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Chapter 15: Chromosomal Basis of Inheritance - Biology E
Chapter 15: Chromosomal Basis of Inheritance - Biology E

... the nuclear envelope. Most of the genes of the X chromosome that forms the Barr body are not expressed. In the ovaries, Barr-body chromosomes are reactivated in the cells that give rise to eggs, so every female gamete has an active X. 15. X inactivation maintains the proper gene dosage. How is the X ...
Genetics Vocab – Unit 4
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... ● Gene Mutation - Permanent change in the DNA sequence that makes up a gene ● Nondisjunction - Failure of homologous chromosome or sister chromatids to separate properly during cell division ● Sex Chromosomes - A chromosome in the genome that is involved in the determination of the sex of the offsp ...
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... multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease • In epistasis, a gene at one locus alters the phenotypic expression of a gene at a second locus • For example, in mice and many other mammals, coat color depends on two genes • One gene determines the ...
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... trait that will only be expressed in the phenotype if two recessive alleles are present.  Represented by lowercase letters.  For example, a.  The genotype aa would express the recessive trait.  IN THE PRESENCE OF A DOMINANT TRAIT, THE RECESSIVE TRAIT WILL NOT BE EXPRESSED. ...
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... genome-wide inverse correlation between intron size and gene density. Gene density of a chromosome is defined as average number of genes per Mb. Extreme chromosomes are indicated. Chromosome 18 has the longest median intron length of all chromosomes. Note: In order to compare all human autosomes in ...
Sex Linked Genes - Malibu High School
Sex Linked Genes - Malibu High School

... corresponding genes on the Y chromosome in most cases. In women, a recessive allele on one X chromosome is often masked in their phenotype by a dominant normal allele on the other. This explains why women are frequently carriers of X-linked traits but more rarely have them expressed in their own phe ...
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... NOT Blending Hypothesis because … In northeast Minnesota there is a creature know as a wildcat. It comes in three colors, blue, red, and purple. This trait is controlled by a single locus gene with incomplete dominance. A homozygous (BB) individual is blue, a homozygous (bb) individual is red, and a ...
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Chapter 12
Chapter 12

... so it affects the offspring and not the parent organism b. somatic cell mutation-change is in an organism’s body cells will affect the organism but not the offspring ex; certain types of skin cancer, leukemia ...
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Skewed X-inactivation

Skewed X chromosome inactivation occurs when the inactivation of one X chromosome is favored over the other, leading to an uneven number of cells with each chromosome inactivated. It is usually defined as one allele being found on the active X chromosome in over 75% of cells, and extreme skewing is when over 90% of cells have inactivated the same X chromosome. It can be caused by primary nonrandom inactivation, either by chance due to a small cell pool or directed by genes, or caused by secondary nonrandom inactivation, which occurs by selection. Most females will have some levels of skewing. It is relatively common in adult females; around 35% of women have skewed ratio over 70:30, and 7% of women have an extreme skewed ratio of over 90:10. This is of medical significance due to the potential for the expression of disease genes present on the X chromosome that are normally not expressed due to random X inactivation. X chromosome inactivation occurs in females to provide dosage compensation between the sexes. If females kept both X chromosomes active they would have twice the number of active X genes than males, who only have one copy of the X chromosome. At approximately the time of implantation (see Implantation (human embryo), one of the two X chromosomes is randomly selected for inactivation. The cell undergoes transcriptional and epigenetic changes to ensure this inactivation is permanent. All progeny from these initial cells will maintain the inactivation of the same chromosome, resulting in a mosaic pattern of cells in females.
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