Genetics test (proper formatting)

Topics /questions to prepare for Genetics test 

1. What does the acronym DNA stand for?  

   Deoxyribonucleic acid.

2. Name the shape of DNA and explain how DNA is like a ladder. 

   The shape of DNA is a double helix it looks like a twisted ladder thanks to the sugar-phosphate backbone and the “rungs” which are the nitrogenous bases.

3. Explain what is meant by DNA being a "blueprint for a living thing"? 

   Since the structure of DNA is seen in the cells of all living things.

4. What are alleles? 

   An alleles is an alternate form of gene, such as dominant alleles and recessive alleles.

   

5. Learn how to explain the difference between Dominant and recessive traits 

   The dominant trait is most likely to be shown as the upper-case of a letter where as the recessive is most likely to be shown as the lower-case. As seen above.

6. Learn how to explain the difference between Genotype and phenotype. 

   A genotype is the letter where as the phenotype is the expressed one such as curly hair.

7. Learn how to explain the difference between heterozygous and homozygous pairs.

    A heterozygous pair is when there is one dominant letter and one recessive letter, homozygous pairs are when there is both of the same letter such as both recessive or both dominant.

8. Understand that diploid means a cell contains two complete sets of chromosomes, one set from each parent, while "haploid" means a cell contains only one set of chromosomes, Eg. After mitosis, daughter cells have a diploid set of chromosomes and after meiosis, daughter cells have a haploid set of chromosomes. 

Using the above understanding answer the following 

1. The skin cell has a diploid/haploid set of chromosomes 

2. The egg cell in a plan has a diploid/haploid set of chromosomes 

   Differences of meiosis & mitosis

   Mitosis

   • somatic cells()

   • 1 cell cycle

   • diploid

   • chromosomes be have independently of each other

   • no crossing over

   • 2 daughter nuclei

   • centromeres divide separate into 2 chromatids

9. learn how to explain the similarities and differences between mitosis and meiosis. 

   Similarities:

   • Both involve DNA replication:

     • Before either mitosis or meiosis begins, the cell's DNA is replicated during the S phase of interphase. This ensures that each resulting cell will have a complete set of genetic information.  

      

   • Both follow a similar sequence of stages:

     • Both processes involve stages like prophase, metaphase, anaphase, and telophase, although these stages have variations in meiosis.  

   • Both involve the separation of chromosomes:

     • Both mitosis and meiosis utilize spindle fibers to move and separate chromosomes.

      

   • Both occur in the cell nucleus:

     • Both are processes that occur within the Eukaryotic cell nucleus.

   Differences:

   • Purpose:

     • Mitosis: Growth, repair, and asexual reproduction. It produces identical daughter cells.  

     • Meiosis: Production of gametes (sperm and eggs) for sexual reproduction. It produces genetically diverse daughter cells.  

   • Number of cell divisions:

     • Mitosis: One cell division.

     • Meiosis: Two cell divisions (meiosis I and meiosis II).  

   • Number of daughter cells:

     • Mitosis: Two daughter cells.  

     • Meiosis: Four daughter cells.  

   • Genetic makeup of daughter cells:

     • Mitosis: Daughter cells are genetically identical to the parent cell (diploid).  

     • Meiosis: Daughter cells are genetically different from the parent cell and from each other (haploid).  

   • Crossing over:

     • Mitosis: Does not occur.

     • Meiosis: Crossing over (exchange of genetic material between homologous chromosomes) occurs during prophase I, contributing to genetic diversity.  

   • Homologous chromosome pairing:

     • Mitosis: Homologous chromosomes do not pair.

     • Meiosis: Homologous chromosomes pair up during prophase I (forming tetrads).  

   • Resulting ploidy:

     • Mitosis: Maintains the same number of chromosomes (diploid to diploid).

     • Meiosis: Reduces the number of chromosomes by half (diploid to haploid).  

   In essence:

   • Mitosis is about making exact copies of cells.  

   • Meiosis is about creating genetic variation for sexual reproduction.

      

10. Learn the order of PMAT and what happens in each phase in mitosis and meiosis. 

    Prophase

11. Metaphase

12. Anaphase

13. Telophase

Here's a breakdown of what happens in each phase, both in mitosis and meiosis:

Mitosis:

• Prophase:

  • Chromatin condenses into visible chromosomes.

  • The nuclear envelope breaks down.

  • The mitotic spindle begins to form.

• Metaphase:

  • Chromosomes line up along the metaphase plate (the center of the cell).

  • Spindle fibers attach to the centromeres of the chromosomes.

• Anaphase:

  • Sister chromatids separate and move to opposite poles of the cell.

  • Spindle fibers shorten.

• Telophase:

  • Chromosomes decondense.

  • The nuclear envelope reforms around each set of chromosomes.

  • The mitotic spindle breaks down.

  • Cytokinesis, the physical splitting of the cell, begins.

Meiosis:

Meiosis has two rounds of division: Meiosis I and Meiosis II.

Meiosis I:

• Prophase I:

  • Chromatin condenses.

  • Homologous chromosomes pair up (synapsis) and crossing over occurs.

  • The nuclear envelope breaks down.

  • The spindle forms.

• Metaphase I:

  • Homologous chromosome pairs line up along the metaphase plate.

  • Spindle fibers attach to the centromeres.

• Anaphase I:

  • Homologous chromosomes separate and move to opposite poles.

  • Sister chromatids remain attached.

• Telophase I:

  • Chromosomes may decondense.

  • The nuclear envelope may reform.

  • Cytokinesis occurs, resulting in two haploid cells.

Meiosis II:

• Prophase II:

  • Chromosomes condense.

  • The nuclear envelope breaks down.

  • The spindle forms.

• Metaphase II:

  • Chromosomes line up along the metaphase plate.

  • Spindle fibers attach to the centromeres.

• Anaphase II:

  • Sister chromatids separate and move to opposite poles.

• Telophase II:

  • Chromosomes decondense.

  • The nuclear envelope reforms.

  • Cytokinesis occurs, resulting in four haploid cells.

Key Differences to Remember:

• Meiosis I is where homologous chromosomes separate, leading to the reduction of chromosome number.

• Meiosis II is very similar to mitosis, where sister chromatids separate.

• Crossing over happens in Prophase 1 of meiosis.

11. Understand that in each organism one pair of chromosomes are sex chromosomes (X and Y), all the rest are autosomes or autosomal chromosomes. 

    Autosomes:

    • These are the chromosomes that determine most of an organism's characteristics, excluding sex determination.

    • In humans, there are 22 pairs of autosomes, making a total of 44 autosomes.

    • These chromosomes carry genes for a wide range of traits, such as eye color, height, and blood type.

    • They are present in pairs, with one chromosome from each parent.

    Sex Chromosomes:

    • These chromosomes determine an organism's biological sex.

    • In humans, there is one pair of sex chromosomes:

      • Females typically have two X chromosomes (XX).

      • Males typically have one X and one Y chromosome (XY).

    • The Y chromosome carries the SRY gene, which plays a crucial role in male sex determination.

    • The X chromosome carries many genes unrelated to sex, which is why X-linked traits exist.

    Key Differences:

    • Function:

      • Autosomes: Determine general traits.

      • Sex chromosomes: Determine biological sex.

    • Pairing:

      • Autosomes: Always occur in homologous pairs.

      • Sex chromosomes: May or may not be homologous (XY in males).

    In Summary:

    • Think of autosomes as the chromosomes that carry the blueprints for most of your body's features.

    • Think of sex chromosomes as the chromosomes that determine whether that blueprint results in a male or female.

12. Understand how to do a monohybrid cross (genetic cross for a single trait) using punnet squares and to identify genotypes. 

    Key Terms:

    • Genotype: The genetic makeup of an organism (e.g., AA, Aa, aa).

    • Phenotype: The physical expression of the genotype (e.g., tall, short).

    • Allele: A variant form of a gene.

    • Homozygous: Having two identical alleles for a trait (e.g., AA or aa).

    • Heterozygous: Having two different alleles for a trait (e.g., Aa).

    • Dominant allele: An allele that masks the expression of the recessive allele.

    • Recessive allele: An allele whose expression is masked by the dominant allele.

    Steps for a Monohybrid Cross:

    1. Determine the parents' genotypes:

       • Identify the alleles each parent carries for the trait.

       • For example, let's say we're looking at pea plant height, where "T" is the dominant allele for tall and "t" is the recessive allele for short.

       • Possible parent genotypes: TT (homozygous dominant), tt (homozygous recessive), or Tt (heterozygous).

    2. Set up the Punnett square:

       • Draw a square divided into four equal boxes.

       • Write the alleles of one parent along the top of the square and the alleles of the other parent along the left side.

    3. Fill in the Punnett square:

       • Combine the alleles from the top and side of each box to determine the possible genotypes of the offspring.

    4. Determine the genotypes and phenotypes of the offspring:

       • Analyze the Punnett square to determine the possible genotypes of the offspring.

       • Use the genotypes to determine the corresponding phenotypes.

    Example:

    Let's cross a homozygous dominant tall plant (TT) with a homozygous recessive short plant (tt):

          T     T
      t   Tt    Tt
      t   Tt    Tt
    

    • Genotypes: All offspring are Tt (heterozygous).

    • Phenotypes: All offspring are tall.

    Another Example:

    Let's cross two heterozygous tall plants (Tt):

          T     t
      T   TT    Tt
      t   Tt    tt
    

    • Genotypes: 1 TT, 2 Tt, 1 tt

    • Phenotypes: 3 tall, 1 short

    Identifying Genotypes:

    • If an individual expresses the recessive phenotype, its genotype must be homozygous recessive (e.g., tt).

    • If an individual expresses the dominant phenotype, its genotype can be either homozygous dominant (e.g., TT) or heterozygous (e.g., Tt). To determine which one, you may need to perform a test cross. A test cross is when you cross the unknown dominant phenotype with a homozygous recessive phenotype.

    Key Points:

    • Punnett squares are a visual tool for predicting the possible genotypes and phenotypes of offspring.

    • Monohybrid crosses involve a single trait.

    • Understanding dominant and recessive alleles is crucial for interpreting the results of a cross.

13. Why do more males inherit sex linked traits compared to females? Explain using an example 

    Understanding the Basics:

    • Sex Chromosomes:

      • Females have two X chromosomes (XX).

      • Males have one X and one Y chromosome (XY).

    • X-Linked Traits:

      • Genes for these traits are located on the X chromosome.

      • Many sex-linked traits are recessive.

    Why Males Are More Susceptible:

    • One X Chromosome:

      • Males only have one X chromosome. Therefore, whatever allele is present on that X chromosome will be expressed.

      • If a male inherits an X chromosome with a recessive allele for a sex-linked trait, he will exhibit that trait because there is no second X chromosome to potentially mask it.

    • Two X Chromosomes:

      • Females have two X chromosomes. So, if they inherit one X

      • chromosome with a recessive allele, they also have another X chromosome that might have the dominant, normal allele.

      • In this case, the dominant allele will mask the recessive one, and the female will be a carrier of the trait but may not express it.

      • For a female to express an X linked recessive trait, she must inherit the recessive allele from both her mother and her father.

    Example: Hemophilia

    • Hemophilia is a classic example of an X-linked recessive disorder.

    • It's a bleeding disorder caused by a deficiency in a blood-clotting factor.

    • Let's say:

      • "H" represents the normal allele.

      • "h" represents the hemophilia allele.

    • If a mother is a carrier (XHXh) and the father is normal (XHY):

      • Their son has a 50% chance of inheriting the Xh chromosome and thus having hemophilia (XhY).

      • Their daughter has a 50% chance of being a carrier (XHXh) and a 50% percent chance of being completely normal (XHXH).

    • In order for a daughter to have hemophilia, the father would have to have hemophilia(XhY) and the mother would have to at least be a carrier (XHXh).

    In essence, males have "one shot" with their X chromosome, while females have a backup. This is why sex-linked recessive traits are far more common in males.

14. Understand pedigree charts and how to analyse them. 

Answer the questions below using the pedigree provided 

1. What is the sex and genotype of individual 2? 

   they are a male and have a recessive genotype.

2. What are Jane’s possible genotypes? 

   her possible genotypes are Nn and NN

3.  What is the probability that individuals 5 and 6 will have a child that is near-sighted? 

   there is a 25% chance of near- sightedness

4. What is Jane’s relationship to individual 1? 

   it’s jane’s great-grandmother

15. What are the common differences between sexual and asexual reproduction. 

    You're asking about the fundamental ways that organisms reproduce! Here's a breakdown of the common differences between sexual and asexual reproduction:

    Sexual Reproduction

    • Involves two parents: Requires both a male and a female parent to contribute genetic material.  

    • Gametes (sex cells): Specialized cells (sperm and egg) are produced through meiosis. These gametes are haploid (containing half the number of chromosomes).  

    • Fertilization: The process where sperm and egg fuse, combining genetic material to form a diploid zygote.  

    • Genetic variation: Offspring inherit a unique combination of genes from both parents, leading to genetic diversity within a population.  

    • Evolutionary advantage: Genetic variation increases the chances of adaptation to changing environments.  

    Asexual Reproduction

    • Involves one parent: A single parent produces offspring.  

    • No gametes: No specialized sex cells are involved.

    • No fertilization: Offspring are produced through mitosis, resulting in genetically identical copies of the parent.

    • Genetically identical offspring: Also known as clones.

    • Rapid reproduction: Can produce large numbers of offspring quickly.