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Biology Partnership (A Teacher Quality Grant) Genetics II Modes of Complex Inheritances and Pedigrees Nancy Dow Jill Hansen Tammy Stundon February 23, 2013 Gulf Coast State College Panhandle Area Educational Consortium 5230 West Highway 98 753 West Boulevard Panama City, Florida 32401 Chipley, Florida 32428 850-769-1551 877-873-7232 www.gulfcoast.edu Pre-test Q and A board Was Mendel wrong? Why aren’t humans as simple as ‘tall’ or ‘short’? Why are most colorblind people males? Florida Next Generation Sunshine State Standards BENCHMARK • SC.912.L.16.2* Discuss observed inheritance patterns caused by various modes of inheritance, including dominant & recessive which are simple inheritance & codominant, sex-linked, polygenic, and multiple alleles (complex inheritance). (HIGH) Florida Next Generation Sunshine State Standards Benchmark Clarifications •Students will identify, analyze, and/or predict inheritance patterns caused by various modes of inheritance. Content Limits •Items referring to general dominant and recessive traits may address but will not assess the P and F1 generations. •Items addressing dihybrid crosses or patterns that include codominance, incomplete dominance, multiple alleles, sex- linkage, or polygenic inheritance may assess the P and F1 generations Florida Next Generation Sunshine State Standards Stimulus Attributes •Inheritance outcomes may be expressed in percent, ratios, or fractions. •Scenarios may refer to codominance or incomplete dominance but not both codominance and incomplete dominance. •Punnett squares may be used to predict outcomes of a cross. Response Attribute •Options may include codominance or incomplete dominance but not both. Mendel’s Results Character Dominant x Recessive F1 F2 Generation Ratio Dominant Form: Recessive Form Flower Color purple x white all purple 705 purple: 224 white 2.96 Seed Color yellow x green all yellow 6022 yellow: 2001 green 3.01 Seed Shape round x wrinkled all round 5474 round: 1850 wrinkled 2.96 Pod Color green x yellow all green 428 green: 152 yellow 2.82 Pod Shape inflated x pinched all inflated 882 inflated: 299 pinched 2.95 Flower Position axial x terminal all axial 651 axial: 207 terminal 3.14 Plant Height tall x short all tall 787 tall: 277 short 2.84 Ways to inherit traits • Simple inheritance – the present of a dominant or two recessive alleles will express the trait – Dominant simple – Recessive simple • Sex-linked (x-linked) – where the 23rd chromosome work on different rules • Complex inheritance – the most common – – – – Multiple Allele – Co-dominance – Polygenetic inheritance Incomplete dominance Simple inheritance (single gene) 1. Dominant Inheritance – Rr or RR Traits include widow’s peak, hitchhiker’s thumb, etc. • Capital letter = Dominant trait . • When just one dominant gene is present, the trait will be shown • Two dominant alleles does not enhance the trait • For a recessive trait to be expressed both parents MUST pass on the recessive allele for this trait to be present • Which genotype would be the carrier for the recessive trait? EXAMPLES OF SINGLE-GENE TRAITS Widow’s peak is Dominant Straight hairline is recessive Regular thumb is Dominant Hitchhiker’s is recessive Six digits (D) Tongue rolling is Dominant Not able to roll the tongue is recessive EXAMPLES OF SINGLE-GENE TRAITS Cleft chin = r Non-cleft chin =D Unattached earlobes = D Attached earlobes = r Simple Dominant Inheritance Disease Huntington’s Disease •Chromosome #4; gene makes the brain cells to basically commit suicide •neurological spasms, mental problems, motor function problems •no treatment •CAG is repeated too many times; the number of repeats predicts the age of onset; 40 reps = late middle age Carriers • Only the genotype Ff is considered to be a ‘carrier’ • If (F) = freckles, what is this person’s phenotype? • What type of simple inheritance are they expressing? • Effect if this was a disorder and not a trait? • Why wouldn’t the other simple inheritance genotype be considered as a carrier? Simple inheritance (single gene) 2. Recessive Inheritance – rr • Disorders – Tay-sachs – Jewish, C#15 Cystic Fibrosis – Caucasians, C#7 PKU – C#12, metabolic disorder • Why certain disorders have appeared?....... • Lack of genetic variation ? Adaptation? A SINGLE BAD GENE WHICH WILL NOT PRODUCE THE ENZYME TO CONVERT PHENYLALANINE TO TYROSINE (BOTH AMINO ACIDS). THIS CAUSES A CONDITION CALLED “PKU”. THIS CAN CAUSE A BUILDUP OF PHENYLALANINE IN THE BRAIN WHICH CAN CAUSE MENTAL RETARDATION---CAN BE TREATED WITH DIET AVOIDING THIS AMINO ACID. Why cover disorders? •Higher order thinking questions! •They have to know what type of inheritance the disorder is in order to answer the question (by either doing a Punnett square or pedigree.) •Many test bank questions will indicate the inheritance of a trait; Freckles are dominant. Human Autosomal Trait Lab Refer to the slides with the simple inheritance traits! Non-Mendelian Genetics • Mendelian genetics describes inheritance patterns based on complete dominance or recessiveness. • There are other types of inheritance that Mendel never considered: – – – – – Incomplete Inheritance Codominance Multiple Alleles Polygenic Traits Sex-linked Non-Mendelian Genetics The relationship between genotype and phenotype is rarely simple Non-Mendelian Genetics • Many researchers have encountered exceptions to Mendelian Principles – so was he wrong? • Majority of heritable characters not as simple as peas – Phenotypes affected by: many alleles or many genes, environmental factors, sex chromosomes, etc. Phenotype can depend on interactions of alleles. • In incomplete dominance, neither allele is completely dominant nor completely recessive. – Heterozygous phenotype is intermediate between the two homozygous phenotypes – Homozygous parental phenotypes not seen in F1 offspring Incomplete Dominance If you cross a RED flower with a WHITE flower, you will get a PINK flower. NOTICE: the RED genotype is RR the WHITE genotype is WW the PINK genotype is RW INcomplete is INbetween If this was blended inheritance – pink • pink would only make what? Let’s Practice! Cross a BLACK chicken (BB) with a WHITE chicken (WW). These alleles show INCOMPLETE DOMINANCE What percent is black? White? Gray? B B W BW BW W BW BW Black: 0% White: 0% Gray: 100% Let’s Practice! Cross a BLACK chicken (BB) with a WHITE chicken (WW). These alleles show INCOMPLETE DOMINANCE What is the genotype and W phenotype of the F1 generation? W B B BW BW BW BW Genotype: BW Phenotype: Gray Let’s Practice! What would the cross look like if you crossed two GREY chickens (BW). These alleles show INCOMPLETE DOMINANCE. What is the genotype and phenotype of the F2 generation? PTC Testers B W B W BB BW BW WW Genotype: 1 BB 1 WW 2 BW Phenotype: 1 Black 1 White 2 Gray CoDominance • Both traits are dominant, and show up in the phenotype together. Co means “together” • Black Cow X White Cow = Spotted Cow (BB) (WW) (BW) CoDominance • Both alleles are expressed in the heterozygous condition • Both alleles contribute to the phenotype. • For Example: In chickens, the allele for black feathers is codominant with the allele for white feathers. These chickens will have BOTH black and white feathers. COdominant alleles COllaborate together Let’s Practice! Cross a Black chicken (BB) with a White chicken (WW). These alleles show CO-DOMINANCE. How many chickens in the W F1 generation are completely black? White? Black and W white? B B BW BW BW BW Black: 0% White: 0% Both: 100% Let’s Practice! Cross a Black chicken (BB) with a White chicken (WW). These alleles show CO-DOMINANCE. B What is the genotype W and phenotype of the F1 generation? W BW BW B BW Genotype: BW BW Phenotype: Black and white or checkered. Let’s Practice! Cross two Black and White (checkered) chickens (BW). These alleles show CO-DOMINANCE B List all possible genotypes and phenotypes of the F2 generation. B W BB BW W BW WW Genotype: 1 BB 1 WW 2 BW Phenotype: 1 Black 1 White 2 Checkered Blood type displays both co-dominance and complete dominance • Blood types are different based on the presence or absence of certain antigens on the red blood cells (RBCs) – The presence of a antigen (I) is dominant to the absence of an antigen (i). • There are two types of antigens that may exist on the surface of RBCs called A (IA) and B (IB). – Cell surface antigens A and B are codominant, which means they could also show up at the same time on an RBC. Blood type displays both co-dominance and complete dominance • Matching compatible blood groups is critical for blood transfusions because a person produces antibodies against foreign blood factors. Blood type also demonstrates inheritance through multiple alleles • Multiple alleles: When more than 2 varieties exist in a trait. In this case, blood can be A/B/O Multiple Alleles—ABO Blood Groups Possible alleles from male At any one time, a parent can only have TWO alleles for blood Possible alleles from female IA IB i IA IAIA IAIA IAi IB IAIB IBIB I Bi i IAi IBi ii Blood Types A AB B O The Genetics of Blood Lab Polygenic Inheritance • The inheritance pattern is controlled by two or more genes (each with two alleles) At the present, three gene pairs controlling human eye color are known (two on chromosome 15 and one on pair 19). Order of dominance: brown/amber > green/hazel > gray/blue. Polygenic Inheritance Creates a ‘bell curve’ distribution • Two or more genes work together to create a single phenotype – Example: Height is controlled by anywhere from 7 – 20 different genes (and the environment!) Wilt Chamberlin stood 7’1” tall, neither of his parents was over 5’9” Polygenic Inheritance Skin color is determined by (at least) 3 genes. Imagine that each gene has two alleles, one light and one dark, that demonstrate incomplete dominance. An AABBCC individual is dark and aabbcc is light. Polygenic Inheritance Activity Sex Linked Traits • When a trait is carried on the X or Y chromosomes, it is called a sex-linked trait • These not only carry the genes that determine male and female traits but also those for some other characteristics as well • Don’t confuse this with linked genes = when 2 genes are on the same chromosome Sex Linked Traits Red – Green Color Blindness • Gene that controls this is on the X chromosome • Who is more likely to be color blind– men or women? – Men: only 1 X chromosome – If they have the recessive allele they don’t have another X to make up for it. Sex Linked Traits If there is not a normal gene present to offset the defective, recessive gene, the disorder will be present. Gene linkage was explained through fruit flies • Attention to detail, accurate lab records were critical • Different than sex influenced genes Females can carry sex-linked disorders. • Males (XY) express all of their sex linked genes. • Expression of the disorder depends on which parent carries the allele and the sex of the child. Y X Question: If a normal male (do those even exist?) has a child with a woman who carries the blindness allele, what are the chances that their children will be colorblind? Will any children be carriers of the trait? X Y X XX XY Xc XXc XcY Pedigrees • A diagram that traces the inheritance of a particular trait through several generations. Pedigrees • Chart showing the genetic connections among individuals in a family – Especially useful in following recessive alleles that are not visible in the heterozygote Royal Pedigrees I’m my own grandpa The environment interacts with genotype. • Phenotype is a combination of genotype and environment. • Height is a example of a phenotype strongly affected by the environment. • diet/exercise • sunlight/water (if you’re a plant) Nature vs. Nurture Virtually all human diseases have some genetic component Eye Color and Polygenic Inheritance/Pedigree Lab Follow up •Q & A •Post Test Everything Mendel Didn’t Know – a review of the more complex inheritance patterns The Ghost in Your Genes – a video with a focus on epigenetics, it should prompt some discussion. Eye Color and Genes –a simple visual for the variety of melanin present in eye colors