A mutation that leads to the absence or decreased biological activity of a particular protein
loss of function mutation
a mutation that confers a new property on a protein, causing a new phenotype. Examples include increased function, increased function on a new substrate for an enzyme, or expression in a new tissue.
gain of function mutation
in a species, the sex that has two types of sex chromosomes (eg X and Y) and therefore produces two kinds of gametes with respect to the sex chromosomes. In mammals, the male is like this.
Heterogametic Sex
In a species, the sex that has one type of sex chromosome, and therefore produces only one kind of gamete with respect to the sex chromosomes. In mammals, the female is like this.
Homogametic Sex
posessing only one copy (allele) of a gene in a diploid cell. usually applied to genes on the X chromosome in males with the XY genotype
Hemizygous
failure of homologues or sister chromatids to separate at anaphase
nondisjunction
condition in which the number of chromosomes differs from an exact multiple of the normal haploid number in a cell or organism. results from gain or loss of individual chromosomes, as well as dupilcation or deletion of parts of a chromosome
Aneuploidy
What is meant by an XO individual
An individual that inherited a single sex chromosome as a result of nondisjunction in one of the parents
system of sex determination found primarily in eukaryotic microorganisms in which sex is determined by different alleles at a small number of gene loci
Genic Sex Determination
system in which sex chromosomes play a decisive role in inheritance and determination of sex
Genotypic Sex Determination
What kind of animals use the Y chromosome mechanism of sex determination?
humans and other placental mammals
why is the testes determining factor important and on what chromosome is it found.
in the Y chromosome mechanism of sex determination, individuals with Y chromosome, and more specifically, with the protein "testes determining factor" switch towards male sexual differentiation.
what is different about the chromosomal composition of someone who has TURNER syndrome and what causes the problem?
Caused by parental nondisjunction, they are "45X females" containing only one sex chromosome
what is different about the chromosomal composition of someone who has KLINEFELTER syndrome and what causes the problem?
caused by parental nondisjunction, they are "47XXY males" containing three sex chromosomes, 2X and a Y.
What is dosage compensation?
any mechanism in organisms with genotypic sex determination for equalizing expression of genes on the sex chromosomes in males and females.
What would happen to a female without dosage compensation?
death early in development
what is a Barr body?
highly condensed and transcriptionally inactive X chromosome found in the nuclei of somatic cells of female mammals - formed by a process called "lyonization" after the researcher who discovered the process
What is the relationship between barr bodies and the number of X chromosomes an individual has?
(# of X chromosomes) - 1
True or False: lyonization of chromosomes allows extra sets of sex chromosomes to be tolerated well but extra autosomes are usually lethal
TRUE
What are the general characteristic of inheritance of X linked recessive inheritane?
1) X linked recessive traits occur much more frequently among males who are hemizygous
2) a female would express a recessive x linked trait only if she were homozygous recessive at that locus
3) affected fathers crossing with normal mothers result in 100% heterozygous carrier daughters, no affected sons, and father to son transmission of X linked alleles generally does not occur
4) affected homozygous recessive mothers crossed with normal fathers results in all sons showing the trait and all daughters carrying the trait
5) Carrier mothers crossed with normal fathers results in half of the sons affected and half of the sons free of the allele, half of the daughters carriers and half of the daughters free of the allele
What are the general characteristics of inheritance of X linked dominant inheritance?
1) patterns of inheritance are the same as Xlinked recessives except when heterozygous females show the trait
2) the trait is more common in females than males since they have 2Xs
3) heterozygous females X normal males = 1/2 sons and 1/2 daughters affected
4) normal female X affected male = no sons affected, and all daughters affected
what are the general characteristics of Y linked recessive inheritance
