Download Patterns of Inheritance

Patterns of
Inheritance
Chromosomes
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Karyotype: Entire set of chromosomes from a single cell
Chromosomes. Each double DNA helix is packaged into a chromosome.
Every species has a particular number of chromosomes
Hereditable information exists in discrete units called genes
A gene is the specific portion of chromosome that has the complete
information to synthesize …
a specific protein
Gregor Mendel
• Before settling down as a monk in the monastery of
St. Thomas in Brünn.
• Gregor Mendel tried his hand at several pursuits,
including health care and teaching.
• He studied botany and mathematics among other
subjects. This training proved crucial to his later
experiments, which were the foundation for the
modern science of genetics.
• Although Mendel worked without
knowledge of genes or chromosomes, we
can more easily follow his experiments.
Genetic concepts
• A gene´s specific physical location on a
chromosome is called locus (plural, loci).
• Homologous chromosomes carry the same genes,
located at the same loci.
• Alternate forms of the gene, is called alleles.
• If both homologous chromosomes in an organism
have the same allele are a given gene locus, the
organism is said to be homozygous at the gene locus
• If two homologous chromosomes have different
alleles at a given locus, the organism is
heterozygous.
Pair of homologous
chromosomes
The M locus contains the M gene,
which is involved in determining leaf
color. Both chomosomes carry the
same allele of the M gene. This tomato
plant is homozygous for the M gene.
The D locus contains the D gene,
which is involved in determining plant
height. Both chromosomes carry the
same allele of the D gene.This tomato
plant is homozygous for the D gene.
The Bk locus contains the Bk gene,
which is involved in determinig fruit
shape. Each chromosome carries a
different allele of the Bk gene. This
tomato plant is heterozygous for the Bk
gene.
Mendel´s results, allow us to develop a five-part
Model:
1. Each trait is determined by pairs of discrete
physical units (alleles), which we now call genes.
Each individual has two genes for a given trait.
2. Pairs of genes on homologous chromosomes
separate from each other during gamete formation,
so each gamete receives only one allele of an
organism´s pair of genes. This conclusion is
known as Mendel´s law of segregation. Each
gamete receives only one of each parent´s pair of
genes for each trait.
3. Which member of a pair of genes becomes
included in a gamete is determined by chance.
4. When two alternate forms of a gene are present,
one (the dominant allele) will mask the
expression of the other (the recessive allele).
5. True-breeding (all the offspring produced are
identical to the parent plant) organisms have two
of the same alleles for a given trait.
Mendel´s model
• Using letters to represent the different alleles, we
will assign the uppercase letter P (dominant allele)
to the allele for purple and the lowercase letter p
(recessive allele) to the allele for white.
• Purple-flowered plant has two alleles for purple
(PP), whereas a white-flowered plant has two alleles
for white (pp). All the sperm and eggs produced by a
PP plant carry the P allele; all the sperm and eggs of
a pp plant carry the p allele.
F1
P
P
p
P
p
P
p
p
P
p
P
p
Result: 100% P
Gametes from F1 plants
Sperm
eggs
|
P
+
F2 offspring
P
PP
P
+
p
Pp
p
+
P
Pp
p
+
p
pp
p
P
F2
P
P
P
P
p
p
P
p
p
p
Results: 75% P, 25% p
• Therefore, three types of offspring can be
produced: PP, Pp, and pp. The three types
occur in the approximate proportions of 1/4
PP, 1/2 Pp, and 1/4 pp.
• The actual combination of alleles carried by
an organism (for example, PP or Pp) is its
genotype.
• The organism´s traits, including its outward
appearance, behavior, digestive enzymes,
blood type, or any other observable feature,
make up its phenotype.
Punnet Square
PPxPp
P
p
P
P
P
P
p
P
P
P
P
p
Result: 50 % PP, 50 % Pp
(Genotype)
Result: 100 % P
(Phenotype)
Punnet Square
Ppxpp
p
P
p
P
p
p
p
p
P
p
p
p
Result:
Result:
Genotype: 50% Pp, 50 % pp Phenotype: 50 % P, 50 % p
• Mendel´s Hypothesis can be used to predict
the outcome of new types of single-trait
crosses.
• Mendel hypothesized that genes on different
chromosomes are inherited independently.
Problem 1
• Your Grandmother (mother side) is diabetic
(Recesive) and so is your Grandfather
(Father side).
• A) What are your chances of being diabetic
if both of them got married with a normal
homozygous?
• (Hint: You must do first your parents.)
Problem 1b
• Your Grandmother (mother side) is diabetic
(Recesive) and so is your Grandfather
(Father side).
• b) What are your chances of being diabetic
if your Grandfather (mother side) is a
normal heterozygous and your Grandmother
(Father side) is a normal homozygous?
Problem 1.c
• Your Grandmother (mother side) is diabetic
(Recesive) and so is your Grandfather
(Father side).
• C) What are your chances of being diabetic
if both of them got married with a normal
heterozygous?