Bio Chapter 14

Mendel’s work

discovered basic principles of heredity by breeding garden peas

identified 2 laws of inheritance by physical traits

pea plant traits

Mendel studied how 7 different traits were passed down

each had 2 distinct forms

advantage of pea plants

short generation time

large number of offspring

can self pollinate or cross pollinate

p-generation

true-breeding

plants produce offspring of the same variety when they self-pollinate

f1 - generation

the hybrid children of the p-generation

f2 - generation

when f1 self pollinate or cross pollinate with another f1 generation it is the f2-generation

alleles

alternate versions of genes account for variations in inherited characters

inherit 2 alleles, 1 from each parent

Genotype letters

Capital letter = dominant

lowercase letter = recessive

law of segregation

2 alleles for a heritable character separate during gamete formation and end up in different gametes

gamete formation = meiosis metaphase —> home pairs line up

law of independent assortment

each pair of alleles segregates independently of any other pair of alleles during gamete formation

law applies only to genes in different non-homologous chromosomes or those far apart on the same chromosome

single gene inheritance

single gene, single trait (sometimes0

alleles that are not completely dominant or recessive

has more than 2 alleles

produces multiple phenotypes

complete dominance

phenotypes of heterozygote and dominant homozygote or identical (RR = red)

incomplete dominance

phenotype of F1 hybrids somehwere between the phenotypes of the 2 parental varieties (Rr =pink)

codominance

two dominant alleles affect the phenotype in separate distinguishable wats (Rr = red and white)

blood typing

uses 3 alleles instead of 2

codominance of alleles is “A” and “B” (I^A and I^B)

both dominant over “O” or “I” but not each other

polygenic inheritance

multiple genes, single trait

leads to continuous distribution or quantitative variation

polygenic inheritance and environment

effects on height or skin color other than genetics: nutrition, hormones, sun exposure

ex. cancer, heart disease, diabetes, alchololism

pedigree

family tree describing inheritance of a trait across generations

recessive disorders

show up only in individuals homozygous for the allele

carriers are heterozygous but healthy (disease shows up randomly but usually when parents are recessive carriers)

Chances of 1 carrier having an affected child

Cc x CC = 0%

Chances of having an affected child with 2 carriers?

Cc x Cc = 25%

Dominant disorders

show up in heterozygotes as well as homozygotes for the alleles

no carriers

Cc + CC = sick cc = healthy

must have a parent with the disease to inherit it

ex. dwarfism and Marfans syndrome

Sickle cell anemia carriers

carrier have no disease except when oxygen is reduced (high altitudes)

Sickle cell anemia

1. substitution of a single amino acid in the hemoglobin protein in RBC

2. beta globin proteins form long fibers

3. cell membrane “sickles”

physical weakness, pain, organ damage, paralysis,

resistance to malaria for carriers