MANDELIAN GENETICS. Crosses that deviate from Mandelian inherintance

Transcription

1 MANDELIAN GENETICS Crosses that deviate from Mandelian inherintance

2 Explain codominant alleles. TO THE STUDENTS Calculate the genotypic and phenotypic ratio (1:2:1). Explain incomplete dominant alleles. Calculate the genotypic and phenotypic ratio (1:2:1). Explain multiple alleles Explain polygenes/polygenic inheritance

3 CODOMINANT ALLELE INCOMPLETE DOMINANT ALLELES MULTIPLE ALLELES POLYGENES/POLYGENIC INHERITANCE LETHAL ALLELES LINKED GENES SEX-LINKED GENES

4 Monohybrid No. Character One Flower colour Genes/ character One Gene for flower colour Alleles/gene Two Dominant: Red (R) Recessive: White (r) Phenotype Two Red (RR, Rr) and White (rr) Genotype Three RR, Rr, rr

5 Dihybrid No. Character Genes/ character Two One/ character Seed colour Seed shape Gene of seed colour Gene for seed shape Alleles/gene Two/gene Seed colour Dominant: Green Recessive: Yellow Seed Shape Dominant: Round Recessive: Wrinkle

6 CODOMINANT ALLELE both alleles of a pair are fully expressed in a heterozygous form It occurs when both of the contributions of both alleles are visible and do not over power each other in the phenotype. Eg :MN blood group MM NN MN

7 Mendel Complete dominance x ---> Codominance x --->

8 CODOMINANT ALLELE The MN blood system is a third (in addition to the ABO and the Rh) system of blood antigens also related to proteins of the red blood cell plasma membrane. Two allele = L M and L N Ability to produce antigen M Ability to produce antigenn L M L M L M L N L N L N have only the M antigen on their red blood cells, and will be type M. Produce both antigen M and N, are type MN have only the N antigen on their red blood cells, and will be type N.

9 Inheritance of MN blood group CODOMINANT ALLELE TRUE BREEDING P : L M L M X L N L N G : L M L M L N L N F1 : L M L N self cross

10 Inheritance of MN blood group CODOMINANT ALLELE F1xF1: L M L N X L M L N G : L M L N L M L N F2 : L M L M L M L N L M L N L N L N 1 2 1

11 CODOMINANT ALLELE x Chestnut Colored Horse Cremello colored horse Palomino colored Horse golden colored coat with a white mane and tail

12 CODOMINANT ALLELE I remember codominance in the form of an example like so: red x white ---> red & white spotted x ---> a cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together.

13 A cattle can be red (RR = all red hairs), white (WW = all white hairs), or roan (RW = red & white hairs together). a) Predict the phenotypic ratios of offspring when a homozygous white cow is crossed with a roan bull. b) What should the genotypes & phenotypes for parent if a farmer wanted only cattle with red fur?

14 A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur together). a) What pattern of inheritence does this illustrate? b) What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?

15 INCOMPLETE DOMINANT ALLELE a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele x ---> Eg : Colour ofantirrhinum (snapdragon) flower

16 Mendel Complete dominance x ---> Incomplete dominance x --->

17 INCOMPLETE DOMINANT ALLELE The effect of heterozygous can be detected in the phenotype 1:2:1 ratio of red:pink:white flowers.

18 INCOMPLETE DOMINANT ALLELE I remember Incomplete Dominance in the form of an example like so: RED Flower x WHITE Flower ---> PINK Flower With incomplete dominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits.

19 INCOMPLETE DOMINANT ALLELE A cross between a blue blahblah bird & a white blahblah bird produces offspring that are silver. The color of blahblah birds is determined by just two alleles. a) What are the genotypes of the parent blahblah birds in the original cross? b) What is/are the genotype(s) of the silver offspring? c) What would be the phenotypic ratios of offspring produced by two silver blahblah birds?

20 INCOMPLETE DOMINANT ALLELE The color of fruit for plant "X" is determined by two alleles. When two plants with orange fruits are crossed the following phenotypic ratios are present in the offspring: 25% red fruit, 50% orange fruit, 25% yellow fruit. What are the genotypes of the parent orange-fruited plants?

21 Inheritance Definition Example Phenotype - Genotype Incomplete dominant allele Codominant allele Multiple allele Polygenic inheritance Lethal gene Linked gene Sex-linked gene

22 MULTIPLE ALLELES One gene having more than two alleles. All alleles control the same character Eg: ABO blood type ( I A, I B, I O )

23 Monohybrid No. Character One Flower colour Genes/ character One Gene for flower colour Alleles/gene Two Dominant: Red (R) Recessive: White (r) Phenotype Two Red (RR, Rr) and White (rr) Genotype Three RR, Rr, rr

24 No. Character One Human ABO blood group Genes/ character One Alleles/gene Three Gene for human blood group I A, I B, I O Phenotype Genotype Four Six A, B, O, AB I A I O, I A I A, I O I B, I B I B, I A I B, I O I O

25 MULTIPLE ALLELES

26 MULTIPLE ALLELES TRY THIS P: TYPE A X TYPE AB I A I A I A I B F1: I A I A I A I B I A I B I A I A A AB AB A

27 MULTIPLE ALLELES Brandon is blood Type O. He has an older brother with blood types A and a sister with blood group B. a) What are the genotypes of his parents with respect to this trait? b) If Brandon s sister married with a man with blood group AB, What is the percentage of their child having blood group B?

28 POLYGENES/POLYGENIC INHERITANCE an additive effect of two or more genes on a single phenotypic character. Quantitative Variation e.g: height

29 POLYGENES AABBCC - very dark AaBbCc - intermediate Aabbcc - very light

30 Differences between multiple alleles and polygenes Multiple Alleles Not influence by environmental factors genes that have multiple alleles discontinuous variation Polygene Influence by environmental factors more than one gene continuous variation/ quantitative variation

31 the interaction between two or more genes to control a single phenotype types of combs on chickens Phenotypes Walnut Rose Pea Single Genotypes R_P_ R_pp rrp_ rrpp

32 One gene masks another coat color in mice = 2 genes pigment (C) or no pigment (c) more pigment (black=b) or less (brown=b) cc = albino, no matter B allele 9:3:3:1 becomes 9:3:4 How would you know that difference wasn t random chance? Chi-square test!

33 Epitasis in Labrador retrievers 2 genes: E & B pigment (E) or no pigment (e) how dark pigment will be: black (B) to brown (b)

34 QUESTIONS 1. A dominant allele W confers black fur for mice. A mice that is homozygous recessive (ww) has white fur. David would like to know whether his pet black-furred mice is homozygous dominant (WW) or heterozygous (Ww). How might he determine his pet s genotype?

35 1. Two pairs of genes affect comb type in chickens. When both genes are recessive, a chicken has a single comb. A dominant allele of one gene, P, gives rise to pea comb. Yet a dominant allele of the other (R) gives rise to rose comb. An epistatic interaction occurs when a chicken has at least one of both dominants, P_R_, which gives rise to walnut comb. Predict the phenotypic ratios resulting from a cross between two walnut-combed chickens that are heterozygous for both genes (PpRr).

36 Given information: Single comb = pprr Pea comb = P _ Rose comb = R _ Walnut comb = P_R_

37 P : PpRr X PpRr G : PR Pr pr pr PR Pr pr pr F1 : Punnet square

38 PR Pr pr pr PR PPRR PPRr PpRR PpRr walnut walnut walnut walnut Pr PPRr PPrr PpRr Pprr walnut pea walnut pea pr PpRR PpRr pprr pprr walnut walnut rose rose pr PpRr Pprr pprr pprr walnut pea rose single 9 walnut : 3 pea : 3 rose : 1 single