BIOE 120 Week 8 - Genetics and Human Inheritance PDF

Chapter 20 Genetics and Human Inheritance Lecture Presentation by Tonya Bates, UNC Charlotte © 2017 Pearson Education...

Chapter 20 Genetics and Human Inheritance Lecture Presentation by Tonya Bates, UNC Charlotte © 2017 Pearson Education, Inc.  Genetics and Human Inheritance Outline:  Principles of Inheritance  Breaks in Chromosomes  Detecting Genetic Disorders © 2017 Pearson Education, Inc. Science of genetics  Heredity: is the transmission of traits from one generation to the next.  Allele: is a variant form of a gene. Some genes have a variety of different forms, which are located at the same position, or genetic locus, on a chromosome.  Genetics (the scientific study of heredity) began with Gregor Mendel’s experiments.  Mendel crossed pea plants and traced traits from generation to generation. He hypothesized that there are alternative versions of genes (alleles), the units that determine heritable traits. © 2018 Pearson Education Ltd.  Mendel’s law of segregation describes the inheritance of a single character Mendel developed four hypotheses, described below using modern terminology. 1) There are alternative versions of genes (called alleles) that account for variations in inherited characters. © 2018 Pearson Education Ltd. Figure 20.1 In a homologous pair of chromosomes, each member carries genes for the same traits. One member of each pair was inherited from the mother, and the other from the father. A gene is a segment of DNA located in a specific site on a specific chromosome that contains information for producing a particular protein (polypeptide). A pair of alleles. An allele is an alternative version of a gene located on a specific site of a specific chromosome. One allele is inherited from the mother, and the other from the father. © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance 12  Homozygous (homo, same; zygo, joined together) Individuals with two copies of the same allele  Heterozygous (hetero, different) Individuals with different alleles of a given gene  Dominant (use uppercase—example “A”) When the effects of an allele can be detected regardless of the alternative allele  Recessive (use lowercase—example “a”) When the effects of an allele are masked in the heterozygous condition © 2017 Pearson Education, Inc. Homozygous vs Heterozygous : 2. For each character, an organism inherits two alleles of a gene, one from each parent. An organism that has two identical alleles for a gene is said to be homozygous for that gene. An organism that has two different alleles for a gene is said to be heterozygous for that gene. © 2018 Pearson Education Ltd.  20.1 Principles of Inheritance  Genotype Alleles that are present Genetic composition of an individual  Phenotype Observable physical traits of an individual For example, the freckled phenotype has two genotypes: FF and Ff © 2017 Pearson Education, Inc. Figure 20.2 Freckles: FF or Ff No freckles: ff Widow’s peak: WW or Ww Straight hairline: ww Unattached earlobes: EE or Ee Attached earlobes: ee Tongue rolling: TT or Tt © 2017 Pearson Education, Inc.  1 Stamen removed 2 Pollen transfer Parents Stamens (P) Carpel  1 Stamen removed 2 Pollen transfer Parents Stamens (P) Carpel 3 Carpel matures into pod  1 Stamen removed 2 Pollen transfer Parents Stamens (P) Carpel 3 Carpel matures into pod 5 4 Seed from pod planted Offspring traits observed Offspring (F1) Character Traits Dominant Recessive Flower color Purple White Flower position Axial Terminal Seed color Yellow Green Seed shape Round Wrinkled Pod shape Inflated Constricted Pod color Green Yellow Stem length Tall Dwarf Table 20.1 © 2017 Pearson Education, Inc.  3) If the two alleles of an inherited pair differ, then one determines the organism’s appearance and is called the dominant allele and the other has no noticeable effect on the organism’s. appearance and is called the recessive allele. © 2018 Pearson Education Ltd.  4) ​A sperm or egg carries only one allele for each inherited character because allele pairs separate (segregate) from each other during the production of gametes. This statement is called the law of segregation. © 2018 Pearson Education Ltd.  Mendel’s Law of segregation P Law of segregation PP – During meiosis, alleles segregate P homologous chromosomes separate – Each allele for a trait is packaged into a separate gamete p pp p P Pp p Figure 20.3 F = freckles f = no freckles Homozygous Homozygous dominant female recessive male F F f f Chromosomes are duplicated before meiosis FF FF ff ff Meiosis I F F f f f f F F Polar body This division may not occur Meiosis II F F F F f f f f Polar bodies Egg Sperm Gamete has All gametes have dominant allele F f recessive allele Fertilization produces heterozygous offspring © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance  Mendelian genetics Gregor Mendel was a monk in the nineteenth century who grew up in a region of what was then Austria, now part of the Czech Republic  He studied how single genes are inherited from parent to offspring  Used pea plants  First used one-trait crosses  Then used two-trait (dihybrid) crosses © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance  Punnett square Matrix used to predict genetic makeup of offspring of individuals of particular genotypes Rows represent possible gametes of one parent Columns represent possible gametes of the other parent Boxes represent possible combinations of gametes © 2017 Pearson Education, Inc. Figure 20.4 F = freckles f = no freckles ff Each sperm contains the recessive allele for no freckles—f. Sperm f f Ff Ff F freckles freckles FF Eggs F Ff Ff freckles freckles Each egg receives All the offspring the dominant allele will be heterozygous for freckles—F. and have freckles. © 2017 Pearson Education, Inc. Figure 9.4 Gene loci Dominant allele P a B Homologous r chromosomes P a b Recessive allele Genotype: PP aa Bb Homozygous Homozygous Heterozygous, for the for the with one dominant dominant recessive and one recessive allele allele allele  The law of independent assortment is revealed by tracking two characters at once A cross between two individuals that are heterozygous for one character is called a monohybrid cross. A dihybrid cross is a mating of parental varieties that differ in two characters. © 2018 Pearson Education Ltd.  20.1 Principles of Inheritance  Monohybrid cross Cross in which both parents are heterozygous for one trait of interest Genotypic ratio of offspring: 1 FF : 2 Ff : 1 ff Phenotypic ratio of offspring: 3 with freckles (FF and Ff) : 1 without (ff)  Dihybrid cross Cross in which both parents are heterozygous for two traits of interest Phenotypic ratio of offspring: 9 : 3 : 3 : 1 © 2017 Pearson Education, Inc. 9.5 The law of independent assortment is revealed by tracking two characters at once  Mendel’s law of independent assortment states that the alleles of a pair segregate independently of other allele pairs during gamete formation. © 2018 Pearson Education Ltd. © 2018 Pearson Education Ltd. Figure 20.6 FF ff FF ff Meiosis I WW ww Diploid reproductive ww WW cell with two pairs of homologous chromosomes Meiosis II FF ff FF ff WW w w ww WW Possible f f F F f f combinations F F w w of alleles in the W W w w W W resulting gametes 1 1 1 1 4 FW 4 fw 4 Fw 4 fW © 2017 Pearson Education, Inc. Figure 20.7 F = freckles f = no freckles W = widow’s peak w = straight hairline Ff Ww Sperm: FW Fw fW fw 1 1 1 1 16 16 16 16 Ff Ww FW FFWW FFWw Ff WW Ff Ww Eggs: 1 1 1 1 16 16 16 16 Fw FFWw FFww Ff Ww Ffww 1 1 1 1 16 16 16 16 fW Ff WW Ff Ww ff WW ff Ww 1 1 1 1 16 16 16 16 fw Ff Ww Ff ww ff Ww ff ww 9 16 freckled, widow’s peak 3 16 freckled, straight hairline 3 16 no freckles, widow’s peak 1 16 no freckles, straight hairline © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance  Pedigrees Charts showing the genetic connections among individuals in a family Especially useful in following recessive alleles that are not visible in the heterozygote © 2017 Pearson Education, Inc. Figure 20.8 I mm Mm II III (a) Pedigree of a dominant trait I Cc Cc II III (b) Pedigree of a recessive trait Unaffected female Affected female Unaffected male Affected male © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance  Genetic disorders Often caused by recessive alleles Carrier  Someone who displays the dominant phenotype but is heterozygous for a trait Carries the recessive allele and can pass it to descendants © 2017 Pearson Education, Inc.   CRISPR: What is the future of gene editing? | Start Her  https://www.youtube.com/watch?v=pVIVSpUgR44&l ist=LL&index=6&t=320s © 2017 Pearson Education, Inc. https://www.youtube.com/watch?v=wsykWqyXSKM https://www.youtube.com/watch?v=Fw0CBMw0ios https://www.youtube.com/watch?v=XbuQCz3kZI0 https://www.youtube.com/watch?v=DqQ806YzEoU  Diagnostic Tests  Chorionic villus sampling (CVS) is a diagnostic test done after 11 weeks of pregnancy to confirm if your baby has a genetic disorders or other chromosome condition.  If a test result is "positive", in 99 out of 100 positive results the baby will have the condition tested for.  Chorionic villus sampling may be advised for women who: Have had positive or worrisome results from a prenatal screening test such as the first-trimester screen or prenatal cell-free DNA screening. Have had a chromosomal condition such as Down syndrome in a previous pregnancy, which increases the risk of it occurring again Are 35 or older, which puts them at increased risk of chromosomal conditions Have a family history of a specific genetic condition, or whose partner is a carrier of a genetic condition, such as Tay-Sachs disease © 2017 Pearson Education, Inc.  CVS utilizes either a catheter or needle to biopsy placental cells that are derived from the same fertilized egg as the fetus. © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance  Dominant allele Often produces a functional protein that the recessive allele does not  Example: albinism Lacking the ability to produce brown pigment melanin  Ability to produce melanin depends on the enzyme tyrosinase  Dominant allele that results in pigmentation produces functional tyrosinase  Recessive allele that results in albinism produces nonfunctional tyrosinase © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance  Complete dominance Heterozygote exhibits the trait associated with the dominant allele but not that of the recessive allele  Codominance Effects of both alleles are apparent in a heterozygote Example: blood type AB  The protein products of both the A and B alleles are expressed on the surface of the red blood cell © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance  Incomplete dominance Expression of the trait in a heterozygous individual is in between the way the trait is expressed in a homozygous dominant or homozygous recessive person Example: sickle-cell allele  Heterozygote has sickle-cell trait (HbAHbS) © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance © 2017 Pearson Education, Inc. Figure 20.11 HbA HbS HbA HbA HbA HbA HbS HbS HbAHbS HbS HbS HbAHbA normal red blood cell HbAHbS sickle-cell trait HbSHbS sickle-cell anemia © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance  Pleiotropy One gene having many effects. © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance  Pleiotropy One gene having many effects  Besides providing an example of incomplete dominance, sickle-cell anemia is an example of pleiotropy Sickling of red blood cells caused by abnormal hemoglobin affects many areas of the body The sickled cells can break down, clog blood vessels, and accumulate in the spleen  These effects can affect the heart, brain, lungs, kidneys, and muscles and joints © 2017 Pearson Education, Inc. Figure 20.12 Two copies of the sickle-cell allele (homozygous recessive) All hemoglobin is the sickle-cell (abnormal) variety. Abnormal hemoglobin causes red blood cells to become sickle shaped when the oxygen content of the blood is low. Normal cell Sickled cell Clump and clog Break down Accumulate in spleen blood vessels Local failures in blood supply Physical weakness and Heart Pain and Brain Lung Kidney Muscle and Anemia fatigue failure fever damage damage damage joint damage Impaired Pneumonia Enlargement Kidney and fibrosis mental Paralysis and other Rheumatism failure of spleen function infections © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance  Multiple alleles When three or more forms of a given gene exist across many people in the population  Example: ABO blood types  Blood type is determined by the presence of certain polysaccharides (sugars) on the surface of red blood cells Type A blood has the A polysaccharide Type B has the B polysaccharide Type AB has both A and B polysaccharides Type O has neither © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance  When three or more forms of a given gene exist across many people in the population (continued) Gene has three alleles: IA, IB, I Alleles IA and IB specify the A and B polysaccharides, respectively  When both of these alleles are present, both polysaccharides are produced  IA and IB are, therefore, codominant © 2017 Pearson Education, Inc. Table 20.2 © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance  Polygenic inheritance Variation in a trait, such as height, independent of environmental influences Involves two or more genes, often on different chromosomes Many traits, including height, skin color, and eye color, vary almost continuously from one extreme to another Environment can play a role in creating such a smooth continuum © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance  Genes on the same chromosome Usually inherited together Described as being linked Linked genes usually do not assort independently  Usually is emphasized here because there is a mechanism that can unlink genes on the same chromosome: crossing over © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance  Sex-linked genes Y is much smaller than X and carries fewer genes Most genes on the X chromosome have no corresponding alleles on the Y chromosome  Known as X-linked genes.  Different pattern of inheritance: recessive phenotype of X-linked genes more common in males because son can inherit X-linked recessive only from mother.  Examples of disorders Red-green color blindness Two forms of hemophilia Duchenne muscular dystrophy © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance © 2017 Pearson Education, Inc. Figure 20.14 Normal father XY Carrier Normal mother × father Sperm XX XY X Y X XX XY Carrier mother XX Eggs X XX XY © 2017 Pearson Education, Inc.  20.1 Principles of Inheritance  Sex-influenced genes Autosomal genes whose expression is influenced by sex hormones Their expression differs in males and females Example: male pattern baldness  More common in men than in women because its expression depends on both the presence of the allele for baldness and the presence of testosterone  Men can be heterozygous for the trait and still show pattern baldness  Women who are homozygous for the trait will develop pattern baldness later in life © 2017 Pearson Education, Inc. © 2017 Pearson Education, Inc. © 2017 Pearson Education, Inc.  20.2 Breaks in Chromosomes  Usually caused by chemicals, radiations, viruses  Result in changes in the structure and function of the chromosome Deletion  Loss of a piece of chromosome  Most common deletion occurs when the tip of a chromosome breaks off  Example: cri-du-chat syndrome Loss of tip of chromosome 5 © 2017 Pearson Education, Inc. Figure 20.15 A piece of chromosome 5 has been deleted. © 2017 Pearson Education, Inc.  20.2 Breaks in Chromosomes  Duplication Addition of piece of chromosome Effects depend on size and position of the addition Example: Fragile X syndrome  Duplication of a region on the X chromosome © 2017 Pearson Education, Inc. Figure 20.16 (a) Normal X Fragile X chromosome chromosome Fragile site (b) (c) © 2017 Pearson Education, Inc.  20.3 Detecting Genetic Disorders  Prenatal genetic testing is recommended when A defective gene runs in the family The mother is older than 35, due to increased risks of nondisjunction © 2017 Pearson Education, Inc.  20.3 Genetic Testing  Newborn genetic testing Blood test screens for phenylketonuria (PKU) Allows doctors and parents to prevent brain damage by keeping the infant on a strict diet that excludes most phenylalanine  Adult genetic testing Many predictive genetic tests are now available or being developed Some identify people who are at risk or predisposed for a specific disease before symptoms appear © 2017 Pearson Education, Inc. © 2017 Pearson Education, Inc. © 2017 Pearson Education, Inc. © 2017 Pearson Education, Inc. © 2017 Pearson Education, Inc. © 2017 Pearson Education, Inc.  9.7 Mendel’s laws reflect the rules of probability  The rule of multiplication calculates the probability of two independent events both occurring together can be calculated by multiplying the individual probabilities of the events.  For example, if you roll a six-sided die once, you have a 1/6chance of getting a six.  If you roll two dice at once, your chance of getting two sixes is:  (probability of a six on die 1) x (probability of a six on die 2) = (1/6) * (1/6) = 1/36 © 2018 Pearson Education Ltd.  Rule of multiplication  In general, you can think of the product rule as the “and” rule: if both event X and event Y must happen in order for a certain outcome to occur, and if X and Y are independent of each other (don’t affect each other’s likelihood), then you can use the product rule to calculate the probability of the outcome by multiplying the probabilities of X and Y © 2018 Pearson Education Ltd.   We can use the product rule to predict frequencies of fertilization events.  For instance, consider a cross between two heterozygous (Aa) individuals. What are the odds of getting an aa individual in the next generation?  The only way to get an aa individual is if the mother contributes an a gamete and the father contributes an a gamete.  Each parent has a 1/2 chance of making an a gamete.  Thus, the chance of an aa offspring is:  (probability of mother contributing a) x (probability of father contributing a)  = (1/2) *(1/2) = 1/4 © 2018 Pearson Education Ltd.  This is the same result you’d get with a Punnett square, and actually the same logical process as well.  The only difference is that, in the Punnett square, we'd do the calculation visually: we'd represent the 1/2 probability of an a gamete from each parent as one out of two columns (for the father) and one out of two rows (for the mother).  The 1 square intersect of the column and row (out of the 4 total squares of the table) represents the 1/4 chance of getting an a from both parents. © 2018 Pearson Education Ltd.  Rule of Addition  The rule of addition calculates the probability of an event that can occur in alternative ways.  In some genetics problems, you may need to calculate the probability that any one of several events will occur.  In this case, you’ll need to apply another rule of probability, the sum rule. According to the sum rule, the probability that any of several mutually exclusive events will occur is equal to the sum of the events’ individual probabilities. © 2018 Pearson Education Ltd.  Rule of addition  For example, if you roll a six-sided die, you have a 1/6 chance of getting any given number, but you can only get one number per roll.  You could never get both a one and a six at the same time; these outcomes are mutually exclusive.  Thus, the chances of getting either a one or a six are:  (probability of getting a 1) + (probability of getting a 6) = (1/6) +(1/6) = 1/3 © 2018 Pearson Education Ltd.  Rule of addition  You can think of the sum rule as the “or” rule: if an outcome requires that either event X or event Y occur, and if X and Y are mutually exclusive (if only one or the other can occur in a given case), then the probability of the outcome can be calculated by adding the probabilities of X and Y.  As an example, let's use the sum rule to predict the fraction of offspring from an Aa x Aa cross that will have the dominant phenotype (AA or Aa genotype). In this cross, there are three events that can lead to a dominant phenotype:  Two A gametes meet (giving AA genotype), or  A gamete from Mom meets a gamete from Dad (giving Aa genotype), or  a gamete from Mom meets A gamete from Dad (giving Aa genotype)  In any one fertilization event, only one of these three possibilities can occur (they are mutually exclusive). © 2018 Pearson Education Ltd.  Rule of addition  Since this is an “or” situation where the events are mutually exclusive, we can apply the sum rule.  Using the product rule as we did above, we can find that each individual event has a probability of 1/4.  So, the probability of offspring with a dominant phenotype is:  (probability of A from Mom and A from Dad) + (probability of A from Mom and a from Dad) + (probability of a from Mom and A from Dad) =(1/4) + (1/4) + (1/4)= 3/4 © 2018 Pearson Education Ltd.  Once again, this is the same result we’d get with a Punnett square. One out of the four boxes of the Punnett square holds the dominant homozygote, AA.  Two more boxes represent heterozygotes, one with a maternal A and a paternal a, the other with the opposite combination.  Each box is 1 out of the 4 boxes in the whole Punnett square, and since the boxes don't overlap (they’re mutually exclusive), we can add them up (1/4 + 1/4 + 1/4 = 3/4) to get the probability of offspring with the dominant phenotype. © 2018 Pearson Education Ltd. © 2018 Pearson Education Ltd. © 2018 Pearson Education Ltd. Figure 9.7 F genotypes 1 Bb female Bb male Formation Formation of eggs of sperm 1 1 2 B 2 b Sperm 1 1 ( 2×2 ) 1 B B B b 2 B 1 1 4 4 F2 genotypes Eggs 1 b B b b 2 b 1 1 4 4 © 2018 Pearson Education Ltd. © 2018 Pearson Education Ltd. © 2018 Pearson Education Ltd.  You Should Now Be Able To:  Define, give an example, of and use the terms homozygous, heterozygous, dominant, recessive, genotype, phenotype, pleiotropy, multiple alleles, and polygenic.  Describe how chromosome deletions and duplications affect the production of proteins, then describe common genetic disorders in humans and their causes.  Compare the methods and advantages of prenatal, newborn, and adult genetic testing. © 2017 Pearson Education, Inc.