Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 12 Chromosomal Inheritance

Chromosomal Theory of Inheritance: simply states that chromosomes are carriers of genetic information (Walter Sutton)

Human Chromosomes (Karyotype) Humans have 22 pairs of autosomes, 1 pair of sex chromosomes Fruit flies have 3 pairs of autosomes, 1 pair of sex chromosomes

Female eggs = XX Male sperm = XY Possible offspring are shown in square: 50% male 50% female What happens when an allele is located on the X chromosome? Males only get ONE !

These are a few of the known alleles located on the X chromosome Disorders that are recessive are masked in females by the other X chromosome.

Sex Linked Genes Genes located on the X chromosome are inherited with that X. When doing crosses you must include the sex chromosomes in your cross. Use superscript letters for the allele. Example: In fruit flies, eye color is a sex linked trait. Red is dominant to whit e. Females Males X R X R X R Y X R X r X r Y X r FRUIT FLY CHROMOSOMES Drosophila melanogaster

Figure 12.6

Figure 12.1

Show the cross between a white eyed male and a red eyed female: X r Y x X R X R Show the cross between a red eyed male and a white eyed female:

Figure 12.2

Human Sex Linked Disorders 1.Colorblindness 2.Muscular Dystrophy 3.Hemophilia 4.Fragile X Syndrome

COLORBLINDNESS

More Tests Color Blindness Simulation Tests

Muscular Dystrophy characterized by the wasting away of muscles life expectancy: ~20 yrs females can be carriers for the disease, where they pass the disease to their sons only Show the cross of a female who is a carrier and a normal male:

Hemophilia also known as "bleeder's disease", blood does not clot properly disease was present in the royal family, starting with Queen Victoria Show the cross between a female with hemophilia and a normal man:

How to analyze a pedigree

Figure 12.5

Identify all of the CARRIERS

Fragile X Syndrome caused by triplet repeats in a gene on the X chromosome causes mental retardation named because the X chromosome had an odd appearance - the tip of the chromosome seemed to be attached only by a small thread the number of repeats of the gene determines the severity of the disease

Figure 12Aa

Figure 12Ab

Figure 12Ac