Intro to Transmission Genetics
A look a the terms around inheritance and chromosomes.
A look a the terms around inheritance and chromosomes.
1/ Transmission Genetics is all about the study of how genetic information is passed from one generation
to the next. It is the study of how DNA gets copied and placed in Gametes for the purpose of reproduction.
to the next. It is the study of how DNA gets copied and placed in Gametes for the purpose of reproduction.
2/ It is study of the patterns of inheritance of traits from parents to children. With patterns of inheritance, we study of how a genetic disease can be passed from one generation to the next. Transmission genetics comes with a bunch of terms that we will have to go over.
3/ Our genetic information in encoded in linear segments of DNA called chromosomes. Each chromosome contains a specific part of the overall genetic information. We get 23 chromosomes from each of our parents for a total of 46.
4/ You get a chromosome 1 from your mother and a chromosome 1 from your father. They encode the exact same genes, but not exactly the same genetic information. These two same chromosomes are called a Homologous pair. The homologous pair contains the same genetic information.
5/ The first 22 chromosome pairs are called the autosomes. They are the same for every single person and encode all the same genes. The last pair (23rd pair) are the sex chromosomes. This determines the sex of the offspring.
6/ If both of the 23rd chromosomes are X chromosomes, the child is female. If it is 1 X and 1 Y chromosome for the 23rd pair, the child is male. The Y chromosome determines male as it encodes all the genes to create testes and testosterone which drives male characteristics.
7/ Males get 1 X and a Y chromosome. When they end up with a defective X chromosome, they have no spare to help them because the X and Y chromosomes encode different genes.. This leads to the some of the genetic disorders we hear about every day.
8/ Since females have 2 X chromosomes, one of them will be deactivated in the fetus. It happens early and
they end up with about 50% of their cells using 1 X chromosome and the other 50% using the other X
chromosome. This is called X chromosome inactivation.
they end up with about 50% of their cells using 1 X chromosome and the other 50% using the other X
chromosome. This is called X chromosome inactivation.
9/ This is done to keep the gene dosing correct since males have only 1 X chromosomes and females get 2. One of them gets inactivated in every cell to keep the level of genes produced equal in both males and females.
10/ The effects of X inactivation can be noticed by the remnant of the inactivated X chromosome which is called a barr body. They can be noticed in the neutrophils of the immune system.
11/ Each chromosome has a centromere that is the center of that chromosome. Not all centromeres are at
the exact center of the chromosome. It tends to vary with each chromosome. These centromeres play a
key role in cell division.
the exact center of the chromosome. It tends to vary with each chromosome. These centromeres play a
key role in cell division.
12/ This is where the sister chromatids will be linked together after DNA synthesis. Its also where the strands from the centrosomes bind to pull apart the sister chromatids during mitosis and meiosis.
13/ The ends of each chromosome has telomeres on them. They actually resemble the aglets on the ends
of your shoelaces. They play a key role in cell life cycles. Each time a cell replicates, the telomere gets
a little shorter.
of your shoelaces. They play a key role in cell life cycles. Each time a cell replicates, the telomere gets
a little shorter.
14/ Once the telomere reaches a certain limit, the cell will no longer be able to replicate any further. This is called the Hayflick Limit and leads to cell senescence of the cell. That means that cell will no longer divide. This limit leads to the effects of aging.
15/ Transmission genetics will be all about how these chromosomes are replicated, segregated, packaged and transferred to offspring. It will also get into genes and the variation of the information in those genes. We will look at these concepts next.
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