cell division an inheritance part 2 Flashcards
homologous pairs
matching genes - one from female parent and one from male parents
alleles
different genes for the same trait
amount of chromosomes in cells
Ex. humans have 46 chromosomes or 23 pairs
One set from dad - 23 in sperm
One set from mom - 23 in egg
Genotype
Combination of genes an organism has (actual gene makeup)
phenotype
physical appearance resulting from gene makeup
Where does an organism get its unique characteristics?
Organisms inherit their set of characteristics from their parents or parent
An individual’s characteristics are determined by factors that are passed from one parental generation to the next
How are different forms of a gene distributed to offspring?
During gamete formation, the alleles for each gene segregate from each other, so that each gamete carries only one allele for each gene
How to allele segregate when more than one gene is involved?
Independent assort, genes for different traits segregate independently during the formation of gametes
What did Mendel contribute to our understanding of genetics? (4 concepts!)
Traits are determined by genes, which are passed from parent to offspring
Principle of dominance, some alleles are dominant and others are recessive
Each adult has two copies of each gene–one from each parent
Segregation, During gamete formation, the alleles for each gene segregate from each other, so that each game carries only one allele for each gene
Independent assortment, genes for different traits can segregate independently during the formation of gametes, inheritance of one trait has no effect on the inheritance of another trait
What are some exceptions to Mendel’s principles?
Codominance
incomplete dominance
Neither dominant nor recessive
Multiple alleles
Many genes exist in several different forms and are therefore said to have multiple alleles
Genes with more than two alleles are said to have multiple alleles
Polygenic traits
Many traits are produced by the interaction of several genes, traits controlled by two or more genes are polygenic
Does the environment have a role in how genes determine traits?
Phenotype of an organism is only partly determined by its genotype, partially determined by environment
Environmental conditions can affect gene expression and influence genetically determined traits
zygote
a fertilized egg
How many sets of genes are found in most adult organisms?
2
How is meiosis different from mitosis?
Mitosis
2 cells made
Final products s2 sets of chromosomes
Diploid (46)
Healing, growth, replace worn out cells
All identical
Meiosis
4 cells made
1 set of chromosomes (half the chromosomes
Haploid (23)
Makes gametes
Sperm and eggs
Chromosomes have crossing over → recombination
Each cell is unique
How can two alleles from different genes be inherited together?
Alleles of different genes tend to be inherited together from one generation to the next when those genes are located on the same chromosome
Homologous chromosomes
Pair of chromosomes (maternal and paternal) that are similar in shape and size.
Homologous pairs (tetrads) carry GENES controlling the SAME inherited traits.
Each locus (position of a gene) is in the same position on homologues.
Humans have 23 pairs of homologous chromosomes:
Diploid
A cell that contains both sets of homologous chromosomes (2n)
haploid
Cells that contain only a single set of chromosomes, and therefore a single set of genes (1n)
Meiosis
A process in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell
The form of cell division by which GAMETES, with HALF the number of CHROMOSOMES, are produced.
DIPLOID (2n) → HAPLOID (n)
Meiosis is SEXUAL reproduction.
TWO divisions (MEIOSIS I and MEIOSIS II)
Sex cells divide to produce GAMETES (sperm or egg).
Gametes have HALF the # of chromosomes.
Occurs only in GONADS (testes or ovaries).
Male: SPERMATOGENESIS -sperm
Female: OOGENESIS - egg or ova
Yields nonidentical daughter cells
spermatogenesis
Makes four sperm cells
oogenesis
makes one egg, other three are polar bodies which die
meiosis interphase
Similar to mitosis interphase.
CHROMOSOMES (DNA) replicate in the S phase
Each duplicated chromosome consist of two identical SISTER CHROMATIDS attached at their CENTROMERES.
CENTRIOLE pairs also replicate
Nucleus and nucleolus visible.
Meiosis I (four phases)
Prophase I
Metaphase I
Anaphase I
Telophase I.
cytokinesis
crossing over
Crossing over may occur between non-sister chromatids at sites called chiasmata, segments of nonsister chromatids break and reattach to the other chromatid chromosomes touch each other and exchange genes
Causes Genetic Recombination
prophase 1
Longest and most complex phase (90%).
Nucleus and nucleolus disappear
Spindle forms
Chromosomes condense.
Synapsis occurs - Homologous chromosomes come together
to form a tetrad.
Tetrad is two chromosomes or four chromatids (sister and non-sister chromatids)
Crossing over occurs
Metaphase I
Shortest phase, Tetrads (pairs of homologous chromosomes) line up across the center of the cell.
Independent assortment occurs – chromosomes line up randomly
Anaphase 1
Homologous chromosomes separate and move towards the poles.
Sister chromatids remain attached at their centromeres.
Spindle fibers pull each homologous chromosome pair toward opposite ends of the cell
telophase 1
Each pole now has haploid (1n) set of chromosomes.
A nuclear membrane forms around each cluster of chromosomes
Cytokinesis occurs and two haploid daughter cells are formed.
Meiosis 2
No Interphase II or very short
No DNA Replication
Remember: Meiosis II is similar to mitosis
prophase 2
Same as Prophase in mitosis
Nucleus & nucleolus disappear
Chromosomes condense
Spindle forms
metaphase 2
Same as Metaphase in mitosis
Chromosomes line up
anaphase 2
Sister chromatids separate.
telophase 2
Same as Telophase in mitosis.
Nuclei and Nucleoli reform, spindle disappears
CYTOKINESIS occurs.
Remember: FOUR HAPLOID DAUGHTER cells are produced.
Called GAMETES (eggs and sperm)
1n chromosomes, 24 instead of 48
variation
Also known as GENETIC RECOMBINATION
Important to population as the raw material for NATURAL SELECTION.
All organisms are NOT alike
Strongest “most fit” survive to reproduce & pass on traits
3 sources of genetic recombination or variation?
CROSSING OVER (prophase I)
INDEPENDENT ASSORTMENT (metaphase I)
RANDOM FERTILIZATION
karyotype
An organized picture of the chromosomes of a human arranged in pairs by size from largest to smallest.
Pairs 1-22 called AUTOSOMES
Last pair are SEX CHROMOSOMES
fertilization
fusion of a sperm and egg to form a zygote
