Genetics Flashcards
Meiosis I
2n2x -> n2x
Meiosis II
n2x -> n
G1
- homologous chromosomes
- 2n1x
G2
- passed through replication already
- 2n2x
- replicated homologous chromosomes
prophase I
- mitotic prophase +
- synapsis to form the tetrad (pairing of homologous chromosomes)
- crossing over may occur between the homologous chromosomes
- recombination
all female gametes
- arrested in prophase I until they are ovulated
metaphase I
- tetrads (replicated homologous chromosomes) align at the metaphase plate
anaphase I
- separate the homologous chromosomes
- begin cytokinesis
telophase I
- partial reversal of mitotic prophase
- finish cytokinesis
- DNA may (rarely) decondense but usually remains condensed
- usually the nuclear envelope doesn’t reform
- spindle fibers break down
- haploid with replicated copies (n2x)
prophase II
- haploid with replicated copies -> haploid
- n2x -> n
metaphase II
- align the replicated copies
female secondary oocyte
- locked in metaphase II after ovulation until fertilization triggers completion
anaphase II
- separate the replicated copies
- separate the sister chromatids
end result of meiosis
- 4 cells
- 2n2x -> n2x (in 2 cells) -> n (in 4 cells)
- very different from each other and from parent cell
nondisjunction
- failure of the DNA to separate during gamete formation
failure during anaphase I
- 4 abnormal gametes
failure during anaphase II
- 2 normal and 2 abnormal gametes
gene
- piece of DNA that codes for a protein/RNA
- includes regulatory regions
allele
- form of a gene
- 1 person = 2 alleles
- population = 2x # of alleles
trait
- physical expression (phenotype)
polymorphic
- a trait with several variations
- hair color
- can’t have several versions of insulin
polygenic
- multiple genes code for 1 trait
- genes for total body height
pleotropic
- 1 gene = many traits
incomplete dominance
- heterozygous offspring of homozygous parents display a blended phenotype
- pink flowers (RR and WW) red and white
two tip offs that you are dealing with nonclassical dominance
- blended phenotype
- two upper case letters in the genotype
codominance
- both alleles are fully expressed
- human ABO blood group gene
- codes for a protein on the surface of a red blood cell
Rh factor
- classically dominant
- R = makes Rh proteins (+)
- r = doesn’t make Rh proteins (-)
universal donor
- O-
- no proteins to trigger reaction
universal acceptor
- AB+
- all proteins are recognized
- already have Rh factor so won’t attack something coming in with it.
Epistasis
- dominance between different genes
- expression of 1 gene depends on expression of another gene
- albino gene prevents expression of pigment genes
Mendel’s Laws
- law of segregation
- law of independent assortment
law of segregation
- alleles are separated during gamete formation
- occurs during anaphase I and anaphase II
law of independent assortment
- how one pair of alleles separates is independent of how other pairs separate.
- comes down to randomness of how chromosomes line up at metaphase I
homozygote x same homozygote
- 100% parents genotype and phenotype
homozygote x homozygote recessive
- 100% heterozygous and 100% dominant phenotype
heterozygote x homozygote dom/rec
- 50% heterozygous: 50% homozygous parent
- 50% dominant: 50% homozygous parent
heterozygote x heterozygote
- 25% homozygous dominant: 50% heterozygous: 25% homozygous recessive
- 75% dominant: 25% recessive
rule of multiplication
- when the question asks “and” or “both
- probability (A and B) = prob (A) x prob (B)
- always gives you a smaller number
rule of addition
- when the question asks “either” or “or”
- probability (A or B) = prob (A) + prob (B) - (prob A x prob B)
- always gives you a bigger number
when they mention possible sex of offspring
- really watch out for this!
- multiply by 1/2 at the end!
- they already say they have a son or daughter there is no need to multiply by 1/2
linked genes
- genes are found close together on the same chromosome
- might not sort independently
recombination frequency
recombinants
_____________
total # of offspring
- higher the RF the greater the distance between genes
Hardy Weinberg equations
- p + q = 1 (allele frequency in entire population)
- pp + 2pq + qq = 1 (genotype frequency)
homo hetero recessive
5 conditions for which the equations hold true
- large population
- random mating
- no mutation
- no migration
- no natural selection
how long to reach new equilibrium if old one is disturbed
1 generation to reach a new equilibrium
exception to mendel’s law of independent assortment
- genes found on the same chromosome might not sort independently
- also called linked genes
Phenotype ratio for dihybrid (double heterozygote) cross for expected unlinked ratio
- 9 dom/dom
- 3 dom/rec
- 3 rec/dom
- 1 rec/rec
if actual ratio does not match unlinked expected ratio
- then the genes are linked
double heterozygote back crossed with homozygous recessive
- 1 dom/dom
- 1 dom/red
- 1 rec/dom
- 1 rec/rec
which are the recombinants?
- the dom/rec and the rec/dom
