3+10 - genetics (SL + HL)

Question 1

explain the use of karyotyping in human genetics [8]

Answer 1

definition
- karyogram shows images of chromosomes in a cell
- cells collected from chorionic villus
- chromosomes arranged in pairs according to size

uses
- determines sex by looking at chromosome pair 23
- male is XY female is XX
- identifies chromosome non-disjunction
- e.g. trisomy 21 leading to Down syndrome

Question 2

explain two types of inheritance (linked and unlinked) for heterozygous parents for genes A and B [8]

Answer 2

unlinked
- unlinked genes are on different chromosomes
- unlinked alleles are inherited independently during meiosis
- due to random assortment in metaphase I
- equal chance of four combinations (AB, Ab, aB, ab) to occur
- more variation than in linked

linked
- linked genes have loci on the same chromosome
- therefore tend to be inherited together
- phenotypic ratio is similar to monohybrid cross
- random crossing over in prophase I can result in variation, since may not be inherited together