Chromosomal Abnormalities and Mutations

Question 1

Karyotypes

Answer 1

An illustration or photograph of chromosomes in the nucleus of a somatic cell in an organism. They help diagnose certain genetic conditions involving chromosome numbers.

Question 2

How are Karyotypes made?

Answer 2

→ Cells grown in a glass container
→ Cell division stopped at metaphase when chromosomes are clearly visible
→ Chromosomes are separated from cells, stained and photographed
→ Enlargements made and chromosomes arranged in homologous pairs according to size, shape, appearance

Question 3

Nondisjunction

Answer 3

Nondisjunction is and error in cell division from the failure of chromosomes to separate properly during meiosis, resulting in the addition or deletion of one or more chromosomes.

→ Sometimes it is because the homologous chromosomes don’t separate in anaphase Ⅰ
→ Sometimes it is because the sister chromatids don’t separate in anaphase ⅠⅠ

Question 4

Nondisjunction in Meiosis Ⅰ

Answer 4

→ Both chromosomes of a homologous pair migrate to the same pole (One cell will have one less chromosome and the other would have one more)
↪ Meiosis ⅠⅠ would go as normal
→ Result is two cells with | n + 1 | chromosome number and two cells with | n - 1 | chromosome number

Question 5

Nondisjunction in Meiosis Two

Answer 5

→ Meiosis Ⅰ proceeds as normal
→ During Meiosis ⅠⅠ both sister chromatids migrate to the same pole
↪ Only one chromosome separates abnormally
Result:
↪ Two cells that have n chromosomes
↪ One cell with | n + 1 | chromosome
↪ One Cell with | n - 1 | chromosome

Question 6

Consequences of Nondisjunction: Trisomy

Answer 6

If a gamete with | n + 1 | chromosomes fuses with a normal gamete with n chromosomes, the result is a diploid zygote with a third copy of one chromosome ( | 2n + 1 | )

→ In humans most trisomies result in fetal death however some are tolerable like down syndrome

Question 7

Consequences of Nondisjunction: Monosomy

Answer 7

If a gamete with | n - 1 | chromosomes fuses with a normal gamete with n chromosomes, the result is a missing chromosome from one of the pairs (the paternal or maternal can be missing), a monosomic zygote ( | 2n - 1 | )

→ In humans, most monosomies would result in fetal death however some can be tolerated like Turner’s Syndrome

Question 8

Consequences of Nondisjunction: Polyploidy

Answer 8

Polyploidy is having more that two chromosome in every set of chromosomes.

For Example…
→ If a 2n gamete fused with a n gamete, the result would be a triploid zygote that has sets of 3 chromosomes (Each set has 3 chromosomes)
↪ This is lethal in humans

Question 9

Chromosomal Abnormalities: Deletion

Answer 9

→ A portion of the chromosome is lost
↪ Mostly caused by abnormal crossing over
→ Genes are lost meaning important proteins are also lost

Example: Cri-du-chat
→ Piece of chromosome 5 is lost
↪ Larynx is no developed properly so the affected sounds like a cat meowing\
↪ Mental disabilities are also a consequence

Question 10

Chromosomal Abnormalities: Duplication

Answer 10

Occurs when a gene sequence repeats a sequence more than one time in one or more chromosomes
↪ Often cause by abnormal crossing over
↪ Often normal and harmless, but at some point it will affect gene function

Example: Fragile X Syndrome
→ Duplication happens of the X chromosome
↪ Causes mental disabilities
↪ More common in Males than Females

Question 11

Chromosomal Abnormalities: Inversion

Answer 11

Happens when a gene segment becomes free from the chromosome and inserted in the reverse order
↪ This can alter gene activity but does not phenotypically affect the individual (Does not change the amount of genetic material)
↪ Can lead to deficiencies and duplications of genetic material after meiosis

Question 12

Down Syndrome

Answer 12

Trisomy at chromosome 21

{ 47 XY/XX +21 }

Question 13

Double Y Syndrome

Answer 13

Extra Y chromosome

{ 47 XYY }

Question 14

Super Female Syndrome

Answer 14

Extra X chromosome

{ 47 XXX }

Question 15

Turner’s Syndrome

Answer 15

Absence of a X chromosome

{ 45 X0 }

Question 16

Patau Syndrome

Answer 16

Trisomy at chromosome 13

{ 47 XY/XX +13 }

Question 17

Edwards Syndrome

Answer 17

Trisomy at chromosome 18

{ 47 XY/XX +18 }

Question 18

Klinefelter’s Syndrome

Answer 18

Extra X Chromosome

{ 47 XXY }