meiosis, karyotypes and aneuploidies

Question 1

interphase

Answer 1

DNA replication - each chromosome contains 2 identical sister chromatids
microtubules extend from centrosomes

Question 2

prophase

Answer 2

chromosomes condense
nuclear mebranes break down
centrioles move to opposite side

Question 3

anaphase

Answer 3

spindle fibres shorten and pull chromatids apart

Question 4

meiosis 1

Answer 4

interphase 1
prophase 1 - genetic material exchanged between homologous chromosomes by recombination
anaphase 1 - one chromosome goes to each pole
prophase 2 - centrioles duplicate
anaphase 2 - sister chromatids pulled apart

Question 5

karyotype

Answer 5

pictorial display of metaphase chromosomes from a mitotic cell
mitotic cells fixed in metaphase - chromosomes stained with Giemsa dye - stain regions with lots of adenine and thymine - give dark bands, each containing many genes
images manipulated to show chromosomes in homologous pairs

Question 6

karyotype notation

Answer 6

total number of chromosomes, sex chromosomes, any extra/missing

Question 7

aneuploidies

Answer 7

genetic conditions arising from an abnormal number of chromosomes and detected on karyotypes

Question 8

monosomy

Answer 8

loss of 1 of homologous pairs of chromosomes

Question 9

trisomy

Answer 9

addition of 1 of the chromosomes in a pair

Question 10

non-dysjunction

Answer 10

failure of separation of homologous chromosomes in anaphase 1
or sister chromatids in anaphase 2
cause aneuploidies

Question 11

downs

Answer 11

autosomal trisomy 
47, XY/XX, +21
maternal age risk factor 
flat nasal ridge 
epicanthic folds
low set ears
single palmer crease 
sandal gap
hypotonia 
developmental delay 
congenital heart defects 
increased risk of alzheimers 
hearing loss
duodenal atresia
increased risk of coeliac disease
increased risk of leukaemia

Question 12

Edward’s syndrome

Answer 12

autosomal trisomy 
47, XY/XX, +18
low birth weight 
low set ears
micrognathia - small jaw 
small facial features - microphthalmia, prominent occiput, microcephaly, cleft lip/palate 
clenched hands with overlapping fingers 
congenital heart defect
GI tract abnormalities 
urological abnormalities 
developmental delay

Question 13

Klinefelter’s syndrome

Answer 13

sex chromosome trisomy
47, XXY
males
infertility - small, firm testes
loss of secondary sexual characteristics - reduced facial and pubic hair 
tall
long legs
narrow shoulders and wide hips 
gynaecomastia

Question 14

Turner syndrome

Answer 14

Females
infertility - gonadal dysgenesis 
short stature 
webbed neck 
broad chest
short 4th and5th metacarpals 
congenital heart defects 
sensineural deafness and recurrent ear infections 
behavioural problems 
increased risk of autoimmune disease - coelic, thyroiditis