Answer to Hands on Pg 77-81

Objective Questions

1	A	9	D
2	C	10	D
3	D	11	C
4	B	12	C
5	A	13	D
6	A	14	A
7	C	15	B
8	D

Section A / Bahagian A

1. (a) (i) Genetic factor

(ii) Various alignments of homologous chromosomes during metaphase together

with crossing over during prophase I produce different combinations of alleles in gametes.

(b)(i) Draw a bar chart

(ii) Discontinuous variation

(iii) No intermediate values among individuals, discrete distribution

(c) Thumbprints, blood groups

(d) The graph of the heights of students shows normal distribution whereas the graph of the presence of dimples shows discrete distribution. There are no intermediate values in the graph of the characteristic of dimples whereas there are no clear cut values for the range of values of students’ heights.

2. a (i)

Lengths (mm)	Number of earthworms
50-53	2
54-57	5
58-61	8
62-65	10
66-69	9
70-73	7
74-77	4
78-81	1

(ii) Draw a histogram

(b) (i) Continuous variation

(ii) There are intermediate values

(iii) Mass of earthworms, size of earthworm

(c) (i) Earthworm in container P has the fastest growth rate.

(ii) Environmental factors such as types of soil and the presence of light affect the growth of earthworms.

Sample answer to Question 1 Paper 3 (Pg 196 Bioscore)

a)

Pattern of thumbprints	No of students with the same pattern of thumbprint
Whorl	12
Loop	10
Composite	22
Arch	6

b) i)

1. The number of students with the pattern of thumbprint composite is 22.

2. The number of students with the pattern of thumbprint arch is 6.

(ii)

1. The number students with the pattern of thumbprint composite is high because

     it is a dominant trait.

2.  The number of students with the pattern of thumbprint arch is low because it

     is a recessive trait.

Variable	Method to handle the variable
Manipulated variable Pattern of thumbprints	Use different types of thumbprints which are composite, loop, whorl and arch
Responding variable Number of students with the same pattern of thumbprints	Count and record the number of student with each pattern of thumbprint by using thumbprint set.
Controlled variable Type of fingers	Fix the type of finger  to be same

(d) When the pattern of thumbprint is composite, the number of students is the highest.

(e)i)

Pattern of thumbprints	No of students with the same pattern of thumbprint
Whorl	12
Loop	10
Composite	22
Arch	6

(ii) Draw a bar chart

(f) The type of variation found in thumbprint is discontinuous variation because the is no range/intermediate values between the different thumbprint pattern and falls in a distinct/discrete category.

(g) Bell shape/normal distribution.

Height is a continuous variation and it has intermediate values and is influenced by genetic and environment factors.

Genetics and Variations

GENETIC DISEASES

What is Klinefelter Syndrome ?

Klinefelter syndrome is the condition where a male has an additional X chromosome in his cells. Under normal conditions, a male has XY chromosome pattern whereas for males with Klinefelter syndrome the pattern differs to XXY (44 + XXY).

This extra X chromosome leads to development of various abnormalities like :

·      small testes,

·      enlarged breasts,

·      infertility

·      long legs,

·      mental retardation

·      and reduced sperm production.

What is Turner syndrome?

Turner syndrome is a condition in which a female does not have the usual pair of two X chromosomes. (44 + XO)

Possible symptoms in young infants include:

·                     Swollen hands and feet

·                     Wide and webbed neck

A combination of the following symptoms may be seen in older females:

·                     Absent or incomplete development at puberty, including sparse pubic hair and

            small breasts

·                     Broad, flat chest shaped like a shield

·                     Drooping eyelids

·                     Dry eyes

·                     Infertility

·                     No periods (absent menstruation)

·                     Short height

What is Down’s syndrome?

Down's syndrome, also known as trisomy 21, is a chromosomal condition caused by the presence of three chromosome 21.

Common physical signs include:

• Flattened nose
• Upward slanting eyes
• Single crease in the palm of the hand
• Small ears
• Small mouth
• Wide, short hands with short fingers

Physical development is often slower than normal. Most children with Down syndrome never reach their average adult height.

Children may also have delayed mental and social development. Common problems may include:

• Impulsive behavior
• Poor judgment
• Short attention span
• Slow learning

When chromosomes fail to separate

Example of Meiotic Nondisjunction that causes disease like Down Syndrome

Down syndrome/Trisomy 21

Down syndrome (DS), also called Trisomy 21, is a condition in which extra genetic material causes delays in the way a child develops, both mentally and physically. It affects about 1 in every 800 babies. Trisomy 21 is caused by a meiotic nondisjunction event.

Normally, a baby inherits genetic information from its parents in the form of 46 chromosomes: 23 from the mother and 23 from the father.

With meiotic nondisjunction, a gamete (i.e., a sperm or egg cell) is produced with an extra copy of chromosome 21; the gamete thus has 24 chromosomes. When combined with a normal gamete from the other parent, the embryo now has 47 chromosomes, with three copies of chromosome 21. It's this extra genetic material that causes the physical features and developmental delays associated with DS.

Kids with Down syndrome tend to share certain physical features such as a flat facial profile, an upward slant to the eyes, small ears,and a protruding tongue with mild to moderate intellectual impairment.

Scientists found that women age 35 and older have a significantly higher risk of having a child with the condition. At age 30, for example, a woman has about a 1 in 900 chance of conceiving a child with DS. The probability increases to about 1 in 350 by age 35. By 40 the risk rises to about 1 in 100.

For genetic testing before birth, pregnant women may decide to undergo amniocentesis or chorionic villus sampling (refer to Blog on Prenatal testing for Down Syndrome).

Example of Meiotic Nondisjunction that causes disease like Down Syndrome

Dihybrid Cross

Genetic factors of variation

CROSSING OVER DURING MEIOSIS

Prenatal Testing for Down Syndrome

Below are Prenatal tests for Down Syndrome(Trisomy 21)

a) Amniocentesis
This procedure is used to collect amniotic fluid, the liquid that is in the womb. It's performed in the doctor's office or in the hospital on an "out-patient" basis. A needle is inserted through the mother's abdominal wall into the uterus, using ultrasound to guide the needle. Approximately one ounce of fluid is taken for testing. This fluid contains fetal cells that can be examined for chromosome tests. It takes about 2 weeks to determine if the fetus has Down syndrome (47 chromosomes) or not.

b) Chorionic Villus Sampling
In this procedure, instead of amniotic fluid being taken, a small amount of tissue is taken from the young placenta (also called the chorionic layer). These cells contain the fetal chromosomes that can be tested for Down syndrome. The cells can be collected the same way as the amniocentesis, but another method is to insert a tube into the uterus through the vagina. CVS is usually carried out between the 10th and 12th weeks of pregnancy.