Karyotype Karyotype a picture of chromosomes Autosomes the first 22 homologous pairs of chromosomes Autosomes are the same for both males and females Sex chromosomes determines the sex of the individual ID: 933492
Download Presentation The PPT/PDF document "Karyotypes and Sex-Linked Traits" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Karyotypes and Sex-Linked Traits
Slide2Karyotype
Karyotype
– a
picture of chromosomesAutosomes: the first 22 homologous pairs of chromosomes. Autosomes are the same for both males and females. Sex chromosomes: determines the sex of the individual. The sex chromosomes are the 23rd pair of chromosomes.
Slide3Male of Female?
Female: XX
Male: XY
Slide4Determining Gender
Which parent determines the sex of an offspring – DAD
Why?
All moms have the genotype XX. When egg cells are made, they will all carry a single X chromosome. All dads have the genotype XY. When sperm cells are made, 50% will have an X chromosome and 50% will have a Y chromosome. Therefore, males and females are born in roughly a 50:50 ratio
Slide5Diagnosing Disorders from Karyotypes
Some disorders can be diagnosed by looking at a person’s karyotype
Most are caused by
nondisjuction during meiosisNondisjunction – failure of chromosomes to separate during meiosisDisorders:Down Syndrome (Trisomy 21) – individual has 3 of the 21st chromosome instead of 2Turner Syndrome – female has only one X for her sex chromosome
Klinefelter’s
Syndrome – male has or more extra X chromosome
Autosomal
Sex-Linked
Slide6Sex-Linked Traits
SEX-LINKED TRAITS
: those traits that are controlled by genes on the X or Y chromosomes.
Most sex-linked traits are on the X chromosome.The Y chromosome is much smaller than the X chromosome and only contains a few genes. Ex:HemopheliaColorblindness
Slide7Example
In humans, hemophilia is a sex-linked trait. Having hemophilia is recessive (
X
H) to being normal (X). The heterozygous female is called a carrier. Cross a carrier female with a normal male. XHX x XY
Genotype Ratio:
Phenotype Ratio:
X
H
X
X
Y
Slide8Example
Cross a
carrier female
with a male with hemophilia. XHX x XHY
Genotype Ratio:
Phenotype Ratio:
X
H
X
X
H
Y
Slide9Example
In humans, red-green colorblindness is a sex-linked trait. People with red-green colorblindness can not tell the difference between red and green. Colorblindness is the result of a recessive allele. Cross a
female with colorblindness
with a male with normal vision. XCXC x XY
Genotype Ratio:
Phenotype Ratio:
X
C
X
C
X
Y
Slide10Why are sex-linked traits more common in males than in females?
Because
a
male only has to inherit ONE recessive allele in order to get a sex-linked trait and a female has to inherit TWO recessive alleles in order to acquire the sex-linked trait. It is easier to inherit one recessive allele than two. If the female only inherits one recessive allele, then they are a carrier but have the normal phenotype.
X’s are dominant to Y’s.
If female gets a “bad” from one parent, she could still get a “good” X, and become a carrier (has the trait but isn’t expressed). The only way for the female to express the trait is to inherit two “bad” X’s.
If a male gets a “bad” X, the only other sex chromosome is a Y. The “bad” X is dominant to the Y, therefore, the male will express the trait.