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Chapter 4 Lesson 2 Understanding Inheritance. Learning Objective: Using your family history to predict genetic outcomes with phenotypes.

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Presentation on theme: "Chapter 4 Lesson 2 Understanding Inheritance. Learning Objective: Using your family history to predict genetic outcomes with phenotypes."— Presentation transcript:

1 Chapter 4 Lesson 2 Understanding Inheritance

2 Learning Objective: Using your family history to predict genetic outcomes with phenotypes.

3 Modeling Inheritance Two tools can be used to identify and predict traits among genetically related individuals. Punnett square – using family histories to predict genotypes and phenotypes. Pedigree – Creating a map using family histories to predict phenotypes.

4 One more thing about Punnetts Human Gender XX = girl XY = boy You ALWAYS have a 50% chance of having a boy or girl EVERY time. X X XYXY XY

5 Pedigrees A pedigree shows genetic traits that were inherited by members of a family. Pedigrees focus more on phenotypes. They are also used with Punnett Squares to determine genotypes.

6 Normal Affected FemaleMale Married Children Pedigree chart

7 Pedigrees to evaluate Go to page 201 and do problems #7 - 9 #7 = Not affected = dd = C #8 = affected = Dd = B #9 = not affected = dd = C

8 Draw a pedigree One couple has a son and a daughter with normal pigmentation. Another couple has one son and two daughters with normal pigmentation. The daughter of the first couple has three children with the son of the second couple. Their son and one daughter have albinism; their daughter has normal pigmentation.

9 Is albinism, recessive or dominant? It is recessive. What must the genotype be of #2 and #3? (hint: make a Punnett Sq.) Albino FemaleMale 1 st couple nd couple Answer

10 Both parents must be Aa. Not all their children are albino. Aa AAAAa a aa

11 Learning Objective – Part 2 By chance, Mendel studied traits only influenced by one gene with two alleles. However, we know now that some inherited traits have There are more complex patterns.

12 Incomplete Dominance Incomplete dominance produces a THIRD phenotype that is a blend of parents phenotype. R = red flowers W = white flowers Red x white = 100% pink RR WRW W

13 Codominance When BOTH alleles can be observed in the phenotype. Black horses (BB) are codominant to white horses (WW). The heterozygous horses (BW) is an appaloosa horse. BB WBW W

14 Codominance continued Blood types are unique because they are an example of: Codominance: A and B are both dominant. AND Multiple Alleles: There are three different alleles.

15 Multiple Alleles Some genes only have two alleles, like in Mendel’s experiments. However, there are genes that have more then two alleles. But remember you can still only inherit two of the alleles. One from each parent.

16 Multiple Alleles continued In a Labrador retriever, coat color is determined by one gene with 4 alleles. Black is dominant to chocolate = B or b. Yellow is recessive epitstatic = E (when present, it blocks the black and chocolate alleles) Phenotype Possible genotypes Black BBEE, BdEE, BBEe, BbEe Chocolate bbEE bbEe Yellow BBee Bbee bbee

17 Sex-linked Because the Y chromosome is shorter than the X chromosome it has fewer genes. Therefore if you are a boy you only get one copy of these genes. So you get what your Mom gives you.

18 Sex-linked continued Examples in humans include: Colorblindness Hemophilia

19 Polygenic Inheritance When multiple genes determine the phenotype. Many phenotypes are possible Examples in humans include: Height Weight Skin color

20 Polygenic - Skin color There may be 100 different genes involved and many mutations. Melanin is a pigment responsible for skin color and is a natural sunblock. Lighter skin allows for more absorption of UV rays from sunlight. This is important for making vitamin D. Darker skin allows for better sun protection.

21 Polygenic - Skin color


23 The long standing hypothesis is that... If you lived near the equator you needed darker skin to protect you from the intense UV rays If you lived farther north you needed lighter skin to help you get more UV rays because there is less sunlight.

24 The Environment and skin Skin cells will produce more melanin within a few hours of exposure. More exposure to the sun gives you a darker complexion, even for dark skinned individuals. Some Northwest Europeans have lost the ability to tan. Their skin burns and peels rather than tans.

25 Genes and the Environment Environment can affect an organisms phenotype. Genes effect heart disease, but so do diet and exercise. Genes affect skin color, so does exposure to sunlight. Go to page 189 and write down, on the left side of your notebook, two more examples of how the environment can affect genes.

26 To learn about different types of genetic disorders. Learning Objective

27 Genetic Disorders If a change occurs in a gene, the organism with the mutation may not be able to function as it should. An inherited mutation can result in a phenotype called a genetic disorder.

28 Sickle Cell Anemia This disease affects millions of people world wide. About 2 million Americans have the sickle cell trait. About 1 in 12 are African Americans.

29 Sickle Cell Continued




33 T-Boz Many people came to know more about SCD through the efforts of Tionne “T-Boz” Watkins of the R&B group, TLC. Many people with SCD grow up knowing that this disease could greatly impact their life, but at 35, T-Boz is going strong and is an inspiration to many. Not only did she sing and dance her way to stardom with the pop group TLC, she gave birth to a child at 30. “Everything I ever wanted to do, I did. I'm all for taking over the disease instead of letting it take over me."

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