The family tree (pedigree) in figure 16.3 shows the incidence of a genetic disease called phenylketonuria (PKU) in four generations of a family. Describe one piece of evidence from the diagram that suggests PKU is caused by a recessive allele.

Phenylketonuria (PKU) is an inherited disorder. It is caused when phenylalanine (an amino acid) build up in the blood. PKU is inherited in an autosomal recessive pattern. Recessive genetic disorders occur when an individual inherits an abnormal gene from each parent. If an individual receives one normal gene copy and one abnormal gene copy, they will be a carrier for the condition, but will not have symptoms. From the pedigree chart, we can observe that person 1 (female) is PKU recessive. Person 3 (male) is also PKU recessive. They are carriers for PKU recessive gene. When offspring from person 2 and person 3 (male) married and have children. Some of their children have an abnormal gene that shows PKU disorder. In recessive diseases, affected individuals often occur every other generation.

The family tree (pedigree) in figure 16.3 shows the incidence of a genetic disease called phenylketonuria (PKU) in four generations of a family. If PKU is caused by a recessive allele, explain why it is unlikely that this allele first appeared in person 4.

PKU is inherited in an autosomal recessive allele. Recessive genetic disorders occur when an individual inherits an abnormal gene from each parent. If an individual receives one normal gene copy and one abnormal gene copy, they will be a carrier for the condition, but will not have symptoms. The PKU first appears in person 4 because there is a chance that person 4 both allele is mutated which result in it inheriting the PKU allele. Thus, person 4 is suffering from PKU disorder.

The family tree (pedigree) in figure 16.3 shows the incidence of a genetic disease called phenylketonuria (PKU) in four generations of a family. In the space below, deduce the possible genotypes of person 1, 2, 3 and 4. Use the symbol q for the PKU allele and the symbol Q for the normal allele.

Phenylketonuria (PKU) is an inherited disorder. It is caused when phenylalanine (an amino acid) build up in the blood. Recessive allele: It refers to a type of allele which will not be manifested in an individual unless both of the individual's copies of that gene have that particular genotype. Genotype Person 1: Q and q (Normal allele) Person 2: Q and Q (Normal allele) Person 3: Q and q (Normal allele) Person 4: q and q (PKU allele)

The family tree (pedigree) in figure 16.3 shows the incidence of a genetic disease called phenylketonuria (PKU) in four generations of a family. Person 5 is worried that her children might have PKU. She talks to a genetic counsellor. What might she be told?

Phenylketonuria (PKU) is a rare autosomal recessive disease. The recessive allele is inherited by person 5 is from its parents. The only way the couple can have a child with PKU is if both of them are heterozygotes. If they are both heterozygous, then one-quarter of their children would have PKU, so the probability that their first child will have PKU is 1/4.

E M B I B E

Biology for Cambridge IGCSE Workbook 4 th Edition Digital Access>Chapter 16 - Inheritance>Exercise 16.3

Mary Jones and Geoff Jones Solutions for Chapter: Inheritance, Exercise 3: Exercise 16.3

Author:Mary Jones & Geoff Jones

Mary Jones Biology Solutions for Exercise - Mary Jones and Geoff Jones Solutions for Chapter: Inheritance, Exercise 3: Exercise 16.3

Attempt the free practice questions on Chapter 16: Inheritance, Exercise 3: Exercise 16.3 with hints and solutions to strengthen your understanding. Biology for Cambridge IGCSE Workbook 4 th Edition Digital Access solutions are prepared by Experienced Embibe Experts.

Questions from Mary Jones and Geoff Jones Solutions for Chapter: Inheritance, Exercise 3: Exercise 16.3 with Hints & Solutions

MEDIUM

Upper Secondary-IGCSE

IMPORTANT

Biology for Cambridge IGCSE Workbook 4 th Edition Digital Access>Chapter 16 - Inheritance>Exercise 16.3>Q 12

The family tree (pedigree) in figure 16.3 shows the incidence of a genetic disease called phenylketonuria (PKU) in four generations of a family.

Question Image

Describe one piece of evidence from the diagram that suggests PKU is caused by a recessive allele.

MEDIUM

Upper Secondary-IGCSE

IMPORTANT

Biology for Cambridge IGCSE Workbook 4 th Edition Digital Access>Chapter 16 - Inheritance>Exercise 16.3>Q 13

The family tree (pedigree) in figure 16.3 shows the incidence of a genetic disease called phenylketonuria (PKU) in four generations of a family.

Question Image

If PKU is caused by a recessive allele, explain why it is unlikely that this allele first appeared in person 4.

MEDIUM

Upper Secondary-IGCSE

IMPORTANT

Biology for Cambridge IGCSE Workbook 4 th Edition Digital Access>Chapter 16 - Inheritance>Exercise 16.3>Q 14

The family tree (pedigree) in figure 16.3 shows the incidence of a genetic disease called phenylketonuria (PKU) in four generations of a family.

Question Image

In the space below, deduce the possible genotypes of person 1, 2, 3 and 4. Use the symbol q for the PKU allele and the symbol Q for the normal allele.

MEDIUM

Upper Secondary-IGCSE

IMPORTANT

Biology for Cambridge IGCSE Workbook 4 th Edition Digital Access>Chapter 16 - Inheritance>Exercise 16.3>Q 15

The family tree (pedigree) in figure 16.3 shows the incidence of a genetic disease called phenylketonuria (PKU) in four generations of a family.

Question Image