AP BIO: 14-15 Short FRQs

Heterozygous advantage

1. This is when the heterozygous genotype has a higher relative fitness than both the dominant and recessive genes

2. In areas where malaria is prevalent, if you’re heterozygous for sickle cell, you don’t get malaria or full-blown sickle cell. 

3. The advantage is that you get immunity from malaria. 

X-linked disorders

1. Why do they show up more frequently in males than in females?

   1. This is because they only have one X chromosome, and they don't have a second X chromosome to mask a recessive gene. They don’t need two recessive traits; once they have the trait, they have the trait; they only need one copy. 

Barr Bodys

1. What are they? How are they formed?

   1. Barr bodies are the unmarked X chromosomes that are found in somatic cells of female mammals. This is when one chromosome becomes inactivated during early embryonic development.

2. One X becomes inactivated during embryonic development

   1. Condense into a compact object = Barr Body

      1. Lies inside the nuclear envelope in females. It comes compact. 

   2. Which X becomes Barr body is random

      1. Patchwork trait = “mosaic”

Disjunction

1. Know what nondisjunction is, and give an example of a disorder that exhibits nondisjunction and the effects on that individual

   1. Chromosomes don't separate properly during meiosis, so you have an incorrect number of chromosomes.

   2. Down syndrome is caused by nondisjunction, in which an extra 21st chromosome is added to the cell due to the cell being trisomic for chromosome 21. Instead of having 46 chromosomes, there is a total of 47. Four characteristics of Down syndrome include facial features, short stature, correctable heart defects, and developmental delays. 

Phenotypic plasticity

1. What is it? What is an example? How is it involved in evolution?

   1. This is the ability of a single genotype to produce different phenotypes in different environments. This is a result of the evolutionary process that causes specific experiences to alter gene expression in ways that alter the phenotype. An example of this is the loggerhead sea turtles, which lay their eggs on the beach, and the location in which the eggs are laid determines the turtle's sex. On the surface of the beach, it's warm, and the offspring produced are females. When dug deeper, the temperature is cooler, and the offspring develop into males.