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How are living organisms distinguished?
by their ability to reproduce their own kind
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What is genetics?
the scientific study of heredity and variation
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What is heredity?
the transmission of traits from one generation to the next
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How is variation demonstrated?
by the differences in appearance that offspring show from parents and siblings
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What is asexual reproduction?
one parent produces genetically identical offspring by mitosis
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What is a clone?
a group of genetically identical individuals from the same organism
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what is sexual reproduction?
two parents give rise to offspring that have unique combinations of genes inherited from two parents
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define gene.
are the units of heredity, and are made up of segments of DNA.
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How are genes passed to the next generation?
through reproductive cells called gametes (sperm and eggs)
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one set of ___________ is inherited from each parent.
chromosome
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What is karyotype?
ordered display of the pairs of chromosomes from a cell
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The two chromosomes in each pair are called ______________________.
homologous chromosomes
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What makes the two chromosomes in each pair homologous? (3)
- same length
- carry gene controlling the same inherited characters
- same banding pattern
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What are the sex chromosomes called, who do they represent?
- x: females (XX)
- y: males (XY)
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The 22 pairs of chromosomes that do not determine sex is called?
autosomes
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Each pair of homologous chromosomes includes ____________________.
one chromosome from each parent
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What is a diploid cell (2n)?
- has two sets of chromosomes
- for humans, diploid number is 46
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What is a haploid cell(n)?
- a single set of chromosomes
- in humans, diploid number is 23
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A gamete, sperm or egg, is haploid or diploid?
haploid, single set of chromosomes
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What is fertilization?
is when the gametes come together (the sperm and egg)
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What is the fertilized egg called and what does it contain?
- its called a zygote (diploid)
- contains one set of chromosomes from each parent
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The zygote produces somatic cells by ___________ and develops into an adult. (human life cycle)
mitosis
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At sexual maturity, the ovaries and testes produce what kind of gametes?
haploid gametes
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Gametes are the only type of human cells produced by ____________.
meiosis
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_________ and _________ alternate in sexual life cycles to maintain chromosome number.
Fertilization and meiosis
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In a cell where DNA synthesis has occurred, each chromosome is ___________.
duplicated
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What does each duplicated chromosome consist of?
It consists of two identical sister chromatids.
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What is the first step of meiosis?
replication of chromosomes
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What does the two meiosis stages result in?
four non-identical daughter cells
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How many chromosomes does the daughter cell in meiosis have?
half as many chromosomes
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In general, what happens in the first cell division (meiosis 1)?
homologous chromosomes separate
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What does meiosis 1 result in? what is this division called?
- results in two haploid daughter cells with duplicated chromosomes
- called the reductional division
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what happens in the second cell division (meiosis 2)?
sister chromatids separate
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What are the results in meiosis 2? What is the division called?
- results in four haploid daughter cells with unduplicated chromosomes
- it's called the equational division
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Meiosis 1 is preceded by interphase, what happens in this stage?
chromosomes are replicated to form sister chromatids
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What are centrosomes?
- microtubules organizing centers
- help organize chromosomes
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What are two main things about sister chromatids?
they are genetically identical and joined at the centromere
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What is the main difference between mitosis and meiosis?
- Mitosis: conserves the number of chromosomes sets, producing cells that are genetically identical to the parent cell
- Meiosis: reduces the number of chromosome sets from diploid to haploid, producing cells that differ genetically from parent cells
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What are the three events that are unique to meiosis, and all three occur in meiosis 1?
- 1. synapsis and crossing over in prophase 1
- 2. at metaphase plate there are paired homologous chromosomes, instead of individual replicated chromosomes
- 3. At anaphase 1, its homologous chromosomes that are separated instead of sister chromatids
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____________ produces in sexual life cycles contributes to evolution
Genetic variation
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What are mutations?
permanent changes in an organisms DNA
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Mutations create different versions of genes called?
alleles
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________________ during sexual reproduction produces genetic variation?
Reshuffling of alleles
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What are the three mechanisms that contribute to genetic variation?
- independent assortment of chromosomes
- crossing over
- random fertilization
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How do homologous pairs orient at metaphase 1 of meiosis?
randomly
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What happens in independent assortment?
the maternal and paternal homologues are separated into different daughter cells independently
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What are the number of combinations possible when chromosomes assort independently into gametes?
2^n where n is the haploid number
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What does crossing over produce?
recombinant chromosomes
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What is a recombinant chromosome?
combine genes inherited from each parent
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Where does crossing over occur?
begins very early in prophase 1
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What happens in crossing over?
homologous portions of two nonsister chromatids trade places
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How does crossing over contribute to genetic variation?
by combining DNA from two parents into a single chromosome
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How does random fertilization add to genetic variation?
because any sperm can fuse with any ovum
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How many possible chromosome combinations can the fusion of two gametes without crossing over produce?
8.4 million
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What does natural selection results in?
results in the accumulation of genetic variations favoured by the environment
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Sexual reproduction contributes to the genetic variation in a population, which originates from _____________.
Mutations
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What is a life cycle?
is the generation-to-generation sequence of stages in the reproductive history of an organism
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What is common to all organisms that reproduce sexually?
the alteration of meiosis and fertilization
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In the animal life cycle, which are the only haploid cells?
Gametes
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The gametes fuse to form a?
diploid zygote
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The diploid zygote divides by __________ to develop a multicellular organism.
mitosis
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Which organisms exhibit an alteration in generation?
plants and some algae
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What are the 2 stages the life cycle of plants and some algae include?
diploid and haploid multicellular stage
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What is the diploid organism in a plant life cycle called? This organism undergoes __________to produce haploid spores.
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Each spore in a plant life cycle grows by mitosis to produce a haploid organism called?
gametophyte
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A gametophyte makes haploid gametes by?
mitosis
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___________ of gametes results in a diploid sporophyte.
fertilization
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In most fungi and some protists, the only diploid stage is the ?
single-celled zygote
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What stage does the fungi life cycle NOT include?
multicellular diploid stage
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In the fungi life cycle, the zygote produce haploid cells by?
meiosis
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In the fungi life cycle, each haploid cell grows by mitosis, into a ?
haploid multicellular organism
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In the fungi life cycle, the haploid adult produces gametes by?
mitosis
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Only_________ can undergo mitosis.
diploid cells
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Which life cycle stage is found in plants but not animals?
Multicellular haploid
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