Lecture 4

Question 1

Incomplete dominance:

Answer 1

The heterozygote is a blended phenotype eg., flower colour Parents homozygous red- CrCr plus homozygous white CwCw Offspring F1: CrCw-pink — get third phenotype, blend of the originals Offspring F2: ¼ red CrCr, ½ pink CrCw, ¼ white CwCw -Different ratios to complete dominance explanation: allele Cr- one unit of red, allele Cw- no unit of red

Question 2

co-dominance:

Answer 2

the effect of each allele can be seen in the heterozygote eg., sickle cell anaemia HbA- normal beta globin HbS- abnormal beta globin- sickled rsbcs If genotype: HbAHbS phenotype: both normal and sickled cells Monohybrid with co-dominance- ¼ HbAHbA normal, ½ HbAHbS normal and sickled, ¼ HbSHbS sickle cell disease

Question 3

What is a haploid organism?

Answer 3

only one allele for each locus e.g. Aspergillus nidulans (fungi) - mostly asexual reproduction, budding off, if under stress can go into sexual reproduction, becomes briefly diploid when reproduction via meiosis- separate at Anaphase I.

Question 4

What is Alkaptonuria? How does it arise?

Answer 4

• urine turns black , tips of noses, ears and eyes have blue spots - defect in the Phenylanine and Tyrosine (amino acid) metabolic pathways, there is a block in the homogentistic acid

Question 5

What is . Phenylketonuria (PKU) an dhow does it arise?

Answer 5

• defect in the Phenylanine metabolic pathway, phenylalanine hydroxylase doesn’t metabolise Phanylalanine into Tyrosine, get accumulation of Phenylpyruvic acid which can be detected in urine
• patients, blond, blue eyes
• untreated leads to mental retardation, seizures, brain damage

Question 6

How is PKU detected and how is it treated?

Answer 6

• PKU is checked for in babies by checking the levels of phenylalanine on Guthrie card (usually after breastfeeding started)
• if detected, severe diet avoiding food with phenylanine content at least till growth complete but now recommended to stay on especially if pregnant as high phenylanine levels in mother’s blood would damage fetus’ brain

Question 7

What is the Phenylanine Tyrosine pathway connected to? (illnesses)

Answer 7

connected to PKU, albinism, dwarfism, tyrosinosis, alkaptonuria.