Example of sex-linked diseases (5) Flashcards
There are more than 120 sex-linked diseases in humans such as… (5)
cleft palate, diabetes insipidus, red-green colour blindness, haemophilia and muscular dystrophy
Certain genetic diseases seem to occur more often in males than in females. Why is this?
This is because the male has only one X chromosome so, if a gene mutates or if a gene for a disease is present, on this X chromosome, the male will get the genetic disease. If the gene is recessive, it will only be expressed in chromosomes that have the allele, so the chances of the female getting the disease are less.
How does red-green colour blindness occur?
The genes that produce photo-pigments (those that are sensitive to different wavelengths of light) in the cones of the retina in the eye are carried on the X chromosome. If these genes are missing or damaged, certain photo-pigments will be affected.
More than __% of all colour blind people suffer from red-green colour blindness.
99
What does an individual with red-green colour blindness
An individual with this form of colour blindness finds it difficult to tell the difference between various hues of red and green.
How is the gene for red-green colour blindness transmitted?
The gene for red-green colour blindness is transmitted from a colour blind male on his X chromosome, to all his daughters who become heterozygote carriers and are usually unaffected.
What is haemophilia?
Haemophilia is a rare, genetically determined condition of frequent, excessive bleeding as the blood clots very slowly.
The ____ allele H allows blood to clot.
The ____ allele h does not allow blood to clot normally.
dominant
recessive
The alleles controlling blood clotting are sex-linked alleles, located on the __ chromosome. There is no gene for blood clotting on the ___ chromosome.
X
Y
Simple traits such as eye colour may be caused by just one pair of ____.
alleles
What is polygenic inheritance?
In polygenic inheritance, there is more than one pair of alleles responsible for a single trait.
What are the most complex traits determined by?
These more complex traits are determined by the interaction of many different alleles, each having small individual effects on the offspring, resulting in a range of phenotypes.
The more pairs of alleles that control a characteristic…
….the greater the number of possible combinations and the greater the variety of phenotypes. Each phenotype differs slightly from the next, forming a graduated series. This is an example of continuous variation.
Define continuous variation.
graduations of a characteristic in a phenotype, e.g. height in humans
What are Traits such as height, skin colour, metabolic rate and longevity usually controlled by?
polygenic inheritance
