Cell Division: Mitosis, Meiosis, and Genetics Explained
Cell Division: Mitosis, Meiosis, and Genetics
1. What are the two types of cell division? There are two types of cell division: mitosis and meiosis. Most of the time when people refer to “cell division,” they mean mitosis, the process of making new body cells. Meiosis is the type of cell division that creates egg and sperm cells.
2. Be familiar with the stages of the cell cycle and what is occurring in each; be able to identify the stages. The phases in the reproduction and growth of a cell are known as the cell cycle. The five stages of the cell cycle are – interphase, which is in turn classified into G1, S and G2 phase, Mitosis, also called as the M phase, which is further divided into 4 parts (prophase, metaphase, anaphase and telophase) and Cytokinesis.
homologous chromosomes → Two chromosomes in a pair – normally one inherited from the mother and one from the father. For example, the two copies of Chromosome 1 in a cell would be referred to as homologous chromosomes.
gametes → Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome.
somatic cells → A somatic cell is any cell of the body except sperm and egg cells. Somatic cells are diploid, meaning that they contain two sets of chromosomes, one inherited from each parent.
diploid → Diploid is a cell or organism that has paired chromosomes, one from each parent. In humans, cells other than human sex cells, are diploid and have 23 pairs of chromosomes. Human sex cells (egg and sperm cells) contain a single set of chromosomes and are known as haploid.
haploid → Haploid is the quality of a cell or organism having a single set of chromosomes. Organisms that reproduce asexually are haploid. Sexually reproducing organisms are diploid (having two sets of chromosomes, one from each parent). In humans, only their egg and sperm cells are haploid.
trisomy → The presence of an extra chromosome in some or all of the body’s cells. This results in a total of three copies of that chromosome instead of the normal two copies. For example, Down syndrome (trisomy 21) is caused by having three copies of chromosome 21 instead of the usual two copies.
heterozygous → The presence of two different alleles at a particular gene locus. A heterozygous genotype may include one normal allele and one mutated allele or two different mutated alleles (compound heterozygote).
homozygous → The presence of two identical alleles at a particular gene locus. A homozygous genotype may include two normal alleles or two alleles that have the same variant.
dominant → Dominant refers to the relationship between two versions of a gene. Individuals receive two versions of each gene, known as alleles, from each parent. If the alleles of a gene are different, one allele will be expressed; it is the dominant gene. The effect of the other allele, called recessive, is masked.
recessive → Recessive refers to a type of allele which will not be manifested in an individual unless both of the individual’s copies of that gene have that particular genotype. 7. Be able to apply the terms diploid and haploid to a cell in different phases of mitosis and meiosis.
Diploid cells reproduce by mitosis making daughter cells that are exact replicas. Haploid cells are a result of the process of meiosis, a type of cell division in which diploid cells divide to give rise to haploid germ cells. A haploid cell will merge with another haploid cell at fertilization. 8.
How many chromosomes do humans have? How many homologous pairs of chromosomes do humans have? The 46 chromosomes of a human cell are organized into 23 pairs, and the two members of each pair are said to be homologues of one another (with the slight exception of the X and Y chromosomes). Human sperm and eggs, which have only one homologous chromosome from each pair, are said to be haploid (1n).
9. What sex chromosomes are associated with human female? Human male? Humans and most other mammals have two sex chromosomes, the X and the Y. Females have two X chromosomes in their cells, while males have both X and a Y chromosomes in their cells. Egg cells all contain an X chromosome, while sperm cells contain an X or Y chromosome.
10. What is the process of crossing over? When does it occur? Crossing over occurs between prophase I and metaphase I and is the process where two homologous non-sister chromatids pair up with each other and exchange different segments of genetic material to form two recombinant chromosome sister chromatids.
11. Be familiar with the different examples of nondisjunction; know what that term means. Failure of homologous chromosomes or sister chromatids to separate subsequent to metaphase in meiosis or mitosis so that one daughter cell has both and the other neither of the chromosomes.
12. Know Mendel’s laws (the two we discussed). Mendel’s first law describes the segregation of the two copies of alleles of a particular gene into the gametes. Mendel’s second law describes the independent assortment of alleles of different genes from each other during the formation of gametes.
14. Understand possible outcomes of incomplete dominance, codominance, multiple alleles. Incomplete dominance is when the phenotypes of the two parents blend together to create a new phenotype for their offspring. An example is a white flower and a red flower producing pink flowers. Codominance is when the two parent phenotypes are expressed together in the offspring. Which both alleles are simultaneously expressed in the heterozygote. Multiple alleles,mendel’s work suggested that just two alleles existed for each gene. Today, we know that’s not always, or even usually, the case! Although individual humans (and all diploid organisms) can only have two alleles for a given gene, multiple alleles may exist in a population level, and different individuals in the population may have different pairs of these alleles.