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31 Cards in this Set
- Front
- Back
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Define karyotype |
the number and visual appearance of the chromosomes in the cell nuclei of an organism or species including length, the position of the centromeres,staining pattern, any differences between the sex chromosomes, and any otherphysical characteristics. |
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Define chromosome |
a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes. |
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Define sex chromosome |
a chromosome involved with determining the sex of an organism, typically one of two kinds. |
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Define X-chromosome |
(in humans and other mammals) a sex chromosome, two of which are normally present in female cells (designated XX) and only one in male cells (designated XY). |
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Define Y-chromosome |
(in humans and other mammals) a sex chromosome that is normally present only in male cells, which are designated XY. |
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Define Autosome |
any chromosome that is not a sex chromosome. |
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Define homogametic |
denoting the sex that has sex chromosomes that do not differ in morphology, resulting in only one kind of gamete, e.g., (in mammals) the female and (in birds) the male.
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Define Heterogametic |
denoting the sex that has sex chromosomes that differ in morphology, resulting in two different kinds of gamete, e.g., (in mammals) the male and (in birds) the female |
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Define SRY Gene |
a sex-determining gene on the Y chromosome in mammals that determines maleness and is essential for development of the testes. |
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Define Hemizygous |
having or characterized by one or more genes (as in a genetic deficiency or in an X chromosome paired with a Y chromosome) that have no allelic counterparts. |
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Define Dosage Compensation |
the equalization of gene expression between the males and females of a species. Because sex chromosomes contain different numbers of genes, different species of organisms have developed different mechanisms to cope with this inequality; thus organisms instead equalize the expression from each gene. |
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Define Barr body |
a small, densely staining structure in the cell nuclei of female mammals, consisting of a condensed, inactive X chromosome. It is regarded as diagnostic of genetic femaleness. |
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Define lyonization |
a process by which one of the two copies of the X chromosome present in female mammals is inactivated. The inactive X chromosome is silenced by its being packaged in such a way that it has a transcriptionally inactive structure called heterochromatin. |
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Define nondisjunction |
the failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei. |
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Define Turner Syndrome |
A chromosomal disorder in which a female is born with only one X chromosome |
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Define Klinefelter syndrome |
A genetic condition in which a male is born with an extra copy of the X chromosome |
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Define triple X syndrome |
An abnormality resulting in an extra X chromosome in some females. |
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Define sex-influenced |
denoting an autosomal trait that is expressed differently, either in frequency or degree, in males and females, as for example,male-pattern baldness. |
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Define sex-limited |
affecting individuals of one sex onl |
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Are there genes other than those determining sex found on the sex chromosomes? |
*Yes |
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Describe how the X and Y chromosomes can be considered “homologous” despite NOThaving the same order and type of genes |
Even though X and Y chromosomes contain different genes, they have regions that are similar enough to lead to proper pairing during prophase of meiosis I. |
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Identify karyotypes of Turner, Klinefelter and Triple X syndromes. |
Turner: X Klinefelter: XXY Triple X: XXX |
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Describe the Y-mechanism of sex inheritance. |
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Why do sex-linked recessive traits appear more often in females than in males? |
Because males only have one X chromosome |
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What is a Barr body? |
the inactive X chromosome in a female somatic cell, rendered inactive in a process called lyonization, in those species in which sex is determined by the presence of the Y (including humans) or W chromosome rather than the diploidy of the X or Z. |
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Describe the 3 step process of lyonization |
5 |
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Explain how lyonization relates to dosage compensation |
Lyonization is necessary for “dosage compensation” which serves to equalize the phenotypicexpression of characteristics determined by genes on sex chromosomes |
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Distinguish between homozygous, heterozygous and hemizygous. |
A cell is said to be homozygous for a particular gene when identical alleles of the gene are present on both homologous chromosomes. A diploid organism is heterozygous at a gene locus when its cells contain two different alleles of a gene. A chromosome in a diploid organism is hemizygous when only one copy is present. |
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Distinguish between the heterogametic and homogametic sexes |
Heterogametic sex (digametic sex) refers to the sex of a species in which the sex chromosomes are not the same. For example, in humans, males, with an X and a Y sex chromosome, would be referred to as the heterogametic sex, and females having two X sex chromosomes would be referred to as the homogametic sex. |
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Why are alterations in chromosome number better tolerated for sex chromosomes? |
The Y chromosome carries very few genes, and dosage compensation ensures that only one copy of the X chromosome is active in the cell |
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Distinguish between sex-influenced and sex-limited traits. |
The genes of Sex influenced traits are present in autosomes; the trait is dominant in one sex and and recessive in other.(ex baldness which is dominant in males). The genes of sex limited traits are present on y chromosomes. So they are limited to only one sex (ie males) |
