IB BIO TOPIC 4.2 : MEIOSIS

Question 1

What is meiosis ?

Answer 1

meiosis is a reduction division of a diploid nucleus to form haploid nuclei.

Question 2

Define what are homologous chromosomes

Answer 2

homologous chromosomes = chromosomes with the same gene loci in the same sequence which are capable of pairing up to form bivalents during the first prophase of meiosis.

Question 3

Outline the process of meiosis

Answer 3

• pairing of homologous chromosomes
• crossing over
• two divisions
• results in four haploid cells

Question 4

Explain that non-disjunction can lead to changes in chromosome number as in Down syndrome:

Answer 4

• in either oogenesis or spermatogenesis, chromosome 21
• moves to pole as a pair instead of singly; thus, egg or sperm contain an extra
copy of chromosome 21, and fertilized egg has 3 copies of chromosome 21,
• which is why Down syndrome is also known as trisomy 21

Question 5

What is karyotyping ?

Answer 5

in karyotyping, chromosomes are arranged in pairs according to their size and structure.

Question 6

How is karyotyping performed ?

Answer 6

karyotyping is performed using cells collected by chorionic villus sampling or amniocentesis, for pre-natal diagnosis of chromosome abnormalities.

Question 7

What are amniocentesis and chorionic villi sampling ?

Answer 7

They allows prenatal karyotyping, by isolation of amniotic fluid or chorion, containing fetal cells in mitosis, which are stained and paired
• diagnosis of chromosomal abnormalities, such as Down syndrome, identifying extra chromosome 21 (trisomy 21)