L5

Question 1

Sexual reproduction - why?

Answer 1

Results in greater genetic variation

Beneficial gene combinations
Deleterious combinations removed

Question 2

Genetic variation - how?

Answer 2

Mutation
Diploid cells
Homologous recombination (meiosis)

Question 3

Diploid/haploid

Answer 3

Somatic = diploid 
Gametes = haploid

Question 4

Prophase I

Answer 4

Early prophase: Chromatin begins to condense after interphase

Mid-prophase: Synapsis aligns homologs and chromosomes condense

Late: Chromosomes continue to coil and shorten. Crossing over

Prometaphase: nuclear envelope breaks down

Question 5

Metaphase I

Answer 5

Homologous pairs line up on equator

Question 6

Anaphase I

Answer 6

Homologous chromosomes move to opposite poles

Question 7

Telophase I

Answer 7

Chromosomes gather into nuclei and original cell divides

Question 8

Homologous recombination

Answer 8

Prophase (Meiosis I)
2-3 cross over events
Highly similar DNA sequence binds to complementary sequence on homologous chromosomes

Question 9

Chiasma

Answer 9

where crossing over occurs on homologs

Question 10

Genetic variation of gamete formation

Answer 10

Independent assortment of chromosomes

Homologous recombination

Question 11

50% miscarriage

Answer 11

Chromosomal abnormalities

Question 12

Trisomy 21

Answer 12

Down's syndrome 
1 in 750 live births 
Mental retardation
Broad flat face, slanting eyes
Congenital heart disease 
Intestinal blockage + enlarged colon

Question 13

Trisomy 13

Answer 13

Patau’s syndrome

Question 14

Trisomy 18

Answer 14

Edward’s syndrome

Question 15

Non-fatal trisomy

Answer 15

13, 18 and 21

Question 16

Monosomy

Answer 16

Turner syndrome
Female
Pubertal failure
Infertility

May have: neck webbing, heart defects and horseshoe kidneys

Question 17

Monosomy fatal except

Answer 17

X chromosomes

Question 18

Sex chrome syndromes

Answer 18

XXY: Klinefelter syndrome (male, reduced fertility, lower IQ) May go undiagnosed

XXX: undiagnosed

XYY: undiagnosed

Question 19

Sickle cell disease

Answer 19

African/caribbean families
More resistant to malria
+ve selection for HbS allele
Malaria parasite unable to replicate inside heterozygote RBCs

Question 20

Haemophilia A

Answer 20

Blood clots slowly: Bleeding, easy bruising, joint and muscle haemorrhages, surgery difficulties

Lack factor VIII

Deletion or inversion in F8 gene - loss of function

Question 21

X-linked recessive disorders

Answer 21

Duchenne muscular dystrophy

Red-green colour-blindness