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
KEY CONCEPT A combination of methods is used to study human genetics.
Inheritance of many human traits is complex. 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
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. X Y
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
Boxes = males Circles = females Shaded = they show the trait White = does not show trait Half shaded = carrier
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
How many females are in this family? 11 How many carriers? 7 Sponge 6 How many females are in this family? 11 How many carriers? 7 How many children were in generation two? 5 How many offspring in generation three are affected by the trait? 2 Generation 1 Generation 2 Generation 3 Generation 4
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
Do his boys have Widow’s Peaks? 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?
Joe Mary Ww ww Isabel Pete WW Ww ww
A karyotype is a picture of all chromosomes in a cell. X Y
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
In down syndrome a person has an extra copy of chromosome 21. In Klinefelter’s syndrome a male has an extra X (XXY).