Meiosis and life cycles
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| Offspring acquire genes from parents by ___. | inheriting chromosomes
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| ___ and ___ alternate in sexual life cycles. | Fertilization / meiosis
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| Meiosis ___ the number of chromosome sets from ___ to ___. | reduces / diploid / haploid
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| ___ produced in sexual life cycles contributes to evolution. | Genetic variation
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| heredity (inheritance) | the transmission of traits from one generation to the next
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| 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.
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| genetics | the scientific study of heredity and hereditary variation
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| gene | a discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA; many different kinds
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| 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.
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| 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
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| chromosomal locus | a gene's specific location along the length of a chromosome
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| asexual reproduction | a single individual is the sole parent and passes copies of all its genes to its offspring without the fusion of gametes
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| sexual reproduction | two parents give rise to offspring that have unique combinations of genes inherited from the two parents
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| clone | a group of genetically identical individuals; the offspring produced by asexual reproduction
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| karyotype | a display of the chromosome pairs of a cell arranged by size and shape
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| homologous chromosomes / "homologs" | two chromosomes composing a pair that have the same length, centromere position, and staining pattern
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| What are autosomes? How many do humans have? | -chromosomes that are not involved in determining sex
-22 pairs, or 44
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| What are sex chromosomes? How many do humans have? | -chromosomes that determine an individual's sex
-1 pair, or 2 (XX or XY)
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| 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)
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| 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)
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| 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)
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| 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
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| synapsis | when paired homologous chromosomes become physically connected to each other along their lengths (by a zipper-like protein structure, the synaptonemal complex)
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| chiasmata | the x-shaped regions where crossing over has occurred between homologous nonsisiter chromatids; they become visible after synapsis
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| 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
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| 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
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| 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
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| 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
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| 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
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| What happens during prophase II of meiosis? | - chromosomes condense
- nuclear envelope breaks down
- NO CROSSING OVER
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| What happens during metaphase II of meiosis? | - chromosomes align at equatorial/metaphase plate
- the 2 sister chromatids are NOT genetically identical
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| What happens during anaphase II of meiosis? | - sister chromatids separate and move to opposite poles as individual chromosomes
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| 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
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| What mechanisms contribute to the genetic variation arising from sexual reproduction? | independent assortment of chromosomes, crossing over, and random fertilization
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| What does the synaptonemal complex do? | - makes sure the breaks in chromatids are aligned
- mediates chromosome pairing, synapsis, and recombination
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| 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
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| 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
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| 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
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| 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
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| 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)
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| 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
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| 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)
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