ap bio unit 5 overview

Genetics!

Important Vocabulary
- Gene- Section of a chromosome that codes for a trait
- Allele- Version of a trait (A, a)
- Dominant- The trait that shows if present
- Recessive- The trait that is hidden if a dominant is present
- Genotype- What was passed by the parents (AA, Aa, aa)
- Phenotype- Physical Appearance
  - ENVIRONMENT CAN CHANGE PHENOTYPE
- Homozygous- Have the same allele twice (AA or aa)
- Heterozygous- Have one of each allele (Aa)
- True breeding- Homozygous for the trait
- Test Cross- Individual showing the dominant trait is bred with one showing the recessive trait to see if the original individual was homozygous or heterozygous

Punnett Squares
- Tool used to determine chances of getting certain traits
  - Only true is alleles are not linked
  - Results are used as the expected results for chi-square analysis
  - Example below- RRxrr

R ↓

→

Dihybrid Cross- looks at odds of individual have two traits simultaneously (AaBbxAaBb)

Make a punnett square for each trait then multiply the fractions.
- E.g what are the odds of having an AaBb offspring if both parents are AaBb?

2/4 are Aa and 2/4 are Bb= 4/16 (((2x2)/(4x4)) would have a heterozygous genotype for both traits

Complete Dominance- The dominant allele completely hides the recessive allele
- Heterozygous individuals only show the dominant phenotype
- Only homozygous recessive individuals express recessive phenotype

Incomplete Dominance- Heterozygous individuals have a blend (white and red make pink) of both parents
- 3 possible phenotypes (R=Red, W= White)
  - RR=Red
  - WW= White
  - RW=Pink

Codominance- Both alleles are expressed COMPLETELY
- 3 phenotypes (R=Red, W=White)
  - RR=Red
  - WW=White
  - RW= Red and White Spots

Polygenic Traits
- Traits affected by several genes working together
  - Creates a gradient of phenotypes

Multi-Allele Traits- Traits that express more than one type of inheritance
- Blood type is common example
  - A and B are codominant
  - o is completely recessive

Sex-Linked Traits
- Males are XY
- Females are XX
- Sex linked traits are only carried on the X chromosome
  - Heterozygous females are carriers
    - X^AX^A= Female who shows dominant trait
    - X^AX^a= Female who shows dominant trait but can pass recessive trait
    - X^aX^a= Female who shows recessive trait
  - Males CANNOT be heterozygous (for sex linked traits)
    - X^AY= Male who shows dominant trait
    - X^aY= Male who shows recessive trait
    - Males only receive a Y chromosome from father so all sex linked traits will match the mother

Environmental Plasticity
- Different enzymes and different genes can be expressed differently in different environments
  - Temperatures change the shapes of enzymes and can turn a gene on or off
  - Chemicals in the environment can trigger signals to activate genes
  - Change in phenotype DOES NOT change the genotype
  - Gene Penetrance- How likely an individual is to express an inherited genotype
  - Gene Expressivity- To what degree a gene is expressed (gray vs.black)

Dihybrid Crosses
- Used when you want to look at two traits at the same time (AaBb x AaBb)
- Punnett square would have 16 boxes
- Instead multiply the allele probability of A and the allele probability of B

Pedigrees

Genes that result from crossing over

You then use chis square to determine significance of the recombination frequency

Diversity

Diversity is required for life to succeed
Without diversity there is no natural selection so no evolution
Low diversity leaves a population vulnerable to change
Sexual reproduction increases diversity
Some things CANNOT change
- All life need ribosomes to make proteins
- All life stores genetic information in a nucleic acid
- Cell membranes have to be present and function the same way
These required components point to common ancestry

Meiosis

Phases
- Meiosis 1
- Prophase 1- CROSSING OVER
  - Homologous chromosomes stack and randomly exchange information (some of moms stuff ends up on dads chromosome and vice versa)
    - Genes closer together cross over together more frequently
  - Only happens once in Meiosis
  - This is the step in meiosis that most increases diversity
- Metaphase 1- Chromosome PAIRS line up in the middle of the cell
- Anaphase 1- Chromosome PAIRS are pulled apart
- Telophase 1- Two nuclei are formed and each cell has 2n chromosomes
  - Cytokinesis separates both cells

Meiosis 2
- These processes happen to both of the new cells from meiosis 1
- Interphase DOES NOT occur a second time
Prophase 2- Nothing happens
Metaphase 2- Chromosomes line up in the middle
Anaphase 2- Chromatids are pulled apart
Telophase 2- New nuclei are formed in all 4 cells
- Cytokinesis cuts the cytoplasms of the cells
- Each cell now has n chromosomes

Reproductive Strategies

“Laws” of diversity through sexual reproduction
- Independent assortment- No gene you inherit affects your ability to INHERIT any other gene (eye color does not determine your hair color)
- Segregation- each allele for a trait is separated on a different gamete
  - E.g- if the father is Aa for a trait then one sperm will carry A and one will carry a.

Mutations

Random changes in DNA
Increase diversity
- Without mutations there would be no natural selection and evolution could not happen.
Mutations in meiosis have MAJOR implications for offspring (every cell made by the individual will have the mutation)
In meiosis mutations normally occur during crossing over, anaphase 1 or anaphase 2

Types of mutations
- During Crossing over
  - Deletion/Insertion- a single base or section of bases are added or removed
  - Duplication- a section gets copied
  - Inversion- a section gets reversed
  - Translocation- two non-homologous chromosomes exchange genes

0.0(0)

Chat with Kai