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.

EASY

Upper Secondary-IGCSE

IMPORTANT

Earn 100

Fruit flies can have normal wings or vestigial (really small) wings. The allele for normal wings, N, is dominant. The allele for vestigial wings, n, is recessive.

Complete the table to show the possible genotype and phenotypes for fruit fly wings. Be very careful to write the letters N and n so that there is no doubt whether each one is a capital letter or a small letter.

Genotype Phenotype

Important Questions on Inheritance

MEDIUM

Upper Secondary-IGCSE

IMPORTANT

Biology for Cambridge IGCSE Workbook 4 th Edition Digital Access>Chapter 16 - Inheritance>Exercise 16.2>Q 10

Complete the genetic diagram to predict the genotypes and phenotypes of the offspring of a heterozygous normal-winged fly and a vestigial-winged fly.

Phenotypes of parents: normal wings vestigial wings

Genotypes of parents: _____ _____

Gametes: _____ and _____ all _____

Question Image

MEDIUM

Upper Secondary-IGCSE

IMPORTANT

Biology for Cambridge IGCSE Workbook 4 th Edition Digital Access>Chapter 16 - Inheritance>Exercise 16.2>Q 11

The two flies had 82 offspring. Predict approximately how many of these would have vestigial wings.

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

Person 5 is worried that her children might have PKU. She talks to a genetic counsellor. What might she be told?

MEDIUM

Upper Secondary-IGCSE

IMPORTANT

Biology for Cambridge IGCSE Workbook 4 th Edition Digital Access>Chapter 16 - Inheritance>Exercise 16.4>Q 16

In fruit flies, as humans, males have an X and a Y chromosome, and females have two X chromosomes.

There is a gene on the X chromosome that affects eye colour. The dominant allele of this gene produces red eyes, and the recessive allele produces white eyes.

Suggest suitable symbols for the two alleles of this gene.

HARD

Upper Secondary-IGCSE

IMPORTANT

Biology for Cambridge IGCSE Workbook 4 th Edition Digital Access>Chapter 16 - Inheritance>Exercise 16.4>Q 17

In the space below, construct a genetic diagram to predict the ratios of eye colour in male and female offspring of a white-eyed male fly and a heterozygous red-eyed female fly.

Genotype	Phenotype

Important Questions on Inheritance

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