distinguish between genotype and phenotype of a given genetic trait
genotype: genetic makeup of individual for given trait (combination of alleles)
phenotype: physical expression of given trait’s genetic makeup
- comes in pairs
humans can have more than 2 genotypes, but only 2 phenotypes
ex. blood
genotypes: A.B.O
phenotypes: A, B, AB, O
describe the importance of gregor mendel’s experiments to our understanding of inheritance
found out about how traits are passed down from one generation to the next through specific predictable patterns
- genetic laws like law of segregation, law of independent assortment and law of dominance
mendel’s law of segregation
each individual has 2 alleles for one trait which separate during gamete (sperm/egg) formation, on each gamete only receives one allele
mendel’s law of independent assortment
genes for different traits are inherited independently of each other
ex. gene for hair + height are different
create a punnett square to predict pheonotype of offspring from parents w known genotype (for both single and 2 independent genes)
single gene punnett square:
parent 1: Aa
parent 2: Aa
outcomes: AA. Aa, Aa, aa
two gene punnett square:
parent 1: AaBb
parent 2: AaBb
each parent can make 4 combinations:
AB, Ab, aB, ab
and then you just cross that like in a punnett square
you should get 16 outcomes
mendelian traits
traits controlled by a single gene w two alleles
ex. traits that follow dominant recessive inheritance patterns
free vs attached earlobes, etc.
complex inheritance
inheritance of traits that dont follow mendelian rules.
traits influenced by multiple genes, environmental factors, interactions between genes
ex. height, skin color, eye color
explain how an individuals phenotype may be determined by multiple genes that interact with one another and the environment
polygenic inheritance:
also known as multiple genes
- some traits controlled by many genes called polygenic traits
ex. human height
epistasis:
aka gene-gene interactions
- one gene can influence / block the expression of another gene
- even if you have a certain allele, its effect might by altered or hidden by a diff gene
ex. gene A determines black or blue (A/a) gene B determines whether it shows up or not (B/b)
if you have the gene Ab, no pigment shows up
environmental influence:
- nutrition, exercise, sun exposure, stress
review human karyotype to identify sex chromosomes + any abnormalities in chromosome number
karyotype: pic of all chromosomes in a cell arranged by size and shape
- 23 pairs, 46 chromosomes in humans
- 1-22 autosomal, 23 sex chromosomes
diagram a chromosome identifying genes, alleles, loci
genes: inside the chromosomes
alleles: different version of a gene (stripes on chromosomes)
locus: where each gene is located on a chromosome
ex. two lines at top can be locus for hair color
describe the genotype and phenotype of a genetic carrier
genetic carrier: has a copy of recessive allele for a genetic trait / disorder
- does not show symptoms
genotype: heterozygous, carries a dominant and a recessive allele
phenotype: unaffected
compare and contrast inheritance of recessive, dominant and sex linked genetic disorders
recessive:
- shows up only when individuals have 2 recessive alleles
- carriers (individuals w heterozygous) are usually unaffected
- affects males and females equally
dominant:
- shows up when individuals have at least one dominant allele (AA, Aa)
- no carriers, anyone w dominant allele has disease
- affects males and females equally
sex linked:
- disorder caused by mutation on sex chromosome (usually X)
- males express the disorder if they inherit the affected x chromosome– they only have one X
- affects more males than females
pedigree: autosomal dominant
trait appears in every generation. at least one individual is affected
affects males and females equally
pedigree: autosomal recessive
trait may skip generations. affected individuals may have unaffected parents. both parents are carriers.
affects male and female equally
pedigree: x linked dominant
affected fathers pass trait to ALL DAUGHTERS, no sons
more common in female
pedigree: x linked recessive
affected sons have unaffected carrier mothers
trait is NEVER passed down from father to son
more common in males
pedigree: y linked
affected father passes down trait to ALL sons
only males affected
pedigree:mitochondrial
mother passes down to ALL children
describe the structure of DNA
double helix shape
made of phosphate group, deoxyribose sugar, nitrogenous base
- 4 bases (A-T + C+G)
2 strands running in opposite directions
- 5’ -> 3’ and 3’ -> 5’
sugar phosphate groups form backbone of DNA
DNA replication
- initiation: helicase enzyme unwinds 2 strands of DNA by breaking H bonds between bases. creates Y fork separating 2 strands
- single strand binding protein attach to separate strands to keep them apart and prevent rejoining
- primase synthesizes RNA primer complementary to DNA strand
(A-U) - DNA polymerase adds complementary DNA nucleotides to 3’ end of RNA primer synthesizing new strand in 5’ to 3’ direction
leading strand: synthesized continuously toward replication fork
lagging strand: synthesized discontinue away from fork - DNA polymerase removes RNA primers, replaces them w DNA nucleotides
- DNA ligase seals gaps between 2 strands
- replication ends when DNA is copied (semi conservative)
explain cause of DNA replication errors, describe how they are repaired
causes:
- mismatched bases– DNA polymerase can pair base with wrong nucleotide
- slippage during replication can cause insertions and deletions
- damage from chemicals, radiation
repaired:
- DNA polymerase proofreads DNA strands
- mismatch repair (MMR) goes through to double check after DNA polymerase
mutation definition
change to sequence of nucleotides in an organisms DNA
point mutations
point mutation: change of one nucleotide in a single base pair
substitution: one nucleotide substituted for another in DNA sequence of gene
insertion: one nucleotide inserted into sequence
deletion: one nucleotide deleted from sequence
how gene expression creates a phenotype from a genotype
genotype: DNA sequence of gene
gene expression: transcription and translation
DNA -> mRNA -> tRNA
read codons from mRNA
phenotype: whatever is expressed from codon
