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Mendelian Patterns of Inheritance Chapter 11
Genetics: the study of heredity Heredity : the passing of traits to the next generation. (from parent to child) Sexual Reproduction and Genetics Trait: a physical feature (blue eyes) Ch 11
Dominant trait: a trait that always shows, can cover the other allele. - represented by a Capital letter EX: Brown eye: B Recessive trait: a trait that only shows of both alleles are present. - represented by lower case letter EX: blue eye: b
Codominant: both alleles are expressed (shown). EX: Bb: Brown (B) and Blue (b) eyes are both expressed
Sexual Reproduction and Genetics Homozygous: two of the same alleles for a particular trait ex: BB or bb also called pure Heterozygous: two different alleles for a particular trait Ex: Bb also called hybrid Gregor Mendel: the father of genetics, studies the traits of pea plants Homozygous: Heterozygous
11.1 Gregor Mendel “Father of Genetics” Developed the fundamental laws of heredity He studied science and mathematics Funfact: Mendel originally wanted to breed mice, but wasn't allowed to because it was considered scandalous discoveries-genetics-and-gregor-mendal-video.htm -chose to study genetics in garden peas (Pisum sativum)as as they are easily grown and their pollination is easily controlled. He controlled pollination by manually moving pollen between plants Developed True-breeding plants by self- pollination
Mendel examined varieties of peas for heritable characters and traits for his study. (stem length, pod shape, seed shape, seed color..etc) Developed hybrid plants by crossbreeding two plants of differing characteristics Tall v Short
P generationF 1 F 2 Sexual Reproduction and Genetics Mendel parents offspring 1 kids offspring 2 grandkids
11.2 Mendel's Law of Segregation (MONOHYBRID CROSS) A monohybrid cross involves one (mono) character and different (hybrid) traits. The F1 seeds were all purple; the white flower trait failed to appear at all. Because the purple flower trait completely masks the white flower trait when true-breeding plants are crossed, the purple flower trait is called dominant, and the white flower trait is called recessive.
Creating the F2 generation *Cross the F1 generation together to create F2 *Ratio is always 3:1 Mendel proposed that the units responsible for inheritance were discrete particles - particulate theory of inheritance
In 1865, Mendel published his findings in a paper called Experiments on Plant Hybridization, which was mostly ignored at the time due to a number of reasons. First, Mendel was not well known in scientific community. Second, his theory ran against the popular model of blended inheritance.Experiments on Plant Hybridization
As Viewed by Modern Genetics During production of gametes, only one of the pair members for a given parent passes to the gamete. (LAW OF SEGREGATION) Mendel's units of inheritance are now called genes. Different forms of a gene are called alleles. Each allele is given a symbol: Parental Cross PP x pp purple x white
Mendel’s Three Laws 1. Dominance & Recessiveness 2. Segregation: the two alleles for a trait separate (or segregate) during the formation of gametes 3. Independent Assortment: during gamete formation, alleles pair independently, meaning a particular allele for one character can be paired with either allele of another character
Two copies of same allele = homozygous. Homo means "the same" Therefore both PP and pp are considered homozygous, just one is purple and the other is white. Some purple-flowered plants could be Pp. Individuals that are purple, but had a white parent, are heterozygous: Pp. Hetero means "different". The F1 cross Pp x Pp purple x purple
Review Terms F1 vs F2 True Breeding vs Hybrid Self Pollination vs Cross Pollination Homozygous vs Heterozygous Particulate Theory vs Blending Theory Segregation
The physical appearance of an organism is its phenotype. Purple-flowered would be a phenotype. The actual composition of the organism's alleles for a gene is its genotype: Pp is a genotype. Organisms have many different genes some have thousands, and complex organisms have 10 times that number. GENOTYPEPHENOTYPE Pp purple flowers rrwrinkled seeds TTtall ttshort
BY CONVENTION: The dominant trait is given a capitol letter, the lowercase of that same letter is the recessive trait. DO NOT MIX LETTERS. Pick one and stick to it. Also, some letters are better than others. Capital S looks a lot like a lowercase (s). Pick a different letter... Okay Better (use H for hair) Short hair = SS HH Short hair = Ss Hh Long hair = ss hh Steps to solving genetics problems 1.Key 2.Parents cross 3.Punnett Square 4.Genotype and ratio 5.Phenotype and ratio
P = Gg x Gg Genotype: ¼ GG; 2/4 Gg; ¼ gg Genotype ratio: 1:2:1 Phenotype: ¾ green; ¼ yellow Phenotype ratio: 3:1 G g G GG Gg g Gg gg F1F1 Punnett Square: to predict outcome of offspring Cross heterozygous green pea (Gg) with heterozygous green pea plant (Gg). Yellow is recessive. Key: GG: Gg: gg green yellow Steps to solving genetics problems 1.Key 2.Parents cross 3.Punnett Square 4.Genotype and ratio 5.Phenotype and ratio
In dragons... Wings are a dominant trait, but some dragons are born wingless. 1. If a wingless dragon is crossed with one that is heterozygous, how many of its offspring will also be wingless? 2. What are the chances that two heterozygous dragons have a whelp that is wingless?
If a wingless dragon is crossed with one that is heterozygous, how many of its offspring will also be wingless? P = ff x Ff Genotype: 2/4= ½ Ff; ½ ff Genotype ratio: 1:1 Phenotype: ½ wing; ½ wingless Phenotype ratio: 1:1 f f F Ff Ff f ff ff F1F1 Key: FF: Ff: ff wings wingless
What is a test cross? Help, help! I don't know what my genotype is!! Am I Ff or FF? I can help you! Let's have offspring! Key: F= winged f=wingless
Practice with Punnett Squares 1. A round seeded plant (RR) is crossed with a wrinkle seeded plant (rr). What are the phenotypes of the offspring? 2. Two heterozygous purple flowered pea plants are crossed. What are the phenotypes of their offspring and in what proportion? 3. A plant with green seeds (yy) is crossed with a heterozygous plant. What percentage of their offspring have yellow seeds?
Why does the punnett square work? It all goes back to meiosis.. each side represents a sperm or egg. The boxes filled out simply give you the statistical chance that a certain sperm will fertilize a certain egg. Probability: The chance that an event will occur - It is a prediction, and it could be wrong.
Mendel’s Laws of Probability - Can use probability and math to solve genetic problems. Ex: If two parents are heterozygous for nostril flaring. P= Ee X Ee Chance of E =½ Chance of e = ½ 1. Chance of EE = ½ x ½ = ¼ 2. Chance of Ee = ½ x ½ = ¼ 3. Chance of eE = ½ x ½ = ¼ Ee= ¼ + ¼ = ½ 4. Chance of ee = ½ x ½ = ¼
If a wingless dragon is crossed with one that is heterozygous, how many of its offspring will also be wingless? P = ff x Ff Key: FF: Ff: ff wings wingless fF= 1 X ½ = ½ ff=1 x ½ = 1/2 ½ ½ 1
Traits appear to "blend" in offspring RR x WW RW (pink) Show: Pink x Red Pink x Pink White x White
Figure This illustrates another style of "letters" to denote genotypes R1 and R2 Coloration in Rodents Black x White = Gray BB x WW = BW
Sickle Cell Trait in Humans Genotypes & Phenotypes Pleiotropic Effect: a single mutant gene affects two or more seemingly unrelated traits - Sickle cell shape, and resistant to malaria parasite
Prevalence of Malaria Prevalence of Sickle Cell Anemia In tropical Africa, where malaria is common: homozygous dominant individuals die of malaria homozygous recessive individuals die of sickle cell anemia heterozygote carriers are relatively free of both reproductive advantage Pleiotropic Effect: a single mutant gene affects two or more seemingly unrelated traits
ROAN COW - What happens when you cross a white and a red cow? Roan is codominant - both alleles R and W are expressed
What happens when two Roan Cows are Crossed? R r R RR Rr r Rr rr
Incomplete Dominance CoDominance In Make believe flowers……. Key: RR = red Rr = purple (BLENDING) rr = blue Key: RR = red Rr = red and blue (both are expressed) rr = blue
Key: BB= Brown Bb = Tan bb = White P = Bb x Bb Genotype: ¼ BB; ½ Bb; ¼ bb Genotype ratio: 1:2:1 Phenotype: ¼ Brown ; ½ Tan ; ¼ White Phenotype ratio: 1:2:1 Ex: A brown bird crosses with a white one and all the offspring produced are tan. If these offspring were crossed and produced 16 birds, how many would be tan? B b B BB Bb b Bb bb F2F2 If these offspring produced 16 birds how many would be expected to be tan? 8
QOD: 1. What does INDEPENDENT ASSORTMENT mean? In your own words, describe what it means with regard to Mendelian genetics. 2. Mendel would have never developed this law if he'd chosen traits located on the same chromosome. Why do you think that would have altered his results?
Mendel's Law of Independent Assortment – Illustrated by the DIHYBRID cross law describes the outcome of dihybrid (two character) crosses, or hybrid crosses involving additional characters. A dihybrid is an individual that is a double heterozygote (e.g., with the genotype RrYy - round seed, yellow seed). What are the gametes that can be produced by this individual?
Dihybrid Cross: RrYy x RrYy cross two traits at same time: remember independent assortment
Key: In pigs, T = curly tailB =brown coat t = straight tailb = white coatComplete dominance P = TtBb x TtBb TB, Tb, tB, tb TB Tb tB tb G TB, Tb, tB, tb X TB, Tb, tB, tb Genotype: 1/16 TTBB 2/16 TTBb 2/16 TtBB 4/16 TtBb 1/16 TTbb 2/16 Ttbb 1/16 ttBB 2/16 ttBb 1/16 ttbb Phenotype 9/16 curly tail & brown coat 3/16 curly tail & white coat 3/16 straight tail & brown coat 1/16 straight tail & white coat Pheno ratio: 9 : 3 : 3 : 1 TTBBTTBbTtBBTtBb TTBbTTbbTtBbTtbb TtBBTtBbttBBttBb TtBbTtbbttBbttbb 1a.
Genotype: 1/16 TTBB 2/16 TTBb 2/16 TtBB 4/16 TtBb 1/16 TTbb 2/16 Ttbb 1/16 ttBB 2/16 ttBb 1/16 ttbb Phenotype 9/16 curly & brown 3/16 curly & white 3/16 straight & brown 1/16 straight & white 1a. Continued…. What percentage of the offspring will be purebred dominant for both traits? Key: In pigs, T = curly tail B =brown coat t = straight tail b = white coat 1/16 or 6% What percentage of the offspring will be hybrid for both traits? 4/16 or 25%
All of these type of crosses will follow the same ratio AaBb x AaBb both heterozygous for both traits 9 - (two dominant traits) 3 - (one dominant, one recessive) 3 - (one recessive, one dominant) 1 - (two recessive traits)
1b. Key: In pigs, T = curly tailB =brown coat t = straight tailb = white coatComplete dominance P = TTbb x ttbb Ttbb Tb tb G Tb X tb Genotype: 100% Ttbb Phenotype 100% curly tail and white coat Pheno ratio: 0 : 1 : 0 : 0
3. Key: In Drosophila fruit flies W = long wingsH = hairless body w = vestigial wingsh = hairy bodyComplete dominance P = W w hh x WWHh WWHhW w Hh WWhhW w hh Wh w h WH Wh G Wh, w h X WH, Wh Genotype: 1/4 WWHh 1/4W w Hh 1/4 WWhh 1/4 W w hh Phenotype 50% long wings and hairless body 50% long wings and hairy body Pheno ratio: 1 : 1 : 0 : 0 What percentage of the offspring will have long wings and hairless bodies? 50%
2. Key: In pea plants L = long stemsG =green pods l = short stemsg = yellow podsComplete dominance P = LLgg x llGG LlGg Lg lG G Lg X lG Genotype: 100% LlGg Phenotype: 100% long stems and green pods Pheno ratio: 1 : 0 : 0 : 0
It may be faster to solve problems mathematically. This one is NOT 9:3:3:1 HhBb x hhBb How many off the offspring will be short haired and red eyed?
Try another mathematical model.. Winged, Fire breathing dragon DdFf x Wingless, Fire breathing dragon ddFf Consider the cross between a plant with round seeds, purple flowers to one with wrinkled seeds and white flowers... RrPp x rrpp
Multiple Alleles: more than two alleles in the population ex: Blood Types
Phenotype Genotype Blood Donor % of population Type A I A I A, I A i O Donate to Type A/AB 42% Type B I B I B, I B i O Donate to Type B/AB10% Type AB I A I B Universal recipient/Donate to AB 4% Type O i O i O Universal Donor/ only receive O 44% There are 3 alleles that code for what type of blood you have. A, B, and O. A and B are Co-Dominant and O is recessive. Blood Type
P = AA x OO Genotype: Phenotype: Practice #1 A A O AO AO Cross: Type A (AA) father with a type 0 mother. What are the possible blood types of the offspring? 4/4 AO 4/4 Type A
Suppose two newborn babies were accidentally mixed up in a hospital, something that rarely happens. In an effort to determine the parents of each baby, the blood types of the parents and the babies were determined. Baby 1-type B Mrs. Davisson-type BMrs. Morgan - type O Baby 2-type O Mr. Davisson- type BMr. Morgan - type AB NameGenotype Mrs. D Mr. D Mrs. M Mr. M Baby 1 Baby 2 1.Which baby belongs to Mr. & Mrs. Davisson? 2. Which baby belongs to Mr. and Mrs. Morgan? BO OO AB BO OO Baby 2 Baby 1 Practice #3 BB, BO OO AB BB, BO OO A B O AO BO
Chapter 9 blood type is located on chromosome #9 Type A, B, AB or O RH factor is a separate gene that codes for another protein. This is the positive or negative part of the blood type, on chromosome #1.
Many Genes Have Multiple Alleles A population might have more than two alleles for a given gene. In Labrador retriever, coat color is determined by one gene with four different alleles. Five different colors result from the combinations of these alleles. (More on labradors later) Eye color is also controlled by multiple alleles
The simulation is a bit simplified, but the idea is that MULTIPLE ALLELES control a single trait (eye color) It is likely that more than 2 alleles control eye color, this is simplified just made it simple to understand.
Polygenic Traits Individual heritable characters found to be controlled by groups of several genes, called polygenes. Each allele intensifies or diminishes the phenotype. Variation is continuous or quantitative (adding up) - also called quantitative inheritance Seed Color in wheat - aabbcc, Aabbcc, AaBbcc, AaBbCc, AABbCc, AABBCC (light, intermediate colors, dark) In humans - hair color, height, skin color
Pg 197 Polygenic Inheritance AABBCC x aabbcc (P) AaBbCc x AaBbCc (F1) Seven Possible Phenotypes in the F2 The more “dominant” alleles for dark pigmentation (caused by melanin), the darker the skin
Environment and Phenotype Temperature, water, food sources can have an affect on how a gene is expressed = “multifactoral” Rabbits have a gene that codes for darker pigments - this gene is more active at low temperatures. Parts of the body that are colder will develop the darker pigmentation - ears and feet
LEGHORN CHICKEN – SINGLE COMB Multiple Alleles control the combs of chickens. Assignment: Multiple Alleles in Chickens
BUTTERCUP CHICKEN - BUTTERCUP COMB
Buckeye Chicken – Pea Comb
Wyandotte Chicken - Rose Comb
Lethal Genes (Not in book, added) Some genes are lethal when both alleles are present. Lethality can occur before or after birth Huntington's disease in humans is caused by a lethal allele, death occurs later in life Other examples: Mouse coat color (yellow), Creeper legs in chickens, Manx Cats (no tails) An example is the "creeper" allele in chickens, which causes the legs to be short and stunted. Manx cat
X- linked traits
Complex Inheritance and Human Heredity X-linked traits: traits on the X chromosome Colorblindness Hemophilia Muscular Dystrophy More common in males
Colorblindness sex-linked recessive condition in which people can’t see certain colors don’t make some of the pigments in the eye that are necessary for color vision. The most common form is red-green colorblindness
Normal color vision : 29 Red green color blind : a bunch of spots!
Normal color vision : 56 Red green color blind : 56
Normal color vision : 8 Red green color blind : spots
Hemophilia: condition that impairs the blood’s ability to clot. Hemophilia is a recessive sex-linked trait. Also known as bleeders disease
Hemophilia: Royal Disease
Muscular Dystrophy (MD ): disease that results in progressive wasting away of skeletal muscle. Caused by a defective protein known as dystrophin
Key: XX = female normal vision XXe = female carrier (normal vision) XeXe = female colorblind P = XY x X Xe Ex: X Y XX XY XXe XeY XY = male normal vision XeY = male colorblind What % of their boys will be expected to be colorblind? Colorblindness X Xe Cross carrier female with normal male 50% Genotype Phenotype 1/4XX: female normal vision 1/4 XXe : female carrier 1/4 XY: male normal vision ¼ XeY: male color blind
Key: XX = normal female XX h = female carrier X h X h = female hemophiliac XY = male normal X h Y = male hemphiliac Hemophilia Key: XX = normal female XX m = female carrier X m X m = female with MD XY = male normal X m Y = male with MD MD
1. XY male normal 2, XXe female carrier 3. XY male normal 4. XXe female carrier 5. XXe female carrier 6, XY male normal 7. XeY male colorblind 8. XXe female carrier 9. XX or XXe 10. XeY male colorblind 11. XY male normal 12. XeXe female colorblind Carrier
Complex Inheritance and Human Heredity Pedigrees: A diagram that traces the inheritance of a particular trait through several generations
Pg 192 Autosomal Recessive vs Autosomal Dominance aa Aa
Name of Disorder Type (autosomal, sex linked, dominant, recessive) Description/ Symptoms Type of people group/ treatment / other Tay Sacks Cystic Fibrosis PKU Sickle Cell Disease Neurofibromatosis Huntington's Disease Hereditary Genetic Disorders
Tay Sachs Autosomal recessive -progressive deterioration of nerve cells and of mental and physical abilities Young children begin showing signs of slowed development Severe impairment and death strikes 1 in 3600 births 100 times greater than incidence among non-Jews non-functional enzyme fails to breakdown lipids in brain cells fats collect in cells destroying their function symptoms begin few months after birth seizures, blindness & degeneration of muscle & mental performance child usually dies before 5yo
Cystic Fibrosis autosomal recessive -More common in Caucasians -Mucus in respiratory tract, difficulty breathing extreme salty sweat -Mucus may cause secondary infections
Effect on Lungs Chloride channel transports salt through protein channel out of cell Osmosis: H 2 O follows Cl – airway mucus secreting glands bacteria & mucus build up thickened mucus hard to secrete normal lungs cystic fibrosis Cl – channel Cl – H2OH2O H2OH2O cells lining lungs
Phenylketonuria (PKU) Lack enzyme for normal metabolism Phenylalanine builds up and causes brain damage Newborns are routinely tested Changes in diet lead to normal life Phenylalanine Hydroxylase is the enzyme needed, absent in those with PKU autosomal recessive -1k lQ
Sickle Cell Disease More common in Africans (African-Americans) Causes blood to be sickle shaped Affects oxygen flow to organs, causing weakness, pain, anemia, etc Heterozygotes are resistant to malaria AA = normal Aa = sickle cell trait aa = sickle cell disease
Neurofibromatosis -Autosomal dominate -carry high risk of tumor formation -Tumors form under skin and can cause skeletal deformities, blindness "The Elephant Man" Several years ago, research teams located the exact position of the NF1 gene on chromosome 17. The product of the NF1 gene is a large and complex protein called neurofibromin, which is primarily active in nervous cells as a regulator of cell division. Intensive efforts have let to the identification of the NF2 gene on chromosome 22. The NF2 gene product is a tumor-suppressor protein called merlin.
Huntington's Disease HH = Huntington's Hh = Huntingtons hh = normal Symptoms appear later in life, often starting with poor muscle control neurodegenerative genetic disorder that affects muscle coordination and leads to cognitive decline Autosomal Dominant
There are different types of dwarfism. Achondroplasia is caused by a dominant allele. Two dwarfs can have a normal child. Dd x Dd Primordial Dwarfism Meet Kenadie bedded&v=_QBy8DFaLR4