Download 1. Inheritance-general

Genes  Traits
Content:
1. Genetic inheritance
2. Gene interactions
3. Polygenic traits
4. Phenotype
The limits of
Mendelian genetics
1.
Types of inheritance:
1. Mendelian inheritance
Genetic
2. Non-Mendelian inheritance
inheritance
3. Polygenic inheritance
4. Epigenetic inheritance
2.
Mendelian inheritance:
1. Autosomal inheritance
a. dominant/recessive inheritance
b. intermediate inheritance
c. codominant inheritance
2. Sex-linked inheritance
a. dominant/recessive X chromosome-linked inheritance
c. Y chromosome-linked inheritance
3.
The limits of Mendelian genetics
- Manifestation of phenotype (penetrance, expressivity)
- The problem of monogenic inheritance
The manifestation of phenotype
4.
frequency, expressed as a percentage, with which a particular gene produces
Penetrance : theits effect
in a group of organisms
Complete penetrance: phenotype is always manifested in the presence of a certain allele
Incomplete penetrance: phenotype is not always manifested in the presence of a paricular allele
An autosomal dominant disease does not affect every individual
degree to which a particular gene produces
Expressivity: the
its effect in an organism
Monogenic traits
5.
Genetics of monogenic traits
A
B
poligenic
Monogenic traits
X
eye color
AB
0
AB0, etc.
blood groups
tongue rolling
----------------------------------------Monogenic diseases
(2% of genetic diseases)
albinism
Albinism (type 1):
Phenylketonuria:
Galactosemia:
Sickle cell anemia:
phenylketonuria
galactosemia sickle cell anemia
mutation of tyrosinase gene (it catalyzes the production of melanin from tyrosine by oxidation)
mutation of hydroxylase gene (role in metabolism of phenylalanine); it causes mental retardation
galactose-1-phosphate uridil transferase (cleaves galactose) deficiency; it causes liver and brain malfunction
glutamate  valin substitution at the 6th position of -globin
White skin
Albinism
- Albinism can be caused by mutation in genes other than tyrosinase gene:
 more gene  1 phenotype
- Mutation in tyrosinase causes other complications :  1 gene  more phenotype
(eye problems, e.g. nystagmus)
-----------------------------------------
Pale skin
H. neanderthalensis
Mutation in MC1R gene
Common ancestor (700K y)
In different position in Neanderthal than in H. sapiens
But: skin color is determined by multiple genes
6.
4.
7.
1 gene - 1 complex trait
homosexuality
speech
intelligence alcoholism
depression
suicide
religious belief
5.
8.
Mendel’s discoveries
1822-1884
What did he observe?
wrinkly smooth
green yellow
1. The specific characters of pea retain their identity during cultivation
2. 3:1 split in F2 generation
-----------------------------------------------------------------------------------What had he concluded?:
√
√
1. The material of inheritance is packed to discrete packages
2. Each gene can have two variants (alleles) in an individual - diploid
---------------------------------------------------------The „1 gene, 1 phenotype” paradigm of Classical and
Modern Genetics
- one gene encodes a single phenotype – the principle is wrong
X
X
- one allele encodes a single phenotype variant – restricted validity
Phenotype: anything that is part of the observable structure, function or behavior of an organism
Paradigm: generally accepted views of a discipline
Mendel’s radio
What is the problem?: Interpretation of 1 gene, 1 phenotype relationship
The function of a transistor:
1. suppression of howl
2. production of music
Real function: modulation of signal and voltage
9.
10.
Messages
1. The 1 gene, 1 phenotype approach is reductionist; the effect of a gene can
only be evaluated in the cellular and genetic context
2. There are few monogenic traits and behaviors in nature
3. The term „monogenic disease” is a disorder (not necessarily with a single symptoms)
caused by a mutation in a single gene
Monogenic trait: a particular phenotype determined by a single gene
Reductionist: so much oversimplified idea that it is mistaken
Non-Mendelian genetics
1.Maternal inheritance
2. Mosaicism
Maternal
inheritance
(= mitochondrial)
11.
Maternal
inheritance
(= mitochondrial)
11.
Maternal versus paternal
mitochondria
11.
Maternal
inheritance
(= mitochondrial)
Homoplasy
no disease
Heteroplasy
mild disease
severe disease
Mosaicism
1. Germline mosaicism: in gonadal cells
- new mutation in germline formation
2. tissue mosaicism: in body cells
- types:
(a) post-zygotic mutations
(b) chimeras
Fusion of 2 genotypes
(c) mitotic errors
(d) X chromosome inactivation
Non-sweating areas
12.