SL Biology topic 4. Go get em IB students.

1. Topic 4
Genetics

2. Genes
• Gene: a heritable factor that controls a
specific characteristic
• Basic unit of inheritance
• Genome: the whole of the genetic
information of an organism

3. Chromosomes
• Chromosomes: large DNA molecules
made up of genes
• Gene locus: the position of a gene on a
chromosome
– In any particular type of chromosome the
same genes are arranged in the same
sequence

4. Alleles
• Allele: a form of a gene, differing from
other alleles of that gene by a few bases;
occupying the same gene locus as the
other alleles of that gene
• Alleles can be recessive or dominant

5. Structure of Chromosomes
• Chromatids: the two parts of a
chromosome
• Centromere: connects the chromatids

6. Gene Mutation
• Gene mutation: change to the base
sequence of a gene
• Base substitution: one base in a gene is
replaced by another base
• Many gene mutations cause diseases
– Example: sickle cell anemia

7. Haploid and Diploid
• Diploid: two full sets of chromosomes; cell
has two of each type of chromosome
• Haploid: only one full set of chromosomes;
cell has one of each type of chromosome
• Homologous: chromosomes with the same
genes in the same sequence, but not
necessarily the same alleles of the genes
• Reduction Division: the number of
chromosomes is halved; change from diploid
to haploid

8. Stages of Meoisis
1. Prophase I
2. Metaphase I
3. Anaphase I
4. Prophase II
5. Anaphase II
6. Telophase II

9. Prophase I
• Homologous chromosomes pair up
• Spindle microtubules grow from each pole
to the equator
• The nuclear membrane begins breaking
down

10. Metaphase I
• The pairs of chromosomes line up on the
equator
• Spindle microtubules attach to different
chromosomes from each pair

11. Anaphase I
• The homologous chromosomes are pulled
from their pairings to opposite poles
– This halves their chromosome number
– Each chromosome still has two chromatids
held with a centromere
• Cell membrane will pull in to divide the cell
in two between the poles

12. Prophase II
• The cell has divided to form two haploid
cells
• New spindle microtubules grow from the
poles to the equator in both cells

13. Anaphase II
• Plasma membrane around the chromosomes
is gone
• Spindle microtubules have attached to the
chromosomes
• Centromeres have divided
• Chromatids pulled to opposite poles
• Cell membrane pulls inward to divide cells

14. Telophase II
• There are now four haploid cells from one
diploid cell
• Nuclear membranes have reformed
• Each nucleus now has half as many
chromosomes as the parent cell

15. Karyotypes
• Karyotype: the number and appearance of
chromosomes in an organism
• Living organisms that are members of the
same species usually have the same
karyotype

16. Deduce Gender
• Amniocentesis:
– Amniotic fluid is removed from amniotic sac around
the fetus
– Needle draws out amniotic fluid that contains cell from
the fetus
• Chorionic villus sampling
– Cells are removed from fetal tissues in the placenta
– They are incubated with chemicals that stimulate
them to divide by mitosis
– A fluid is used to spread out the chromosomes
– A microscopic image is taken of the chromosomes
and then arranged into pairs according to their size
and structure (this process is karyotyping)

17. Analysis of Karyotypes
• Can identify gender or abnormalities
• Non-disjunction: non-separation of
chromosomes
– Gametes are produced with either one
chromosome too many or too few
• Games with one chromosome too few
usually die; one chromosome too many
sometimes survive

18. Mendel’s Monohybrid Crosses
• Mendel crossed varieties of pea plants
– Round and wrinkled peas
• F1 Generation: first set of offspring
• F2 Generation: offspring of the offspring
• Inheritance is based on factors that can be
passed on from generation to generation

19. Genetic Terms
• Homozygous: two identical alleles of a
gene
• Heterozygous: two different alleles of a
gene
• Dominant Allele: an allele that has the
same effect on the phenotype whether it is
heterozygous or homozygous
• Recessive Allele: an allele that effects the
phenotype only in the homozygous state

20. Pedigree Charts
• Shows the members
of a family and how
they are related to
each other
• Circles = females
Squares = males

21. Sex Chromosomes and Gender
• Two sex chromosomes determine the
gender of a child
• X chromosome is relatively large and
carries many genes
• Y chromosome is much smaller and
carries only a few genes
• XX = Female, XY = Male
• Women pass on X; Men pass on X or Y

22. Sex Linkage
• Sex Linkage: association of a
characteristic with gender, because the
gene controlling the characteristic is
located on a sex chromosome

23. Choosing Symbols for Alleles
• One dominant and one recessive allele:
– A letter is chosen (Example: B)
– Dominant allele is capitalized (B); recessive allele is
lower case (b)
• Co-dominant alleles:
– A letter is chosen (Example: C)
– This letter and a superscript letter represent each
allele (Example: Cw and CJ)
• Sex-linked dominant and recessive alleles
– Letter X shows X chromosome; Y shows Y
chromosome
– Example: XH XG

24. Using Pedigree Charts
• Can deduce whether a character is
caused by a dominant or recessive allele
and whether or not it is sex-linked
• Can deduce the genotypes of individuals

25. Using Test Crosses
• Test cross: an individual that might be
heterozygous is crossed with an individual
that is a homozygous recessive
• This allows you to deduce the genotype of
the unknown organism being tested

26. Polymerase Chain Reaction
• Polymerase Chain Reaction: DNA is
copied repeatedly to produce many copies
of the original molecules
• DNA from very small samples can be
amplified using a DNA polymerase
enzyme from Thermus aquaticus

27. Gel Electrophoresis
• Gel Electrophoresis: method of separating
mixtures of proteins, DNA or other molecules that
are changed
• Stages:
1. The mixture is placed on a thin sheet of gel
2. An electric field is applied to the gel by electrodes on
both ends
3. Positively and negatively charged particles will move
towards their respective electrodes
• The rate of particle movement depends on the
size and charge of the molecules
– The smaller the moelcule, the faster

28. DNA Profiling
• Satellite DNA: short sequences of bases
that are repeated many times
• Using PCR and Gel Electrophoresis, the
DNA can be distinguished
• Can be used for forensic investigations
(court cases) and paternity investigations
(finding the father)

29. Genetic Modification
• Genetically Modified Organisms: Organisms
that have had genes transferred to them
• Two examples:
– Transfer of a gene for blood clotting from
humans to sheep, where it is produced in the
sheep’s milk
– Transfer of a gene for resistance to the
herbicide glyphosate from a bacterium to a
crop, allowing the crop to be sprayed with the
herbicide

30. Clones and Cloning
• Clone: A group of genetically identical
organisms or genetically identical cells
derived from a single parent cell
• Reproductive cloning: creating more
organisms from a parent with a desirable
combination of characteristics
• Therapeutic cloning: producing skin or
other tissues needed to treat a patient

31. Plant and Animal Cloning
• Plant cloning is simple: take a piece from
the root, stem, or leaf
• Animals are not as simple: it is hard to
predict which embryos will develop into
animals with desirable characteristics and
should therefore be cloned

32. Cloning Techniques
• Stages
1. Udder cells taken from a donor sheep
2. Unfertilized egg cells taken from another sheep
3. Nucleus is removed from each egg cell
4. Egg cells are fused with donor cells using
electricity
5. Fused cells become an embryo
6. Embryo implanted into a surrogate mother
7. Lam successfully born genetically identical to
sheep who donated udder cells

33. Therapeutic Cloning in Humans
Arguments for therapeutic cloning: Arguments against therapeutic cloning:
Embryonic stem cells can be used
for therapies that save lives and
reduce suffering
Every human embryo is a potential
human being, which should be given a
chance of developing
Cells can be removed from embryos
that have stopped developing, so
would have died anyway
More embryos may be produced than
needed, so some may have to be killed
Cells are removed at a stage when
embryos have no nerve cells and
cannot feel pain
There is a danger of embryonic stem
cells developing into tumor cells

34. Human Genome Project
• Human Genome Project: aims to find the
location of all of these genes on the human
chromosomes and the base sequence of all
of the DNA that makes them up
• International cooperative project
• It will make it easier to study how genes
influence human development, easier
identification and curing of genetic diseases,
and new insights into the evolution of
humankind