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Making a Pedigree Pedigree – a graphic representation of genetic inheritance Geneticists often need to map the inheritance of genetic traits from generation.

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Presentation on theme: "Making a Pedigree Pedigree – a graphic representation of genetic inheritance Geneticists often need to map the inheritance of genetic traits from generation."— Presentation transcript:


2 Making a Pedigree Pedigree – a graphic representation of genetic inheritance Geneticists often need to map the inheritance of genetic traits from generation to generation

3 Male - Female - Marriage - Children - Death - Symbols of a Pedigree Twins - Homozygous Recessive (affected individual) Heterozygous (carrier)


5 Analyzing a Pedigree I II III IV AA Aa AA Aa AA Aa aa A = normal a = albino

6 Recessive Alleles Genetic Disorders – the harmful effects produced by mutated genes Most genetic disorders are caused by recessive alleles Most are rare but few are common in certain ethnic groups

7 Cystic Fibrosis Recessive disorder Carried on chromosome #7 Fairly common in white Americans 1 in 20 carrier the allele 1 in 2000 have the disorder Due to a defective protein, thick mucus accumulates in the lungs and digestive tract Usually don’t survive to adulthood New drug therapies and special diets have raised the life expectancy


9 Tay-Sachs Recessive disorder Affects central nervous system Lipids build up in brain Death in early childhood Common in US among the Jewish

10 Phenylketonuria (PKU) Recessive disorder Carried on chromosome #12 Failure of brain to development in infancy Phenylalanine is not broken down so it builds up in body and causes mental retardation Common in people whose ancestors came from Norway and Sweden Newborns appear normal until they drink milk PKU test is given at birth Infants affected by PKU are given a diet low in phenyalanine until their brains are fully developed

11 Dominant Alleles A single dominant allele inherited from one parent is all that is needed to show the trait

12 Huntingtons Disorder Dominant disorder Breakdown of certain areas of the brain Uncontrollable movements Onset usually occur between 30-50

13 Achondroplasia Dominant disorder Dwarfism

14 Sickle Cell Anemia Recessive disorder Most common in African Americans 1 in 12 African Americans is heterozygous for the trait In homozygous individuals the oxygen carrying protein hemoglobin is defective This causes red-blood cells to be sickle shape and reduces there oxygen carrying capacity Heterozygous individuals have both normal and sickle shaped red-blood cells because they are codominant


16 Sex Determination 23 pairs of chromosomes 22 pairs are autosomes 1 pair is sex chromosomes Female XX Male XY


18 Sex-Linked Inheritance Sex-linked traits – traits controlled by genes on sex chromosomes Any allele on the X chromosome of a male will not be masked by a corresponding allele on the Y chromosome Several human traits are determined by genes that are carried on the sex chromosome Most are located on the X chromosome If a son receives a recessive X chromosome from mom he will express the recessive phenotype because he has no chance of inheriting a dominant allele from his father to mask the recessive allele More males have sex-linked disorders

19 Red-Green Color Blindness Sex linked recessive Can’t tell the difference between red and green



22 Hemophilia Sex linked recessive Failure of blood to clot

23 Muscular Dystrophy Sex linked recessive Wasting away of muscles

24 X-Chromosome Inactivation If one X is enough how do cells adjust to the extra X in females? In females 1 X is randomly switched off The turned off X is called a Barr body Example: Calico Cat In cats the gene for fur color is on the X chromosome 1 X could have the allele for orange and the other the allele for black So depending on which allele is turned off or on gives the different colors All cats with 3 colors are female.

25 Human Heredity-Changes in Chromosome Numbers Karyotype – a chart of chromosome pairs that is valuable in pinpointing unusual chromosome numbers in cells A picture is taken of chromosomes in metaphase. Why? They are cut out and arranged in pairs according to length and location of the centromere Because the chromosomes are easy to see


27 Chromosomal Disorders Most of the time meiosis works very well, but every now and then something can go wrong. Nondisjunction Gametes will have an abnormal number of chromosomes When chromosomes don’t separate correctly in Metaphase I

28 Down Syndrome – Trisomy 21 Some degree of mental retardation Incidence of down syndrome births is higher in older mothers especially over 40 3 chromosomes on pair number 21 Due to nondisjunction


30 Patau Syndrome – Trisomy 13 Multiple abnormalities Condition usually fatal by one year of age


32 Edward Syndrome – Trisomy 18 Varying degrees of mental retardation Usually fatal by three months of age


34 Unusual Numbers of Sex Chromosomes Many abnormalities in number of sex chromosomes do exist

35 Turner Syndrome X ___ Females Sterile Shorter, stocky

36 Triple X XXX Females Usually fertile Abnormalities vary

37 Klinefelter Syndrome XXY Males Sterile May be mentally retarded Slight breast development Underdeveloped genitalia Sparse body hair

38 Jacob Syndrome XYY Males Sterile

39 Environmental Influences As an organisms develops many factors can influence how the gene is expressed or if it is expressed at all Temperature, nutrition, light, chemicals can all influence gene expression Ex. Leaves of different sizes, colors Ex. Himalayan rabbit fur color Ex. Arctic Fox fur color



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