Lecture 13 - Chromosome Variation And Sex Determination

Question 1

What’s the difference between haploid and diploid cells?

Answer 1

Diploid have 2 sets of chromosomes while haploid have 1 (gametes)

Question 2

What are diploid species with only 1 set of chromosomes called?

Answer 2

Monoploid

Question 3

What are organisms with multiples of the basic chromosome set called?

Answer 3

Euploid

Question 4

What are polyploids?

Answer 4

Organisms that have 2+ chromosome sets
- triploid (common in miscarriages), tetraploid, pentaploid

Question 5

What are Aneuploids?

Answer 5

Individuals whose chromosome number differs by one or a small number of chromosomes:

Question 6

What are the names for different degrees of aneuploidy in autosomes?

Answer 6

2n+1 = trisomic
2n-1 = monosomic
2n-2 = nullisomic

Question 7

How does aneuploidy apply to sex chromosomes?

Answer 7

Chromosomes can be XXY, XYY, XXX or XO

Question 8

What is non-disjunction and what are its consequences?

Answer 8

Chromosomes not separating during meiosis:
If in meiosis I - gametes are 2 trisomic 2 monosomic
If in meiosis II - gametes are 2 normal 1 trisomic 1 monosomic

Question 9

How does having extra chromosomes affect phenotype drastically?

Answer 9

Monosomies: autsomes die in utero and sex can result in missing X causing Turner’s syndrome
Trisomies: in Chromsome 21 = Down syndrome or Klienfelter from extra X chromosome (XXY)

Question 10

How may chromosomes have differing structure?

Answer 10

1. Duplications
2. Deletions (small visualised with FISH or large visualised in a karyotype)
3. Copy number variations (extra pieces)
4. Inversion
5. Translocation

Question 11

What are the 2 types of translocation?

Answer 11

1. Reciprocal = breaking off and swapping parts with another chromosome
2. Robertsonian = 2 chromosomes joining together

Question 12

What is an example of how reciprocal translation causes disease?

Answer 12

Occurs In CML cells creating a fusion gene that codes for a hybrid tyrosine kinase that at always on causing the cell to divide uncontrollably leading to cancer

Question 13

What are the key features of the Y chromosome?

Answer 13

1. Discovered by Nettie Steven’s
2. Mostly repeated sequence
3. Pairs with X
4. Inheritance father to son

Question 14

What are the key features of the X chromosome?

Answer 14

1. Bigger than Y
2. Many genes
3. Males are hemizygous (have 1)
4. Result in X linked traits

Question 15

What is lyonisation and what does is prevent?

Answer 15

One X chromosome being epigenetically inactivated in early development to prevent aneuploidy having significant effect

Question 16

What are 3 clues to a trait being X linked?

Answer 16

1. More males express it
2. Characteristic skips a generation
3. If the female has it all male offspring will have it