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Types of Inheritance Dominant, Recessive, X-linked.

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1 Types of Inheritance Dominant, Recessive, X-linked

2 Chromosome Review Every cell has 23 pairs of chromosomes (46 chromosomes total). We inherit one member of each pair from our mother and the other member from our father. In females all 23 pairs of chromosomes look similar. In males, 22 pairs of chromosomes look similar but the 23 rd pair is mismatched.

3 The 23 rd pair of chromosomes are the sex determining chromosomes. – In the cells of females, both members of the 23 rd pair are X chromosomes. – In the cells of males, both members of the 23 rd pair are mismatched with two unlike chromosomes called X and Y. QUESTION: Based on what you have learned, can you identify which partner, mom or dad, is responsible for the sex of the child? EXPLAIN.

4 Definitions: Gene = tiny packets of information that contain instructions for how our bodies develop and function. Genes are a part of chromosomes. Autosomal = not sex-linked Karyotype = a photograph of the entire set of chromosomes with the images of the individual chromosomes arranged by shape and size in an orderly manner. /karyotype/

5 Homologous chromosomes = two chromosomes of a pair. (same length, same pattern of light and dark bands when stained, and carry the genes for the same inherited characteristics) Alleles = different versions of the same gene – An individual with two genes the same for a trait is said to homozygous for the trait. – An individual with two different alleles for the same trait is heterozygous for the trait.

6 Autosomal Dominant Inheritance There is a 50% chance the dominant trait (or disorder) will be passed on to a child (male or female). A child gets this dominant trait (or disorder) from one parent. This dominant trait (or disorder) will be visible/present in the parent who is passing the trait (disorder) on to a child.

7 Examples of autosomal dominant disorders: – Achondroplasia – Familial high cholesterol – Huntington’s disease – Some forms of glaucoma – Polydactyly – Marfan syndrome

8 Autosomal Recessive Inheritance Carrier = a person with one recessive gene for a trait or disorder. A carrier is not affected by the trait (or disorder), but can pass it on to his/her children. Both parents must be “carriers” of the autosomal recessive trait (or disorder). A child with a recessive trait(disorder) must receive the trait(disorder) from BOTH parents. If both parents are carriers, there is 25% chance that any child (male or female) will inherit the trait (or disorder). There is a 50% chance that any child (male or female) will be an unaffected carrier just like the parents. There is a 25% chance that any child will be neither affected or a carrier.

9 Autosomal recessive disorders: – Sickle cell anemia – Tay-Sachs disease – Cystic fibrosis – Phenylketonuria (PKU) – Thalassemia (Cooley’s anemia)

10 X-linked Recessive Inheritance Mother is a carrier of a recessive trait (or disorder) on her 23 rd pair of chromosomes. She is unaffected because the trait (or disorder) is recessive. Dad is not a carrier of the recessive trait (or disorder. He has no genes for this trait (or disorder) and is unaffected.

11 Mother has a 50% chance of passing this recessive trait (or disorder) on to a child. – A female child will be a carrier of the trait (or disorder) because she has a normal gene on the paired 23 rd chromosome. – A male child who inherits the affected X chromosome from his mother does not have a matching X in the 23 rd pair to off-set the disorder. His 23 rd pair is mismatched (XY). He will have the trait (or disorder) even though it is transferred from only one parent.

12 X-linked disorders are always passed from mothers to sons. The rule that says recessive disorders must be inherited from both parents does not apply because the males 23 rd chromosomes are mismatched.

13 X-linked recessive disorders: – Hemophilia – Red-green colorblindness – Duchenne muscular dystrophy

14 Carrier tests for some recessive disorders are available. – Hemophilia – Thalassemia (Cooley’s anemia) – Sickle cell anemia – Tay-Sachs disease – PKU – Duchene muscular dystrophy – Cystic fibrosis

15 Question—Why is this true? Some genetic disorders tend to be more common in certain groups of people. – Cystic fibrosis—more common in Caucasian people of Northern European descent – Tay-Sachs disease—more common in people of Central or Eastern European Jewish heritage. – Thalassemia (Cooley’s anemia)—more common in people of Greek, Italian, or Middle Eastern descent. – PKU (Phenylketonuria)—more common in Caucasians of Northern European descent. – Sickle cell anemia—more common in people of African American and Hispanic descent.


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