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Degrees of Dominance Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical Copyright © 2008 Pearson Education.

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Presentation on theme: "Degrees of Dominance Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical Copyright © 2008 Pearson Education."— Presentation transcript:

1 Degrees of Dominance Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

2 Extending Mendelian Genetics for a Single Gene Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations: –Sex Linked Traits -When alleles are on the sex chromosomes. (color blindness) –Incomplete Dominance -When alleles are not completely dominant or recessive (pink flowers from red and white phenotype) –Multiple Alleles - When a gene has more than two alleles. (Blood Type) Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

3 Sex linked traits *Hemophilia *Muscular dystrophy *Red/green colorblindness *Rickets

4 Discovery of Sex Linkage Thomas Hunt Morgan First to associate a specific gene on a specific chromosome (early 1900’s) Mated flies

5 Sex linked genes Genes located on sex chromosomes Most are usually genes on X chromosomes Have unique patterns of inheritance –Mothers pass sex-linked alleles to daughters and sons –Fathers pass sex-linked alleles to daughters, NOT sons

6 Muscular Dystrophy Absence of a key protein called dystrophin Symptoms: weakening of muscles 1 out of 3500 males in US Rarely live past 20’s

7 Hemophilia Sex linked recessive Absence of proteins required for blood clotting Sons born to women with a family history of hemophilia Queen Victoria of England –Introduced to royal family thru a mutation in one of sex cells: carrier of allele –The royal families of Prusia, Russia, Spain had Hemophilia genes that spread thru their families

8 In Codominance, phenotypes of both alleles are exhibited in the heterozygote Example: Pink/white flower, Roan horse both colors are being expressed.

9 How can I make lots of money? If I was a horse breeder and I wanted to sell Roan horses what horse color do I want for my breeding stock? RR (red), rr (white), Rr (Roan)? Draw Punnent Square.

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12 Incomplete Dominance Offspring has a phenotype that is intermediate between the traits of its two parents. Ex. Red flowering Snapdragon is crossed with a white flowering Snapdragon the offspring is pink flowers. Neither the red or the white Allele is dominant. There is just less pigment.

13 Fig Red P Generation Gametes White CRCRCRCR CWCWCWCW CRCR CWCW

14 Fig Red P Generation Gametes White CRCRCRCR CWCWCWCW CRCR CWCW F 1 Generation Pink CRCWCRCW CRCR CWCW Gametes 1/21/2 1/21/2 In incomplete dominance, the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties

15 Fig Red P Generation Gametes White CRCRCRCR CWCWCWCW CRCR CWCW F 1 Generation Pink CRCWCRCW CRCR CWCW Gametes 1/21/2 1/21/2 F 2 Generation Sperm Eggs CRCR CRCR CWCW CWCW CRCRCRCR CRCWCRCW CRCWCRCW CWCWCWCW 1/21/2 1/21/2 1/21/2 1/21/2

16 Incomplete Dominance

17 What would happen? Could a plant breeder produce only pink flowering snapdragons by crossing pink- flowering snapdragons and white – flowering snapdragons? Why?

18 Multiple Alleles Most genes exist in populations in more than two allelic forms For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: I A, I B, and i. Multiple alleles control the ABO blood groups. Different combinations of three alleles result in four blood phenotypes (A, AB, B, and O) Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

19 Fig IAIA IBIB i A B none (a) The three alleles for the ABO blood groups and their associated carbohydrates Allele Carbohydrate Genotype Red blood cell appearance Phenotype (blood group) I A I A or I A i A B I B I B or I B i IAIBIAIB AB iiO (b) Blood group genotypes and phenotypes

20 Antigens – Located in Plasma. “Bad Guy” Antibodies – located on surface of red blood cells. “Anti-A antibodies” Blood Group AntigensAntibodiesCan give blood to… Can receive blood from… ABA, BNONEABAB, A, B, O Universal Receiver AABA, ABA, O BBAB, ABB, O ONONEA & BA,B,AB,O Universal Donor O

21 What Blood Types will be… An Universal Donor? O. Does not contain any A or B antigens (bad guys) at all. An Universal Recipient? AB. Can receive blood from all other blood groups.

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23 Did you know? Another inheritance pattern demonstrated by the ABO blood group is CODOMINANCE. Explain why?

24 Oh No! We need to go the ER! You need blood now what?

25 ABO Blood System

26 Rh Factor Rh is a protein that is attached to a red blood cell. Rh- is the absence of the Rh factor on the red blood cell. (Just like the O blood cell.) You can give Rh- blood to a patient with Rh+ blood but not vice versa. Mother has 1 st child…the child is Rh+ (from the father)…baby’s and mother’s blood mix at time of delivery. Once exposed to Rh+ mother makes Rh antibodies. Mother is pregnant with 2 nd child (Rh+, same dad) The mother has Rh antibodies so her body attacks the babies blood cells and she miscarries.

27 Rh factor Treatment: Rh Immune Globulin- It destroys baby cells in mom’s blood and suppresses mom’s Rh antibody production.

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31 Fig b 1st generation (grandparents) 2nd generation (parents, aunts, and uncles) 3rd generation (two sisters) Widow’s peakNo widow’s peak (a) Is a widow’s peak a dominant or recessive trait? Wwww Ww ww Ww wwWW Ww or

32 Fig c Attached earlobe 1st generation (grandparents) 2nd generation (parents, aunts, and uncles) 3rd generation (two sisters) Free earlobe (b) Is an attached earlobe a dominant or recessive trait? Ff ffFf ff FFor FF Ff


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