chapter 13
chapter 14
chapter 15
1. When a sperm cell fertilizes an egg cell, it produces a zygote that has inherited a certain number of chromosomes (for most animals it's 23) from each parent.
2. In asexual reproduction, a clone is produced from a single individual (all the genes are exactly the same) by mitosis in the parent. In sexual reproduction, the offspring inherit genes from each parent, undergoing meiosis 1 and 2 (synapsis and cross over) allowing for more genetic variations in the zygote.
3. Somatic cells are all body cells except the reproductive cells or gametes (sperm & egg cells).
4. Offspring inherit 23 chromosomes from each parent (inmost animals). Sex is determined by the the 23rd chromosome (in most animals the sex chromosomes are X and Y), there is a 50% chance that it will contain two XX (female) or XY (male). Genes from both chromosme pairs mix by random fertilization adding to increased genetic diversity in offspring. If a sperm contains an X chromosme, the result would be XX (female) and if it has a Y chromosome it would be XY (male), the egg cells contains X chromosomes.
5. In Zygotic Meiosis, gametes are the only haploid cells, and it occurs in most animals including us. In Sporic Meioisis, alteration of generations occurs because during meiosis, and the diploid cell produces haploid spore cells. The haploid spores then divide miotically (they don't fuse with cells like gametes). This creates another stage called gameophyte, where gameophyte cells use mitosis to make gamete cells. Then two gametes fuse to make a new diploid zygote, and this occurs in plants and some algae. In most fungi and protists, only one zygote is produced and during meiosis haploid cells are produced then divide through mitosis to make either unicellular offspring or an adult haploid multicellular organism.
6. In Meiosis 1, homologous pairs of chromosomes are separated, synapsis happens, and genes are exchanged between the non homologous pairs (crossing over). 2 cells result from meiosis 1 and they each have 46 chromosomes. In Meiosis 2, the sister chromatids are seperated into 4 haploid cells (with 23 chromosomes each).
7. Crossing over happens in chromsomes (during synapsis, four chromatid stage) when they cross eachother on their chaisma points, then they break and rejoin, exchanging genes in the process. This allows for more genetic variation because the chromatids aren't the same after genes have been exchanged, this results in some daughter cells receiving the shuffled genes, therfore not having the same genes as the parent.
8. Independant Assortment contributes to increased biodiversity because in meiosis 1 at the metphase stage the homolgous pairs of chromosomes can pair up in any random combination at the metaphase plate, lining up at either pole. There is a 50% chance that the daughter cells after Meiosis 1 will get a maternal or paternal chromosomes from a homologous pair. These different chromosome pairings allow for more gentic variation.
9. Meiosis is cellular division for sex cells, mitosis is for somatic cells. Chromosomes in Mitois line up individually at the metaphase plate while in Meosis chromosomes line up by homologous pairs. Meosis also includes the exchange of genes in chromosomes crossing over and syanpsis, and at anaphase the chromosomes move to poles but are still attached, unlike in mitosis where the sister chromatids seperate.
10. A gene is an inherited trait, a chromosome is a long strand of DNA coiled up (usually sex chromosomes are the in the shape of an X or Y for most animals), composed of two sister chromatids connected by a centrosome. Homologous chromosomes are in the same position and nonhomologous chromosomes are not in similar positions.