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X-Linked and Autosomal Gene
Polygenic (Quantitative) Inheritance
Organelle genes (Cytoplasmic inheritance)
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4 individuals in an
ascus- meiotic division is over
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Quantitative genetics involves the study of quantitative traits- ones that you
need to measure and then quantify the trait of interest
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Major genes- have a large or major effect on genotypes
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Numerous genes affect a trait
so they may be independently assorted
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Polygenes- Traits - genes sorted independently, however the environment
also plays a role in the trait produced
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Galton and his group of scientists studied quantitative inheritance- traits that
you have to measure whereas mendel studied easy traits
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Lets imagine we follow
height [n
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It is a measured value
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You give up studying individual phenotypes and
instead you study collective variation- how much of the variation is due to
genes?
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People

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This way they can genetically map the location of the polygenes
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You can also
get an estimate of the contribution of each gene for that particular trait
(effect sizes)
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With
molecular markers you can map genes and chromosomes to see where
the genes occur and the magnitude of their effects
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Organelle genes (Cytoplasmic inheritance)
• Mitochondria have their own genomes and so do chloroplasts
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Mitochondria will have one in circular copy
but will have numerous copies of that circular copy of the genome that is
identical to each other
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Here, when cells divide there is no process that guarantees that half of
the genes of the genome go to one cell and one to another
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It’s the same thing with
chloroplasts- each chloroplast has many copies of the same circular
genome
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Many of these genes that are necessary for mitochondrial
function are in the nucleus or in the genome
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Many work on the chloroplast genome but some come in as
proteins
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• The method of recognizing this was due to reciprocal crosses
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• Cytoplasmic because the female contributes a lot more cytoplasm than the
sperm does
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So in animals,
humans, you have mitochondria of your mother
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If you’re a male you will not
pass on your mitochondria to anyone
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• In plants however you could have maternal inheritance of chloroplasts- most
of them
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• Some plants show bi-parental inheritance
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