Patterns of Inheritance Chapter 10 PDF

Patterns of Inheritance Chapter 10  Study for Inheritance Attempts to discover inheritance have deep roots – Both Hippocrates and Aristotle struggled with this attribute to life By the early 19th century it was established that offspring had traits from both parents –...

Patterns of Inheritance Chapter 10  Study for Inheritance Attempts to discover inheritance have deep roots – Both Hippocrates and Aristotle struggled with this attribute to life By the early 19th century it was established that offspring had traits from both parents – Previously they had thought all traits come from the father – Had the mechanism wrong  Gregor Mendel Considered the father of classical genetics Austrian Monk who worked with pea plants in 1860’s – Pea plants are easy to grow, came in many varieties, and easy to manipulate genetically Established that parents pass heritable factors to their offspring – Peas studied because they reproduce rapidly  Terms coined by Mendel Hybrid: offspring of 2 different genetic varieties of plants – Example, offspring of a purple flower and a white flower Cross (or hybridization): The process of mating 2 different organisms Generation classification – P Generation: a parents/parental generation – F1 Generation: offspring of the P generation – F2 Generation: offspring of the F1 generation  More Terms Genotype: actual genetic make up or in other words the actual genes in the DNA. Phenotype: physical appearance or the expression of the genes (i.e. a person with genes that encode red hair, the genotype, and the actual red hair the person has, the phenotype)  Alleles Most organisms of the same species have the same genes, but those genes can be written in different nucleotide patterns. The different patterns are called alleles. For example there people in general have the same pattern of eye construction, but people have different eye colors. The different alleles lead to different eye colors We have terms used to describe the general allele package someone has. Homozygote/Homozygous: means the individual has the same alleles within their genome. Heterozygote/Heterozygous: means the individual has different alleles within their genome. Zygote/Zygous is in reference to the zygote stage, the resulting cell from the union of the sperm and egg together. Just because you are heterozygous or homozygous for one trait (say eye color) doesn’t mean you are heterozygous or homozygous for another trait.  Dominance versus Recessive When 2 genes are of different alleles and one is visible (fully expressed) and the other is not visible, the alleles are called the dominant alleles and the recessive allele, respectively. – Dominant alleles are often symbolized with a capital letter – Recessive alleles are often symbolized with a lower case letter – Homozygous Dominant means a genotype of AA, homozygous recessive means a genotype of aa, while heterozygous means a genotype of Aa Note A and a are just examples, other letters maybe used to signify other traits Gregor Mendel’s Seven Pea Plant Traits  Punnett Square A Punnett square is device The parents genotypes are Aa and Aa for predicting offspring Diploid genotypes from a cross between two individuals. Ova genotypes Genotypical ratio is the Haploid amount of homozygous dominant: heterozygous: homozygous recessive individuals In this case 1:2:1 Sperm Genotypes Penotypical ratio is the Haploid amount that display one phenotype (dominant) versus another phenotype (recessive) In this case 3:1 The genotypes of the offspring are in the box.  Hidden alleles Gregor Mendel eventually came to the conclusion that organisms carry (at least) two copies of instructions. – Recessive instructions were often hidden in organisms which display a dominant trait. He noticed this by crossing organisms with one another.  Mendel’s Principle/Law of Segregation Pairs of genes separate (segregate) during meiosis (gamete formation); the fusion of gametes at fertilization pairs up genes again when the diploid number is re-established  Test Cross In order to determine the genotype of an organism which has the phenotype of the dominant trait you can mate the organism with an individual of who is demonstrating recessive phenotype individual – If individual is heterozygous, then some offspring will show the recessive allele – If individual is homozygous dominant, then all offspring will express the dominant allele Allows you to determine the unknown genotype  Mendel’s Principle of Independent Assortment Each pair of alleles segregate independently during gamete formation – Linked genes often provide an exception to this rule genes found on the same chromosome Used a dihybrid cross to study how alleles segregate during meiosis. Mating 2 individuals that are different in 2 traits  Conclusions Mendel came to his conclusions via an experiment using pea plants – Studying traits for coating type and color. – Observations support independent assortment, not dependent assortment Variations of Mendel’s Principles Relationship of Genotype to Phenotype is rarely simple There are often more than just 2 alleles to a gene also For example eye color is a product of at least three genetic traits – EYCL1, EYCL2, and EYCL3 are they designations of the genes – Maybe more than just these three  Incomplete Dominance This is where one gene is not dominant over the other – Both genes express themselves Results in a blending of the expression of the traits.  Co-Dominance This is when neither allele is dominant and both are expressed Blood types are an example – ABO blood types (R1=A, R2=B, and o=O) Type A: the type “A’ Carbohydrate on the cell – Results from genotypes of R1R1 and A1o Type B the type “B” Carbohydrate on the cell – Results from genotypes R2R2 and R2o Type O the type “O” Carbohydrate on the cell – Results from genotype oo Type AB the type “AB” carbohydrate on the cell – Results from genotype R1R2  Sickle Cell Anemia Sickle Cell trait changes he shape of hemoglobin – Results from a single point mutation – When in sickle form unable to efficiently bind and carry oxygen, but does make it possible to take care of the malaria organism (Plasmodium sp.) When both a sickle cell allele and a normal hemoglobin allele is present, both types of hemoglobin are produced When is homozygous for the sickle cell allele it is fatal – People often die at a very young age  Pleiotropy This is where a single gene Infants with this trait can have these affects multiple traits symptoms if not treated properly. Musty odor in breath ,skin, or urine A classic example is PKU or (build up of phenylalanine) phenylketonuria Neurological Problems (including – A single mutation of a gene seizures) results in a change in the Skin rashes (eczema) enzyme phenylalanine Abnormally small head (microcephaly) hydroxylase that converts Hyperactivity Intellectual disability phenylalanine to tyrosine Delayed development – With the mutation, Behavioral, emotional, and social phenylalanine builds up to problems toxic levels and affects Psychiatric disorders several traits May Clinic: https://www.mayoclinic.org/diseases-conditions/phenylketonuria/symptoms-causes/syc-20376302  Regulatory Genes and Pleiotropy Regulatory genes are genes that control multiple other genes for either metabolic processes or development Humans, Chimpanzees and Bonobos are very similar genetically. – Differences are in the regulatory genes which lead to different development.  Epistasis or Polygenic Inheritance This is where two or more genes are needed to complete a trait As aforementioned eye color is an example of polygenic inheritance – Humans it is the result of several different genes – Birds are products of other pigments, encoded by other genes  Linked Genes Genes that lie close together on the same chromosome tend to be inherited together – Do not follow Mendel’s Principle of Independent Assortment Genes that are further apart from each other on the chromosome tend to be separated more often via crossing over than genes close together.  Inherited disorders caused by a single gene Autosomal Disorders – These are disorders on chromosomes that are not involved with sex identity Range from relatively harmless to deadly – Albinism is harmless (although may not be harmless if you hang out in the sun too much) – Tay-Sachs (deadly in early childhood)  Tay-Sachs This is a result of mutations on the HEXA gene found on chromosome 15 Results in builds up of a fatty acid derivative called a ganglioside – These are common, but too much can prove fatal. Three types – Infantile: Deterioration of mental and physical abilities. Blindness and deafness sets in, as well as an inability to swallow. Muscle atrophy and paralysis sets in, and then death. Age usually is around 3. – Juvenile are the same, death usually occurs between ages of 5-15 – Adult are the same, death usually occurs in the 20’s to early 30’s – Juvenile and adult form are typically less sevee The HEXA gene encodes a portion of the enzyme beta- hexosaminidase A. – This enzyme is involved with regulating ganglioside proportions A genetic pedigree representing Tay-Sachs  Disorders can be recessive or dominant Most disorders are considered to be recessive – Only express the disorder if you are homozygous recessive Dominant disorders are expressed if you are homozygous dominant or heterozygous – Homozygous recessive individuals do not express this trait  Carriers People who carry a recessive allele of a disorder are called carriers – They often do not know they carry the disorder Genetic testing can detect fatal abnormalities on the genetic level – Helps parents make decisions – People who are worried about being carries should get tested  Incest Incest is for most people considered naturally wrong, because people closely related to each other will often share the same recessive disorders – More chance of offspring having a recessive disorder Sex Chromosomes  Sex Identity A pair of chromosomes determine sex in many species Humans XX = females, XY= Male – other species have other systems – Some insects have a system where the female has XX and the male only has X, lacking the other chromosome all together  Sex Linked Genes Not all genes found Lovebirds feather color is a result of sex-linked genes. Can help on the sex differentiate males from females. chromosomes are involved with sex identity – Called sex-linked genes Also referred to as sex-linage  Mammals Sex-linked genes are those genes found on the X Chromosome – The Y chromosome only carries genes involved with creating male sex identity – If any non sex identity traits were only found on the Y chromosome, then females would not inherit that trait Other groups of organisms have non-sex identity genes found on the Y Chromosome – Flies  X linked gene expression Any X linked gene that a male has, he gets from his mother – She donates the only X chromosome the male receives A woman on the other hand could have received her X linked genes from both her father and her mother – A woman would have to get recessive alleles from both mother and father to have a recessive trait expressed – A man only needs one recessive allele to have the recessive trait expressed Recessive X linked disorders  Red-Green Color Blindness Inability to distinguish shades of red from shades of green – These colors are seen as shades of grey Males with their “x” with the recessive allele are color blind An individual with normal vision will see a 5 – An individual with red- green color blindness will see a 2  Hemophilia This is when an individuals blood does not clot – When cut, bleeding is harder to control Actually three different genetic disorders can lead to hemophilia – Two on the X chromosome and one on an autosomal chromosome Can be treated with clotting agents added via injections