Meiosis Flashcards
what is the sexual life cycle of animals?
1) gamete formation (meiosis)
2) fertilization
3) growth (mitosis + development)
what is meiosis
- only function is to produce haploid gametes
- 2n cell -> 1n cells / diploid -> haploid
- daughter cells not identical to parent cells or each other
what is the human karyotype?
2n = 46
what are sex chromosomes?
XX (female), XY (male)
- X is bigger than Y
what are autosomes?
any chromosome that’s not a sex chromosome
what stage are the chromosomes in karyotypes at?
metaphase, has been duplicated and condensed
what are homologous chromosomes?
- at same position -> same gene
- may have different allele = alternative form of gene
what do gametes do?
vehicles that transmit genes
what is the locus?
a gene’s specific location along length of chromosome
what are the stages of meiosis?
interphase, meiosis I, meiosis II
what happens during interphase of meiosis?
pair of homologous chromosomes in diploid parent cell -> chromosomes are duplicated -> pair of duplicated homologous chromosomes, diploid cell with duplicated chromosomes
what happens during meiosis I?
homologous chromosomes separated, haploid cells in duplicated chromosomes
what happens during meiosis II?
sister chromatids are separated, haploid cells with unduplicated chromosomes
What are the origins of genetic variation among offspring?
- independent assortment of chromosomes
- crossing over
- random fertilization
- genetic variation is the raw material for evolution by natural selection.
what is nondisjunction?
mishap where members of a pair of homologous chromosomes don’t move apart properly during meiosis I or sister chromatids fail to separate in meiosis II, so one gamete receives 2 oof the same type of chromosome and another gamete receives no copy
what is aneuploidy?
zygote will also have an abnormal # of a particular chromosome, aneuploid is monosomic (2n-1) for that chromosome
- aneuploid cell is trisomic if chromosome is present in triplicate for zygote (2n+1)
what are the results of abnormal chromosome numbers?
nondisjunction, aneuploidy, polyploidy
what is polyploidy?
when organisms have more than 2 complete chromosome sets in all somatic cells
what are the results of alterations in chromosome structure?
deletion, duplication, inversion, translocation
what is deletion?
when a chromosomal fragment is lost so chromosome is missing certain genes
what is duplication?
when a broken fragment reattaches as an extra segment to a sister or nonsister chromatid
what is inversion?
when fragment reattaches to original chromosome but in reverse orientation
what is translocation?
when fragment joins nonhomologous chromosome
what are the human conditions due to chromosomal alterations?
- down syndrome (trisomy 21): extra chromosome 21, body has 47 total
- Klinefelter syndrome (XXY) and Turner syndrome (XO) due to aneuploidy of sex chromosome
- cri du chat (deletion of chromosome 5)
- chronic myelogenous leukemia (translocation-caused)
