Patterns of Inheritance

1
Patterns of Inheritance

• Chapter 10

2
Blending Hypothesis of Inheritance

• Blending hypothesis (1800s)
• Early explanation of how offspring inherit trait
  from both parents
• Example if a red flower plant crossed with a
  yellow flower, the offspring would be orange
• Later discarded

3
Gregor Mendel

• Austrian monk
• Father of Genetics (study of heredity)
• Said parents pass on to their offspring separate
  and distinct genes
• Studied 7 characteristics in pea plants

4

• True breeding plants
• A true plant will show the same physical
  appearance generation after generation after
  self-fertilization
• Cross fertilization
• The sperm from the pollen of one true flower
  fertilizes the eggs in the flower of a different
  plant

5
Mendel's Experiments

• Cross-fertilized 2 true-breeding plants each with
  contrasting traits (i.e. white and purple
  flowers)
• What color of flowers do you think the offspring
  plants were?

6
Mendelss Principle of Segregation

• P generation
• Parental plants (purebred and true breeding)
• F1 generation ( F for filial son)
• Hybrid offspring
• Hybrids
• The offspring of 2 different true-breeding
  varieties
• F2 generation
• When F1 self-fertilize or fertilize each other

7
Monohybrid Cross

• Monohybrid cross
• Cross fertilization in which only one physical
  characteristic is considered
• In Mendel's cross, all F1 were purple but ¼ of F2
  were white

8

• There are alternative forms of genes which
  determine physical appearances
• Allele is the term
• Example Flower color can be white or purple

9

• For each characteristic, an organism has 2
  alleles for genes controlling the physical
  appearances (one from each parent)
• If 2 alleles are the same homozygous
• If 2 alleles are different heterozygous

10

• Dominant alleles determine the physical
  appearance in a heterozygous individual.
• Recessive allele is the other allele that does
  not affect the physical appearance
• Capital letter represents dominant allele P
• Lower case letter represents recessive allele p

11

• Phenotype is the physical appearance
• Genotype is the genetic makeup
• Possible genotype are PP, Pp, pp.

12

• The two alleles for a character segregate
  (separate) during meiosis so that each gamete
  carries only one allele for each character, known
  as principle of segregation.

13
(No Transcript)
14
Dihybrid Crossa cross that shows the possible
offspring for two traits
Coat Texture R Rough r Smooth
Fur Color B Black b White
15
Intermediate Dominance/Incomplete Dominance

• Heterozygotes have a phenotype intermediate
  between the phenotypes of the two homozygote
• This is referred to as INCOMPLETE DOMINANCE
• Rules (example snapdragon flowers)
• Capital/lower case letters not used
• Instead, a C for color is paired with a
  superscript R for red and W for white
• CR CR is red and CW CW is white
• CR CW is pink

16
(No Transcript)
17
There is a breed of chicken called Andalusians,
black and white parents produce F1 hybrid
offspring, called "blues," with grayish-blue
feathers. Because neither the black nor white no
allele is dominant, capital and lowercase letters
are not used to represent them.
18
Instead, a C for "color" is paired with a
superscript B for "black" or W for "white" to
represent the two alleles. A heterozygote
chicken has one of each allele, CBCW, and is
grayish-blue in color
19
Although the F1 phenotypes are intermediate, this
inheritance pattern does not support the blending
hypothesis. This is because the parent
phenotypes can reappear in the F2 generation.
20
Multiple alleles

• Heterozygote express the distinct traits of both
  alleles
• Example Human blood system
• A, B, AB, or o
• The letters are antigens found on the surface of
  red blood cells
• Red blood cells may be coated with one protein
  (A), the other (B), both (AB), or neither (O)
• There are six possible genotype combinations

21
ABO blood type is a genetic example of multiple
alleles. There are three alleles in the gene pool
for ABO blood type. IA IB i
22
IA codes for protein A IB codes for protein
B i codes for neither protein A nor protein B.
23
Within this multiple allele pool the gene
interactions illustrate both simple dominance as
well as co-dominance.
Remember each individual has only two alleles for
each trait even if there are multiple alleles in
the gene pool. IAIA both
code for A type blood IAi
24
Phenotype Genotype Protein on RBC (antigen) Antibodies in the blood plasma
Type A IA IA and IA i A b
Type B IB IB and IB i B a
Type AB IA IB A and B -------------
Type O ii ----------- a and b
25
ABO Blood System

• Antibodies (proteins) also found in the blood
  serum that attacks foreign antigens
• Blood A has antibody Anti-B
• Blood B has antibody Anti-A
• Blood AB has no antibody
• Blood O has Antibody Anti A and B
• Blood O is the universal donor
• Blood AB can receive any blood type

26
Rh Factor

• Rh positive (Rh ) has protein in blood
• Rh negative (Rh -) has no protein in blood
• Rh is dominant

27
Some of us have it, some of us don't. If it is
present, the blood is Rh positive, if not it's Rh
negative. So, for example, some people in group
A will have it, and will therefore be classed as
A (or A positive). While the ones that don't,
are A- (or A negative). And so it goes for
groups B, AB and O. 85 of the population is Rh
positive, the other 15 of the population is
running around with Rh negative blood.
28
(No Transcript)
29

• A person with Rh- blood can develop Rh
  antibodies in the blood plasma if he or she
  receives blood from a person with Rh blood,
  whose Rh antigens can trigger the production of
  Rh antibodies.

• A person with Rh blood can receive blood from a
  person with Rh- blood without any problems.

30
Definition

• Some traits are determined by the combined effect
  of two or more pairs of alleles. These traits
  are called polygenic traits.
• Each pair of alleles adds something to the
  resulting phenotype.
• Other names for polygenic traits are
  multi-factorial traits, or quantitative traits.

31
Polygenic traits are continuous

• Because so many alleles contribute to the final
  phenotype, a variety of phenotypes can occur!
• For example, height is a polygenic trait.

32
Polygenic Traits are Continuos

• When dealing with polygenic traits that are only
  controlled by two pairs of alleles, we can
  complete Punnett squares to determine the
  genotypes and phenotypes of the F1 generation.

33
Blood Typing
Blood Type Anti-a Sera Anti-b Sera
A Clumping No clumping
B No clumping Clumping
AB Clumping Clumping
O No clumping No clumping
34
(No Transcript)
35
Sex-linked genes

• The eggs contain a single X chromosome and sperm
  contain either an X or a Y
• Sex of the offspring depends on whether the sperm
  that fertilizes the egg has an X or a Y
• Any gene located on a sex chromosome (X) is
  called a sex-linked gene
• Most are found on the X (2,000) and few on the Y
  (24)

36
Sex-linked traits

• Written as a XRXr for heterozygous.
• Y chromosome carries no allele and the phenotype
  is dependant upon the womans allele
• Therefore, males carry one allele for a
  sex-linked trait.

37
Sex-linked disorders

• Red-green blindness
• Hemophilia (inability of blood to clot)