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Unit 5: Heredity


Sexual Life Cycle: alteration of halving and doubling chromosome count in each generation
Meiosis: halving chromosome count in testes and ovaries to make sperm and egg, makes germline cells (all about halving chromosomes and creating variation)
Fertilization: doubling chromosome count, sperm meets egg, creates a zygote
Every single life cycle contains both of these events
but only applies to organisms that reproduce sexually with male and female, not asexuals who require only mitosis (no variation, with redwoods or hydras) without a mate, so without mutation there is no evolution. Asexual reproduction keeps species going without available mates
Haploid (n): cells with half of the number of chromosomes (sperm and egg/ova)
Gametes: sperm and egg created thru meiosis
Diploid (2n): cells with two sets of chromosomes
Number of chromosomes varies per species
Somatic Cells: (normal) body cells, that have 46 chromosomes, half from mom half from dad, really 23 pairs of chromosomes
Each pair is a homologous pair, NOT sister chromatids, each chromosome is duplicated, two sister chromatids on either side of the X held together by a centromere. Homologous means they have the same genes located in the same regions not necessarily the same versions of the genes
Allele: different versions of the same gene
Locus (loci): exact location of a gene on a chromosome
Karyotype: picture showing 23 pairs of chromosomes (only visible in mitosis because of condensing)
Autosomal pairs (22): all of the genes for normal traits
Sex chromosomes (23rd): XY male and XX female
What changes for organisms to organism, one or the other, either diploid or haploid stage is dominant
Animals are mainly diploid because their body cells are somatic and not germline
Fungi usually haploid with only one set of chromosomes, can’t cut one set of chromosomes in half so they do not have meiosis use mitosis is reproduce asexually to make haploid spores (like a gamete but do not fertilize each other) spores find a good environment and grow into a new fungus (everything is haploid and no variation)
However, if two fungi come into contact, they will fertilize each other to produce a zygote, and then goes thru meiosis to produce more haploids for variation (evolution)
Plant Life Cycle:both haploid and diploid split equally there is no dominant stage, for every species of plant there is a haploid and diploid form of that plant
Alternation of generations: one gen is haploid and the next may be diploid, it flips every gen
Sporophyte:diploid (2n) generation of a plant, (e.g. ferns that we usually see), goes through meiosis next → produces haploid (n) spores
Gametophyte: spores grow into a haploid (n) generation, produces GAMETES BUT THRU MITOSIS (sperm + egg) that create a zygote to reenter the sporophyte stage: haploid egg + haploid sperm = diploid plant

Meiosis I: chromosome number is cut in half
Two types of meiosis: I and II
Only germline cells go thru mitosis (ovum and sperm) but ova are already produced at birth, whereas sperm is produced all thru a male’s lifetime
Prophase I: mitotic chromosomes form, nuclear envelope disappears, spindle fibers reach out (e.g. four total chromosomes and 2 homologous pairs)
Homologous pairs have the same gene in the same place (locus) one from dad and one from mom
Tetrads: homologous pairs come together (4 sister chromatids) during PROPHASE I
Chiasma: where the homologous pairs overlap, the pairs exchange pieces of chromosomes, through crossing over important to create genetic variation
The areas that cross over are completely random
Metaphase I: tetrads line up on the equator of the cell using spindle fibers, not like mitosis, they line up in their homologous pairs, but in mitosis has the chromosomes lined up single file not in pairs
Anaphase: cell splits in half
Meiosis I: 2n diploid parent splits to two n haploid daughters
Meiosis II: anaphase II the sister chromatids are pulled apart
End with four haploid variable gametes

Genetic recombination: put back together after mixing the genes “genetic lottery”
Crossing Over: in meiosis
Independent Assortment of Chromosomes:
Pairs that line up in metaphase determines the combination of chromosomes that end up in the gametes, completely random order of lining up
2# of homologous pairs=number of possible combinations(typically 8M combos)
Random Fertilization: random chance decides which sperm gets to each egg
Each sperm is 1/8M combos and each egg 1/8M combos, each person is 1/64 trillion combos, not even considering crossing over events
All new variation came about/created from mutation at some point, but a limited role in genetic variation, variation is about mixing up preexisting genes


Gregor Mendel: Austrian monk who is the father of modern day genetics
Worked with Pisum satium plant
Came up with laws of inheritance based off pea plant experiments
Characters: big overarching things (color, height, shape, etc.)
Trait: different form of a character (tall, short, blue, yellow)
Controlled which pea plants breed with other pea plants, or he self-pollinated and bred the pea plant with itself
Self-bred pea plants became purebred/true breeding, 100% the same organism without any variation
Mendel’s First Cross:
P generation: Parental generation, crossed a purebred purple with a purebred white plant
People used to believe in blending inheritance: traits are mixed so tall person mates with short person would equal a medium height baby
F1 generation: created only purple plants, traits didn’t blend, so it proves blending inheritance wrong
Hybrids: combination of two organisms, half-purple and half-white
F2 generation: bred purple hybrids and created 75% purple and 25% white flowers
Traits do not blend together
Traits can be hidden and come out in a later generation
Genotype: genetic makeup of an organism containing all of the alleles
Homozygous Dominant
Heterozygous (shows Dominance)
Homozygous Recessive
Phenotype: the physical appearance
If someone has a dominant phenotype, you cannot figure out the genotype, either AA or Aa
Dominant (heterozygous, homozygous dominant)
Recessive (homozygous recessive)
One allele cannot suppress another allele, every allele is always expressed
AA making correct proteins → dominant trait
Aa making enough correct proteins → dominant trait
aa making defective proteins → recessive trait
Don’t need two functioning alleles, only one is necessary
Laws of Segregation: for every character there are two different forms/versions called alleles (two different versions of a gene, but Mendel didn’t know that)
During formation of gametes, the two alleles for each character separate. (During anaphase)
Each gamete gets one of the alleles randomly
Homozygous: (same) two of the same allele are inherited
Heterozygous: (different) two different alleles are inherited
One allele will be expressed → dominant
One allele will not be expressed → recessive
Punnett square demonstrates that two alleles from one character (for example Aa) segregate and can match up with the other parent’s segregated alleles to make percentages of possible combinations
Genotypic Ratio: 1:2:1 if (AA, Aa, Aa, aa) homozygous dominant:heterozygous:homozygous recessive of the possible combinations
Phenotypic Ratio: 3:1 dominant(D):recessive(R) expressing of the possible combinations
For dihybrids, the ratio is D/D : D/R : R/D : R/R
Double Heterozygous (AaBb) x Double heterozygous = 9:3:3:1
Double Heterozygous x Double homozygous (aabb) = 4:4:4:4
Double Homozygous x Double homozygous = 0:0:0:16
Law of Independent Assortment: inheritance of one character doesn’t affect the inheritance of another character, each is inherited independently
Each pair of alleles segregates into gametes independently
E.g. brown hair doesn’t mean you’ll get brown eyes
Dihybrid Cross: a cross involving two characters to find all of the possible allele results (16 squares, there are also trihybrid crosses with 64 square and quadra hybrid crosses) (SEE PHOTO ON GOOGLE DRIVE)
Testcross: find out the unknown dominant allele that corresponds with the dominant phenotype of an organism
Cross the dominant organism with a homozygous recessive organism, if any of their offspring are recessive, then the dominant organism is heterozygous (Bb) because you need a recessive copy from this parent in order to have recessive (bb) offspring.
Rule of Multiplication: likelihood of multiple genetic events happening consecutively which depends on the individual likelihoods of each individual event.
E.g. have four male children in a row = 6.25% chance, because each child is a 50/50 chance, so ½ * ½ * ½ * ½ = 1/16
Complete Dominance: simple dominance, one allele is expressed over another allele BUT not all characters are completely dominant
Incomplete Dominance: one allele is not dominant over the other, you cannot use capital and lowercase letters (GREY OR PINK)
The heterozygote is an intermediate phenotype (sort of like blending == pink) half way between the two alleles
Codominance: both alleles are equally expressed (both red and white) it creates spots on organisms only thing that really exists at the level of the protein
BLOOD TYPES: use multiple alleles to decide type, but only inherit two alleles like normal
A allele (I^A)
B allele (I^B)
O allele (ii)
O is recessive to both A and B, but A and B are codominant
Type O: OO
Type A: AA, AO
Type B: BB, BO
Type AB: AB (codominance)
If you’re blood type A you have A antigens (glycoprotein MHCs) on blood cells, if you’re blood type B you have B antigens, if you are blood type AB you have both A and B antigens, and if you are type O then you have no antigens
You have antibodies that fight off foreign blood, if type A, you have B antibodies, if type B you have A antibodies, if you are type AB, you have no antibodies, bec. You would target your own cells with A or B antigens, and if you are blood type O you have A and B antigens
O is the universal donor because it has no antigens, cannot read blood type O as being foreign, AB is the universal receiver because it has no antibodies to detect and fight off foreign blood
RH Factor: important antigen another way to detect foreign blood, either positive (+) if you have it or negative (-) if you don’t
O negative is the real universal donor because it’s an extra antigen on cells
AB positive is the true universal receiver because it has no RH factor
RH factor is controlled by complete dominance you can only be RH negative if you’re are (nn, but if you’re Nn or NN) you’re positive
Do not need to have the same blood type as your parents
In reality the only type of dominance that exists at the molecular level is codominant (two different alleles, half of one protein and half of another)
Two characters control blood type, A/B/O and RH
Pleiotropy: when one gene has multiple phenotypic effects (most human genes are pleiotropic)
E.g. PKU, caused by a single gene, causes severe mental impairment and reduced skin pigmentation (gene involved in skin and in brain, does multiple things in the body) Most genetic diseases have multiple effects
Epistasis: when one gene directly affects another gene
E.g. one gene B/b in mice determines if fur coat is brown or black, another gene determines if B/b pigment is deposited in skin if homozygous recessive (cc) for second gene, B/b dominant or recessiveness doesn’t matter → creates albinism
Polygenic Inheritance: multiple genes work together to create a character
Quantitative Characters: characters that vary along a continuum, not caused by one gene, but caused by multiple genes that add up
E.g. three genes produce melanin, if you get two dominant alleles and one recessive, two genes are producing melanin, and one is producing nothing → determines skin color
Any human character that is polygenic, cannot be predicted (like eye color)
Norm of reactions: Environment plays a large role in converting genotype to phenotype, norm is the normal phenotype that goes with a genotype
But sometimes your environment can change your phenotype away from the original norm prescribed by the genotype
Some genes are not affected by the norm of reactions (environment plays no role)
E.g. affects height if you work out too much early on you stunt growth
Multifactorial Character:
E.g. hydrangeas color depends on pH of soil even though they have the same genotype, so color is considered multifactorial
Trait determined by the effects of multiple genes
Pedigree Analysis: information about the presence/absence of a particular phenotypic trait is collected from as many individuals in a family as possible and across generations.
Square is male, circle is female, painted in means they have that trait
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