Presentation on theme: "Chapter 12: Patterns of Heredity & Human Genetics"— Presentation transcript:
1 Chapter 12: Patterns of Heredity & Human Genetics Section 1: Mendelian Inheritance of Human Traits
2 Making a PedigreeWhen genetic inheritance is represented by a picture, this is called a pedigree.Pedigrees are used by geneticists to map inheritance from generation to generation.
3 It is a diagram made of symbols that identify three things: 1. Male or female2. Individuals affected by the trait being studied3. Family relationships
4 Symbols of a pedigree: ***need to know*** Carrier –heterozygous individual
5 Constructing and Reading a pedigree ****a horizontal line between a male and female with a strike means the persons are divorced.**** (Need to know)***an inverted “v” means the married couple had twins*** (know)
6 Constructing and Reading a pedigree 12II.12345III.123456***Roman Numerals (I, II, III) refers to the generations.****Arabic numbers refers to individuals. (1, 2, 3, 4, 5, …)
7 How many generations are there? How many children did II-1 have? II-7? Reading the pedigree…I.12II.1234567III.12345How many generations are there?How many children did II-1 have? II-7?How are III-5 and III-2 related?Who is III-2 in reference to I-2?
8 Types of PedigreesPedigrees can be: a.) autosomal *There is a 50/50 ratio between men and women of affected individuals. b.) X- linked *Most of the males in the pedigree are affected.
9 Colorblindness Pedigree Facts about X-linked Disorders *carried on the X-chromosome*X-linked are carried by females, but not expressed in females.*X-linked are expressed most often in MALES.*In males, to express an X-linked disorder, he only needs to have one gene. (XY - heterozygous)*In females, to express an X-linked disorder, she needs TWO alleles to show the disorder. (XX – homozygous recessive)Ex: Colorblindness, hemophilia, baldnessColorblindness Pedigree
10 Test Name: Ishihara Test Colorblindness TestsNormal color:yellow square &faint brown circleColorblind sees:yellow squareColorblind sees:the number 17Normal Color sees:the number 15Test Name: Ishihara Test
11 Simple Recessive Heredity Most genetic disorders are caused by recessive alleles. This means the disorder is inherited when both parents have a recessive allele.
12 Common Recessive Disorders Cystic Fibrosis (CF):A defective protein in the plasma membrane of cells causes thick mucus to build up in the lungs and digestive system.Mostly found among white Americans.
14 Tay-Sachs Disease:The absence of an enzyme causes lipids to accumulate in the tissues and nerve cells of the brain.blind, deaf, and unable to swallow. Muscles begin to atrophy and paralysis sets in and other neurological symptomsDeath usually by age 4
18 Disorders: Huntington’s Disease A lethal genetic disorder that causes certain areas of the brain to break down.Does not occur until years of age so this is why it can be passed along.There is a genetic test that can test the presence of the allele…would you want to know?
19 Is it Dominant or Recessive… 1234II.645123III.123Dominant, only one parent has the disorder.
20 Is it Dominant or Recessive… 1234II.645123III.123Recessive, neither parent has the disorder. Both are heterozygous.
21 Section 2: When Heredity Rules are Different Chapter 12Section 2: When Heredity Rules are Different
22 Complex Patterns of Heredity Most traits are not simply dominant or recessiveIncomplete dominance: when the phenotype of the heterozygous individual is in between those of the two homozygotes (homozygous dominant & homozygous recessive)
23 Red flower color (RR) is dominant White flower color (rr) is recessivePink colored flowers (Rr)
24 Codominace: when the alleles of both homozygotes (BB or WW) are expressed equally in the heterozygous individualIf a black chicken (BB) is crossed with a white chicken (WW), all offspring will be checkeredExample: sickle-cell anemia
25 X-linked disorders: generally passed on from mother to son Sex-linked traits: when traits are controlled by genes located on sex chromosomesX-linked disorders: generally passed on from mother to sonThe genetic abnormality is found on the X chromosomeFemales are XX, males are XY
26 If a female has a normal X, it would be dominant over the defective X In males, it will not be masked by a corresponding dominant allele because they have a “Y” chromosomeEx: hemophilia & Lesch-Nyhan syndrome
27 Y-linked disorders: only passed on from father to son Examples: excessive hair growth of the ears & male infertility
28 Polygenic inheritance: when a trait is controlled by many genes Examples: height, eye color, skin color, & blood type
29 Changes in Chromosomal Numbers Humans have 23 pairs of chromosomes (46 total); more or less = disorderAutosomes: a non-sex chromosomeKnown as chromosomes 1-22
30 Sex chromosomes: 23rd pair in humans that determine a person’s sex Example: Down’s Syndrome (trisomy 21)