Unit 7 Study Guide Inheritance Name ____________________ 1. I can describe the process of meiosis. Meiosis produces cells called gametes (sperm or egg) which are the sex/reproductive cells for the organism. One purpose of meiosis is to create genetic diversity because the process shuffles the cell's genes around. There are 2 back-to-back divisions in meiosis (PMAT twice). You still have to remember PMAT, but now you do it twice. You also need to remember that 4 cells are created where there was originally one. That’s 4 cells with half of the amount of DNA needed by a cell. When a cell has half the number of chromosomes,it is called a Haploid cell. Only Gametes are Haploid. Haploid (n) means the cell only has 1 copy of each gene. Diploid (2n) means the cell has two copies of each gene. Normal body cells are considered to be diploid cells. MEIOSIS I: (This is basically like the PMAT of a regular mitosis with a few differences.) During Prophase I, the homologous chromosomes pair up (form a tetrad) and cross over. The homologous chromosomes have the same genes on them. Crossing over is where the homologous chromosomes swap genes, which increases genetic diversity. This is because the cells produced by meiosis are now different from each other and from the original cell. During Metaphase I, the homologous pairs (tetrad) are lined up along the equator of the cell (looks like 2 lines down the middle). During Anaphase I, the homologous pairs are separated and pulled to each side, which finishes the process of crossing over. This is also when nondisjunction (failure to separate) can occur. During Telophase I, cytokinesis occurs and you now have 2 haploid cells. The cells are now ready for the second stage of division. DNA replication does NOT occur between Telophase I and Prophase II. MEIOSIS II: In Prophase II the DNA that remains in the cell begins to condenses again and attach to the spindle. Homologous chromosomes are in separate cells (cells are haploid). In Metaphase II all of the chromosomes line up along the center of the cell. This looks like 2 cells each with a single line of chromosomes (look like X). During Anaphase II, the sister chromatids are pulled apart and move to opposite sides of the cell. Each daughter cell will get one-half of the DNA needed to make a functioning cell. Nondisjunction (failure to separate) can also occur here, which would result in too many or too few copies of the chromosome in a cell. During Telophase II, the chromosomes unwind, the nuclear membrane reforms and cytokinesis occurs. When it's all over, you are left with four haploid cells that are called gametes (sperm or egg). The eventual purpose of the gametes will be to find other gametes with which they can combine. When they do, they will form a new organism.
Transcript
Unit 7 Study Guide Inheritance Name ____________________
1. I can describe the process of meiosis. Meiosis produces cells called gametes (sperm or egg) which are the sex/reproductive cells for the organism. One
purpose of meiosis is to create genetic diversity because the process shuffles the cell's genes around.
There are 2 back-to-back divisions in meiosis (PMAT twice). You still have to remember PMAT, but now you do it twice.
You also need to remember that 4 cells are created where there was originally one. That’s 4 cells with half of the amount
of DNA needed by a cell. When a cell has half the number of chromosomes,it is called a Haploid cell. Only Gametes are
Haploid. Haploid (n) means the cell only has 1 copy of each gene. Diploid (2n) means the cell has two copies of each
gene. Normal body cells are considered to be diploid cells.
MEIOSIS I: (This is basically like the PMAT of a regular mitosis with a few differences.)
During Prophase I, the homologous chromosomes pair up (form a tetrad) and cross over. The homologous
chromosomes have the same genes on them. Crossing over is where the homologous chromosomes swap
genes, which increases genetic diversity. This is because the cells produced by meiosis are now different from
each other and from the original cell.
During Metaphase I, the homologous pairs (tetrad) are lined up along the equator of the cell (looks like 2 lines
down the middle).
During Anaphase I, the homologous pairs are separated and pulled to each side, which finishes the process of
crossing over. This is also when nondisjunction (failure to separate) can occur.
During Telophase I, cytokinesis occurs and you now have 2 haploid cells. The cells are now ready for the second
stage of division. DNA replication does NOT occur between Telophase I and Prophase II.
MEIOSIS II:
In Prophase II the DNA that remains in the cell begins to condenses again and attach to the spindle. Homologous
chromosomes are in separate cells (cells are haploid).
In Metaphase II all of the chromosomes line up along the center of the cell. This looks like 2 cells each with a
single line of chromosomes (look like X).
During Anaphase II, the sister chromatids are pulled apart and move to opposite sides of the cell. Each daughter
cell will get one-half of the DNA needed to make a functioning cell. Nondisjunction (failure to separate) can also
occur here, which would result in too many or too few copies of the chromosome in a cell.
During Telophase II, the chromosomes unwind, the nuclear membrane reforms and cytokinesis occurs. When it's
all over, you are left with four haploid cells that are called gametes (sperm or egg). The eventual purpose of the
gametes will be to find other gametes with which they can combine. When they do, they will form a new organism.
Unit 7 Study Guide Inheritance Name ____________________
2. I can compare and contrast mitosis and meiosis.
Mitosis
Produces 2 genetically identical diploid
body cells
Homologous chromosomes do not pair up
No crossing over
No nondisjunction
For growth & repair
Meiosis
Produces 4 genetically different haploid gametes
Homologous chromosomes do pair up (Prophase I)
Crossing over creates genetic diversity (Prophase I)
Nondisjunction may occur (Anaphase I or II)
For sexual reproduction
Unit 7 Study Guide Inheritance Name ____________________
3. I can apply the laws of inheritance to determine genotypes and phenotypes. Alleles are different forms of the same gene; this means that they code for different versions of the same trait.
Example: blue eye color vs. brown eye color; both are alleles for eye color.
A phenotype is the physical expression of a gene (Example: what the person’s eye color actually is). Phenotype is
determined by genotype. A genotype is the genetic makeup of an individual for a particular gene. Each individual
inherits one copy of the gene from each parent; therefore, having 2 copies of the same gene. This means that the
genotype can be homozygous (have 2 identical alleles) or be heterozygous (have 2 different alleles). Only the
phenotype is observable. Genotype can be determined in most cases if enough information is known about the
parents and their families.
Recessive alleles, represented by a lower case letter, are weaker forms of a gene that are completely masked (not
shown in the phenotype) if a dominant allele is present. Dominant alleles, represented by an upper case letter, are
always expressed in the phenotype. The way to tell if an allele is dominant or recessive is to see what is expressed as
a heterozygote (Bb). Example: Heterozygote with 1 allele for Brown eyes (B) and 1 allele for Blue eyes (b) has
Brown eyes because Brown is dominant.
Unit 7 Study Guide Inheritance Name ____________________
Mendel’s Laws of Inheritance: 2 copies: In sexually reproducing organisms, each parent contributes one allele for each gene to their offspring.
This results in the offspring having 2 copies of the gene. This means that it will be either homozygous or
heterozygous for that trait.
Segregation: In diploid organisms, chromosome pairs (and their alleles) are separated into
individual gametes (eggs or sperm) to transmit genetic information to offspring.
Dominance: A dominant allele completely masks the effects of a recessive allele. A dominant allele produces the same phenotype in heterozygotes and in homozygotes.
Independent assortment: Alleles on different chromosomes are distributed randomly to individual gametes. In practice, Mendel's laws can be seen by using a dihybrid cross and in characteristic phenotypic ratios, such
as 3:1 and 9:3:3:1. Further, the Mendelian principles just stated include the simple assumption that one allele is
dominant to the other allele. In the time since Mendel's original experiments, we have come to learn that there are
extensions to Mendelian principles, including the fact that some alleles are incompletely dominant, that some genes
are sex-linked, and that some pairs of genes do not assort independently because they are physically linked on a
chromosome.
Unit 7 Study Guide Inheritance Name ____________________
4. I can apply the laws of inheritance to solve problems using monohybrid and dihybrid punnett squares .
Dihybrid Cross: crossing for 2 traits at the same time
