Post on 02-Jan-2016
transcript
1. Somatic Cell- a typical body cell
a) Ex: muscle cells, skin cells
2. Each cell has a set number of chromosomes
3. The number chromosomes in each somatic cell depends on the species.
4. Humans have 46 chromosomes in each somatic cell
5. Homologous Chromosomes (homologs)- four chromosomes (2 sets one set comes from the mom the other set comes from the dad); that have same genes.
8. Sex Chromosomes- determines an individual’s gender.
X X = femaleX Y = male
Scanning electron micrograph of an X and Y chromosome Image courtesy of Indigo Instruments, Canada
X Chromosome
Y Chromosome
Autsosomal DNA
1. Sexual Reproduction results in individuals having two sets of chromosomes; one set inherited from each parent.
2. Haploid n (half)- one set of chromosomes; 22 autosomes and an X or Y chromosome in the nucleus of the cell
3. Autosomes are in the diploid state
4. Diploid 2n (double)- there are 2 sets of homologous chromosomes in the nucleus of the cell
5. n= number of chromosomes
Discuss w/ Partner: Which set of
chromosomes is in the haploid state, set A or set B?How do you know?
Answer: Set A because there
is only one set of chromosomes. Set B is in the diploid state because it has two sets of chromosomes.
6. Gametes a.k.a sex cells: egg cells & sperm cells have a single set of chromosomes.
An Egg coming out it’s ovary were it is stored
Human sperm cells
Egg
Ovary
7. In humans 2n= 468. N= 239. Fertilization-
happens when a haploid sperm cell from the father fuses with a haploid egg (ovum) inside the mother.
A human fertilized eggSource image:
www.wellcome.ac.uk/
Sperm fertilizing and eggSource image: sciencephoto.com
10.Zygote- A fertilized egg which is diploid (2n), has a set of c’somes from mom and one set from dad
A human zygote in the 8 cell stageSource image www.wellcome.ac.uk/
A four day old human zygote Source: www.wellcome.ac.uk/
11.All sexual life cycles involved alternation of generations; alterations of diploid & haploid stages
12.Haploid gametes prevents the c’some number from doubling in each generation.
13.Somatic cells are made by mitosis14.Gametes are made by meiosis which
only occurs in the ovaries & testes in animals
15.Meiosis- sperm and egg cells that are haploid are produced inside of an organism that is diploid.has two main divisions:
a) Meiosis I- homologous c’somes separate
b) Meiosis II- sister chromatids separate
Copyright Pearson Prentice Hall
1. Meiosis I: Homologous Chromosomes Separate
Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis
Interphase I
Meiosis I
Copyright Pearson Prentice Hall
3. Prophase IEach chromosome
pairs with its corresponding homologous chromosome to form a tetrad.
There are 4 chromatids in a tetrad.
Copyright Pearson Prentice Hall
When homologous chromosomes form tetrads in prophase I, they exchange portions of their chromatids in a process called crossing-over.
Crossing-over produces new combinations of alleles.
6. Telophase INuclear membranes form.
7. Cytokinesis The cell separates into
two cells.The two cells produced by
meiosis I have chromosomes and alleles that are different from each other and from the diploid cell that entered meiosis I.
8. Meiosis IIMeiosis I results in two
haploid (N) daughter cells, each with half the number of chromosomes as the original cell.
The two cells produced by meiosis I now enter a second meiotic division.
Unlike meiosis I, neither cell goes through chromosome replication.
Each of the cell’s chromosomes has 2 chromatids.
9. Prophase II- The centrioles duplicate. The two pairs of
centrioles separate into two centrosomes.The nuclear envelope breaks down, and the
spindle apparatus forms.
12.Telophase IIA nuclear envelope forms
around each set of chromosomes
13.Cytokinesis II produces four daughter
cells (gametes, in animals), each with a haploid set of chromosomes.
14.Meiosis II results in four haploid (N) daughter cells.
15.Because of crossing-over, all four daughter cells or gametes are genetically different from each other and their parent cell
Telophase II
Cytokinesis
Mitosis MeiosisCells produced by
mitosis have the same number of chromosomes and alleles as the original cell.
Mitosis allows an organism to grow and replace cells.
Some organisms reproduce asexually by mitosis.
Cells produced by meiosis have half the number of chromosomes as the parent cell.
These cells are genetically different from the diploid cell and from each other.
Meiosis is how sexually reproducing organisms produce gametes.
1. Crossing over- The exchange of parts of the chromatids of homologous chromosomes.
2. Crossing over takes place on the chiasma which is an x-shaped area of the c’some