Sex-linked traits and adaptation Flashcards
What are human traits controlled by?
- single genes with two alleles
- others by single genes with multiple alleles.
- Still other traits are controlled by many genes that act together
Describe single gene with two alleles with an example
Have 1 dominant and 1 recessive allele
Have 2 distinctly different phenotypes
Ex. Widow’s Peak, dimples
Describe single genes with multiple alleles examples
-Some traits have more than 2 alleles although a person can have only 2 of those alleles because chromosomes exist in pairs. Each chromosome in a pair carries only 1 allele for each gene
-Ex. Human blood type –
3 alleles A, B, O
A and B are codominant
O is recessive
Describe traits controlled by many genes with examples
-Produce a large variety of phenotypes
-Genes act together as a group to produce a single trait
Ex. Height – at least 4 genes
Skin color – at least 3 genes
Sex chromosomes
-One of the 23 pairs of chromosomes that carries the genes that determine whether a person is male or female
-Also carries genes that determine other traits
-The only chromosome pair that does not always match
-Girl – two sex chromosomes match (X,X)
-Boy –don’t match, one is an X other is a Y
-The Y chromosome is smaller than the X
X carries 2000 genes, y carries only 86
Sex-linked traits
-Genes for some human traits are carried on the sex chromosomes
-Traits controlled by sex-linked genes are called sex-linked traits
-EX. Red-green colorblindness
-Most of the genes on the X chromosome are not on the Y chromosome
-An allele on the X may not have a match on the Y
-Sex-linked genes can have dominant and recessive alleles
In females a dominant allele on one x will mask a recessive on the other X
-In males, there is no matching allele on the Y to mask a recessive allele on the X
-Any trait on the X chromosome in males (even a recessive trait) will produce the trait in a male who inherits it.
-Colorblindness is a trait controlled by a recessive allele on the X chromosome
-Many more males have colorblindness than females
-Females can be carriers. They have one dominant trait for normal color vision and one recessive trait for colorblindness. They have normal color vision
-If the mother passes on the X chromosome to a son, he will be colorblind
-If she passes it onto a daughter, she will also have an X chromosome from her father. If her father has normal color vision, then she will inherit the dominant allele for normal color vision from him and she will have normal color vision
Other examples of sex-linked traits
In humans, sex linked disorders are usually passed on from mother to son by a defective gene on the X chromosome.
– Hemophilia: Rare, inherited bleeding disorder in which your blood doesn’t clot normally
–Duchenne Muscular Dystrophy
– Baldness
What is the purpose of adaptation?
- Homeostasis
- Survival and Reproduction
- Passing on one’s genes to the next generation
What is the hierarchy of adaptation?
- Cultural adaptations which may be the most rapid
- which may include behavioral adaptations
- which may be adaptive or maladaptive
What is the advantage of a hierarchy?
- if cultural adaptation solves the problem, we may not need ot activate a funcational response
- initiation of a functional response in time may limit the energy costs of futher adaptive responses.
- we may or may not create a selective pressure on genetic frequencies.
Example of Maladaptation
- Two Eskimos sitting in a kayak were chilly, so they lit a fire in the craft.
- Not surprisingly it sank, proving once again that you can’t have your kayak and heat it too.
Functional adaptations
Functional Adaptations: If the cultural changes do not right the issue and rebalance the internal environment, then functional adaptations may be employed to protect you
Acclimatization of the sweating mechanism
- when a normal person is exposed ot hot weather for 1 to 6 weeks, two changes take place which are called acclimatizaiton of the sweating mechanism
- sweat production increases to as much as 2 liters/hour. Decreased concetration of Na+/Cl- in the sweat glands caused by increased secretion of aldosterone, a steroid horomone released by the adrenal gland.
Describe Bergmans rule
-Larger body in cold climate, leaner, longer body in the hot climate
Describe Allens Rule
-Longer limbs in hot climate, shorter limbs in colder climate.
