Chromosomes & DNA

Wild type

a trait that is the most common phenotype in natural populations 

Mutant phenotype

traits that differ from the wild type

Morgans findings

specific genes are carried on specific chromosomes

Sex-linked genes

genes on either sex chromosome

Heterogametic 

half of the sperm gets an X and the other half gets an Y (XY)

Homogametic

all eggs have X chromosome (XX)

Y chromosome

carries genes for male development

X - linked traits 

traits controlled by genes on the X chromosome 

Hemizygous

have just one allele for a gene

Homozygous

have two identical alleles for one gene 

X - inactivation

one X chromosome inactivates to equalize gene dosage within a female

Barr body

inactivated X chromosome which modifies DNA methylation

DNA

deoxyribonucleic acid

Transformation 

a change in genotype or phenotype due to assimilation of external DNA 

Nucleotides

monomers of nucleic acids

3 parts of a nucleotide

1. phosphate group (P)

2. Sugar (5 Carbon)

3. Nitrogen base (varies)

Purines

nitrogen base made of large molecules (2 rings)

1. adenine

2. guanine

Pyrimidines 

nitrogen base made of small molecules (1 ring)

1. Cytosine 

2. Thymine 

Double helix

2 strands of DNA wound around each other

Outside DNA strand 

sugar phosphate backbone 

Inside DNA strand

made of nitrogenous bases

How many bonds hold A & T strands together

2 hydrogen bonds 

How many bonds hold G & C strands together

3 hydrogen bonds

Antiparallel

causes strands to run in opposite directions

Semi-conservative replication

each existing strand acts as a template for a new strand

Replication initiation 

occurs at the origin of replication 

DNA helicase

enzyme that unwinds the double helix

Primase

enzyme that creates new strands

DNA polymerase

enzyme that starts the leading strand in the 5’ to 3’ direction

Phosphodiester bond

connects the phosphate group in one nucleotide to the sugar in another nucleotide

Ligase

enzyme that connects the lagging strands