BIOL 110 Lecture Notes - Lecture 17: Allosome, Color Blindness, Y Chromosome

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19 Oct 2015
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BIOL 110 - Lecture 17 - Chromosome Behavior and Sex Chromosomes
Linking Genes and Chromosomes
Wild-type - the phenotype that is prevalent in natural populations
Mutant - a phenotype that is not prevalent in natural populations
In Drosophila, fruit flies,, red eyes are the wild-type
The proper nomenclature used by Drosophila geneticists is to name a gene for a
particular character by naming it for the first mutant phenotype discovered, and to
use that same letter with the superscript + to indicate the wild-type
Ex: Curly wings is symbolized by Cy, and straight wings are identified as
Cy+
Sex-linked Genes and Sex Chromosomes
Sex chromosomes - this refers to the X and Y chromosomes because they are involved
in determining sex of an individual
Sex-linked genes - genes that are located on the x and Y chromosomes
Autosomes - this refers to all other chromosomes in the cell than sex chromosomes
Ex: Color blindness is a sex-linked gene in humans
The genes for red and green color perception are x-linked with mutations that are
recessive
Color blindness affects males more than females
Ex: Hemophilia is a sex-linked genes in humans
Hemophiliacs lack a protein involved in blood clotting and thus may bleed
profusely from even slight abrasions
Has relatively high frequency in many royal houses of Europe
Thought to have began from a spontaneous mutation in one of Queen
Victoria’s parents in the 1800’s
Sex Determination
There are several different systems for determining
The X-Y system is used for sex determination in humans
During meiosis, the two X chromosomes found in females or the X and Y
chromosomes found in males will pair together
Little crossing over occurs due to the small region of homology
The resultant offspring will be female if an ovum with an X chromosome and a
sperm with an X chromosome undergo fertilization (XX)
The resultant offspring will be male if an ovum with an X chromosome and a
sperm with a Y chromosome undergo fertilization (XY)
It appears that a gene (or genes) on Y chromosomes may provide a
biochemical signal that initiates male sexual development
The X-O system is used to determine the sex of some insects
Females have two copies of the X chromosomes
Males only have one copy of the X chromosome
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Document Summary

Biol 110 - lecture 17 - chromosome behavior and sex chromosomes. Wild-type - the phenotype that is prevalent in natural populations. Mutant - a phenotype that is not prevalent in natural populations. In drosophila, fruit flies,, red eyes are the wild-type. Ex: curly wings is symbolized by cy, and straight wings are identified as. Sex chromosomes - this refers to the x and y chromosomes because they are involved in determining sex of an individual. Sex-linked genes - genes that are located on the x and y chromosomes. Autosomes - this refers to all other chromosomes in the cell than sex chromosomes. Ex: color blindness is a sex-linked gene in humans. The genes for red and green color perception are x-linked with mutations that are recessive. Color blindness affects males more than females. Ex: hemophilia is a sex-linked genes in humans. Hemophiliacs lack a protein involved in blood clotting and thus may bleed profusely from even slight abrasions.

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