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AP Bio Unit 5: Heredity Cheat Sheet by

AP Bio Unit 5: Heredity


altern­ative forms of a gene found on the same locus on a chromosome


2 identical alleles
BB (homoz­ygous dominant)
bb (homoz­ygous recessive)

Law of Segreg­ation (Random Fertil­iza­tion)

two copies of each hereditary factor (allele) segregate
offspring acquire one factor from each parent

Crossing Over

the reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis


blood groups
both alleles are expressed in the hetero­zygote
neither is dominant or recessive, but there is no blending

Pedigree Analysis

pedigree: family tree
males: squares
females: circles
shaded: showing exhibited trait
half shaded: carrier

Nature vs. Nurture

nature: geneti­cally determined
nurture: enviro­nme­ntally determined

Genes Inherited Located on Sex Chromo­somes

in humans:
~ females: XX
~ males: XY
examples of sex linked disorders:
~ duchenne muscular dystrophy
~ hemophilia
~ colorb­lin­dness

Calculate Recomb­ination Frequency

if RF is >50%, the traits are considered to be indepe­ndently assorted and on DIFFERENT chromo­somes
if RF is <50%, the traits are on the SAME chromosome (any variants from the parent type are due to crossing over)

Asexual Reprod­uction

two identical cells

Examples of Asexual Reprod­uction

Fission: bacteria
Fragme­nta­tion: starfish
Budding: coral


haploid: cells that contain a single set of chromo­somes in an egg or sperm cell (23 gametes)
diploid: two complete sets of chromo­somes (46 somatic)
triploid: Extra set of chromo­somes (69 chromo­somes)

Why are triploid plants seedless?

3 sets of chromo­somes make it very unlikely for meiosis to succes­sfully produce spores and gameto­phytes. Uneven number of chromo­somes that won’t pair correctly

Meiosis Results

4 haploid cells
not geneti­cally identical

Mitosis vs. Meiosis

~ prophase, metaphase, anaphase, telophase (pmat)
~ cell division
~ cytoki­nesis: complete division of cytopl­asmic contents
~ mitosis: single set of divisions
~ meiosis: two divisions
~ mitosis: production of 2n cells
~ meiosis: production of 1 n cells
~ mitosis: production of 2 cells
~ meiosis: production of 4 cells

Vertical Gene Transfer

parent to daughter cell


a trait is expressed when dominant allele is present
capital letter (B)


one dominant and one recessive allele
aka hybrids or carriers

Law of Indepe­ndent Assortment

hereditary factors (alleles) assort into gametes indepe­ndently from one another (every combin­ation)

Genetic Variation

crossing over
indepe­ndent assortment
random fertil­ization


different genes can interact to control the phenotypic expression of a single trait
nonallelic genes affect one another

Test Cross Image

X-Inac­tiv­ation in Females

barr bodies
DNA methyl­ation

Gene Linkage (Linked Genes)

genes that are on the same chromosome
usually linked genes will be inherited together (unless separated by crossing over)
exhibit recomb­ination freque­ncies less than 50%

Recomb­ination Frequency Equation (x100%)

Sexual Reprod­uction

gametes (sperm and egg)
two parents

Examples of Sexual Reprod­uction

internal fertil­iza­tion: humans, sharks, turtles
external fertil­iza­tion: frogs, many fish
hermap­hro­dites: most worms, flowering plants
pollin­ation: flowers


reduces the chromosome number
1) Interphase I
2) Prophase I
~ synapsis: the lining up of homologous chromo­somes
~ chiasma: exchange of genes between non sister chromatids
~ crossing over: results in recomb­ination of genes so they assort indepe­ndently
3) Metaphase I
~ lining up of homologous chromo­somes
4) Anaphase I
~ indepe­ndent assortment
5) Telophase I and Cytoki­nesis I
6) Prophase II
7) Metaphase II
8) Anaphase II
9) Telophase II and Cytoki­nesis II

Nondis­jun­ction in Meiosis 1(left) and 2(right)

Horizontal Gene Transfer

donor to recipient cell
transf­orm­ation (uptake of external DNA (plasmid))
transd­uction (virus -> bacteria)
conjug­ation (bacteria -> bacteria)


a trait is masked in the presence of a dominant allele
lower case letter (b)


physical charac­ter­istic of a trait
color, size


genetic makeup of the chromosome
letters (B, b, G, g)

Incomplete Dominance

neither allele is completely dominant
hybrids are in between the homozygous traits

Polygenic Inheri­tance

mode of inheri­tance in which additive effects of two or more genes determines a single trait
quanti­tative characters that vary in degree
AABBCC: dark
aabbcc: light


Dominant disorders:
~ anchon­dra­plasia (dwarfism)
~ huntin­gton's (late acting lethals)
Recessive disorders:
~ cystic fibrosis
~ tay-sachs
~ sickle cell

Barr Bodies Image

Calculate Chi Square

if we accept the null hypothesis (1:1:1:1), then the genes indepe­ndently assort on DIFFERENT chromo­somes
if we reject the null hypothesis (1:1:1:1), then the genes are on the SAME chromosome

Asexual vs. Sexual Reprod­uction

do not have to find a mate or expend energy to find a mate
not much genetic variation
genetic variation
must find a mate and expend energy to find and/or court a mate

Meiosis Image

Crossing Over Image

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