Lesson 3 Flashcards
Basic Laws of Inheritance
The Basic Laws of Inheritance
Mendelian Genetics
Mendelian Genetics
- Law of Dominance
- Law of Segregation
- Law of Independent Assortment
Any pattern of Inheritance in which traits do not segregate in accordance with Mendel’s Laws
Non-Mendelian Inheritance
Non-Mendelian Inheritance
Co-dominance
Incomplete Dominance
Polygenic Inheritance
Multiple Alleles
Pleiotropy
Gene Linkage
Extra-nuclear Inheritance
Sex-linked Inheritance
In crossing between homozygous organisms for contrasting characters of a pair, ONLY ONE character of the pair appears in the first generation
Law of Dominance
The character that dominates
Dominant
The one that remains unexpressed
Recessive
Only expressed when the offspring has two copies in the same way as the dominant character
Recessive character
T/F: Law of Dominance is strictly only used for genotypic characters and does not represent the phenotype of the individual
True
Law of Dominance: When do homozygous chromosomes separate so that the chromosome with T or t gene is passed to the gamete
Gametogenesis
Law of Dominance: When do two gamete combine and produce a new individual with both the character
Fertilization
The offspring is now called _____ as it contains two different genes for a pair of contrasting characters
Heterozygote or hybrid
This law is not applicable for all living organisms as it is ONLY VALID in the case of DIPLOID organisms and the organisms that undergo sexual reproduction
Law of Dominance
The hybrids or heterozygotes of F1 generation have two contrasting characters of dominant and recessive nature where the alleles though remain together for a long time do not contaminate or mix with each other and separate or segregate at the time of gametogenesis so that each gamete receives only one allele of a character either dominant or recessive
Law of Segregation
This law states that only a single gene copy from a parent is distributed in a gamete and the allocation of the gene copies is entirely random
Law of Segregation
Allows the concept of hereditary factors that remain as separate entities even when present together with other similar entities
Law of Segregation
T/F: Law of Segregation was used to disprove a blending theory by the generation of traits encoded by recessive alleles in the F1 generation
True
Law that is based on the first phase of the meiotic cell division, where homologous chromosome with two copies of the same gene are segregated into individual daughter nuclei
Law of Segregation
Example of Law of Segregation in human skin
Albinism in humans
The lack of pigment production in humans due to the presence of an abnormal recessive trait that results in the lack of production of the tyrosinase enzyme required for the synthesis of melanin
Albinism
This law is ONLY applicable to DIPLOID that are formed FROM HAPLOID gametes during sexual reproduction
Law of Segregation
The law is NOT VALID for genes that are COLLABORATIVE and might vary in expression & COMPLEMENTARY
Law of Segregation
What Mendelian Law works well with a monohybrid cross
Law of Segregation
When the parents differ from each other in two or more pairs of contrasting characters, the inheritance of one pair of characters is independent of the other
Law of Independent Assortment
The law that states all transfer of particular character from parents to the offspring remains unaffected by other characters
Law of Independent Assortment
What Mendelian Law works well with a dihybrid cross
Law of Independent Assortment
Based on meiosis cell division where diploid chromosomes in parents are separated to form haploid gametes that occurs independently from each other in a random manner
Law of Independent Assortment
This law does NOT hold TRUE for LINKED GENES present on the SAME LOCI that are usually inherited together
Law of Independent Assortment
This law is NOT APPLICABLE for genetic traits where they exhibit INCOMPLETE DOMINANCE or CO-DOMINANCE or MULTIPLE FACTORS
Law of Independent Assortment
Believed to be a violation of the Law of Dominance
Co-dominance
Equal expression of traits at the same time
Co-dominance
When sometimes a heterozygote dominant allele does not completely mask the phenotypic expression of the recessive allele; occurs an intermediate phenotype in the heterozygote
Incomplete dominance
Traits are blended together
Incomplete dominance
Example: AB blood type
Co-dominance
Example: Red & White = Pink
Incomplete dominance
When one characteristic is controlled by two or more genes
Polygenic Inheritance
Example: Skin Color
Polygenic Inheritance
Multiple alleles of a given gene
Multiple alleles
Example: ABO blood type & rabbit coat color
Multiple alleles
Some genes that affect MANY different characteristics, not just a single characteristic
Pleiotropy
Example: Marfan Syndrome
Pleiotropy
Each chromosome contains more than one gene; fairly close to each other, tend to be inherited together
Gene Linkage
Occurrence of certain extranuclear genes or DNA molecules in the cytoplasm of many prokaryotic and eukaryotic cells
Extra-nuclear Inheritance
Example: Mitochondria and chloroplasts
Extra-nuclear Inheritance
The inheritance of a trait (phenotype) that is determined by a gene located on ONE of the sex chromosomes
Sex-Linked Inherited
Genes that occur exclusively on the X chromosome
X-Linked genes
Genes that occur exclusively in the Y chromosome
holandric genes
Inheritance in X-Linked or holandric genes
Sex-linked inheritance
Genes in the differential regions are called ___ in males
hemizygous
Shows criss-cross pattern of inheritance
X-Linked Recessive Genes
X-linked recessive are usually found more frequently in
Males
Are usually carriers
Females
X-Linked: When father is affected
Affected: all daughters, 1/2 sons
X-Linked: When both the mother and father bear recessive allele
Affected Female
X-Linked: When only the mother carries the gene
Affected Male
X-Linked: Affected Recessive male
None of the sons are affected
A defect in which a person cannot distinguish between red, green or both colors from other colors
Color-blindness
royal disease; lack of blood protein (clotting factor VIII and clotting factor IX) that causes the inability of blood to clot normally even after a minor injury
Hemophilia (Bleeder’s disease)
X-Linked are usually detected on
Females
X-Linked Males pass it on ____, none on ____
Daughters, Sons
X-Linked Females pass it on ______
1/2 to sons and daughters
- hypophosphatemia (Vit D - resistant rickets)
- hypoplastic amelogenesis (enamel hypoplasia imperfecta)
X-Linked examples
Male to male direct transmission of genes in the non-homologous region of the Y chromosome
Y-Linked Gene Inheritance
- ichthyosis hystrix hypertrichosis (hair on pinna of ear)
- H-Y antigen, height, etc
Y-Linked examples
A table checkboard grid based on the principle of independent assortment
Punnett Square
Who introduced the concept of the Punnett square
Reginald Punnett in 1905
Used to predict genotypes
Punnett squares
