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BIO152H5 Study Guide - Final Guide: Genetic Disorder, Fundamental Theorem Of Arithmetic, Y Chromosome

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Fiona Rawle
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BIO 152 Fall 2014 Final Exam Study Guide: Chapter 15
Chapter 15: Chromosomes
1. Describe how Mendelian inheritance has its physical basis in the behavior of chromosomes.
Chromosome theory of inheritance states:
oMendelian genes have specific loci/ positions on chromosomes
oChromosomes undergo segregation and independent assortment
2. Describe the unique patterns of inheritance that are exhibited by sex-linked genes.
The chromosomal basis of sex:
oHumans and other mammals have two varieties of sex chromosomes, larger X and
smaller Y
oOnly ends of Y have regions homologous with corresponding regions of X
oSRY gene on Y chromosome codes for a protein that directs development of male
anatomical features
Human sex chromosomes:
oFemales are XX and males are XY
oOvum contains an X chromosome while sperm can contain either X or Y
oOther animals have different methods of sex determinations
Genes on sex chromosomes:
oGene located on either sex chromosome called sex-linked gene
oGenes on y chromosome are Y-linked genes (few of these)
oGenes on X chromosome are X-linked genes
Inheritance of X-linked genes:
oX chromosome has genes for many characters unrelated to sex while Y mainly
encodes genes related to sex determination
oX linked genes follow specific patterns of inheritance
oFor recessive x linked trait to be expressed, females need two copies of allele
(homozygous) and males only need one copy of allele (hemizygous)
oTransmission of X-linked recessive traits: X linked recessive disorders more common
in males than females
oX inactivation in female mammals:
One of two X chromosomes in each cell randomly inactivated during
embryonic development
This inactive X condenses into a Barr body
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