Genetic Disorders & Sex Linked Traits. Honors Biology Unit 5 2012-2013. Recessive Disorders. Disorders that are only expressed in the phenotype when 2 recessive alleles are present. DD = Normal Dd = Carrier dd = Affected by disorder. 2 Examples of Recessive Disorders.
Most common in Caucasian (white) populations
(1 in 2500 to 3500)
1 in 17,000 African Americans
1 in 31,000 Asian Americans
25% Cystic Fibrosis
Disorders that are expressed in the phenotype of heterozygous and homozygous dominant individuals
Hh x hh
Huntington’s is most common in certain parts of Venezuela (700 in 100,000)Generally affect 3-7 in 100,000 of European ancestryLess common in African-American & Asian American
duplication(an extra copy of a region of chromosome)
deletion(missing a region of chromosome)
inversion(part of the chromosome is inserted backwards)
translocation(two different chromosomes switch pieces).
The rate of aneuploidy in males is constant: 1-2% of sperm have an extra or missing chromosome.
In each cell one of the X chromosomes ‘turns off’.
This turned off chromosome is known as a Barr body.
The effect of Barr bodies can be seen in Calico colored cats.
A calico cat has patches of orange and patches of black
X = orange X1 = black
Males: XY = orange / X1Y = black
Females: XX = orange / X1X1 = black / XX1 = calico
Because individual cells determine which X chromosome to deactivate, the patches of color arise
What number do you see?
But if you were red-green colorblind….
You would see the #:
Types of Colorblindness
No color vision
Protanopia: no red
Deuteranopia: no green
Tritanopia: no blue
Small cuts, scrapes and bruises can be life threatening
1 in 10, 000 males
1 in 100,000,000 females
Queen Victoria = Carrier
In some cases, androgen insensitivity is only partial: the cells respond a little bit to testosterone produced by the testes. The embryo develops with ambiguous genitalia, neither completely male not completely female.
Another condition, congenital adrenal dysplasia, causes the adrenal glands to produce an abnormally large amount of testosterone in a female embryo, This can also cause development of ambiguous genitalia.
A single zygote splits into two. This happens between 1 to 9 days after the zygote forms.
The twins share the same genome
Two separate eggs are fertilized with two separate sperm. Two totally independent zygotes are created.
The twins have different genomes
Identical twins who fail to completely separate after the 13th day after fertilization
This may be due to the fusion, or incomplete separation of zygotes
May be two fully formed individuals connected at various locations, or rarely, parasitic twins, where one is much smaller and less formed, or even completely contained.