Post on 24-Feb-2016
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Write down and complete the data table below
Types of Reproduction
Advantages Disadvantages
Sexual
Asexual
• Allows for genetic variation
• Can result in better species
• Requires partner
• Does not require partner
• Generally faster• Does not allow for
genetic variation
Through asexual reproduction a
clone is produced. Asexual
reproduction is usually derived
by mitosis.
ParthenogenisisAsexual Reproduction where the female produces offspring from unfertilized eggs.
WHAT IS SEXUAL REPRODUCTION?
TWO PARENTS GIVING RISE TO AN OFFSPRING THAT IS A GENETIC MIX
OF THE PARENTS.
HUMAN LIFE CYCLE
The only haploid cells in humans
are the gametes.
Angiosperm Life Cycle
Fungi Life CycleUnion of the cytoplasm of the 2 parent mycelia
Haploid nuclei contributed by the 2
parents fuse, producing diploid cells
Haploid and diploid cells may undergo mitosis but only diploid cells will undergo meiosis
Each cycle of chromosome halving and doubling contributes to genetic variation among offspring
THREE TYPES OF LIFE CYCLES
Meiosis
A reduction division, followed by fertilization ensures genetic diversity
in sexually reproducing organisms
Meiosis
• Makes gametes• Reduces a diploid cell to form multiple haploid
cells.– Each haploid cell is genetically different from the
other cells.– Each haploid cell contains a mix of half of the
genetic information of the parent cell.• Meiosis is divided into 2 divisions:
– Meiosis I and Meiosis II
Phases of Meiosis
• Step by step process where a diploid reproductive cell produces 4 haploid daughter cells.
• First up is Interphase– Same as the cell cycle
• Cell must divide 2 times in order to produce 4 haploid cells.– The 1st meiotic division makes 2 cells & then each of
these cells divides during the 2nd meiotic division producing the 4 cells total.
Meiosis 1
Homologous chromosomesThey are similar in shape & size
and the 2 chromosomes carry the same genes.
n represents the number of chromosomes in a haploid cell & 2n
for diploid cells.
Prophase I
Homologous chromosomes cross over-break & twist around each other; then connect at each other’s initial position
=recombinant chromosome
Can occur 2 to 3 times between a pair of homologous chromosomes depending on size of chromosomes & position of centromeres
Metaphase IWHAT’S DIFFERENT IN THIS METAPHASE COMPARED TO THE ONE DURING MITOSIS?
WHAT DOES INDEPENDENT ASSORTMENT MEAN?
Anaphase I
WHAT’S DIFFERENT IN THIS ANAPHASE
COMPARED TO THE ONE DURING MITOSIS?
Telophase I
AFTER CYTOKINESIS, WILL THESE CELLS BE HAPLOID OR DIPLOID? EXPLAIN
QUICK RE-CAP OF MEIOSIS I
Takes place in order to produce two cells with a single set of chromosomes each.
Why don’t the cells go through interphase again before entering prophase II ?
Random Fertilization• Adds to genetic variation arising from meiosis
– In humans, the fusion of a sperm and egg will produce a zygote with any of about 64 trillion diploid combinations.
WHERE IN MEIOSIS DOES GENETIC DIVERSITY OCCUR?
Sometimes chromosomes don’t separate the way they are
suppose to = non-disjunction
Nondisjunction (Trisomy 21) - An Animated Tutorial
PLAY VIDEO
Ex: Down’s Syndrome (aka Trisomy 21
Most common chromosome anomaly.Affects 1 in 800 births
Non-disjunction can happen with other chromosomes & all having a major impact on a child’s development
Other non-disjunction disorders
Edward’s Syndrome – Trisomy 18
Patau’s Syndrome- Trisomy 13
Turner’s Syndrome- Monsomy X
Karyotypes
• A photograph of chromosomes found in a cell (during metaphase of mitosis) arranged according to size and shape.
• The shape depends largely on the location of the centromere.
• The homologous pairs are place together.• These are usually done on unborn fetuses to
determine any chromosomal anomalies.
Methods of obtaining cells for karyotyping
Amniocentesis Chorionic villus sampling
Were these chromosomes taken from a male or female? Is there any non-disjunction? Explain your answers
Were these chromosomes taken from a male or female? Is there any non-disjunction? Explain your answers
Were these chromosomes taken from a male or female? Is there any non-disjunction? Explain your answers
Were these chromosomes taken from a male or female? Is there any non-disjunction? Explain your answers