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Haploid
| What it's not: |
An unlucky person. |
| What it is: |
Haploids (in contrast to diploids) are cells that have a single set of chromosomes. Happily (and not haplessly) for us human beings who don’t want everyone to look the same, human gametes (sex cells: egg & sperm cells) are haploid, producing new combinations of alleles when they come together in tiny chance ecstasies. So, the two haploid sets come together to make up the diploid baby. (1+1=2). |
Heritability
| What it's not: |
An extreme variation of Irritability
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What it is:
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Heritability is how much of the variation
in a trait in a population is due to genes as compared to how much is
due to environment. If a trait has a high heritability it generally
means that genetic factors strongly influence the expression of the
trait, whereas environmental factors have less of an influence. If a
trait has a low heritability then environmental factors are important
influences in the expression of the trait and genes contribute a small
amount. For example, blood pressure has a reasonably high heritability
whereas the virus measles has a low heritability. One commonly used
way to estimate heritability is to do twin studies using monozygotic
(identical) and dizygotic (non-identical) twins. One important thing
to remember is it is the measure of variation within a population, not
within individuals.
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Heterozygous
| What it's not: |
Different types of no smoking meds (i.e. zybain) |
| What it is: |
This describes an individual who has two different alleles of the same gene. When one allele is dominant over the other, you would only see the phenotype of the dominant (stronger) allele. For example, brown eye colour is dominant over blue. When a person is heterozygous for eye colour and inherited a ‘brown gene’ and a ‘blue gene’, (s)he would have brown eyes. |
Homologous Genes
| What it's not: |
The latest style from Levi-Strauss that promise to reverse gravity/aging |
| What it is: |
Genes are homologous when, due to a shared ancestry, their sequences are significantly related.
Homology (try pronouncing that!) can be subdivided into orthology (between species) and parology (within species). For example, the various hemoglobins and myoglobin in muscles are classified as paralogous genes because an ancestral gene duplicated, creating different versions within this one species. And of course, if we were comparing a hemoglobin gene in chickens with one in humans, we would then be talking about orthologs– the same genes in two different species. |
Homozygous
| What it's not: |
A processed dairy product with approximately 4% milk fat |
| What it is: |
This refers to two copies of the same allele at a given locus on a pair of homologous chromosomes. This is important in recessive conditions where normally the recessive allele is covered up by the dominant allele and not shown in the phenotype. But when someone inherits two copies of the recessive allele, the recessive phenotype shows up. This can be seen in a trait as simple as eye colour. Until someone inherits two blue copies of the eye colour gene, those incredible blue eyes stay hidden below other colours.
The recessive phenotype can be important in disease as well. Until someone inherits two copies of the disease-causing recessive allele, they are only carriers and often show no ill effects. Some better known recessive disorders are cystic fibrosis, sickle cell anemia, and Tay Sachs. |
Hotspot
| What it's not: |
A place to access free wireless internet. |
| What it is: |
A sequence with a very high frequency of recombination (recombination hotspot) or mutation (mutation hotspot). |
Housekeeping Gene
| What it's not: |
Source of the deep-seated urge to own property. |
| What it is: |
A gene whose product is essential for most cells. For example, anything needed for RNA transcription or DNA replication. |
Human Genome Project
| What it's not: |
A progressive rock band from the mid
70's, known for driving instrumentals and soothing lyrics. |
What it is:
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The Human Genome Project was an international
effort to map and sequence all human genes. The project first began
in 1990 and was declared completed in 2003, although work continues
on certain aspects of the project. The motivation behind the project
was that sequencing and identifying all human genes would help us to
better understand genetic disorders and find ways to diagnose, treat
and perhaps prevent these conditions. The Human Genome website describes
the major goals of the project were to identify all of the approximately
25 000 genes in human DNA, to sequence the over 3 billion base pairs
that make up human DNA, to improve tools for analyzing this data, to
make the information available to public companies and to address ethical,
legal and social issues that may happen because of the project.
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Huntington’s Disease
| What it's not: |
The ailment afflicting hunters who have
been in the forest too long. |
What it is:
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Huntington’s disease is an inherited
brain disorder where there is a gradual loss of brain cells that cause
symptoms like movement and walking problems, personality changes and
intellectual decline. It is inherited in a dominant pattern which means
that an individual who has HD has a 50% (1/2) chance of passing the
faulty gene to their child and a 50% (1/2) chance of passing on the
normally functioning gene. All individuals with the faulty gene will
develop HD at some point in their life, usually between 30-50 years
of age but the age of onset can be variable. Unfortunately there is
no cure for Huntington’s although a lot of research is currently being
done in this area.
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