Chapter 10 - Cell Reproduction and Meiosis Flashcards
Genome
a cell DNA, packaged as a double-stranded DNA molecule
Genome - Prokaryote
in prokaryotes, the genome is composed of a single double-stranded DNA molecule in the form of a loop or circle
-plasmids = smaller loops of DNA, not essential for normal growth but allow the exchange of beneficial new genes such as antibiotic resistance
Genome - Eukaryote
in eukaryotes, the genome consists of several, double-stranded linear DNA molecules
-a typical body cell (somatic) contains 2 matched or homologous sets of chromosomes
-human cells that contain one set of chromosomes are called gametes and are designed as haploid
-sex cells form in reproductive organs, 2 types: sperm and egg
Sexual Reproduction
Fertilization: occurs when an egg cell and sperm cell join together; a new cell is formed
-the new cell that forms from fertilization = zygote
-after fertilization, the zygote goes through mitosis and cell division
-mitosis and cell division produce nearly all cells in a multicellular organism
-23 pairs of homologous chromosomes in a female human somatic cell
Chromosomes and Alleles
-a variation of individuals within a species is due to the specific combination of the genes inherited from both parents
-even a slightly altered sequence of nucleotides within a gene can result in an alternate trait (blood type)
Blood Type
-humans have 4 blood types (A, B, AB, O)
-A and B are codominant to each other
-O is recessive to A and B
Diploid vs Haploid Cell
-in humans, each somatic cell has 46 chromosomes (23 mom and 23 dad) or 23 homologous chromosomes (homologs)
-Haploid Cells - somatic cells, have one set of chromosomes, n
-Diploid Cells - gametes, have 2 sets of chromosomes, 2n
-pairs of chromosomes that have genes for the same traits in the same order (locus) are called homologous chromosomes because one chromosome is inherited from each parent so chromosomes are not always identical.
Ophioglossum reticulatum
species with the most chromosomes (1260)
-chromosome number is very important
Fusion vs Polyploidy
-chromosome number can change over time
-Fusion: they can stick together by accident; decreases the number of chromosomes but little/no genetic information is lost
-Polyploidy: extra chromosomes can happen through mistakes when cells divide; increases the number of chromosomes
-BOTH happen by chance
Chromosome # Importance
-important to have the correct # of chromosomes
-if a zygote has too many or too few chromosomes, it will not develop properly
-the process of meiosis helps maintain the correct number of chromosomes
-if a mistake occurs in animal cells (sometimes the zygote dies, if the zygote lives, every cell in that organism will have the wrong amount of chromosomes and may not grow normally)
Haploid Cells
organisms that reproduce sexually also form egg and sperm cells (sex cells)-sex cells have one chromosome from each pair of chromosomes
-cells that have only 1 chromosome in each pair
-organisms that produce sex cells using a special type of cell division (meiosis)
Meiosis
-one diploid cell divides and makes 4 haploid sex cells
-occurs only during the formation of sex cells
-meiosis involved 2 divisions of the nucleus and cytoplasm
-results in 4 haploid cells, each with half the # of chromosomes as the original cell
Phases of Meiosis
-reproductive cell goes through interphase before beginning meiosis I
-during interphase, the reproductive cell grows and copies, or duplicates its chromosomes
-each duplicated chromosome consists of 2 sister chromatids joined by a centromere
Cell Cycle
4 phases of cell cycle of replication
-G1, S, G2, M
-interphase: G1, S, G2, M; mitotic phase
G1 Phase
-the cell is quite active at biochemical level
-accumulate building blocks of chromosomal DNA and associated protein
S Phase
synthesis of DNA
G2 Phase
-the cell replenishes its energy stores and synthesizes proteins necessary for chromosome manipulation
Mitotic Phase
-a multistep process during which duplicated chromosomes are aligned, separated, and moved to opposite poles of the cell, and then the cell is divided into 2 new identical slaughter cells
-DNA replication occurs during “S” Phase
Meiosis 1 –> Prophase 1
-duplicated chromosomes condense, or shorten, and thicken
-homologous chromosomes come together and form pairs
-membrane around the nucleus break apart and nucleolus disappears
Meiosis 1 –> Metaphase 1
-homologous chromosome pairs line up along the middle of the cell
-spindle fiber attaches to each chromosome
Meiosis 1 –> Anaphase 1
-chromosome pairs separate and are pulled towards opposite ends of the cell
-sister chromatids stay together
Meiosis 1 –> Telephase 1
-membrane forms around each group of duplicated chromosomes
-cytoplasm divided through cytokinesis and 2 daughter cells form
-sister chromatids remain together
-after meiosis 1, 2 cells formed go through second division of nucleus and cytoplasm
Meiosis 2 –> Prophase 2
-chromosomes NOT copied again before prophase II
-they remain short and thick sister chromatids
-membrane around the nucleus breaks apart and the nucleus disappears in each cell
Meiosis 2 –> Metaphase 2
-pairs of sister chromatids line up along middle of cell single file
Meiosis 2 –> Anaphase 2
-sister chromatids of each duplicated chromosome pulled apart then move toward opposite ends of cells
Meiosis 2 –> Telophase 2
-the final phase of meiosis
-nuclear membrane forms around each set of chromatids
-cytoplasm divides through cytokinesis and 4 haploid cells form
Crossing Over
-exchange of DNA segments produces new combos of alleles among offspring = genetic recombination
-the main difference between recombination and crossing over is that recombination is the production of different combinations of alleles in offspring while crossing over ONLY happens at the very beginning of meiosis, during prophase 1
Meiosis Importance
-important to sexual reproduction
-forms the correct haploid number of chromosomes in organisms when sex cells join
-meiosis also leads to genetic variation
-helps maintain diploid cells in offspring by making haploid sex cells
-when haploid cells join together during fertilization, diploid zygote of fertilized egg forms
-zygote divided by mitosis and cell division and creates diploid organism
Advantages of Sexual Reproduction
-offspring inherit 1/2 of their DNA from each parent
-inheriting different DNA means each offspring has a different set of traits
-some may have traits to survive harsh conditions
-some traits may help organisms keep from getting infected with disease
-selective breeding: breeding with certain individuals because of the traits they have; used to produce many types of plants/animals
