Download Meiosis and Sexual Reproduction Notes

Meiosis and Sexual
Reproduction Notes
To be used with Meiosis and
Sexual Reproduction Guided
Notes
Before Meiosis lets look back at
Mitosis
Genes and Heredity
• Heredity the passing of traits from parents to offspring.
• Genetics the study of heredity (the passing of traits)
• Each human cell contains 30 thousand different
genes
Genes and Heredity
Genes:
• Factors that control organism traits or characteristics.
• Part of a chromosome containing the genetic code
• Passed on from parent to offspring.
• All of your genes are located
on 23 pairs of chromosomes
Alleles
• Alleles: part of a gene that is located on a
chromosome.
Example:
– Height(gene):
– tallness or shortness(alleles)
• The alleles determine
how each gene is expressed.
At least two alleles for one gene.
Locus: Location of gene on
a chromosome.
TT
t t
Chromosomes
Sister
Chromatid
Chromosome
Homologous
Chromosome
Homologous Chromosomes:
-a pair of chromosomes that contain genes for the
same traits.
-one chromosome is from mom the other from dad.
-same size & centromeres are in same location.
Amniocentesis
• Amniocentesis:
a medical procedure used in prenatal diagnosis of
chromosomal abnormalities.
• Chromosomes are taken from the
amniotic fluid.
Karyotype
• The chromosomes from the amniotic fluid are
then placed on a karyotype.
• A karyotype is a chart
of an organism’s chromosomes.
Karyotype
Next, the chromosomes are matched up according to:
1. if they came from mom or dad.
2. how tall they are.
3. centromere location.
Karyotype
A karyotype can reveal if a person…
1. is, male or female
2. has a normal number of chromosomes
3. has an abnormal number of chromosomes.
Example: Down’s syndrome
Meiosis
• Meiosis:
A type of cell division where the
chromosome number is reduced to half.
The process in which cells undergo
two dividing phases to form
gametes.
Meiosis only produces sex cells
(gametes).
Meiosis
Gametes are your sex cells.
Your egg and sperm cells.
Sexual reproduction
(sperm + egg)produces a zygote.
Meiosis
Diploid vs. Haploid
• Diploid Number (2n): the number of
chromosomes found in all body cells.
Humans 46.
-found in the somatic(body) cells
• Haploid Number (n): 1/2 the diploid number of
chromosomes. Humans 23.
– found in the egg and sperm cells of a species
DIPLOID
HAPLOID
Diploid vs. Haploid
Organism
Diploid # (body cells) Haploid # (sex cells)
Human
46
23
48
Chimpanzee
24
39
Dog
78
8
Fruit fly
4
7
Garden pea
14
630
Adder’s fern
1260
Terms
• Gametes:
eggs or sperm
• Gonads:
specialized organs in higher
animals where the gametes
are made
• Ovaries:
female gonads
• Testes:
male gonads
Meiosis
Meiosis I
• Has all the phases mitosis has. I P M A T
Meiosis II
• Has all the phases meiosis I has,
except Interphase.
P M A T
Prophase I of Meiosis
• During Prophase 1 crossing over takes place.
• Crossing over is : the exchange of chromosome
pieces.
– Crossing over increases the variability of the offspring
– This is why the offspring of sexual reproduction show many
variations
- Crossing over occurs only during Prophase I
Mitosis vs. Meiosis
Problems during Meiosis
Normally, homologous chromosomes
separate and move toward opposite poles
of the cell.
– Problems during anaphase: this disorder
is called non Disjunction
– Nondisjunction: the failure of homologous
chromosomes to separate
Nondisjunction
• Down's syndrome: results from
the nondisjunction of chromosome 21
– individual has an extra 21st chromosome
Down’s Syndrome Rates
Mistakes in Mitosis can be
Good
• polyploidy:
having an entire extra set of chromosomes
– Will result in the 3n or 4n number of chromosomes
- Many plants are a result of polyploidy; banana & day
lily
Summary of Mitosis & Meiosis
1. Meiosis is very similar to two divisions of mitosis.
2. The diploid number (2n) of chromosomes is
reduced by half to the haploid number (n)
3. Eggs and sperm are formed
4. Crossing Over causes lots of variations
5. Variations rarely occur in MITOSIS
6. Variations often occur in MEIOSIS
Summary
7. Mitosis is associated with asexual reproduction.
8. Mitosis takes place in somatic (body) cells.
9. What is produced from mitosis?
Two identical daughter cells
How many? 4
10. Meiosis is associated with sexual reproduction.
11. Meiosis takes place in sex cells.
12. Meiosis produces gametes and three polar bodies.