Inheritance and Genetic Diseases

Question 1

Why is sexual reproduction (meiosis) important? (3)

Answer 1

Results in greater genetic variation which allows:

1. Beneficial combinations of genes
2. Non-beneficial genes to be removed
3. Important for evolution for fight against microbes (red queen hypothesis)

Question 2

Describe Meoisis (7)

Answer 2

1. Starts with diploid germline cell with paternal and maternal homologs
2. Prophase: The chromosomes of each homolog duplicates.
3. The dupilcated homologs pair up and recombine
4. Metaphase - line up ready to be pulled apart by spindles
5. Anaphase (pulled apart) and Telophase (Cytoplasm + cell membrane separation). This forms 2 new cells
6. The 2 new cells undergo
   PMAT again, ending with seperation the two sister chromatids.
7. Four new unidentical haploid gametes formed.

Question 3

What is the kinetochore and chiasma? (2)

Answer 3

1. Kinetochore (in centromere) is the point where microtubules attach on chromatids.
2. Chiasma is point where the two duplicated chromosomes cross over during recombination.

Question 4

What happens when meiosis gametes are improperly formed during meiosis (Non-disjunction)? (4)

Answer 4

Could lead to:

1. Trisomy (1 additional chromosome)
2. Monosomy (1 less chromosome)

Question 5

What are examples of Trisomy which are not fatal? (3)

Answer 5

1. Down’s syndrome (3 copies of chromosome 21)
2. Patau’s Syndrome (Trisomy 13)
3. Edward’s Syndrome (Trisomy 18)

Question 6

In what situation is Monosomy non-fatal? What is an example of Monosomy? (2)

Answer 6

Monosomy is normally fatal unless on X chromosome, only shows in females.
1. Turner Syndrome

Question 7

Example of XXY chromosome disorder? (1)

Answer 7

1. Klinefelter Syndrome (Male, reduced fertility, lower IQ).

Question 8

Who was Gregor Joahnn Mendel, why was he important? (2)

Answer 8

1. An Austrain Frair who used on pea plants to study inheritance of monogenetic genetic diseases. Published work in 1866.
2. This is the basis of genetic counselling.

Question 9

What type of inheritace pattern are the following Conditions:

1. Cystic Fibrosis
2. Sickle Cell
3. Huntingtons
4. Harmophilia A

Answer 9

1. Cystic Fibrosis - Autosomal Recessive
2. Sickle Cell - Autosomal ‘incomplete’ recessive - retained due to increased protection to malaria
3. Huntingtons - Autosomal Dominant
4. Haemophilia A - X-linked recessive trait. Therefore more dominant in Males. Deletion/inversion to F8 Gene causing loss of function to blood clotting factor.