T3L4 - Inheritance and Genetic Disorder

Question 1

Sexual reproduction

Answer 1

Beneficial combinations of genes to come together

Deleterious combinations of genes to be removed

Genetic diversity

Question 2

Genetic variation via

Answer 2

1. Mutation (errors in DNA replication and repair)

Diploid cells (inherit one set of chromosomes from each parent)

Homologous recombination (HR) between chromosomes during meiosis

Question 3

Meiosis I

Answer 3

Prophase
Metaphase
Anaphase
Telophase

Question 4

Meiosis I - Prophase

Answer 4

Early Prophase - Chromatin begins to condense following interphase

Mid Prophase - Synapsis aligns homologs and chromosomes condense more

Late Prophase I - Promometaphase - Chromosomes coil and shorten. Crossing over and nuclear envelope breaks down.

Question 5

Meiosis I - Metaphase

Answer 5

Homologous pairs line up on equatorial metaphase plate

Question 6

Meiosis I - Anaphase

Answer 6

Homologous chromosomes each with 2 chromatids move to opposite pole

Question 7

Meiosis I - Telophase

Answer 7

Chromosome gather into nuclei and cell divides

Question 8

Meiosis II

Answer 8

Prophase - condense
Metaphase - Centrosome of paired chromatids line up at equator plate of each cell
Anaphase - Chromatids finally separate and pulled to opposite poles
Telophase

Question 9

Homologous recombination

Answer 9

Occurs during long prophase of meiosis I

2-3 crossover events/chromosome/meiosis
Highly similar DNA sequence binds to complementary sequence on homologous chromosome

Question 10

Non fatal trisomy

Answer 10

21, 13 or 18

Question 11

Trisomy 21

Answer 11

Down's syndrome 
1 in 750 live births
	Non-specific effects	
	Mental retardation
	Broad flat face, slanting eyes
	Congenital heart disease
	Intestinal blockage
	Enlarged colon

Question 12

Trisomy 13

Answer 12

Patau’s Syndrome

Question 13

Trisomy 18

Answer 13

Edward’s Syndrome

Question 14

Monsomy: Turner’s

Answer 14

• Female
  
  • Pubertal failure
  • Infertile
  • Normal intelligence
  • May have:
  • neck webbing, heart defects and horseshoe kidneys

Monosomy fatal except X chromosome

Question 15

Sex chrome syndromes

Answer 15

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

Question 16

Sickle cell disease: Heterozygous advantage

Answer 16

Autosomal Incomplete Recessive SCD

Sickle cell disease common in African/Caribbean families
SCD carriers more resistant to malaria
Positive selection for HbS allele in malaria endemic areas
Malaria parasites unable to replicate as well inside heterozygote (carrier) red blood cells…therefore SCD allele retained in the population

Question 17

X-linked recessive disease: Haemophilia A

Answer 17

Blood clots slowly: Bleeding, Easy bruising, Joint and muscle haemorrhages & Problem after surgery or trauma

Lack of blood clotting factor VIII
X-linked recessive trait: Deletions or inversions in F8 gene & Resulting in loss of function

Question 18

Other X-linked recessive disorders

Answer 18

Duchenne muscular dystrophy

Red-green colour-blindness