Chapter 12: Patterns of Heredity & Human Genetics Section 1: Mendelian Inheritance of Human Traits

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    21-Dec-2015

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  • Slide 1
  • Chapter 12: Patterns of Heredity & Human Genetics Section 1: Mendelian Inheritance of Human Traits
  • Slide 2
  • Making a Pedigree When genetic inheritance is represented by a picture, this is called a pedigree. Pedigrees are used by geneticists to map inheritance from generation to generation.
  • Slide 3
  • It is a diagram made of symbols that identify three things: 1. Male or female 2. Individuals affected by the trait being studied 3. Family relationships
  • Slide 4
  • S ymbols of a pedigree: ***need to know*** Carrier heterozygous individual
  • Slide 5
  • Constructing and Reading a pedigree ***an inverted v means the married couple had twins*** (know) ****a horizontal line between a male and female with a strike means the persons are divorced.**** (Need to know )
  • Slide 6
  • Constructing and Reading a pedigree ***Roman Numerals (I, II, III) refers to the generations.*** *Arabic numbers refers to individuals. (1, 2, 3, 4, 5, ) 321456 1 1 2 2 345 I. III. II.
  • Slide 7
  • Reading the pedigree How 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 ? 32145 61 1 2 2 345 I. III. II. 7
  • Slide 8
  • Types of Pedigrees Pedigrees 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.
  • Slide 9
  • *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, baldness Facts about X-linked Disorders *carried on the X-chromosome Colorblindness Pedigree
  • Slide 10
  • Colorblindness Tests Test Name: Ishihara Test Colorblind sees: yellow square Normal color: yellow square & faint brown circle Colorblind sees: the number 17 Normal Color sees: the number 15
  • Slide 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.
  • Slide 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.
  • Slide 13
  • Pedigree for Cystic Fibrosis
  • Slide 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 symptoms Death usually by age 4
  • Slide 15
  • Pedigree for Tay-Sachs
  • Slide 16
  • Simple Dominant Heredity Dominant disorders are inherited as Mendels rule of dominance predicted: Only one dominant allele has to be inherited from either parent.
  • Slide 17
  • Common Dominant Traits & Disorders Simple Dominant Traits 1. cleft chin 2. unattached earlobes 3. almond shaped eyes
  • Slide 18
  • Disorders: Huntingtons Disease A lethal genetic disorder that causes certain areas of the brain to break down. Does not occur until 30-50 years of age so this is why it can be passed along. There is a genetic test that can test the presence of the allelewould you want to know?
  • Slide 19
  • Is it Dominant or Recessive Dominant, only one parent has the disorder. 3 214 5 6 1 1 2 23 4 3 I. III. II.
  • Slide 20
  • Is it Dominant or Recessive Recessive, neither parent has the disorder. Both are heterozygous. 3 214 5 6 1 1 2 23 4 3 I. III. II.
  • Slide 21
  • Chapter 12 Section 2: When Heredity Rules are Different
  • Slide 22
  • Complex Patterns of Heredity Most traits are not simply dominant or recessive Incomplete dominance: when the phenotype of the heterozygous individual is in between those of the two homozygotes (homozygous dominant & homozygous recessive)
  • Slide 23
  • Red flower color (RR) is dominant White flower color (rr) is recessive Pink colored flowers (Rr)
  • Slide 24
  • Codominace: when the alleles of both homozygotes (BB or WW) are expressed equally in the heterozygous individual If a black chicken (BB) is crossed with a white chicken (WW), all offspring will be checkered Example: sickle-cell anemia
  • Slide 25
  • Sex-linked traits: when traits are controlled by genes located on sex chromosomes X-linked disorders: generally passed on from mother to son The genetic abnormality is found on the X chromosome Females are XX, males are XY
  • Slide 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 chromosome Ex: hemophilia & Lesch-Nyhan syndrome
  • Slide 27
  • Y-linked disorders: only passed on from father to son Examples: excessive hair growth of the ears & male infertility
  • Slide 28
  • Polygenic inheritance: when a trait is controlled by many genes Examples: height, eye color, skin color, & blood type
  • Slide 29
  • Changes in Chromosomal Numbers Humans have 23 pairs of chromosomes (46 total); more or less = disorder Autosomes: a non-sex chromosome Known as chromosomes 1-22
  • Slide 30
  • Sex chromosomes: 23 rd pair in humans that determine a persons sex Example: Downs Syndrome (trisomy 21)
  • Slide 31
  • Slide 32
  • 8 Environmental Factors That Can Also Influence Gene Expresssion 1. temperature 2. light 3. nutrition 4. chemicals 5. infectious agents 6. hormones 7. structural differences 8. age *** know examples***