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43 Cards in this Set
- Front
- Back
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Offspring acquire genes from... (general term)
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Parents
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Heredity (flow chart)
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Gene -> Protein -> Traits
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Human somatic cells have... (number of chromosomes)
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22 pairs of autosomes
1 pair of sex chromosomes |
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Each pair of autosomes... (main characteristics)
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- have same size and centromere position
- are homologous (similar but not identical DNA sequences) - carry genes controlling the same inherited characters |
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Sex chromosomes... (function)
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determine sex
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The two sex chromosomes are...
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X and Y
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Females have _____ sex chromosomes
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XX
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Males have _____ sex chromosomes
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XY
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We inherit... (chromosome inheritance)
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one chromosome from each parent in each pair
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Gamete cells (define and give examples)
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reproductive cells
e.g. sperm and ova/egg cells |
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How many chromosomes do gamete cells have of each type?
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One set of chromosomes
22 autosomes + 1 sex chromosome |
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A cell with a single chromosome set is a...
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haploid
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A sperm and an egg fuse together to form...
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a fertilized egg (zygote)
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Haploid + Haploid = ?
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Diploid
In humans: 23 + 23 = 46 n + n = 2n |
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Diploid cells have... (number of chromosomes)
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2 sets of chromosomes (2n)
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Gametes are produced... (location + method)
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in the ovaries or testes
by meiosis |
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Meiosis (function)
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produces haploid cells with half the chromosomal content
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Fertilization... (function [chromosomes])
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restores the diploid condition (reduced by meiosis)
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Meiosis reduces the chromosome number from... (terms)
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diploid to haploid
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The two major steps in meiosis are... (steps + resultant)
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I. DNA replication
II. Two cell divisions - resulting in four daughter cells expressing half the number of chromosomes |
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DNA starts replicating in the cell during... (phase)
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the S phase
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First cell division (Meiosis I)
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Separates homologous chromosomes
Divided into four phases: - Prophase - Metaphase - Anaphase - Telophase |
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Prophase I
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- Synapsis: homologous chromosomes pair up to form tetrads
- Chiasma: chromosomes cross; segments are exchanged |
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Synapsis
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process of homologous chromosomes pairing up during Prophase I of Meiosis
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Chiasma (plural: chiasmata)
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the intersection between homologous non-sister chromatids
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Synaptonemal complex
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another name for tetrads
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Metaphase I
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Tetrads arrange at the metaphase plate (equator)
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Anaphase I
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Homologous chromosomes separate, moving to opposite poles
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Telophase I
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- Haploid set of chromosomes at each pole
- Sister chromatids linked - Cytokinesis occurs |
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Cytokinesis
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the process in which the cytoplasm of a single eukaryotic cell is divided to form two daughter cells
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Second cell division (Meiosis II)
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- separates sister chromatids
- similar to mitosis |
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Meiosis produces...
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4 daughter cells
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Meiosis vs. Mitosis
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Meiosis:
- haploid (2n -> n) - 4 different daughter cells (non identical to each other and parents) - 2 cell divisions Mitosis: - diploid (2n -> 2n) - 2 identical daughter cells (clones) - 1 cell division |
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Origins of genetic variation (due to?)
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Due to meiosis and fertilization
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Mechanisms causing genetic variation (three)
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1. Independent assortment (metaphase I)
2. Crossing over (prophase I) 3. Fertilization |
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Independent assortment
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- random orientation of tetrads at the metaphase plate
- daughter cells of meiosis I have 50/50 chance of receiving either maternal or paternal chromosome |
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In independent assortment, homologous pairs are... (position)
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oriented/positioned independently of other pairs (e.g. heads or tails does not depend on the last result)
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During independent assortment, there are ___ possible combinations of chromosomes.
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2^n
n: haploid number e.g. humans 2^23 = 8 388 608 |
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Crossing over... (result)
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- produces recombinate chromosomes
- the recombinate chromosomes have genes from each parent |
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Random fertilization
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Any sperm can fuse with any egg
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Variation due to independent assortment
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sperm: 8 million combination
egg: 8 million combination zygote : 1 out of 70 trillion possible combinations (without taking cross overs into account) |
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Independent assortment, crossing over and fertilization cause:
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a shuffling of genes
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Mutations create...
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additional variations.
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