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7.4 Human Genetics and Pedigrees SPONGE 4 What is the difference between incomplete dominance and codominance? (7.2) • Give an example of each 7.4 Human Genetics and Pedigrees • In incomplete dominance, neither allele is completely dominant nor completely recessive. + = Codominant alleles will both be completely expressed. + = The flower will show both red and white Set CornellGenetics Notes on pg. 7.4 up Human and Pedigrees 91 7.4 Human Genetics and Pedigrees 2.1 Atoms, Ions, and Molecules •Topic: 7.4 Human Genetics and Pedigrees •Essential Questions: •Don’t forget to add it to your T.O.Contents! 7.4 Human Genetics and Pedigrees KEY CONCEPT A combination of methods is used to study human genetics. 7.4 Human Genetics and Pedigrees • The basic principles of genetics are the same in all sexually reproducing organisms. – Inheritance of many human traits is complex. – Single-gene traits are important in understanding human genetics. Ex: widow’s peak Widow’s peak 7.4 Human Genetics and Pedigrees Females can carry sex-linked genetic disorders. • Males (XY) express all of their sex linked genes. • Expression of the disorder depends on which parent carries the allele and the sex of the child. Y X 7.4 Human Genetics and Pedigrees A pedigree is a chart for tracing genes in a family. • Phenotypes are used to infer genotypes • Autosomal genes show different patterns on a pedigree than sex-linked genes. Widow’s peak No Widow’s peak 7.4 Human Genetics and Pedigrees Boxes = males Circles = females Shaded = they show the trait White = does not show trait Half shaded = carrier 7.4 Human Genetics and Pedigrees 1. 2. 3. 4. How many females are in this family? How many carriers? How many children were in generation two? How many offspring in generation three are affected by the trait? Generation 1 Generation 2 Generation 3 Generation 4 7.4 Human Genetics and Pedigrees Sponge 6 1. How many females are in this family? 11 2. How many carriers? 7 3. How many children were in generation two? 5 4. How many offspring in generation three are affected by the trait? 2 Generation 1 Generation 2 Generation 3 Generation 4 7.4 Human Genetics and Pedigrees • If the phenotype is more common in males, the gene is likely sex-linked (meaning the trait is on the X chromosome). Ex: Color blindness males females 7.4 Human Genetics and Pedigrees Please draw a pedigree chart: Mary and Joe were married in 1912. Joe had a Widow’s Peak (Ww) which is dominant, while Mary did not have a Widow’s Peak (ww) They had two children: A son named Pete who had a Widow’s Peak and a girl named Isabel who did not have a Widow’s Peak. Pete married a woman who was homozygous for a Widow’s Peak (WW), but their daughter Isabel never married. Pete and his wife had three boys. Do his boys have Widow’s Peaks? 7.4 Human Genetics and Pedigrees WW Joe Mary Ww ww Pete Isabel Ww ww 7.4 Human Genetics and Pedigrees • A karyotype is a picture of all chromosomes in a cell. XY 7.4 Human Genetics and Pedigrees • Karyotypes can show changes in chromosomes. – deletion of part of a chromosome or loss of a chromosome – large changes in chromosomes – extra chromosomes or duplication of part of a chromosome 7.4 Human Genetics and Pedigrees • In down syndrome a person has an extra copy of chromosome 21. • In Klinefelter’s syndrome a male has an extra X (XXY).