Biology Unit 1: Genetics - Human Karyotypes and Chromosomal Abnormalities

What does Karyotype do?

It shows all chromosomes in a cell and they are

→ Arranged from largest to smallest

→ In pairs

→ Their centromere are lined up

True or False:
Sex chromosomes can only be found in sex cells

(Gametes)

False, sex chromosomes can be found in all cells

What does Karyotyping do?

Detects certain chromosomal abonormalities

What are the chromosomal abnormalities that can be detected by Karyotyping?

1. Extra of missing chromosomes

2. Deletion - a part of the chromosome is missing)

3. Translocation - Chromosome pieces are mixed up

What can’t Karyotyping show?

• DNA or individual genes

• Small mutations within genes

What are some disorders that can occur from missing or extra chromosomes?

• Down syndrome (Trisomy 21; extra chromosome 21) *Can also be translocation

• Turner syndrome (sex chromosomes missing one X with no Y)

• Klinefelter (sex chromosomes with extra X in XY)

• Edwards syndrome (Trisomy 18; extra chromosome 18)

How does extra or missing chromosomes happen?

Non-disjunction occurs during anaphase stage in Meiosis 1 and 2

Characteristics of Down Syndrome

→ Heart defect

→ Physical abnormalities (round full face, large forehead, short height)

→ Varies levels of intellectual disabilities

Characteristics of Klinefelter Syndrome

→ Usually tall and slim

→ Feminine features

→ Few secondary sexual characteristics (facial pubic, underarm hair)

→ Most likely sterile

Characteristics of Turner Syndrome

→ Short stature 

→ Lack of ovarian development 

→ Sterile

Characteristics of Edwards syndrome

→ Low survival rate

→ Clenched fists

→ Clubbed foot

→ Organ defects*

Deletion

Karyotype can also detect large deletions in the chromosomes

What is a disorder that can be caused by deletion of chromosomes?

Cri du chat

Characteristics of Cri du Chat syndrome

→ Infant cries like a cat due to mis-shapen larynx

→ Low birth weight

→ Respiratory problems*

→ Wide set eyes

→ Small hand

What is the cause of cri du chat?

A deletion of a small part of the short (p) arm of chromosome 5

Translocation

Results when a piece of the chromosome breaks off and attach to another crhomosome

An example of Translocation

• Philadelphia chromosome

• Down syndrom

What is Philadelphia chromosome

It is the Translocation between chromosome 9 and 22 resulting in Chronic Myelogenous Leukemia in which a person’s bone marrow produced too much white blood cells it begins to attack its own cells.