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4) Gene/chromosome

Biology Revision 2

QuestionAnswer
Explain what happens when 2 chromosomes are too close together? When they're too close together, they may not often get separated during crossover in meiosis. They're linked. See diagram in notebook
What is a recombinants and a non-recombinant? Recombinant contains a new combination of genetic elements while non-recombinant contains the parents sequences of genetic elements. See example in notebook.
What is linkage map? It's contructed from measuring the frequency of crossing over between homologous chromosomes., so shows order and relative distance of the genes on the chromosome.
Name a few examples of sex determination Drosophilia , Y chromo doesn't determine maleness, it's # of X's. In alligators, hot/cold=female, in between=male. Most mammals, Y chromo-»SRY-»Testis determining factor-»testits develops-»Either testosterone and male develops, or anti mullerian hormone
What is a Barr Body? It's the inactive X chromosome in the female somatic cell
Why does one X chromosome becomes inactive? So that only the necessary amount of genetic information is expressed, rather than the double or more. In short, the amount of X chromosome genes expressed must be equal in males and females.
What is non-disjunction? It refers to the chromosome failing to separate correctly, resulting in gametes with one extra or one missing chromosomes.
How can a chromosome fail to separate and cause non-disjunction? 1)Failure of homologues to separate in anaphase 1 (resulting in 4 affected daughter cells) 2)Failure of sister chromatids to separate in anaphase 2 (resulting in 2 daughter cells affected). See diagram in notebook
When does n+1, n-1 and n happens? n+1 and n-1 for the 4 daughter cells in anaphase 1 (2 of each), n+1, n-1, n and n for anaphase 2. See notebook!
Give the 3 examples of non-disjunction associated with sperm. 1) XXY male zygote with klinefelter's disease 2)XXX female zygote with Trisomy X syndrome 3) XO femlae zygote with Turner's syndrome. Seee notebook.
Give the 5 examples of non-disjunction associated with the egg. 1)XXY=male zygote with klinefelter's syndrome 2)XYY= male zygote with Jacob's syndrome 3)XXX=female zygote with Trisomy X syndrome 4)YO=doesn't developp 5)XO=femlae zygote with turner's syndrome
Explain the increased risk of chromosomal abnomalities with older parents, why? The chances of disfunction increase with the age of the parents, especially the maternal age. This may be due to developping oocytes being arrested in prophase 1 until ovulation as part of the process of oogenesis.
What is ammiocentesis and CVS? Both are prenatal disagnotic procedures that are performed to detect fetal abnormalities.
What's the difference between ammiocentesis and CVS? Chorionic villus sampling (CVS) uses a needle to biopsy PLACENTA CELLS that are derived from the same fertilised egg as the fetus. Process= several hours. Ammiocentesis takes a small sample of the AMMIOTIC FLUID that surroinds the fetus. Several weeks
Created by: Malayka
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