Biology Chapter 13 2
Terms
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- Genetics
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the scientific study of the transmission of traits from parents to offspring (heredity) and the varitions between and within generations
The scientific study of heredity and hereditary variation - Living Organisms
- Are distinguished by their ability to reproduce
- Heredity
- The transmission of traits from one generation to the next
- Variation
- Shows that offspring differ somewhat in appearance from parents nad siblings
- Asexual Reproduction
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Mitosis produces genetically identical cells
May result in clones of one parent - Sexual Reproduction
- Two parents give rise to offspring that have unique combinations of genes inherited from parents
- Meiosis
- reduces the number of chromosome sets from diploid to haploid
- Haploid Cell
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contains only one set of chromosomes
Generally in humans 23 chromosomes (n=23)
Haploid cells produce Diploid cells with fertilization (fusing two gametes) - Diploid Cell
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has 2 sets of each of its chromosomes
One set of chromosomes from mother and one set from the father
Generally humans, 26 chromosomes (2n=46)
Diploid produce Haploid daughter cells with Meiosis (halving the chromosome number) - Types of haploid and diploid cells in animals
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Gamete (germ cells) (sperm and egg cells) are haploid cells
Somatic cells (body cells) are diploid cells
many exceptions - Sexual Maturity
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the ovaries and testes produce haploid gametes by meiosis
During fertilization these gametes, sperm and ovaum, fuse, forming a diploid zygote - The Zygote
- Develops into an adult organism by mitosis
- Chromosomes in Human Cells
- A Kayotype is an ordered, visual representation of the chromosomes in a cell
- Homologous Chromosomes
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occur in pairs
have the same characteristics: length, centromere position, gene Loci
Both homologous chromosomes carry genes controlling the same inherited characters but usually pairs are not identical - Sex Chromosomes
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Determines the sex of the individual
In Humans
are represented by X and Y
XX being female
XY being male
are non-homologous - Autosome chromosomes
- Do not dtermine sex (body genes)
- Behavior of Chromosomes in Life Cycle
- In cell in which DNA synthesis has occurred all the chromosomes are duplicated and thus each consists of two identical sister chromatids
- Meiosis I
- called reductional division because it reduces the chromosome sets from two (diploid) to one (haploid). The sister chromatids of each homologue do not separate until meiosis II
- Meiosis II
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Produces 4 haploid daughters
Looks like a regular mitotic division in which chromosomes line up individually on the metaphase plate and sister chromatids separate and move apart in anaphase II. At the end of telophase II there are four haploid daughter cells. - Interphase I
- Interphase I (each chromosome replicates, producing 2 genetically identical sister chromatids that remain attached to their centromeres. During prophase I homologous chromosomes synapse and crossovers may occur forming chiasmata
- Stages of Meiosis
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Stage 1 - Interphase I
Stage 2 - Metaphase I
Stage 3 - Anaphase I
Stage 4 - Telophase I
Stage 5 - Cytokenesis
Meiosis II
Stage 1 - Anaphase II
Stage 2 - Telophase II - Differences between Mitosis and Meiosis
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2 division in Meiosis
1 division in Mitosis
By events in Meiosis I
Tetrad Information
synapsis with crossing over at chiasmata
Homologous pairs separate
Meiosis makes non-identical daughter cells (haploid cells from diploid cells)
Mitosis makes identical daughter cells - Prophase I of Meiosis
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Tetrads form
Tetrads are paired, homologoug, duplicated chromosomes
Synapsis and crossing over occur in tetrads. Homologous chromosomes physically connect and exchange genetic information - Separation of chromosomes
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Anaphase I of meiosis, tetrads separte into homologous pairs that move toward opposite poles of the cell
In anaphase II of meiosis, the sister chromatids separate - Comparison of Mitosis and Meiosis
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