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Unit 5 Heredity Cheat Sheet by

ap bio unit 5 Heredity

Haploids vs. Diploids

Diploid cell
2n, two sets of chromo­somes
Haploid Cell
n, one set of chromosome
homologous chromo­somes
duplicate versions of each chromo­some, essence of sexual reprod­uction: each parent donates half its chromo­somes to its offspring.
*sex cells are haploid cells.
The position of a gene on a chromosome is called a locus.
Diploid organisms
alleles: two gene copies may be different from one another.
Homozygous: two identical alleles for a given trait
Hetero­zygous: two different alleles for a given trait
Non Mendelian Genetics
Linked Genes
when genes on the same chromosome stay together during assortment and move as a group. (ex: flower color and pollen shape show up together)
cannot segregate indepe­nde­ntly, violating Law of Indepe­ndent Assort­ment.
in the unlinked, there are four (TG, Tg, tG, tg), in the linked, there are only two (Tg and tG).
If a crossover event occurs between linked genes, then recomb­inant gametes can occur, however, it's unlikely to occur.
if certain combin­ations of alleles are found more often in offspring than they should, probably the two genes are close together and linked.
offspring formed from recomb­ination events
frequency of crossi­ng-over between any two linked alleles is propor­tional to the distance between them, he farther apart two linked alleles are on a chromo­some.
Sex-li­nke­d/X­-linked traits
Some traits, such as color blindness and hemophilia, are carried on sex chromo­somes.
most are found on the X chromosome
A female with one color blind-X is called a carrier
Barr Body
X chromosome that is condensed and visible. In every female cell, one X chromosome is activated and the other X chromosome is deacti­vated during embryonic develo­pment.
Incomplete dominance (blending inheri­tance
Traits are blend.
equal expression of both alleles.
Polygenic inheri­tance
a trait results from the intera­ction of many genes (height, skin color, weight)
Non-nu­clear inheri­tance
genetic material not from nucleus, but from mitoch­ondria or chloro­plast. mitoch­ondrial inheri­tance is always through the matern­al(­female) line, not the male line.
Traits that skip genera­tions are usually recessive. Traits that appear more in one sex than the other are usually sex-li­nked.
Phenotypic plasticity
two indivi­duals with the same genotype have different phenotypes because they are in different enviro­nments


production of gametes, only sex cells, female gamete (n) + male gamete (n) = zygote (2n)
more variations in a popula­tion, more likely survive extreme changes in the enviro­nment.
Meiosis is far more likely to produce these sorts of variations than is mitosis
same as miosis
Meiosis I
the homologous chromosome pairs separate
Prophase I
synapsis: two sets of chromo­somes that come together to form a tetrad, then crossing over(exchange of segments) - genetic variaion
Metaphase I
line up. the alignment during metaphase is random, so the copy of each chromosome that ends up in a daughter cell is random.
Anaphase I
moves to opposite poles.
Telophase I
nuclear membrane forms around each set of chromo­somes.
Meiosis II
to separate sister chroma­tids, same as mitosis
Meiotic Errors
chromo­somes failed to separate properly during meiosis. can occur in anaphase I (meaning chromo­somes don’t separate when they should), or in anaphase II (meaning chromatids don’t separate).
occurs when a segment of a chromosome moves to another nonhom­ologous chromo­some.


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