T5 module 3: chromosomes + linkage

Question 1

pedigee

Answer 1

family tree

square: male
circle: female
blank: unaffected
dark: affected

• order of birth L to R
• horz. line = mating
• double line = incest
• identical twins have no vertical line on split

Question 2

X and Y chromosomes

Answer 2

• non-homologous
• no recombination
• small regions allow for meiosis I pairing
• sex linked genes - genes found on sex chromosomes

Y: 50% of genes code for sex
X: most have non sex-related functions

• plant’s don’t have sex chromosomes
• medel’s laws don’t apply

Question 3

hemizygosity

Answer 3

offspring only has 1 pair from chromosome

e.g. if disease sex linked, person could be hemizygous for that disease

Question 4

X chromosome

Answer 4

P arm (short), Q arm (long)

Question 5

linked genes

Answer 5

• inherited together
  e.g. colour blindness + hemophelia
• however, can be separated during recombination (depends on distance between linked genes)

Question 6

linkage maps

Answer 6

frequency of recombination can help determine distance between linked genes

HIGH DENSITY LINKAGE MAPS
- use SNPs
- maps them as markers to determine disatnce between linked genes