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26 Cards in this Set
- Front
- Back
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What is the function of meiosis?
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To produce cells with half the normal chromosome number.
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What is the process of meiosis called in males? females?
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In males it is spermatogenisis, in females it is oogenisis.
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How do identical twins result?
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When the cells at step 1 seperate and each develop into a seperate individual. They have identical DNA.
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How do conjoined twins result?
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There is an incomplete seperation of the zygote into 2 embryos, so they share some organs.
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How do fraternal twins result?
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When a woman releases 2 eggs at the same time and they both are fertilized. No more alike than brother an sister.
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What is a monozygotic twin?
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identical twin
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What is a dizygotic twin?
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fraternal twin
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What is the human haploid number?
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23
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What is the law of independant assortment?
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Random assortment of pairs of homologous chromosomes seperate into gametes inependently of other pairs.
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What is crossing over?
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During synapsis of prophase parts of chromosome strands exchange between homologous pairs.
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What is genetic recombination?
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Genes occuring together in new combinations.
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What is the purpose of random assortment and crossing over?
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To increase variation... natural selection.
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What occurs in prophase I?
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- homologous chromosomes pair up to form a tetrad
- crossing over |
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What happens in metaphase I?
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- homologous chromosomes line up in pairs along the equator.
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What happens in anaphase I?
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- homologous chromosomes seperate (centromere intact)
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What happens in anaphase II?
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Sister chromatids seperate (centromere splits)
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What happens in telophase II?
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4 non-identical haploid cells are created.
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What is nondisjunction?
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2 homologous chromosomes move to the same poles.
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Why is nondisjunction serious in embryos?
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It can result in gametes having either 47 or 45 chromosomes.
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What is trisomy?
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3 copies of one chromosome.
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What is monosomy?
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Only one copy of one chromosome.
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What is trisomy 21?
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Down's syndrome, mentally deficient, large tongue, forehead
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What is turner's syndrome?
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X0, females don't develop sexually, thick-wide necks, most miscarried.
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What is klinefelter's syndrome?
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XXY, male at birth but develop female hormones and characteristics, sterile.
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What is amniocentesis?
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Withdrawal of amniotic fluid which containes fetal cells... then possible to karyotype for disease.
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What is CVS?
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(chorionic villus sampling) - withdrawing cells from the outside of the embryo as early as 8 weeks.
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