Unit 8: Genetics & Heredity Unit 9: Human Genetic Disorders Ch Unit 8: Genetics & Heredity Unit 9: Human Genetic Disorders Ch. 26: Inheritance of Traits & Ch. 27: Human Genetics

Unit 8: Genetics & Heredity What is genetics? the study of heredity passing of traits from parents to offspring Genetics is the study of heredity. Heredity the passing of traits from parents to offspring

Chromosomes in Cells Remember… body cells are diploid 2 of each chromosome 1 from mom & 1 from dad gametes (sperm & eggs) are haploid 1 of each chromosome Why? So zygote gets right # of chromosomes… Why? So that when fertilization occurs the zygote has the correct # of chromosomes… if gametes were diploid then the zygote would have double the correct # of chromosomes

Genes Why is your combination of genes unique? Chance… don’t know which sperm will fertilize which egg… get ½ of your chromosomes from mom & ½ from dad meiosis (formation of gametes) crossing-over during prophase 1 alignment of chromosomes during metaphase 1 Genetics is the study of heredity. Heredity the passing of traits from parents to offspring Why is your combination of genes/traits unique? ½ your genes (on chromosomes) came from your mom, ½ from your dad! But – you also have your own unique gene combination! b/c when the egg and sperm that became your first cell were formed during meiosis, crossing over & independent assortment mixed up your genes, giving you a one-of-a-kind genotype…unless you are an identical twin! This genetic recombination, all based on chance, is what gives all living things variation, and this is what drives the process of evolution.

Genes & Alleles What is a “gene”? section of chromosome that codes for a specific protein & determines a specific trait (ex. hair color, eye color, ear shape, etc.) genes are paired on homologous chromosomes different forms of genes for the same trait are called “alleles” Organisms have thousands of different traits. Each chromosome has different kinds of genes that control different traits… Remember… chromosomes in body cells are paired (homologous)… so, the genes on chromosomes are paired too…. Different forms of genes for the same trait are called alleles

Dominant & Recessive Alleles Each parent contributes 1 allele (form of gene) for trait & can be dominant or recessive What is a dominant allele? allele that prevents expression of (“masks”/“hides”) recessive trait What is a recessive allele? allele whose trait can be seen only when the organism is pure (homozygous) for that trait Different forms of genes for the same trait are called alleles Dominant  “speaks for both alleles” for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype (2 copies of recessive allele) Use same letter to represent dominant & recessive… dominant shown by CAPITAL & recessive shown by lowercase

Dominant & Recessive Alleles How are alleles represented? with letters usually the first letter of the dominant trait If the same letter is used for dominant & recessive, how do we know which allele is which? CAPITAL = DOMINANT lowercase = recessive Different forms of genes for the same trait are called alleles Dominant  “speaks for both alleles” for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype (2 copies of recessive allele) Use same letter to represent dominant & recessive… dominant shown by CAPITAL & recessive shown by lowercase

Allele Combinations What does “homozygous” mean? both alleles are the same homozygous (pure) dominant (ex. AA) homozygous (pure) recessive (ex. aa) What does “heterozygous” mean? both alleles are different heterozygous (hybrid) (ex. Aa) Different forms of genes for the same trait are called alleles Homozygous  inherited two identical forms (or alleles) of the gene can be homozygous dominant can be homozygous recessive… This is the ONLY way for the recessive trait to be expressed Heterozygous  inherited two different forms (or alleles) of the gene dominant allele is always expressed; recessive allele is “hidden” by dominant allele

Genotype vs. Phenotype What is “genotype”? What does the genotype do? organism’s actual genetic “code”/make-up (alleles) What does the genotype do? codes for protein that causes trait (phenotype) How do we represent an organism’s genotype? 2 letters (one for each allele) one from mom & one from dad ex. PP, Pp, pp Genotype: Collection of alleles (genes) Represented by capital letters for dominant alleles, and lowercase letters for recessive alleles Two alleles/genes/letters for each trait Phenotype: Collection of proteins; expressed in traits (form and function) Traits may be dominant or recessive, because they are coded for by dominant or recessive alleles for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype

Genotype vs. Phenotype What is “phenotype”? the outward (physical) expression of the genotype (trait we “see”) What actually causes the “phenotype” (trait) we see? the protein that is produced (due to the organism’s genotype “code”/alleles) How do we represent an organism’s phenotype? usually an adjective ex. purple, white, tall, short, etc. Genotype: Collection of alleles (genes) Represented by capital letters for dominant alleles, and lowercase letters for recessive alleles Two alleles/genes/letters for each trait Phenotype: Collection of proteins; expressed in traits (form and function) Traits may be dominant or recessive, because they are coded for by dominant or recessive alleles for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype

Genotype is Expressed as a Phenotype Ex. Let P = purple & p = white homozygous (pure) dominant genotype PP phenotype = purple homozygous (pure) recessive genotype pp phenotype = white heterozygous (hybrid) genotype Pp dominant trait “masks/hides” recessive trait Genotype: Collection of alleles (genes) Represented by capital letters for dominant alleles, and lowercase letters for recessive alleles Two alleles/genes/letters for each trait Phenotype: Collection of proteins; expressed in traits (form and function) Traits may be dominant or recessive, because they are coded for by dominant or recessive alleles for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype

PP Pp pp genotype = actual genetic make-up of individual (alleles) codes for phenotype (trait) represented by 2 letters 1 to represent gene from mom & 1 from dad ex. PP, Pp, pp phenotype = outward (physical) expression of the genotype trait we “see” (due to) the protein that is produced usually represented by an adjective ex. purple, white, etc. for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype

Predicting Traits in Offspring What are Punnett Squares? a way to predict the results of crosses (mating) letters outside represent possible alleles in gametes of each parent top = one parent & side = other parent letters inside boxes represent possible allele combinations (genotypes) in offspring (& phenotypes) can be used to determine probability and ratios BB Bb 1. determine the genotypes of the parent organisms 2. write down your "cross" (mating) 3. draw a Punnett square 4. "split" the letters of the genotype for each parent & put them "outside" the Punnett square (one on left & one on top) to represent the possible alleles in the gametes 5. determine the possible genotypes of the offspring by filling in the Punnett square 6. summarize results (genotypes & phenotypes of offspring) Parent Pea Plants ("P" Generation) Genotypes: Tt x tt Phenotypes: tall x short Offspring ("F1" Generation) Genotypes: 50% (2/4) Tt & 50% (2/4) tt Phenotypes: 50% tall & 50% short http://www.hobart.k12.in.us/jkousen/Biology/psquare.htm

Making a Punnett Square Parents are Tt & tt genotypes… So… Tt x tt is our cross (mating) 1. determine the genotypes of the parent organisms 2. write down your "cross" (mating) 3. draw a Punnett square 4. "split" the letters of the genotype for each parent & put them "outside" the Punnett square (one on left & one on top) to represent the possible alleles in the gametes 5. determine the possible genotypes of the offspring by filling in the Punnett square 6. summarize results (genotypes & phenotypes of offspring) Parent Pea Plants ("P" Generation) Genotypes: Tt x tt Phenotypes: tall x short Offspring ("F1" Generation) Genotypes: 50% (2/4) Tt & 50% (2/4) tt Phenotypes: 50% tall & 50% short http://www.hobart.k12.in.us/jkousen/Biology/psquare.htm

Passing Traits to Offspring & Probability What is probability? chance an event will occur What is the chance of getting heads? tails? ½ If you flip two coins, of getting 2 heads? 2 tails? ½ x ½ = 1/4 What is the chance of a couple having a boy? a girl? 1/2 of having five girls? ½ x ½ x ½ x ½ x ½ = 1/32 or ( ½ )5 = 1/32

Passing Traits to Offspring & Ratios What is a “genotypic ratio”? probable ratio of genotypes (alleles) in offspring of a given cross Ex. If cross Pp & Pp 1PP : 2Pp : 1 pp Expected & observed ratio can differ b/c it is possible (although less probable) that 4 offspring with the same traits…. The larger the # of offspring, the more likely the 2 ratios will be closer…  The phenotype ratio in a monohybrid cross is never exactly 3:1. This is because of the random nature of fertilization and the fact that some embryos die during early stages.

Passing Traits to Offspring & Ratios What is a “phenotypic ratio”? probable ratio of phenotypes (traits) in offspring of a given cross resulting from the genotypes of the offspring Ex. If cross Pp & Pp 3 purple : 1 white

Passing Traits to Offspring & Ratios What is an “expected ratio”? ratio we expect to get based on probability (Punnett Square) What is an “observed ratio”? ratio we actually get Why would these be different? fertilization is random some embryos die during early stages Expected & observed ratio can differ b/c it is possible (although less probable) that 4 offspring with the same traits…. The larger the # of offspring, the more likely the 2 ratios will be closer…  The phenotype ratio in a monohybrid cross is never exactly 3:1. This is because of the random nature of fertilization and the fact that some embryos die during early stages.

Gregor Mendel Father of Genetics studied garden pea plants 1822-1884 7 different traits with clearly different forms tried to determine how they were passed from parent to offspring Austrian monk did his work around 1865…. Used peas b/c reproduce much more quickly and could use many plants at once

Mendel’s Experiments What happened when Mendel mated a pure purple parent (PP) & a pure white parent (pp)? all offspring had: purple phenotype heterozygous (hybrid) genotype Pp Noticed purple flowered-plants mated with white-flowered plants always resulted in purple-flowered offspring

Mendel’s Experiments What happened when Mendel let the heterozygous (hybrid) offspring from his first experiment self-pollinate? So… Pp x Pp new offspring weren’t all purple… all (F1) offspring (of pure purple w/ pure white parents) should have Pp genotype …. & should produce ½ their gametes w/ P gene & ½ w/ p gene… So if cross two (F1) first generation offspring (Pp x Pp) there will be 3 possible combinations for 2nd generation offspring…. PP, Pp (x2), and pp w/ a 3:1 phenotypic ratio expected….

Mendel’s Principle of Dominance What did Mendel notice from his experiments? that one form dominates over the other …dominant trait prevents the expression of the recessive trait What trait was dominant in these plants? PUPRLE = dominant What trait was recessive? white = recessive Genes (Mendel called them “factors”) come in pairs – one from the egg and one from the sperm. Each gene of a pair is called an allele. An allele may be either dominant, which means only one copy of the allele is needed in the organism’s genotype for its protein product to be expressed in the phenotype, or it may be recessive, in which case two copies of the allele need to be present in the genotype for its protein product to be expressed in the phenotype. Principle of dominance When an organism has two different alleles for a trait, the allele that is expressed, overshadowing the expression of the other allele, is said to be dominant. The gene whose expression is overshadowed is said to be recessive

Dominant/Recessive is Not Always the Method of Inheritance Traits are not always as clearly defined as the 7 pea plant traits Mendel studied. examples of non-dominant/recessive inheritance sex determination sex-linked traits codominance multiple alleles Called non-Mendelian modes of inheritance

Sex Determination How many chromosomes do humans have (in body cells)? 46… 23 pairs pairs 1 – 22 = autosomes (body chromosomes) 23rd pair determines gender = sex chromosomes XX = female XY = male Which parent’s chromosomes determines if the offspring will be a boy or girl???? Why? Dad’s b/c he is the only one that can give a Y; mom always gives X. What is the probability of having a son? A daughter? Which parent’s chromosomes determines if the offspring will be a boy or girl???? Father b/c mother always contributes X chromosome… if dad contributes X  girl… if dad contributes Y chromosome  son So…. Blame dad if you didn’t get the little brother/sister you wanted….

Sex-linked Inheritance X & Y chromosomes not fully homologous. Why? X is bigger & carries more genes X-linked traits & disorders more common in males Why??? b/c female has XX, more likely she will have a copy of dominant allele… males XY… can only get dominant allele on X Hemophilia is a group of bleeding disorders in which it takes a long time for the blood to clot.

Sex-linked Inheritance How many alleles will a male have for traits carried only on the X chromosome? 1 b/c only have 1 X chromosome (Y doesn’t have allele) What is this called? X-linked or sex-linked Ex. eye color in fruit flies, hemophilia in humans, colorblindness in humans X-linked traits & disorders are more common in males. Why??? b/c female has XX, more likely she will have a copy of dominant allele… males = XY… can only get dominant allele on X (& only have 1 X) X-linked traits & disorders more common in males Why??? b/c female has XX, more likely she will have a copy of dominant allele… males XY… can only get dominant allele on X Hemophilia is a group of bleeding disorders in which it takes a long time for the blood to clot.

Sex-linked Inheritance How do we make predictions made using Punnett squares for sex-linked traits? Consider the sex chromosome (X/Y) & allele for the trait it carries (“exponent”) TOGETHER as a unit… ex. XG (= X w/ dominant allele), Xg (= X w/ recessive allele), Y (= Y w/ NO allele) What if a female is heterozygous (XGXg)? she does not show the trait/have the disorder, but is a carrier & can pass gene to offspring Can a male be a carrier? No, b/c only has one X chromosome w/ allele… so either has it or doesn’t XG Xg XG XG XG Xg XG Y Xg Y XG Y

Sex-linked Inheritance Drosophila (fruit fly) eye color is sex-linked What are the sex, genotype, & phenotype of each offspring? Are there any carriers for the white eye gene? Left picture: 2 females with red eyes = XRXr (carrier white eye gene) & 2 males with white eyes = XrY Right picture: female w/ red eyes = XRXR, female w/ red eyes = XRXr (carrier white eye gene), male w/ red eyes = XRY, & male w/ white eyes = XrY XR Y Make sure students know symbols for male & female… Male… arrows… hunting… female… arms… gathering (or hugging) What are the sex, genotype, & phenotype of each offspring? left picture  2 females with XRXr red eyes (carrier for white eye gene) 2 males with XrY white eyes right picture  Female XRXR red eyes Female XRXr red eyes (carrier for white eye gene) Male XRY red eyes Male XrY white eyes XR XR XR Y XR Xr Xr Y XR Xr

Multiple Alleles & Codominance What is meant by multiple alleles? more than 2 different forms of an allele exist but individual still has just 2 Ex. human blood types (3) multiple alleles A (IA) B (IB) o (i) How many possible genotypes are there? How many phenotypes? Can you spot the blood type that is the result of codominance? How many possible genotypes are there? 6 (AA, AO, BB, BO, AB, O) How many phenotypes? 4 (A, B, AB, O) Can you spot the blood type that is a product of codominance? AB

Multiple Alleles & Codominance What is meant by codominance? both alleles are “expressed” equally Ex. human blood types also exhibit codominance (as well as multiple alleles) A & B are codominant and are “expressed” equally A = B (codominant) o (recessive) So… (A = B) > o How many possible genotypes are there? How many phenotypes? How many possible genotypes are there? 6 (AA, AO, BB, BO, AB, O) How many phenotypes? 4 (A, B, AB, O) Can you spot the blood type that is a product of codominance? AB

Unit 9: Human Genetic Disorders What causes genetic disorders? DNA mutation (usually recessive) or chromosome abnormalities (in # or structure) that cause the production of abnormal proteins http://ghr.nlm.nih.gov/BrowseConditions

Human Genetic Disorders How can we group genetic disorders? autosomal recessive disorders (*most genetic disorders) allele is recessive & found on a chromosome from pairs 1 – 22 (autosomes or body chromosomes) cystic fibrosis, sickle-cell anemia, Tay-Sachs disease autosomal dominant disorders allele is dominant & found on a chromosome from pairs 1 – 22 (autosomes or body chromosomes) Huntington’s Disease sex-linked disorders allele (which is usually recessive) is found on the 23rd pair of chromosomes (sex chromosomes)… Usually on the X chromosome hemophilia, color blindness chromosomal abnormality disorders result from errors in chromosome # or structure Down Syndrome (trisomy 21), Klinefelter’s Syndrome (XXY) http://ghr.nlm.nih.gov/BrowseConditions

Autosomal Recessive Disorders What genotype(s) must a person have to be affected? homozygous recessive (gg) cystic fibrosis sickle-cell anemia Tay-Sachs Disease Can someone be a carrier? Why/why not? yes b/c if heterozygous (Gg), person carries the gene, but isn’t affected due to having the “normal” dominant gene in all of these examples Do the parents have the disorder? No (both ARE carriers) If they only had one child, what would the chance be for that child to be affected by the disorder? ¼ or 25% What is the probability that the child would be a carrier? 2/4 or ½ or 50% autosomal recessive disorders (*most genetic disorders) allele is recessive & found on a chromosome from pairs 1 – 22 (autosomes or body chromosomes) cystic fibrosis, sickle-cell anemia, Tay-Sachs disease

Autosomal Dominant Disorders What genotype(s) must a person have to be affected? can be homozygous (GG) or heterozygous (Gg) b/c allele is dominant Huntington’s Disease Can someone be a carrier? Why/why not? No b/c even if person is heterozygous (Gg), person will have disorder due to dominant “disease” gene blocking “normal” recessive gene autosomal dominant disorders Allele is dominant & found on a chromosome from pairs 1 – 22 (autosomes or body chromosomes) Huntington’s Disease

Sex-linked Disorders Remember from earlier… hemophilia is X-linked & recessive What are the possible genotypes & phenotypes? Can someone be a carrier? XHXH = normal female XHXh = carrier female (but not affected) XhXh = female w/ hemophilia XHY = normal male XhY = male w/ hemophilia Why can’t a male be a carrier? b/c only has one X chromosome w/ allele… so either has it or doesn’t Ex. mom = carrier & dad = normal: Make a Punnett square. genotypic ratio? phenotypic ratio? P. Sq.: Mother carrier & father normal Genotypic ratio 1 XHXH : 1 XHXh : 0 XhXh: 1 XHY : 1 XhY Phenotypic ratio: 1 normal female : 1 female carrier : 0 female w/ hemophilia: 1 normal male : 1 hemophiliac male sex-linked disorders allele (which is usually recessive) is found on the 23rd pair of chromosomes (sex chromosomes)… Usually on the X chromosome hemophilia color blindness 1 XHXH: 1 XHXh: 0 XhXh: 1 XHY: 1 XhY 1 normal female: 1 carrier female : 0 female w/ hemophilia: 1 normal male: 1 hemophiliac male

Sex-linked Disorders Remember from earlier… colorblindness is X-linked recessive What are the possible genotypes & phenotypes? Can someone be a carrier? XCXC = normal female XCXc = carrier female (but not affected) XcXc = colorblind female XCY = normal male XcY = colorblind male In this Punnett square, what are the genotypes & phenotypes of the parents? father: genotype = XCY & phenotype = normal mother: genotype = XCXc & phenotype = carrier Ishihara test for red- green color- blindness In this Punnett square, what are the genotypes & phenotypes of the parents? Father: genotype = XCY phenotype = normal mother: genotype = XCXc phenotype = carrier for color blindness Color blindness is the inability to see certain colors in the usual way. Color blindness occurs when there is a problem with the color-sensing materials (pigments) in certain nerve cells of the eye. If you are missing just one pigment, you might have trouble telling the difference between red and green. This is the most common type of color blindness. Other times, people have trouble seeing blue-yellow colors. People with blue-yellow color blindness almost always have problems identify reds and greens, too. sex-linked disorders allele (which is usually recessive) is found on the 23rd pair of chromosomes (sex chromosomes)… Usually on the X chromosome Hemophilia, color blindness

Chromosomal Abnormalities in Number What causes an abnormal number of chromosomes? non-disjunction failure of paired chromosomes to separate during meiosis 1 or meiosis 2 chromosomal abnormality disorders result from errors in chromosome # or structure Down Syndrome (trisomy 21), Klinefelter’s Syndrome (XXY)

Disorders Due to Abnormal Chromosome # What is Down Syndrome (trisomy 21)? when person has 3 copies of chromosome # 21 What is Klinefelter’s Syndrome? a sex-chromosome disorder in which males have extra copy of X chromosome XXY (or 47, XXY b/c 47 total chromosomes) What causes Down Syndrome (trisomy 21) & Klinefelter’s Syndrome? non-disjunction failure of paired chromosomes to separate during meiosis 1 or meiosis 2 Down Syndrome (trisomy 21) = 3 copies of chromosome # 21 Klinefelter’s Syndrome = Scientists believe the XXY condition is one of the most common chromosome abnormalities in humans.  About one of every 500 males has an extra X chromosome, but many don’t have any symptoms. Klinefelter's syndrome is typically caused by what is called non-disjunction. If a pair of sex chromosomes fails to separate during the formation of an egg (or sperm), this is referred to as non-disjunction. When that egg unites with a normal sperm to form an embryo, that embryo may end up with three copies of the sex chromosomes (XXY) instead of the normal two (XY). The extra chromosome is then copied in every cell of the baby's body. chromosomal abnormality disorders result from errors in chromosome # or structure Down Syndrome (trisomy 21), Klinefelter’s Syndrome (XXY)

Chromosomal Abnormalities in Structure What is causes structural abnormalities in chromosomes? pieces are added, deleted, inverted, or translocated chromosomal abnormality disorders result from errors in chromosome # or structure Down Syndrome (trisomy 21), Klinefelter’s Syndrome (XXY)

Review & Animations Vocab interactive Crosses Drag & drop genetics http://nortonbooks.com/college/biology/animations/ch10a02.htm Crosses http://www.sonefe.org/online-biyoloji-dersleri/grade-12/monohybrid-cross/ Drag & drop genetics http://www.zerobio.com/drag_gr11/mono.htm Various http://www.abpischools.org.uk/page/modules/genome/dna4.cfm?coSiteNavigation_allTopic=1 Genetic disorders http://www.humanillnesses.com/original/Gas-Hep/Genetic-Diseases.html