Ch 6.1 Complex Patterns of Inheritance.notebook April 19, 2018

Transcription

1 Name 3 "Big Ideas" from our last notebook lecture: * * * 1

2 6.1 Beyond Mendel's Observations of Inheritance Mendel's work was the foundation for further understanding as more sophisticated experimental technologies became available, scientists realized that patterns of inheritance are more complicated. 2

3 Learning Goals Understand Non Mendelian Traits Understand and know how to use Punnett Squares to solve problems involving: incomplete dominance, codominance, multiple alleles, and polygenic traits/continuous variation 3

4 A) Incomplete Dominance Not all traits are purely dominant or purely recessive Sometimes neither of the two alleles for the same gene completely conceals the presence of the other, so it results in an intermediate or blending expression of the trait it makes a heterozygote that has a phenotype somewhere between a dominant phenotype and a recessive phenotype This is called Incomplete Dominance Upper case letters and lower case letters are not used to represent the alleles because neither allele is dominant over the other... so... 4

5 Text p242 When true breeding red (C R C R ) snapdragons are crossed with true breeding white (C W C W ) snapdragons the resulting F1 offspring have an intermediate pink colour (C R C W ). Self fertilize two pink colours and all three colours (red, pink, white) appear in the F2 generation in a 1:2:1 ratio P generation C W C W C R C R C W C R C W C R C R C W C R C W 5

6 The crosses are the same as before, but because none of the alleles are dominant in the P generation, only pink flowers are produced in the F1 generation 6

7 B) Co Dominance Sometimes both alleles for a trait are dominant These alleles are co dominant since both alleles are expressed equally in the heterozygous offspring Ex: Roan Cow C R C W where both the red and white are fully expressed Text p243 7

8 Text p244 Video 1: Sickle Cell Anemia Patient Video 2: Heterozygous Advantage GGimI Highlight: Sickle Cell Anemia A heterozygous advantage is defined as "a situation where heterozygous individuals have an advantage over both homozygous dominant and homozygous recessive" Hemoglobin is a protein that carries oxygen in the blood (Hb A ) Sickle Cell Anemia (Hb S ) individuals have a mutated gene for the hemoglobin molecule it changes the shape of red blood cells to a C shape or sickled shape (like a half moon) oxygen blood flow is restricted through small blood vessels and therefore this leads to blockages, tissue damage, strokes, etc. Heterozygous, Hb A Hb S, or codominant individuals, have some normal and some sickled red blood cells they have the sickle cell trait, but do not have any symptoms of the genetic disorder The "advantage" is that they are resistant to Malaria Malaria is a disease caused by a parasite that is transmitted by mosquito bites the parasite needs oxygen to survive as oxygen blood flow is low in sickled cells, the parasite can not infect these red blood cells so heterozygous individuals have the advantage of not being able to get malaria! 8

9 Highlight: Deafness & Thicker Skin Text p249 Dr. David Kelsell, University of London Another heterozygous advantage is for individuals that have hereditary deafness due to a mutation in gene C26 Dr Kelsell, and his team, discovered that these individuals have thicker skin which provides better protection against skin diseases, and their skin heals faster Dr. Kelsell was asked: "How is it that one gene can affect two such different and seemingly unrelated things deafness and thickness of skin? His answer: "This is one of the great mysteries in life." 9

10 C) Multiple Alleles So far... we have only studied traits that have been controlled by one gene with two alleles Many traits in humans, and other complex species, have genes with more than two alleles, or multiple alleles Text p245 Human Blood Groups: 3 alleles are involved: A, B and i **various combinations of these 3 alleles results in 4 blood types: A, B, AB, O 10

11 In humans, a single gene determines what type of antigen protein (immunoglobulin) is attached to the cell membrane of our red blood cells This protein stimulates our immune system The gene is designated as an I and it has 3 alleles: I A, I B, i People with type A blood have the I A protein allele People with type B blood have the I B protein allele People with type AB blood have both I AB protein alleles People with type O blood lack all i protein alleles 11

12 The three alleles for human blood types are: I A I B i Alleles I A and I B are dominant over i. Blood type AB is co dominant since the alleles are expressed equally. 12

13 Text p245 Summary Table: homozygous or heterozygous homozygous or heterozygous codominant recessive Video 3: Amoeba Sisters on Multiple Alleles (Blood Types) 13

14 Human Blood Type Groups 14

15 15

16 Who can help out who? 16

17 I A I A Sample Problem #1 A woman with type A blood marries a man with type AB blood. Can they have a child with type O blood? Show all possible crosses. Woman: I A I A or I A i Man: I A I B I A I A I A I B I A I B OR I A I A I A I B I A i I A I A I A I A i I B I A I B I B i No they can not have a child with type O 17

18 Sample Problem #2 What are the genotypes and phenotypes of the offspring between a cross of an heterozygous Agouti rabbit and a homozygous Himalayan rabbit? Text p245 gene that controls coat colour has 4 alleles in this **order of dominance**: Agouti C > Chinchilla c ch >Himalayan c h > Albino c c h c h C Cc h Cc h 2 Agouti c h c h c h c h c h 2 Himalayan 18

19 D) Polygenic Inheritance Polygenic inheritance occurs when a trait is controlled by more than one gene Traits that are controlled by more than one gene are called polygenic traits The proteins produced by several genes work together resulting in a range of variation in the trait, or continuous variation Examples: human height can not just be defined as tall or short and skin and eye colours range in many shades the variation among individuals in a population in which there is a gradient of phenotypes for one trait. 19

20 text p248 20

21 Video 4: Amoeba Sisters on Incomplete Dominance, Codominance, Polygenic Traits, and Epistatis 21

22 E) Epistasis Interactions of genes that do not have alleles (nonallelic genes) One gene depends on another modifier gene for it to be expressed Note: not in textbook so only need to know definition :) **ends up having a 16 box Punnett Square just like dihybrid crosses** 22

23 Let's read together textbook page

24 Let's try... Practice Problems 1 10 p247 24

25 Review & Learning Check Read p Answer Q's 1,3,4,6 p250 25

26 Apr 19 5:07 AM 26