Exam 2 Genetics
Chapter 7
Nondisjunction in meiosis – can cause XXX Syndrome or XYY Condition
47 XYY – famous
o There’s this idea that there is an over representation of XYY of men in prison
o Some people think that people with XYY are more likely to become criminals or
get put ...
Exam 2 Genetics Chapter 7
Nondisjunction in meiosis – can cause XXX Syndrome or XYY Condition
47 XYY – famous
oThere’s this idea that there is an over representation of XYY of men in prison
oSome people think that people with XYY are more likely to become criminals or get put in jail
oAbove average in height and below average in intelligence Sex determination oAt 5 or 6 weeks there is a potential for the fetus to get a Y chromosome and become a male PAR: pseudoautosomal region
SRY: sex-determining region Y
MSY: male-specific region of the Y
Primary sex ratio: ratio of males and females conceived
Secondary sex ratio: ratio of males to females actually born
Barr Body: an inactivated X chromosome
The Lyon Hypothesis: oX inactivation: occurs at random in human cells, it will turn into a Barr Body
All females are genetic mosaics depending on what they are expressing
Methylation: if methyl groups are attached to nucleotides in DNA, that shuts down gene expression oXIC – X-inactivation center
XIST – X-Inactive Specific Transcript The Ratio of X Chromosomes to Sets of Autosomes Determines Sex in Drosophila
Dosage Compensation in Drosophila
The X chromosome in males is turned up in expression
oInduce higher levels of gene expression and transcription
Bilateral gynandromorph – left half is male, right half is female
Right after fertilization, there were two x chromosomes, one with wild type eye color and wild type wings, the other side had normal eye color and normal wings
Everything on right side is female cause of two Xs
Everything on left is going to be male
oHas the two mutant alleles Temperature Variation Controls Sex Determination in Reptiles
Different temperature profiles for different species and sexes
CHAPTER 8
Variation in the Number of Chromosomes Results from Nondisjunction
Monosomy and Trisomy Results in a Variety of Phenotypic Effects
Turner syndrome
Partial Monosomy in Humans
oCri-du-Chat Syndrome – karyotype can be described as 46, 5p- There is a deletion on the p arm on chromosome 5Exam 2 genetics portage learning 2023 complete study guide This can be a described as a partial monosomy
Intellectual disability, microcephaly
oNot going to find true monosomy’s in humans because they cannot survive Trisomy involves the addition of a chromosome to a diploid genome
Plants can tolerate this situation better than animals Most monosomy’s and trisomy’s are going to be lethal
A trisomy in theory and reality can be passed on
Down Syndrome: 47, 21+
oAn extra copy of chromosome 21
o47 – number of chromosomes
oThe severity can vary from person to person
oIf mom is 50 or so, the odds of giving birth to a child with down syndrome increases largely
oNondisjunction is occurring in mom
oLife expectancy is lower than someone without down syndrome
Variability in Human Aneuploidy
oUp to 30% of all fertilized eggs from all spontaneous abortions in humans may contain an error in chromosome number o45,X has one of the highest incidence rates among abortuses. Also, about 80% of 45,X have the maternal X
Polyploidy, in Which More Than Two Haploid Sets of Chromosomes Are Present, Is Prevalent in Plants
Two sperm can fertilize a single egg and result in a triploid organism
Tetra gametic chimerism – there can be two eggs fertilized and can fuse together but not
fusion of the nuclei
oYou can get an embryo that is two fused embryos
oThey should have been twins but fused together to become one person
oTwo different genomes o4 gametes – 2 eggs, 2 sperms, 2 embryos come together to form one person
Auto polyploidy – more copies of that individuals genome
Allopolyploidy – take two species and make a hybrid of them
oIndividual with two different genomes, but they are very closely related Endopolyploidy – some cells are diploid and some are polyploidy
Variation Occurs in the Internal Composition and Arrangement of Chromosomes
Deletion – part of the chromosome is missing Duplication – extra copies of chromosomes If deletion and duplication are big enough, you can see them in a karyotype Inversions – flip around one or two chromosomes Translocations – where pieces of nonhomologous chromosomes move from one chromosome to another oNot normal for nonhomologous chromosomes to exchange with another Nonreciprocal translocation Alternate segregation – when two opposite chromosomes segregateExam 2 genetics portage learning 2023 complete study guide
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