1. Human Heredity, Part 1

2. What We Should Already Know:
In order to reproduce, organisms must pass on their genes to the next generation.
Genes, which are made of DNA, are stored in large, tangled structures called chromosomes.

3. What We Should Already Know:
Humans, like other animals, are diploid:
that is, their cells contain two copies of each chromosome.

4. What We Should Already Know:
If they were like bacteria, human beings would just copy all of their chromosomes and their offspring would be clones (genetically identical copies)

5. What We Should Already Know:
But human beings are not like bacteria! Instead, humans (like all other animals) reproduce sexually: that is, they exchange genes with other members of their species, producing offspring which are genetically unique.

6. What We Should Already Know:
In order to do this, however, species which practice sexual reproduction must manufacture two different kinds of haploid cells, called gametes, that each have only one copy of each chromosome.

7. What We Should Already Know:
One type of gamete is typically small and manufactured in large quantities. Individuals that make this kind of gamete (called sperm) are known as males, and adult males manufacture millions of gametes every day!

8. What We Should Already Know:
The other type of gamete is typically large, complex and manufactured in tiny quantities. These cells, called eggs, are made by females. If these cells fuse with a sperm, the fertilized cell (or zygote) can develop into a new human being.

9. Chromosomes can be isolated under a microscope and photographed.
Human Chromosomes
Chromosomes can be isolated under a microscope and photographed.

10. Human Chromosomes
The separate images can be assembled into a single picture that shows the entire set of chromosomes, called a karyotype.

11. Human Chromosomes
Here we see a set of chromosomes. They are arranged in pairs of similar size and shape, called homologous chromosomes.

12. How many pairs in this karyotype? How many total chromosomes?
Human Chromosomes
How many pairs in this karyotype?
How many total chromosomes?

13. One pair, position 23, shows two chromosomes
Human Chromosomes
One pair, position 23, shows two chromosomes
that do not have the same size and shape.

14. Human Chromosomes
The larger one is often called the X chromosome, while the smaller is referred to as the Y chromosome.

15. Human Chromosomes
It is this pair that determines whether an individual is male or female, and so position 23 are often called the sex chromosomes.

16. Human Chromosomes
Positions 1-22, which are not involved in sex determination, are classified as autosomes.

17. All genetically-normal human beings have
Human Chromosomes
All genetically-normal human beings have
at least one copy of the X chromosome. . .

18. Human Chromosomes
Females have two copies, and so they are said to be XX; males, on the other hand, are XY.

19. Since only males have Y, it is the father
Human Chromosomes
Since only males have Y, it is the father
that determines the child’s sex.

20. Gametes (eggs and sperm) are produced in a version
of cell division called meiosis. In the first part
of meiosis, the homologous chromosomes seen in a
normal karyotype are each copied, then come together
in groups of four called tetrads.

21. They are so close that whole chunks of chromosome
may be exchanged, a process called ‘crossing-over’.
This process generates new combinations of genes
and is one of the reasons that sexual reproduction
leads to genetically-unique individuals.

22. Ordinarily, the tetrads separate, undergo
two rounds of cell division right after
another,producing four haploid daughter
cells, each with just one copy of each
chromosome,and it is these cells
that will become either eggs and sperm.

23. But what if the chromosomes
don’t properly separate?

24. This condition, called non-disjunction,
will lead to daughter cells (and,
eventually, gametes) that have
the wrong number of chromosomes.

25. If one of these defective egg or sperm
are fertilized, this can lead to
an individual with
a chromosomal disorder . .

27. Meiosis Gone Wrong: Down's Syndrome

28. Meiosis Gone Wrong: Down's Syndrome

29. Meiosis Gone Wrong: Down's Syndrome

30. Meiosis Gone Wrong: Down's Syndrome

31. Meiosis Gone Wrong: Down's Syndrome
is a chromosomal disorder caused by
non-disjunction

32. Meiosis Gone Wrong: Down's Syndrome
is a chromosomal disorder caused by
non-disjunction
is caused by trisomy (having 3 copies) of
chromosome 21

33. Meiosis Gone Wrong: Down's Syndrome

34. Meiosis Gone Wrong: Down's Syndrome
is a chromosomal disorder caused by
non-disjunction
is caused by trisomy (having 3 copies) of
chromosome 21

35. Meiosis Gone Wrong: Down's Syndrome
leads to mental retardation, birth defects
and other health problems
occurs in about 1 out of every 800 live
births in the U.S.

36. Down’s Syndrome: is more likely to affect
the babies of older mothers, whose eggs have
accumulated more mutations.

38. Down’s Syndrome: is a condition that affects the
Meiosis Gone Wrong: Down's Syndrome
Down’s Syndrome: is a condition that affects the
lives of human beings, who despite their limitations
can still lead productive, happy lives

39. Sex Chromosome Disorders:
typically lead either to death or sterility
no individual can survive without an X
chromosome, while the wrong number of
either X or Y usually makes the individual
sterile

40. Sex Chromosome Disorders:
typically lead either to death or sterility
no individual can survive without an X
chromosome, while the wrong number of
either X or Y usually makes the individual
sterile
Sex Chromosome Disorders:

41. Sex Chromosome Disorders:
Turner’s Syndrome produces females who
often appear and act normal, but who never
develop ovaries capable of making eggs;
they are sterile.
Sex Chromosome Disorders:

42. Turner’s Syndrome produces females who
often appear and act normal, but who never
develop ovaries capable of making eggs;
they are sterile.

43. Sex Chromosome Disorders:
Kleinfelter’s Syndrome produces males
whose appearance and behavior as adults is
often unusual: a relatively high number of
these individuals are institutionalized.
Sex Chromosome Disorders:

44. Kleinfelter’s Syndrome produces males
whose appearance and behavior as adults is
often unusual: a relatively high number of
these individuals are institutionalized.

45. Sex Chromosome Disorders:
Students often ask
whether or not any
individual human beings
are truly hermaphroditic:
that is, naturally having the
appearance or function of
both sexes?
The answer is no!

46. However, for a variety of reasons, some
Sex Chromosome Disorders:
However, for a variety of reasons, some
individuals appear to suffer from gender identity
problems, and this may have a genetic basis.
Affected individuals may choose surgery to alter
their appearance, and some (not all) experience
an improvement in the quality of their lives
as a result.
As with Down’s Syndrome, those affected by
conditions which affect their identity or appearance
deserve to be treated as human beings.