ch 14: mendel and the gene idea

gregor mendel

father of modern genetics → studied garden peas to follow their traits through generations

character

a heritable feature (ex. flower color)

trait

a specific variant of a character (ex. purple or white)

how did mendel control cross pollination?

1. remove stamens → prevent self pollination

2. transfer pollen from another plant → controlled cross

hybridization

crossing two contrasting, true-breeding varieties

p generation

parental gen

f₁ generation

offspring of the p gen

f₂ generation

offspring produced by the f₁ gen

alleles

alternate versions of genes

what does each gene have?

a specific locus on a specific chromosome

how many alleles does an organism have?

they inherit two, one from each parent

homozygous

identical alleles (ex. AA or aa)

heterozygous

different alleles (ex. Aa)

dominant allele

determines the phenotype in a heterozygote (ex. PP or Pp → purple)

recessive allele

is masked in a heterozygote (ex. pp → white)

what does mendel’s model of inheritance include?

1. alleles

2. dominance

3. law of segregation

what is the law of segregation?

the two alleles for a gene separate during gamete formation → each gamete receives only one allele

what does the law of segregation correspond to?

the separation of homologous chromosomes during meioisis

punnett square

predicts possible allele combos in offspring

genotype

the particular pair of alleles for any given gene

phenotype

an observable trait

testcross

breeding the mystery individual w/ a homozygous recessive individual to determine genotype

what does it mean if any offspring displays the recessive phenotype?

the mystery parent = heterozygous

dihybrids

heterozygous for two genes (ex. YyRr)

dihybrid cross

YyRr x YyRr

law of independent assortment

alleles of diff genes assort independently during gamete formation

how many traits does one gene affect?

multiple

what is one trait consisted of?

many genes (produces continuous variation)

epistasis

one gene at one locus masks or modifies the phenotypic expression of another gene at a second locus

what is phenotype influenced by?

genes + environment

phenotypic plasticity

the same genotype can produce diff phenotypes in diff environments

how are inheritance patterns studied?

through families

what do the mendelian principles help to explain?

human genetic disorders

carriers (Aa)

have the recessive allele but usually do not show the recessive phenotype

homozygous recessive (aa)

affected individuals

multiplication rule

for two independent events, multiply their probabilities (and = multiply)

addition rule

for mutually exclusive outcomes, add their probabilities (or = add)