2Mendel’s dihybrid crosses: Mendel also performed crosses involving two pairs of traits, e.g., seed shape (smooth vs. wrinkled) and color (yellow vs. green).If alleles sort independently, four possible phenotypes (2n) appear in the F2 generation in a 9:3:3:1 ratio.“Mendel’s Principle of Independent Assortment”:Alleles for different traits assort independently of one another.Modern formulation of independent assortment:Genes on different chromosomes behave independently in gamete production.
3The Independent Alignment of Different Pairs of Homologous Chromosomes At Meiosis Accounts for the Principle of Independent AssortmentThe alignment of one pair of homologs is independent of any other.Principle of Independent Assortment: The assortment of one pair of genes into gametes is independent of the assortment of another pair of genes.
4RREE All gametes are RE RE RE RE RE Possible Gametes: To determine the number of different gametes a parent can have use the FOIL method.RREEREREREREAll gametes are RE
5You have 2 possible gametes: Re and RE To determine the number of different gametes a parent can have use the FOIL method.RREeReREREReYou have 2 possible gametes: Re and RE
6You have 2 possible gametes: rE and re To determine the number of different gametes a parent can have use the FOIL method.rrEererErEreYou have 2 possible gametes: rE and re
7Number and kind of gametes How many gametes?To determine the number of different gametes a parent can have use the FOIL method.Number and kind of gametesTTYY=one TYTtYY=two TY and tyTtYy=four TY, Ty, tY, ty
8There are 4 total different gametes Possible Gametes (sperm/egg):If I cross:What are the different possible gametes for these parents??RRTT x RrTtRTRT, Rt, rT, rtThere are 4 total different gametes
9I have 4 possible offspring If I cross:What are the possible gametes?RRTT x RrTtRTRtrTrtRRTTRRTtRrTTRrTtRTI have 4 possible offspring
10I have 4 possible offspring If I cross:What are the possible gametes and offspring?rrTt x RRTtRTRtRrTTRrTtrTRrTtRrttrtI have 4 possible offspring
11I have 16 possible offspring If I cross:What are the possible gametes?RrTt x RrTtRTRtrTrtRRTTRRTtRrTTRrTtRTRRTtRRttRrTtRrttRtI have 16 possible offspring9:3:3:1rTRrTTRrTtrrTTrrTtrtRrTtRrttrrTtrrtt
12Because it’s the only way to explain the pattern of inheritance! Why Did Mendel Conclude That The Inheritance of one Trait is Independent of Another?Phenotype Ratio:9 yellow/smooth3 yellow/wrinkled3 green/smooth1 green/wrinkledBecause it’s the only way to explain the pattern of inheritance!
13What Works for Peas Also Works for Humans Consider a cross between parents heterozygous for both deafness and albinism.This is the same 9:3:3:1 ratio seen for Mendel’s cross involving pea color and shape.
14January 10, 2012 Get your homework out on your desk! Warm Up #1: A pea plant with the genotype TtWW is crossed with a pea plant with the genotype ttWw. How many different genotypes can be expressed in the offspring?(SHOW ALL WORK!)a. 1 b. 2 c. 3 d. 4
15Warm Up #2If a corn plant has a genotype of Ttyy, what are the possible genetic combinations that could be present in a single grain of pollen (sperm, male gamete) from this plant?a. Ty, tyb. TY, tyc. TY, Ty, tyd. Ty, ty, tY, TY
16Warm Up #33. The pea plant produces plants of two different sizes and seeds that are two different shapes. Tall pea plants (T) are dominant to dwarf pea plants (t) and round seeds (R) are dominant to wrinkled seeds, r. Two plants heterozygous for both traits are mated. What fraction of their offspring will be dwarf and have wrinkled seeds?(SHOW ALL WORK!)
17Great job on your quizzes! Hand back quizzes and work – review most common mistakes.Tonight: Talk to your parents about their blood type. Write down each parent and yours if you know yours. Turn this in tomorrow for extra credit.What do you know about blood types?
18Multiple AllelesMore than two allelic forms of a gene that code for a traitPhenotype is still determined by a pair of alleles! The gene pool simply contains more than two.These alleles can be expressed in various ways:Complete dominanceCo-dominanceIncomplete dominance
19Multiple Alleles: Human Blood Type Blood Type is Coded by Multiple Alleles A, B, and O.*A and B are co-dominant.*A and B are completely dominant over O.GenotypesAAAOBBBOABOOPhenotypesType AType BType ABType O*The genes cause the production of a cell surface protein A or B.Type O cells have neither protein, so Type O individuals are Universal DONORS. Which individuals are Universal RECEPIENTS (have both proteins)?
21The AB phenotype (genotype IA IB) is an example of codominance!! Multiple AllelesMany genes are present in 3 or more versions (alleles) – this is known as multiple alleles.The human ABO blood group is determined by three alleles (IA, IB, and i) of a single gene.The AB phenotype (genotype IA IB) is an example of codominance!!
22CodominanceThe human ABO blood group illustrates another genetic phenomenon – codominance.Codominance occurs when the phenotype associated with each allele is expressed in the heterozygote – both are expressed!
23Problem 11. In humans, the blood types A, B, AB and O are determined by three alleles. A man who has AB blood marries a woman with O blood. What are the genotypes and phenotypes of the offspring?
24Problem 22. A man who is heterozygous type A marries a woman who is heterozygous type B. What percentage of their offspring will be Type 0?
25Problem 33. If a man with blood type B, one of whose parents had blood type O, marries a woman with blood type AB. What percentage of their children should have blood type B?
26Problem 44. A man with type O blood and a woman with type AB blood get married. One of their children needs an operation. This child has type B blood. Can the child safely receive a blood transfusion from either parent? If not, why?
27Multiple Alleles: Whose Baby ? A major mix-up occurred. Have the babies been returnedto the correct set of parents?1Baby A - Type O Blood Baby B - Type B BloodSmiths - Types O and AB Jones - Types A and B2Baby C - Type AB Blood Baby D - Type A BloodSquares -Types AB and AB Angles -Types AB and O
281/13/11: Warm UpBoth Mrs. Smith and Mrs. Jones had babies the same day in the same hospital. Mrs. Smith took home a baby girl, whom she named Shirley. Mrs. Jones took home a baby girl, whom she named Jane. However, Mrs. Jones began to suspect that her child had been accidentally switched with another baby in the nursery.Mr. Smith – type A Mr. Jones – type AMrs. Smith – type B Mrs. Jones – type AShirley – type O Jane – type B**Did a mix-up occur? SHOW YOUR WORK!!!
29Sex – Linked Genes Review: What are the two sex chromosomes? What is a woman’s genotype?What is a man’s genotype?Which do you think there are more of – x-linked genes or y-linked genes?Who do you think inherits sex-linked disorders more – males or females?
30X-linked Genetics Genes that are located on the X chromosome but not the YMALES receive only ONE copyFEMALES receive TWO copies
31Color Blind TestAre you red-green colorblind?Lets find out…
32Sex- Linked Inheritance A male always receives a sex-linked condition from his mother, from whom he inherits an X chromosome.A female must receive 2 alleles, one from each parent, for the trait to be expressed.X-linked disorders are often recessive.
33Sex-linked ( X-linked) disorders Color –blindnessHemophilia – protein for blood clotting is missingDuchenne Muscular dystrophy- progressive wasting of muscles(There are about 205 X-linked recessive disorders)
34More males than females are affected by this type of disorder. WHY? Color-blindnessFather(normal vision)MaleFemaleSon(normal vision)Daughter(normal vision)Mother (carrier)Daughter(carrier)Son(colorblind)More males than females are affected by this type of disorder. WHY?
35True or False?The X chromosome carries alleles that are not on the Y chromosome. Therefore, a recessive allele on the X chromosome is expressed in males.Certain traits that have nothing to do with the gender of the individual are controlled by genes on X chromosomes.Males have 2 X chromosomes, and therefore, X-linked recessive alleles are expressed.
36Solving X-linked Problems How do you know if x-linked?Know color-blindness and hemophilia are!Make Punnet Square using XX and XYAttach alleles to X’s ONLYTo help determine percentages, circle the male offspring
37Let’s Practice1. Both the mother and the father of a male hemophiliac appear to be normal. From whom did the son inherit the allele for hemophilia? What are the genotypes of the mother, the father, and the son?
382. A woman is color blind. What are the chances that her sons will be color blind? If she is married to a man with a normal vision, what are the chances that her daughters will be color blind? Will be carriers?
39Cont…3. A husband and a wife give birth to a baby girl. Mom’s vision was normal, so she assumed the baby’s would be normal too. However, she gave birth to a color-blind daughter. What can you deduce about the girl’s parentage?
40Cont…4. A man with normal color vision marries a woman who carries the recessive gene, although her vision is normal. What percentage of male children will be colorblind? What about females?
41Cont…5. If a hybrid female for the colorblind trait marries a colorblind male, what percentages of offspring will be colorblind?
42Paternity Suit6. One of the sons from question #5 is involved in a paternity suit. The child in question is a cb female. The judge rules that the child could not possibly belong to this man. Which sons, of problem #5, was involved in this case? Give his genotype and phenotype and tell how you know.
44Article Anticipation Guide Read the statements on your guide and mark your educated guesses in the boxesSkin Color and Genetics Article
45Polygenic Inheritance – when a Single Trait is Polygenic Inheritance – when a Single Trait is influenced by many genesExamples:Height Hair texture3. Skin color eye color
46Types of Traits – Single Gene Some traits are controlled by single geneExpressed as “either/or”Discontinuous Variation
47Types of Traits – Polygenic Traits Polygenic Traits are controlled by the additive effects of 2 or more genesShows a range of phenotypesContinuous Variation
48Types of Traits Example: A Biology Class Single Gene TraitPolygenic TraitDiscontinuous VariationContinuous Variation
49Human Population - Skin Color Types of Traits – Polygenic TraitsHuman Population - Skin ColorControlled by many genesA given individual can have as many as six alleles (possibly more!) for pigmentation
50PolygenicsWhat are other traits that are coded for by MANY genes????
51Multifactorial Traits Influenced by genetic and environmental factors*Even with a the same genetic make-up, environment can affect the phenotype, as seen in the Hydrangea above. The color variation is a reaction to acid in the soil. Similar environmental influence is observed in humans such as skin color and body build, giving even identical twins slight differences.
52Review Problems Gametes: For each of the diploid genotypes presented below, determine all of the possible haploid gametes.a. Rrb. RrYyc. RrYyBb
53Example 1In turkeys a R produces a bronze color and is dominant over red color. Another dominant gene H, results in normal feathers; its recessive allele h produces feathers without webbing. Two heterozygous bronze turkeys with normal feathers were mated.What kind of problem is this? ___________________Give the genotypes of P:_________________Give the genotypes of F1:________________Give the phenotypes of F1:_______________
54Example 2 In pea plants purple flowers are dominant to white flowers. If two white flowered plants are cross, what percentage of their offspring will be white flowered? ______________What kind of inheritance is this? __________Monohybrid or dihybrid? ________________
55Example 3A cross between a blue-flowered plant and a white-flowered plant gives all pale-blue-flowered plants.What kind of inheritance is this?___________What are the genotypes of the offspring?_______Monohybrid or dihybrid?_________________
56Example 4A father and mother claim they have been given the wrong baby at the hospital! Both parents are blood type A. The baby they have been given is blood type O. Could they have the right baby?What kind of inheritance is this?___________P genotypes: ______________
57Example 5In a certain cactus, prickly spines can be two-pronged or one-pronged. If a one-pronged cactus is crossed with a two-pronged cactus, the F1 generation has a both types of spines, some are two-pronged, some are one-pronged.What kind of inheritance is this?___________Monohybrid or dihybrid?_________________Give the genotypes of P:_________________Give the genotypes of F1:________________
58Example 6Located on the X chromosome of a cat is a gene that codes for deafness. This gene is recessive. A black female cat that is is heterozygous for deafness (Dd) is crossed with a yellow male cat that is not deaf.What type of problem is this?_____________P genotypes:__________________________
59Human TraitsGenetic counselors analyze how the trait is passed from one generation to the next. They construct pedigree charts that show the pattern of inheritance for a particular condition, and show if a disorder is dominant or recessive.
61Genetic DisordersAutosomal ( non-sex linked) Dominant- individuals with alleles AA or Aa will have the disorder.Autosomal Recessive – individuals with alleles aa with have the disorder.
62Autosomal DisordersDo you remember what an autosome was?
63Autosomal Dominant Disorders: Dwarfism known as achondroplasiaHuntington’s diseaseAutosomal Recessive Disorders:Phenylketonuria ( PKU)Tay-Sachs diseaseCystic FibrosisAlbinismIncompletely dominant disorders:- Sickle-Cell disease
64Ways to recognize autosomal dominant disorders: Affected children usually have an affected parent.Two affected parents can produce an unaffected child.Two unaffected parents will not have affected children.Inheritance Pattern I:
65Ways to recognize autosomal recessive disorders: Most affected children have normal parents.Two affected parents will always have affected children.Affected individuals with homozygous normal mates will have normal children.Inheritance Pattern II: