Download Inheritance

PATTERNS OF INHERITANCE
Chapter 11
Pre-Mendel’s Theories
Blending Hypothesis: when parents
with different traits have offspring,
they will always show a blending of
the traits
Spontaneous generation: Non-living
matter giving rise to living matter
Homunculus: The little man inside
the sperm
Mendel’s experiments with pea plants
Particulate hypothesis: Parents
pass on to their offspring separate
and distinct factors (genes) that are
responsible for inherited traits
Gene: factors pass on from parents
to offspring. Sequence of DNA that
determines a trait
Trait: a specific characteristic of an
individual
 Genetics: the study of heredity
https://www.youtube.com/watch?v=hf9XlqXcal0 3:00
https://www.youtube.com/watch?v=ExaQ8shhkw8 10:00
Mendel’s experiments started with
True-breeding plants: when selffertilized, a true-breeding plant
produces offspring identical in
appearance to itself generation
after generation
 Cross-fertilization, sperm from the pollen of one
flower fertilizes the eggs in the flower of a
different plant
the offspring of two different true-breeding
varieties are called hybrids.
Monohybrid cross: pairing in which the parent
plants differ in only one (mono) character.
HUMAN KARYOTYPE
A display of all the 46
chromosomes of an
Individual.
9.5 page 2
Genus species (organism)
NUMBER OF CHROMOSOMES
 Homo sapiens (human)______________________________46
 Mus musculus (house mouse)_________________________40
 Drosophila melanogaster (fruit fly)_____________________8
 Caenorhabditis elegans (microscopic roundworm)_________12
 Saccharomyces cerevisiae (budding yeast) ______________32
 Arabidopsis thaliana (plant in the mustard family) ________10
 Xenopus laevis (South African clawed frog)______________36
 Canis familiaris (domestic dog)________________________78
 Gallus gallus (chicken) ______________________________28
 Zea mays (corn or maize)____________________________20
 Muntiacus reevesi (the Chinese muntjac, a deer) _________23
 Muntiacus muntjac (its native american cousin) __________6
 Myrmecia pilosula (an ant) ___________________________2
 Parascaris equorum var. univalens (parasitic roundworm)___2
 Cambarus clarkii (crayfish)___________________________200
 Equisetum arvense (field horsetail, a plant)______________216
Horsetail
Mendel’s principle of segregation
There are alternative forms of factors
(genes) called alleles.
For each character, an organism has
two alleles for the gene controlling that
character, one from each parent.
Homozygous = same alleles
Heterozygous = different alleles
Principle of segregation (cont.)
When only one of the two different alleles
in an heterozygous individual appears to
affect the trait, that allele is called the
dominant allele. The allele that does not
appear to affect the trait is called the
recessive allele
The two alleles for a character segregate
(separate) during the formation of
gametes (sex cells). Each gamete carries
only one allele of each character
(Principle of segregation)
Phenotype refers to the
observable trait (purple flowers)
Genotype refers to the
combination of alleles (PP)
Phenotypic ratio: ratio of
plants with purple flowers to
those with white flowers (3
purple : 1 white)
Genotypic ratio: ratio of
possible combinations of
alleles (1 PP : 2 Pp : 1 pp)
Phenotype refers to the
observable trait (purple flowers)
Genotype refers to the
combination of alleles (Pp)
• Phenotypic ratio: ratio of
plants with purple flowers to
those with white flowers (3
purple : 1 white)
• Genotypic ratio: ratio of
possible combinations of alleles
(1 PP : 2 Pp : 1 pp)
Probability and Punnett Squares
Probability: Chance of
Something happening
Punnett Square: Diagram
used to show the probability
of a genetic cross
How can you find out the
genotype of an individual
showing the dominant trait?
TESTCROSS
In a testcross, an individual of
unknown genotype, but
dominant phenotype is crossed
with a homozygous recessive
individual
DIHYBRID CROSS
crossing of organisms
differing in two characters
Possible allele combinations from
a heterozygous dihybrid for
round an yellow seed
Rr Yy
DHYBRID CROSS
Principle of Independent Assortment
During gamete formation in an F2
cross, a particular allele for one
character can be paired with either
allele of another character
Not all traits are inherited
following the patterns found by
Mendel in pea plants
Intermediate or incomplete
inheritance
Codominance
Multiple alleles
Polygenic inheritance
Environment - Epigenetics
 http://www.biologycorner.com/bio2/genetics/notes_incomplete
_dominance.html
Intermediate or Incomplete Inheritance
The heterozygotes have a
phenotype that is intermediate
between the phenotypes of the
two homozygotes
Codominance
 condition in which both alleles for a gene
are expressed when present (cattle: red,
white, roan coat = codominant)
Multiple Alleles -
Genetic Determination of Blood Type
For many genes several alleles exist in the
population.
Phenotype
Genotypes
(Blood type)
Multiple alleles control the character of blood type
ii
in humans. O
A
IA IA or IA i
B
IB IB or IB i
There are six possible genotypes.
The alleles IA and IB exhibit codominance,
IA IB
AB
meaning that a heterozygote expresses both traits
 http://ww
w.youtube
.com/watc
h?v=L06T
JTMVkBo
Polygenic inheritance
 When two or more genes affect a single
character
 In humans, height, eye and skin color
have polygenic inheritance
The Environment - Epigenetics
Phenotype depends on
environment as well as genes
Temperature affects fur color in
Siamese cats
In humans
Nutrition affects built
Exposure to sun affects skin
tone
Sex-Linked Genes (any gene
located on sex chromosomes)
 http://www.youtube.com/watch?v=EGzFsme22s8
Bill Nye – Greatest Scientific Discoveries (genetics 3:408:00)
HUMAN KARYOTYPE
A display of all the 46
chromosomes of an
Individual.
 http://www.youtube.com/watch?v=CWyrp3hu4KE
Morgan's monohybrid
cross for fly eye color
produced a 3 : 1
phenotypic ratio of
red to white eyes in
the F2 generation.
However, none of the
flies with white eyes
were female.
Chromosome Theory of Inheritance
Genes are located on chromosomes
Behavior of chromosomes during
meiosis and fertilization accounts for
inheritance patterns – chromosomes
undergo segregation and independent
assortment during meiosis
INDEPENDENT
ASSORTMENT OF
CHROMOSOMES
DURING GAMETE
FORMATION
Gene locus: location at which alleles
of a gene reside on homologous
chromosomes
Linked genes: genes that are located
in the same region of a chromosome
Genetic linkage: tendency for the
alleles on one chromosome to be
inherited together. The closer two
genes are on a chromosome, the
greater the genetic linkage
Meiosis
• Organisms that reproduce sexually have
specialized cells called gametes (sex cells)
• Gametes are the result of a type of cell
division called meiosis
Diploid and haploid
• Almost all human cells are diploid or containing two
homologous sets of chromosomes
2n = 46
• Eggs and sperm cells (gametes) are haploid or
containing a single set of chromosomes
n = 23
MITOSIS
Meiosis
haploid egg and sperm
diploid zygote
In the human life cycle a haploid egg and sperm fuse and form a diploid zygote. Mitosis
produces an embryo with numerous cells that continue to multiply and develop.
http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio17.swf::Comparison%20of%20Meiosis%20and%20Mitosis
MEIOSIS
MITOSIS
Original diploid cell
2n
2n
2n
2 diploid daughter cells
Genetic variation is a result of two
processes that occurs during meiosis:
• Independent assortment of chromosomes, and
• Crossing over
• During metaphase I, the independent assortment
of chromosomes that end up in the resulting cells
occurs randomly
• Crossing over:
exchange of genetic
material between
homologous
chromosomes during
prophase I of meiosis
• Genetic recombination: new combination of
genetic information in a gamete as a result of
crossing over during prophase I of meiosis
(pages 195, 200, & 201)
TYPE OF CELL (that undergoes
this division)
# OF CELL DIVISIONS
Starts/ends as diploid or
haploid cell
# OF DAUGHTER CELLS
# OF CHROMOSOMES AFTER
DIVISION
EXCHANGE OF DNA (Y/N)
UNIQUE OR IDENTICAL CELL
AFTER DIVISION
MITOSIS
MEIOSIS
Development of egg and sperm