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BIO Exam I - Stack 1

Meiosis and life cycles

Offspring acquire genes from parents by ___. inheriting chromosomes
___ and ___ alternate in sexual life cycles. Fertilization / meiosis
Meiosis ___ the number of chromosome sets from ___ to ___. reduces / diploid / haploid
___ produced in sexual life cycles contributes to evolution. Genetic variation
heredity (inheritance) the transmission of traits from one generation to the next
What is variation? Why is there variation among siblings? -Variation is differences between members of the same species. -Variation is due to crossing over and independent assortment.
genetics the scientific study of heredity and hereditary variation
gene a discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA; many different kinds
What are gametes and what do they have to do with heredity? -Gametes are reproductive cells that transmit genes from one generation to the next. -They are the vehicles that carry out heredity.
somatic cells -all cells of the body except for the gametes and their precursors -do not undergo meiosis -humans have 46 chromosomes in each somatic cell
chromosomal locus a gene's specific location along the length of a chromosome
asexual reproduction a single individual is the sole parent and passes copies of all its genes to its offspring without the fusion of gametes
sexual reproduction two parents give rise to offspring that have unique combinations of genes inherited from the two parents
clone a group of genetically identical individuals; the offspring produced by asexual reproduction
karyotype a display of the chromosome pairs of a cell arranged by size and shape
homologous chromosomes / "homologs" two chromosomes composing a pair that have the same length, centromere position, and staining pattern
What are autosomes? How many do humans have? -chromosomes that are not involved in determining sex -22 pairs, or 44
What are sex chromosomes? How many do humans have? -chromosomes that determine an individual's sex -1 pair, or 2 (XX or XY)
What is a diploid cell? What is the diploid number for humans? -any cell with two chromosome sets; has a diploid number of chromosomes abbreviated "2n" -46 (so, 2n=46)
What is a haploid cell? What is the haploid number for humans? -any cell with a single set of chromosomes; each has a haploid number of chromosomes abbreviated "n" -23 (so, n=23)
What is fertilization? What is the result of it? -the union of gametes (each haploid), culminating in the fusion of their nuclei -a fertilized egg, or zygote (diploid)
How are the sexual life cycles of animals, plants/algae, and fungi/protists similar? Different? -meiosis and fertilization alternate in all 3 -the cycles differ in the timing of meiosis and fertilization
synapsis when paired homologous chromosomes become physically connected to each other along their lengths (by a zipper-like protein structure, the synaptonemal complex)
chiasmata the x-shaped regions where crossing over has occurred between homologous nonsisiter chromatids; they become visible after synapsis
What is crossing over? Where does it occur? When does it begin? When does it end? -a genetic rearrangement between nonsister chromatids involving the exchange of corresponding segments of DNA - occurs at chiasmata -begins during pairing and synaptonemal complex formation -completed while homologs are in synapsis
What happens during prophase I of meiosis? - [PRO = BEFORE ... so prophase before the other stages] - chromosomes condense - homologs come together as pairs (tetrads) - synapsis - crossing over - nuclear envelope breaks down
What happens during metaphase I of meiosis? - [META = AFTER ... so metaphase after the 1st stage] - homolog pairs arrange at metaphase plate - law of segregation, independent assortment
What happens during anaphase I of meiosis? - [ANA = BACK ... the chromatids move back] - homolog pairs separate and move towards opposite poles of the cell - sister chromatids move as a unit
What happens during telophase I (and cytokinesis) of meiosis? - [TELO = END ... this, along with cytokinesis, is the end of meiosis I] - nuclear envelopes form - chromosomes decondense - cell splits and forms 2 haploid cells
What happens during prophase II of meiosis? - chromosomes condense - nuclear envelope breaks down - NO CROSSING OVER
What happens during metaphase II of meiosis? - chromosomes align at equatorial/metaphase plate - the 2 sister chromatids are NOT genetically identical
What happens during anaphase II of meiosis? - sister chromatids separate and move to opposite poles as individual chromosomes
What happens during telophase II (and cytokinesis) of meiosis? - nuclear envelopes form - chromosomes decondense - cells split for a total of 4 haploid cells - each daughter cell is genetically distinct from each other and parent cell
What mechanisms contribute to the genetic variation arising from sexual reproduction? independent assortment of chromosomes, crossing over, and random fertilization
What does the synaptonemal complex do? - makes sure the breaks in chromatids are aligned - mediates chromosome pairing, synapsis, and recombination
What are chiasmata? What occurs there? - the x-shaped regions where crossing over has occured between homologous nonsister chromatids; they are visible after synapsis - where crossing over occur; recombinant chromosomes produced
What are recombinant chromosomes? Why are they special? - individual chromosomes that carry genes (DNA) derived from two different parents - variation...these chromosomes are ones that have never existed before
independent assortment - when allele pairs separate independently during the formation of gametes; traits are transmitted to offspring indep. of each other - ex: if a cell has 2 pairs of chrom.s, it's random which way they will orient at metaphase I; 2 diff ways, 4 diff combos
random fertilization - describes the concept that the probability of any set of genes has an equal likelihood of combining to form the offspring - a zygote represents the combination of parental probabilities
The number of different types of gametes that are possible as the result of independent assortment of parental chromosomes is: - 2^n - where n = the number of chromosome PAIRS - (this does not count for crossing over)
What are the chances that two people will have a second child who is genetically identical to their first child? - 2^23 is about 8 million - so, 8 mil x 8 mil = 64 tril possible combinations in zygotes
What is natural selection? What does natural selection act on? - the process in which individuals what have certain inherited traits tend to survive and reproduce at higher rates than other individuals BECAUSE of those traits - acts on phenotypic traits (think, heterozygote wont express rec. disorder)
Created by: jessica.gvc



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