Unit 5 - Ch 16 - Genetic Disorders

Question 1

Genetic Disorders. Three major types:

Answer 1

1. Mendelian Inheritance - dominant or recessive allele that is autosomal or sex-linked
2. Variations in Chromosome Number
3. Variations in Chromosome Structure

Question 2

Two major types of Variations in Chromosome Number:

Answer 2

1. Polyploidy - exact multiples of the haploid condition

2. Aneuploidy - the absence or addition of individual chromosome(s)

Question 3

Triploid

Answer 3

A polyploidy organism with homologous triplets.
3n
3 of every chromosome
=> in humans 3n=69 (66 autosomes and 3 heterosomes)
- lethal, found in miscariages

Question 4

Tetraploid

Answer 4

A polyploidy organism with homologous quads.
4n
4 of every chromosome
=> humans 4n=92 (88 auto and 4 hetero)

Question 5

Pentaploid

Answer 5

5n organism
5 of every chromosome
=> dog rose 5n=35

Question 6

Hexaploid

Answer 6

6n organism
6 of every chromosome
=> wheat 6n=42

Question 7

What causes polyploid organisms?

Answer 7

When 2n tissue acts as a gamete (2n + n = 3n or 2n + 2n = 4n)

Question 8

What results occur in polyploid plants and animals?

Answer 8

Plants tolerate well. They produce larger fruits, leaves, seeds and flowers, desirable in agriculture.

Usually lethal to animals.

Question 9

Reproductive viability of polyploid organisms

Answer 9

Even multiples are fertile. Odd multiples are sterile.

Question 10

What causes aneuploidy?

Answer 10

Nondisjunction - chromosomes fail to separate during meiosis I or II

Question 11

Nullisomic

Answer 11

An aneuploid (2n-2)
Missing a homologous pair

Both parents have nondisjunction for the same chromosome (rare)
=> humans 44 chromosomes
- lethal (miscariages)

Question 12

Monosomic

Answer 12

An aneuploid (2n-1)
Missing one chromosome of a homologous pair 

One parent has nondisjunction
=> humans 45 chromosomes, 22 homologous pairs

Question 13

Trisomic

Answer 13

An aneuploid (2n+1)
One homologous triplet 

Abnormal gamete from one parent
humans => 47 chromosomes

Question 14

Tetrasomic

Answer 14

An aneuploid (2n+2)
Abnormal gametes from both parents (n+1); rare. 

humans => 48 chromosomes

Question 15

Turners Syndrome (XO)

Answer 15

Monosomic condition

• no barr bodies (suggests male)
• actually sterile female
• webbed neck

Question 16

Kleinfelter’s Syndrome (XXY)

Answer 16

Trisomic condition

• one barr body (appear female)
• actually male with small testes
• sterile

Question 17

Superfemale (XXX or XXXX)

Answer 17

Trisomic or tetrasomic

• tri X comes from one parent
• tetra X from both parents
• usually fertile

Question 18

XYY

Answer 18

Trisomic condition

• from father
• used to think this led to anti-social behavior (discredited)

Question 19

YO

Answer 19

Monosomic condition

• from mother
• egg cell missing the sex chromosome; lethal in utero

Question 20

What are four variations in chromosome structure?

Answer 20

Deletion
Duplication
Inversion
Translocation

Question 21

What is a deletion in chromosome structure? Homozygous and heterozygous?

Answer 21

The chromosome is missing segments

Homozygous - impacts both homologs (rare) - usually lethal

Heterozygous - only one homolog impacted
a. Cri-Du-Chat Syndrome - part of #5 missing

Question 22

Duplication in chromosome structure

Answer 22

Gene segment present more than once in a homologous chromosome

Question 23

Inversion in chromosome structure. Homozygous and heterozygous

Answer 23

Chromosome segment “rotates” within a chromosome

Homozygous - both homologs are inverted
- often no impact

Heterozygous - impacts one homolog

• problem if crossing over occurs
• results in duplication and deletion

Question 24

Translocation in chromosome structure

Answer 24

Gene segments exchanged between non-homologous chromosomes.