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This article explores the human chromosome composition in males and females, highlighting that human males have 44 autosomes and 2 sex chromosomes (X and Y), while human females have 22 autosomes and one X chromosome. It examines color blindness, a condition affecting color vision, often inherited and affecting the ability to distinguish reds and greens. The work of Thomas Hunt Morgan in genetics, particularly regarding sex-linked traits in Drosophila, is also discussed, alongside the implications of hemophilia as a hereditary condition, famously associated with Queen Victoria's lineage.
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DO NOW 1.What is the correct number of autosomes and sex chromosomes in the somatic cell of a human male? 2. How many autosomes and sex chromosomes would be in the ovum of the human female?
ANSWERS 44 autosomes and 2 sex chromosomes(X and Y) 22 autosomes and an X
WHAT DO YOU SEE? A person with normal color vision sees the number 5.
Color blindness (color vision deficiency) • is a condition in which certain colors cannot be distinguished, and is most commonly due to an inherited condition. • Problems in distinguishing reds and greens are the most common.
A pedigree for color-blindness Normal male Carrier female P1 F1 Color-blind male Carrier female Normal female Normal male
Thomas Hunt Morgan was awarded the Nobel Prize in Physiology or Medicine in 1933. The work for which the prize was awarded was completed over a 17-year period at Columbia University, commencing in 1910 with his discovery of the white-eyed mutation in the fruit fly, Drosophila.
Morgan’s work with Drosophila demonstrated that genes for certain traits are located on the X chromosomes. • These genes are said to be sex-linked. • These genes do not appear to have corresponding alleles on the Y chromosome. • Since many sex-linked genes are recessive, they are expressed more frequently in males than in females.
XX x X’Y where X’=allele for white eye X X X’ X’ X X’ X Y X Y X Y
Summary of Results PARENTS (Female: +) x (Male: W) OFFSPRING Phenotype Female: + Male: + Number 5016 5087 TOTAL 10103 Proportion 0.49649 0.50351 Ratio 1.000 : 1.014
X’X x XY where X’=allele for white eye X X’ X X’ X X X Y X Y X’ Y
Summary of Results PARENTS (Female: +) x (Male: +) OFFSPRING Phenotype Female : + Male: + Male: W Number 5056 2521 2467 TOTAL10044 Proportion 0.50339 0.25100 0.24562 Ratio 2.049 1.022 1.000
HEMOPHILIA • Hemophilia is often called the disease of kings • because it was carried by many members of • Europe’s royal family.
Queen Victoria • Queen Victoria of England was a carrier of hemophilia and passed The disease to many of her descendants (including the Russian emperor’s family and the Spanish royal family).
The history of Queen Victoria's descendants illustrates the hereditary characteristics of hemophilia. We can take a look at her family tree(pedigree).
