Showing posts with label Genetics. Show all posts
Showing posts with label Genetics. Show all posts

X-Linked and Y-Linked Traits




In humans, males and females are represented by different sex chromosomes

• Females have two X chromosomes in the nucleus of their cells.
• Males have one X chromosome and one Y chromosome in the nucleus of their cells.

Depending on whether the trait is dominant or recessive, the expression pattern of the trait differs in males and female

X-linked traits are traits where the genes for the trait is found on the X chromosome, while a
Sex-influenced trait in a diploid organism have expression which are affected by an individual’s biological sex and occurs at a higher frequency in one sex over the other

Sex-limited traits in a diploid organism have expression that are limited to just one biological sex 

Example.

Hemophilia is an X-linked recessive trait where an affected individual suffers from delayed blood clotting during injuries.




Problem Exercise :

The last Emperor of Russia, Nicolas II, was married to Empress Alexandra, and they had five children, Olga, Tatiana, Maria, Anastasia, and Alexis. Alexis was the only one who was afflicted with hemophilia or the royal bleeding disease; all other members were normal.

If only Prince Alexis was afflicted with the disease, 

a.) determine his genotype.

b.) What could be the genotypes of the Emperor and Empress?

c.) Is it possible that each daughter could have been a carrier?
 
Write your answers in the comments.

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Pedigree Analysis

The Pedigree makes use of diagrams showing the ancestral relationships and transmission ofgenetic traits over several generations in a family. It describes the mode of inheritance of a trait. It also calculate the probability of occurrence an affected offspring in a given cross

The individual in the pedigree that led to the construction of the pedigree is known as the proband. For example, a couple consults a medical geneticist because they have an offspring who is afflicted with a disease and they want to find out the mode of transmission of this disease.When the medical geneticist constructs the pedigree, the offspring will be labeled as the proband. Through the pedigree, the probability of having other affected children may be determined.



Symbols for creating pedigrees

I. Male (square) vs female (circle)

II. Affected (shaded) vs unaffected (unshaded) individual

III. Marriage/mating line (line connecting mates) vs. sibship line (line connecting siblings)

IV. Fraternal twins (one birth line branching out into the individual twin) vs. identical twins (same as fraternal twins but with a horizontal bar connecting the branches)

V. Generation (Roman numerals) vs. individuals in the same generation, counting left to right (Hindu- Arabic numerals)

VI. Proband (arrow)





PRACTICE EXERCISES :



A. Look at the family of IV-9 and IV-10. If the trait is dominant, is it possible for them to have an affected offspring?

B. If the trait is recessive, is it also possible for IV-9 and IV-10 to have an unaffected offspring?

C. Based on your answers for a) and b), is the trait dominant or recessive?

D. Give the genotypes of the following:

     i. IV-9

     ii. IV-10

     iii. V-1

     iv. I-1

     v. I-2

E. If IV-9 and IV-10 were to have another child, what is the probability that they will have an affected offspring?

More Practice on Pedigree Analysis .

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BioMolecules Quiz 1

This is a level of assessment and analysis. After lessons on Genetics and Inheritance. Human cell analysis. Test your knowledge on DNA, RNA, and Protein molecular structure and function.

Determine structures and the functions of each molecule and compound. Understand the  corresponding uses and their importance in the inheritance or heredity of children in the family and in the next generations.


Lesson Review on BioMolecules : Structure and Function
Lesson Review on Biomolecules : DNA Replication and Protein Synthesis
BioMolecules Practice Quiz 2 mirror site BioMolecules Practice Quiz 2
Genetics Disorders Practice Quiz

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Mendel’s Law of Inheritance


1. Law of Dominance (First Law):

The law of dominance states that when two alternative forms of a trait or character (genes) are present in an organism, one factor expresses itself and is called dominant, while the other that remains masked is called recessive.

2. Law of Segregation (Second Law):

It says that the alleles that make up a gene separate from each other, or segregate, during the formation of gametes.

3. Law of Independent Assortment (Third Law):

This law states that when two pairs of traits are combined in a hybrid, segregation of one pair of character is independent of the other pair of characters at the time of gamete formation.

MonoHybrid Cross

DiHybrid Cross ,  Exercise

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The Dihybrid Cross

Gregor Mendel performed crosses in which he followed the segregation of two genes. These experiments formed the basis of his discovery of his second law, the law of independent assortment.

A Dihybrid cross is a cross between two parents that differ by two pairs of alleles (AABB x aabb)

The dominance relationship between alleles for each trait was already known to Mendel when he made this cross. The purpose of the dihybrid cross was to determine if any relationship existed between different allelic pairs.




Let's now look at the cross using our gene symbols.






In Mendel's experiments, a monohybrid cross produces 4 different possible combinations in the F2 Generation.This results to a phenotypic ratio of 3:1.

1.) What about a dihybrid cross, how many combinations are possible in the F2 Generation?

2.) What is the ratio of the resulting phenotypes in the F2 Generation?

Write your answers in the comments.

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BioMolecules Quiz 2

This is a higher level of assessment and analysis. After lessons on Human cell analysis, Genetics and Inheritance, Human Traits and Development. Understanding the  corresponding uses and their importance in the inheritance or heredity of children in the family and in the next generations.Test your knowledge on DNA, RNA, and Protein molecular structure and function. Determine structures and the functions of each molecule and compound. Analysis if synthesis of new protein molecules from amino substances.


Lesson Review on BioMolecules : Structure and Function
Lesson Review on Biomolecules : DNA Replication and Protein Synthesis
BioMolecules Practice Quiz 1
Genetics Disorders Practice Quiz

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The MonoHybrid Cross



Gregor Mendel conducted artificial pollination/cross-pollination experiments using several true-breeding pea lines. A true-breeding line refers to one that have undergone continuous self-pollination and showed stable trait inheritance and expression for several generations.

 



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