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Cytogenetics: Inheritance Patterns, Chromosomal Abnormalities, and Molecular Techniques, Study notes of Genetics

Philippine Women's University (PWU)Genetics

A comprehensive overview of cytogenetics, focusing on patterns of inheritance, including mendelian and non-mendelian inheritance. It delves into various types of non-mendelian inheritance, such as incomplete dominance, codominance, polygenic inheritance, lethal genes, non-lethal genes, and pleiotropy. The document also explores extranuclear inheritance, including maternal inheritance, maternal effects, and mitochondrial dna. It further examines chromosomal abnormalities, their causes, and types, including numerical and structural abnormalities. Finally, it discusses molecular techniques used in cytogenetics, such as chromosome banding.

Typology: Study notes

2022/2023

Uploaded on 01/28/2025

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Cytogenetics 5-7 Reviewer
Lesson 5: Patterns of Inheritances
Gregor Mendel: Father of Genetics
Non-Mendelian: Does not follow the traditional Laws of Mendel
Factors that influenced the Non-Mendelian
● Gene Location (In or outside the nucleus)
● Environmental Effects
● Protein Variation
● Encoding of Alleles
6 Types of Non-Mendelian Patterns
1. Incomplete Dominance: The Dominant gene does not overpower the Recessive gene in a sense
it is like mixing paint, both traits BLEND.
Example: Red Flower (RR) and White Flower (WW) = Pink Flower (RW) The physical traits
(Phenotype) blend together.
2. Codominance: The Dominant gene and Recessive gene both are expressed in the offspring
equally without blending.
Example: Red/Brown cow (Rr Rr) and White Cow (Rw Rw) = The offspring’s coat is an
equal mixture of Rr and Rw.
3. Polygenic Inheritance: Traits are controlled by multiple genes, meaning many genes can be
influenced by one characteristic, such as skin tone/color, this can determine the offsprings skin
tone/color, how light or dark depending on the parents' genes.
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Cytogenetics 5-7 Reviewer

Lesson 5: Patterns of Inheritances

Gregor Mendel: Father of Genetics Non-Mendelian: Does not follow the traditional Laws of Mendel Factors that influenced the Non-Mendelian ● Gene Location (In or outside the nucleus) ● Environmental Effects ● Protein Variation ● Encoding of Alleles 6 Types of Non-Mendelian Patterns

  1. Incomplete Dominance: The Dominant gene does not overpower the Recessive gene in a sense it is like mixing paint, both traits BLEND. Example: Red Flower (RR) and White Flower (WW) = Pink Flower (RW) The physical traits (Phenotype) blend together.
  2. Codominance: The Dominant gene and Recessive gene both are expressed in the offspring equally without blending. Example: Red/Brown cow (Rr Rr) and White Cow (Rw Rw) = The offspring’s coat is an equal mixture of Rr and Rw.
  3. Polygenic Inheritance: Traits are controlled by multiple genes, meaning many genes can be influenced by one characteristic, such as skin tone/color, this can determine the offsprings skin tone/color, how light or dark depending on the parents' genes.
  1. Lethal Genes: Bad Genes that's can cause death to the organism that carries it, if there are two copies. But but one parents has a bad genes and the other a normal, the offspring will mostly survive. Unlike if a couple who both have dwarfism, their offspring has a higher chance of dying.
  2. Non-Lethal Genes: Genes that are in the lethal category but do not cause death, however it can be life changing ad have serous effects such as sickle cell disease, cystic fibrosis, and Huntington's disease. If an offspring has only 1 copy, they are a carrier, however if they carry 2 copies then is lethal.’
  3. Pleiotropy: One gene that affects many traits, instead of controlling one trait, the gene can control numerous characteristics.

Extranuclear Inheritance:A specific phenotype is not controlled by genes on the chromosomes in the nucleus. Involves genes outside the nucleus, found in the mitochondria, and usually passed down from the mother. Maternal Inheritance:Traits passed down from mother to offspring. Maternal effects: When the mother’s genetic influence the offspring traits/ characteristics. Mitochondrial DNA: In humans, children get it from their mothers not fathers. Infectious Inheritance: Infectious agents (like bacteria or viruses) that are present in a parent can influence traits in their offspring such as STD’s Heteroplasmy: A cell has a mix of normal and mutant mitochondria

Lesson 6: Chromosomal Abnormalities

Chromosomal abnormalities:refers to changes that result in visible alterations of the chromosome. Factors or the causes that affects the abnormalities: ● Misrepair of broken chromosomes: When it is broken and the cells failed to properly fix the chromosome so it gets all messed up and does not work correctly which can then cause issues. ● Improper recombination (exchange of chromosome segments): When the DNA swapping (Recombination) of the offspring doesn't not happened correctly, such as the egg or sperm cell can have too much or too little DNA which can cause genetic issues. ● Erroneous segregation: When cells do not properly divided during cell division. Two main reason are:

  1. Nondisjunction:chromosomes fail to separate, so a cell during cell division can have an extra or lacking chromosomes.
  2. Anaphase lag: Where the chromosome lags behind and is lost because it was moving way too slow ● Meiotic Nondisjunction: A type of nondisjunction that occurs during meiosis when the sperm and egg cells get the wrong number of chromosome. The Major cause of abnormalities with 75% of it happening Oogenesis (formation of the egg cells), which is more common in older women (increases with maternal age). ● Mutation rate for sperms: Cell division for the sperm occurs more then the egg cell therefore the mutation rate for some Mendelian traits is higher in spermatogenesis. So in older men, their sperm cells have most likely have already mutated.. ● Monosomy: Where 1 chromosome from a homologous pair is missing. Example: 45,X Indicates a female with only one X chromosome (Turner syndrome). Lacking of 1 chromosomes since normal set is 46. ● Trisomy: Where there are 3 copies of a particular chromosome instead of the usual two. Example: 47,XX,+21 Indicates a female with an extra chromosome 21 (Trisomy 21 or Down syndrome).

● Autosomes: Non-sex chromosomes that control most of the body’s traits and functions such as eye color, height, and ect. Nomenclature of Chromosome ● Chromosome Number: Humans have typically have 46 chromosomes, which are arranged in 23 pairs. 2

  • 2 pairs are autosomes (non-sex chromosomes) -1 pair is made up of sex chromosomes (XX for females, XY for males). ● Karyotype: Is a complete set of chromosomes in an individual (46,XX normal female. 46,XY normal male) ● Nomenclature of chromosomal abnormalities: Happens during the formation of egg and sperm cell. ● De Novo Mutations:chromosomal abnormalities occur as new mutations that are not inherited from either parent , so the mutation or abnormality occurs in the in the egg or sperm cell. ● Nomenclature of Numerical Chromosomal Abnormality
  1. Triploidy: 69,XXX, 69,XXY, 69,XYY
  2. Trisomy: 47,XX, +
  3. Monosomy: 45,X
  4. Mosaicism: 47, XXX / 46,XX

Code in Standard Nomenclature

  • Deletion – 46,XX,del(4)(p15) ● Interstitial Deletion:When a chromosome has two breaks, the part between those breaks gets lost. ● Terminal Deletion: A single break happens at one end of a chromosome, and the segment beyond the break is lost. Type of Chromosomal Abnormalities ● Constitutional abnormality: Found in all cells of the body and occurs when there is a defect in the sperm or egg cell during early development, ● Somatic or acquired abnormality: Present only in certain tissues or cells ● Mosaic: Cells that come from the same zygote ● Chimera: Cells come from two different zygotes (resulting in two genetically different cell lines).