GENETICS

1
GENETICS
2
Gregor Mendel

• Genetics is the study of heredity.
• Gregor Mendel (1860s) discovered the fundamental
  principles of genetics by breeding garden peas.

3
Mendel cross-pollinated pea plants

• He cut away the male parts of one flower, then
  dusted it with pollen from another

4
What did Mendel conclude?

• He concluded that factors are passed from one
  generation to the next.

5
The Principle of Dominance

• The Principle of Dominance some alleles are
  dominant and other are recessive.

• Alleles
• 1. Alternative forms of genes.
• 2. Units that determine heritable traits.

6
Dominant and Recessive alleles

• Dominant alleles upper-case
• a. homozygous dominant
• (BB Brown eyes)
• Recessive alleles lower case
• a. homozygous recessive
• (bb blue eyes)
• b. Heterozygous (Bb Brown eyes)

7
Phenotype vs. Genotype

• Arrangement of genes that produces the phenotype
• Example
• 1. TT, Tt
• 2. tt

• Outward appearance
• Physical characteristics
• Examples
• 1.Brown eyes 2.blue eyes

8
SegregationAlleles separate during meiosis
9
Recessive traits show up about 1/4th of the time.

• Because there is only a 25 chance that two
  recessive alleles will be paired together.

10
Punnett square

• A Punnett square is used to show the possible
  combinations of gametes.
• Monohybrid Cross

11
Monohybrid Cross

• Example Cross between two heterozygotes for
  brown eyes (Bb)
• BB brown eyes
• Bb brown eyes
• bb blue eyes

12
Monohybrid Cross
13
Dihybrid Cross
14
Dihybrid Cross
15
Dihybrid Cross
16
Dihybrid Cross

• Example cross between round and yellow
  heterozygous pea seeds.
• R round
• r wrinkled
• Y yellow
• y green

RrYy x RrYy
17
Independent Assortment
This means all gametes will be different!

• Chromosomes separate independently of each other

B F
Bb Ff
b f
Bb Ff
B f
Bb Ff
B F
18
Independent Assortment

• Genes for different traits can segregate
  independently during the formation of gametes
  without influencing each other
• Question How many gametes will be produced
  for the following allele arrangements?
• Remember 2n (n of heterozygotes)
• 1. RrYy
• 2. AaBbCCDd
• 3. MmNnOoPPQQRrssTtQq

19
Answer
1. RrYy 2n 22 4 gametes RY Ry rY
ry 2. AaBbCCDd 2n 23 8 gametes ABCD
ABCd AbCD AbCd aBCD aBCd abCD abCD
3. MmNnOoPPQQRrssTtQq 2n 26 64 gametes
20
Incomplete Dominance

• One allele is not completely dominant over another

21
(No Transcript)
22
Codominance
Black cow white cow spotted cow

• Both alleles are expressed
• Example blood
• 1. type A IAIA or IAi
• 2. type B IBIB or IBi
• 3. type AB IAIB
• 4. type O ii

23
Which shows more genetic variation. (more
combos?)

• Male CC with female Cc

• Male cc with female Cc

24
Genetic Engineering
25
Gene Therapy
26
Is cloning a possibility?

• Is it right to use cloning to create an entirely
  new human being?
• Is it ethical to create an embryonic copy of
  John Doe to supply cells to keep John alive?
• Does a multicellular ball of tissue -- an
  embryo -- have the same rights and status as a
  human being?

27
How does Mendels principles apply to organisms

• The basic principals can be applied to humans as
  well as any other living organism.

28

• Consider thisPunnett square

29

• Many traits are controlled by multiple alleles or
  multiple genes.
• Multiple alleles (more than 2 choices)
• Polygenic (multiple genes control a single trait)

30
Multiple alleles

• the case where three or more alleles of the same
  gene exist. Remember, an organism will have only
  two of these alleles (one from mom and one from
  dad).
• Examples Coat color in rabbits, blood type in
  humans

31
Multiple alleles
32
Polygenic traits

• traits that are determined by alleles from more
  than one gene these traits usually have a range
  of phenotypes
• Examples skin color in humans, height in humans

33
Mapping Genes

• Its easy to imagine that genes on different
  chromosomes assort independently, but what about
  genes that occur on the same chromosome? Dont
  they always appear together?
• Not always due to crossing over. Genes that
  occur together on a chromosome will be separated
  when homologous chromosomes exchange genes.
• The frequency of genes occurring together can
  help us generate a gene map.

34

• The more often two genes occur together, the
  closer they are to each other on the chromosome.
  
• If the genes are never separated by crossing
  over, they always occur together. All offspring
  will look like one of the parents (in reference
  to the genes in question).

35

• If half of the offspring are parental and half
  are recombinations of the parents (in reference
  to the genes in question), then they are said to
  be independent. This means they are either on
  separate chromosomes or they are almost always
  separated during meiosis.
• You will learn to calculate distances and create
  a map in AP Bio, or in college

36
(No Transcript)
37
Human chromosomes

• There are two types of chromosomes.
• Autosomes Of the 46 chromosomes, 44 of them (22
  pairs of chromosomes) are called autosomes
  (non-sex chromosomes).
• Sex chromosomes The last two chromosomes are
  called the sex chromosomes because they determine
  the sex of the person. Females have two X
  chromosomes (XX) and males have one X and one Y
  chromosome (XY).

38

• Gametes
• All gametes are haploid. In humans, that means
  each egg cell and each sperm cell has 1 copy of
  each chromosome for a total of 23 chromosomes.
• Egg cells All human egg cells carry 23
  chromosomes, one of which is a single X
  chromosome. This is written as 23, X.
• Sperm cells In males, there are two types of
  sperm cells- one carries an X chromosome (23, X)
  and one carries a Y chromosome (23, Y).

39

• When a sperm and egg cell combine, half of the
  time the fertilized eggs (also called zygotes)
  are female (46, XX) and half of the time they are
  male (46, XY).

X
X
eggs
X
XX
XX
female
female
Y
XY
XY
male
male
sperm
40

• Sex Linked traits traits that are determined by
  alleles that are found on the X or Y chromosome.
• The Y chromosome is shorter and does not carry
  all the same alleles as the X chromosome.

41

• Females are XX and males are XY.
• Females can be homozygous or heterozygous for a
  trait carried on the X chromosome, but males
  (having only one X chromosome) are hemizygous.

42

• If they inherit a defective gene from the parent,
  then they will exhibit the trait because they
  cannot inherit a second gene to mask it.
• Conversely, a healthy male cannot be hiding a
  bad recessive allele because they only have one X
  chromosome.

43

• Example of a sex-linked Punnett square
• XBXb (heterozygous female with normal vision)
  crossed to XBY (hemizygous male with normal
  vision)

XBY
Y
XB
XB XB
XBY
XB
XB Xb
XbY
XB Xb
Xb
44
Genetics and the Environment

• Characteristics are determined by both genes and
  the environment.
• External While genes will influence the height
  of a plant, the amount of water, sun, and other
  climate conditions will also affect the height.

45
Genetics and the Environment

• Internal There are recent findings that
  proteins involved with DNA can turn genes on or
  off based on environmental factors.
• Certain chemical exposure can turn genes on or
  off (make the traits show up or not) for
  generations after exposure, but there are no
  changes to the DNA (no mutations).
• This new understanding of how genes are expressed
  is called epigenetics.