedigree analysis and representation of affected individuals (The notes above cover the key information presented in the given video transcript excerpts.) Heredity and Genetic Inheritance (00:18:34 - 00:18:58) Importance of analyzing pedigrees to determine the mode of inheritance of a trait or disease Genotyping can be used to identify carriers and determine genetic makeup, even without knowing family history (00:18:58 - 00:19:10) This trait is not sex-linked, as both affected and unaffected males and females are present in the pedigree Sex-linked traits typically only affect males or have a higher prevalence in males (00:19:10 - 00:19:25) In sex-linked inheritance, males would only have the disease, and females would be carriers or affected if they inherited two copies of the disease allele The presence of both affected and unaffected males and females suggests an autosomal mode of inheritance (00:19:25 - 00:19:50) Analyzing the pedigree can help determine the mechanism of inheritance, whether it is autosomal dominant, autosomal recessive, or sex-linked https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce6bf3e81bb65113fe36b1/document?go=note 5/6 8/27/24, 8:27 PM Platform | Study Fetch Typically, autosomal dominant traits will have many affected individuals across multiple generations, while autosomal recessive traits are less common in a pedigree with this many affected individuals (00:19:50 - 00:20:04) For an autosomal dominant trait, the affected male in the third generation could be either homozygous dominant or heterozygous dominant (00:20:04 - 00:20:32) Since the father in the second generation is unaffected, he must be homozygous recessive The mother in the second generation is likely heterozygous dominant, as she has an affected child but is not affected herself Therefore, the affected male in the third generation is most likely heterozygous dominant (00:20:32 - 00:20:46) The father in the second generation is homozygous recessive (little y, little y) The mother in the second generation is likely heterozygous dominant (Little Y, little y) (00:20:46 - 00:20:58) Considering the genotypes of both parents, the affected male in the third generation is most likely heterozygous dominant (Little Y, little y) (00:20:58 - 00:21:14) Linked genes are genes that are located close to each other on a chromosome For autosomal dominant linked genes, all offspring with the affected allele will have the disorder (00:21:14 - 00:21:28) In the case of X-linked dominant inheritance, the affected allele on the X chromosome will cause the disorder in both males and females Individuals with the affected allele will have the disorder, regardless of sex (00:21:28 - 00:21:54) X-linked recessive inheritance typically only affects males, as they only have one X chromosome Females would need to inherit two copies of the affected allele to have the disorder, which is rare in the population (00:21:54 - 00:22:15) Y-linked inheritance is passed from father to son, as the father determines the sex of the offspring by providing either an X or Y chromosome Females cannot be affected by Y-linked traits, as they do not inherit the Y chromosome (00:22:15 - 00:22:30) The father determines the sex of the offspring by providing either an X or Y chromosome, while the mother always provides an X chromosome Mastering the concepts of heredity and genetic inheritance will be crucial for success on the upcoming test (00:22:30 - 00:22:31) Congratulations on your progress in understanding these important genetic principles! https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce6bf3e81bb65113fe36b1/document?go=note 6/6