AP Bio- Chapter 14 genetics

• Earliest hypothesis: blending hypothesis. states that we are a perfect blend of our parents

• particulate (gene) idea: parents pass on heritable particles (genes) to offspring

  • Introduced after Mendel’s work with pea plants

True breeding: the genes of the parent are homozygous, (AA or aa). When truebreeding plants self-pollinate, offspring are ALWAYS the same as the parents

Parent generation: P

First generation offspring: F₁

Second generation offspring: F₂

Rules Mendel established:

1. Alternative versions of genes cause variations in characters. The alternative versions of genes are called alleles.

2. Each organism inherits 2 alleles from each parent for each characteristic

3. if the 2 genes differ at the locus (location of a gene on the chromosome), then the dominant gene is the one that determines the organism’s trait

4. LAW OF SEGREGATION: the 2 alleles for an inherited trait separate during meiosis and end up in different gametes.

Test-cross: a test done to see if an unknown parent is homozygous dominant or heterozygous. It is always crossed with a homozygous recessive

Law of independent assortment: 2 alleles will segregate independently of each other

Common ratio in dihybrid cross: 9:3:3:1

Dihybrid: when two traits are looked at (AaBb)

Laws of probability: if a parent is Aa, there is a ½ chance a gamete will carry ‘a’ and ½ chance a gamete will carry ‘A’

Complete dominance: ex- white pea breed with red pea, offspring is red

Codominance: 2 dominant alleles are both expressed- Blood AB

Incomplete dominance: 1 dominant allele is not completely dominant over the other. (snap dragon being pink)

Pleiotropy: 1 gene can have multiple phenotypic effects- cystic fibrosis

Epistasis: one gene can override another gene- mouse color

Polygenetic inheritance: additive effect of 2 or more genes on a single phenotypic character- skin color

“Norm of reaction” for a genotype: a genotype has a range of phenotypic outcomes

Multifactoral characteristics: both genotype and the environment can change a phenotype

Recessively inherited disorders: only have it if is ‘aa’

Person with heterozygous genotype is a carrier of the disorder but doesn’t express it phenotypically

Dominant inherited disorder: have it if ‘Aa’, have it bad and most likely do not survive if ‘AA’

Testing for multifactorial disease (where genotype and environment effect the individual- heart disease)

Amniocentesis: removal of amniotic fluid to test for genetic disorders

CVS- chorionic villus sampling, where tissue is removed from the placenta