What is sexual reproduction?

1
What is sexual reproduction?

• The human life cycle
• What is cell division?
• Mitosis- one cell gives rise to two identical
  cells
• Meiosis- one cell gives rise to four gametes
• What is genetic diversity?
• What happens if a cell does not divide
  correctly?

2
How many chromosomes do humans have?
3
What is a chromosome? (pp. 440, 446)
4
what does mitosis accomplish?

• Many organisms reproduce this way (asexually)
• Increase in size
• Repair damage
• Mitosis is part of the cell cycle is carefully
  controlled

5
The cell cycle

• Cell division is controlled
• When
• How many times
• Cell differentiation
• Loss of control leads to tumor formation

6
Highlights of the cell cycle

• G1- cell matures and becomes functional
• May stay in G1 indefinitely
• Receives signal to proceed into S phase
• S phase- chromosomes are copied
• So each new cell gets a complete set of
  chromosomes
• Chromatids copies are joined together at the
  centromere
• G2- cell prepares for mitosis
• Process may be stopped here if there are problems
• Mitosis- chromosomes divide, then the organelles
  and cytoplasm do
• New cells enter G1- the cycle continues

7
What is a stem cell, what is an adult cell, and
what is cloning?
8
Meiosis the formation of haploid gametes

• Humans are diploid half of our chromosomes come
  from our mothers, and half from our fathers
• Gametes (ova, sperm) consist of half a set (23
  chromosomes in humans)
• In fertilization, the two sets come together to
  form a complete set (46 chromosomes)

9
Gametes are NOT genetically identical to the
parent cell

• Fewer chromosomes
• May be a mixture of maternal and paternal
  chromosomes (and each gamete may have a different
  mixture)
• In process of meiosis, chromosomes may physically
  exchange information (genes) so that chromosome
  is now unique

10
Independent assortment correct number of
chromosomes, but different combinations
11
What if the chromosomes dont separate correctly?
12
What are the consequences of nondisjunction?

• Usually fatal (many miscarriages occur because
  chromosome number is wrong)
• A few survive most briefly
• Edwards syndrome (trisomy 18) Patau syndrome
  (trisomy 13)
• Why is health so adversely affected?
• Down syndrome (trisomy 21) affected persons can
  survive to adulthood

13
Effects of sex chromosome nondisjunction are
often less severe

• Turner syndrome (female)
• Short stature
• Infertile
• May not develop secondary sexual characteristics
• Klinefelter syndrome
• Effects be not be obvious usually sterile
• XYY (Jacob) syndrome
• Tend to be tall other effects controversial

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Summary

• Hereditary information is contained in
  chromosomes.
• Chromosomes are inherited from two parents in
  sexual reproduction.
• Chromosomes contain genes.
• Different combinations of genes may be inherited
  by offspring, even from the same parents.