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26 Cards in this Set

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  • Back
What is the function of meiosis?
To produce cells with half the normal chromosome number.
What is the process of meiosis called in males? females?
In males it is spermatogenisis, in females it is oogenisis.
How do identical twins result?
When the cells at step 1 seperate and each develop into a seperate individual. They have identical DNA.
How do conjoined twins result?
There is an incomplete seperation of the zygote into 2 embryos, so they share some organs.
How do fraternal twins result?
When a woman releases 2 eggs at the same time and they both are fertilized. No more alike than brother an sister.
What is a monozygotic twin?
identical twin
What is a dizygotic twin?
fraternal twin
What is the human haploid number?
What is the law of independant assortment?
Random assortment of pairs of homologous chromosomes seperate into gametes inependently of other pairs.
What is crossing over?
During synapsis of prophase parts of chromosome strands exchange between homologous pairs.
What is genetic recombination?
Genes occuring together in new combinations.
What is the purpose of random assortment and crossing over?
To increase variation... natural selection.
What occurs in prophase I?
- homologous chromosomes pair up to form a tetrad
- crossing over
What happens in metaphase I?
- homologous chromosomes line up in pairs along the equator.
What happens in anaphase I?
- homologous chromosomes seperate (centromere intact)
What happens in anaphase II?
Sister chromatids seperate (centromere splits)
What happens in telophase II?
4 non-identical haploid cells are created.
What is nondisjunction?
2 homologous chromosomes move to the same poles.
Why is nondisjunction serious in embryos?
It can result in gametes having either 47 or 45 chromosomes.
What is trisomy?
3 copies of one chromosome.
What is monosomy?
Only one copy of one chromosome.
What is trisomy 21?
Down's syndrome, mentally deficient, large tongue, forehead
What is turner's syndrome?
X0, females don't develop sexually, thick-wide necks, most miscarried.
What is klinefelter's syndrome?
XXY, male at birth but develop female hormones and characteristics, sterile.
What is amniocentesis?
Withdrawal of amniotic fluid which containes fetal cells... then possible to karyotype for disease.
What is CVS?
(chorionic villus sampling) - withdrawing cells from the outside of the embryo as early as 8 weeks.