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Unit 2 Biological Perspectives

1. Briefly describe the following:

• Mitosis and meiosis: Mitosis is a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus. Meiosis is a process of chromosome reduction through cell division that forms sex cells called gametes.

• Crossing over: During the first phase of meiosis, sometimes the genetic material is exchanged between a pair of chromosomes. This process of exchange of genetic material is called crossing over. 

• Identical and fraternal twins: 
• When ovum is fertilised by one sperm and at the time of the first division of the cell, the new cells separate instead of remaining together, the twins formed are called identical or monozygotic twins. They are always of the same sex and carry the same genes. 
• When two ova released at the same time are fertilised simultaneously by two different sperms, the individuals developed from these two ova are non-identical twins called fraternal or dizygotic twins. They may be of the same sex or of opposite sex. 
• Homozygous and heterozygous: For a given trait, the child is said to be homozygous if she or he has inherited two genes of the same allelic form for the trait from both the parents. 1f the alleles are different, then the child is heterozygous for the given trait. 
• Dominant and recessive alldes: When only one allele affects the child's characteristics, it is called dominant allele. The second allele which has no effect in singul ar form is called a recessive allele. 
• Co-dominance: Co-dominance is a pattern of inheritance in individuals for a gi ven trait which is heterozygous in which characteristics of both alleles are expressed, for example blood group. 
• X-Linked characteristics: Human characteristics which are affected by genes found on X-chromosomes arc called X-linked characteristics.
• Genetic diseases: Genetic diseases are passed from parents to children. Some of these are haemophilia, sickle-cell anaemia, phenylketonuria, Tay-Sachs disease, and cystic fibrosis. All these diseases are single-gene defects because a single gene is the cause of the disease.  For example, Phenylketonuria (PKU) is a genetic disorder that interferes with a child's ability to metabolise an amino acid called phenylalanine. If both parents are heterozygous carriers of PKU, these parents may have two carrier children, one normal child, and one affected child. 
• Down syndrome: Down syndrome is one of the most common and widespread consequences of a chromosomal error. The primary cause of Down syndrome is the failure of 21st pair of chromosomes to separate properly while undergoing meiosis during the production of the ovum and sperm. Down syndrome children have three of these chromosomes rather than two, therefore, also known as trisomy 2l.
• Sex chromosome abnormalities: Sex chromosome abnormalities are caused by an incomplete or incorrect division of sex chromosomes. One such example is Turner's Syndrome (TS) in which females are born with XO combination instead of the typical XX combination. Other examples of sex chromosome abnormalities: males with Klinefelter's syndrome carry an extra X chromosome, resulting in an XXY combination; Males born with the XYY syndrome carry an extra Y chromosome . 
• Genetic counselling: A couple needs genetic counselling if they have had repeated miscarriages, a still birth, have had difficulties in child bearing, have one child with a genetic disorder, any one close relative has a genetic problem, are over aged and want to have children; and the woman has been taking drugs or other dangerous substances during pregnancy. During counselling, parents are explained the likelihood of having an abnormal child. 
• Alternative methods of conception: When a couple is not able to conceive a child normally, then they opt for alterative methods of conception to fulfill their wish of parenthood. These are donor insemination method, in vitro fertilisation. and surrogate motherhood. 
• Prenatal diagnostic methods: With the help of prenatal diagnostic methods, problems can be detected before birth. Some of these methods are amniocentesis, ultrasound, foetoscopy and maternal blood analysis. Foetal blood can also be obtained to diagnose disorders such as haemophilia, sickle cell anaemia. and other neural defects. 

2. What are the different stages of the birth process? 

Different stages of the birth process are: 

• Dilation and effacement of the cervix, 
• Delivery of the baby, and 
• Delivery of the placenta. 

3. List down the childbirth complications. 

Important birth complications are: 

• Anoxia, 
• Haemorrhaging, and 
• Low birth weight. 

4. State the functions of the following: 

1) Functions of placenta: Placenta is the prenatal life support system. It separates the circulatory system of the foetus and the mother. Nutrients, oxygen, and waste are exchanged across the placenta. The placenta serves all of the functions provided by the lungs, kidneys, stomach and intestines. 

2) Functions of umbilical cord: The umbilical cord i  the link between the foetus and the placenta that delivers nutrients and removes waste products. 

3) Functions of amniotic fluid: It protects the foetus from injury or physical shocks and maintains relatively constant foetal body temperature

5. What are the physical hazards of prenatal period?

Physical hazards of prenatal period include: a possibility that the zygote will die of starvation; a tubal pregnancy; zygote getting attached to a small area of fibroid tissue; spontaneous abortion; developmental irregularities; premature and post-mature birth with complications; and complications of delivery

6. What are the psychological hazards of prenatal period?

Psychological hazards of prenatal period are traditional beliefs, preference for a particular sex of the child, and maternal stress that have long lasting impact on the child's development.

7. Name the teratogens which cause damage during the prenatal period.

Teratogens causing damage during prenatal period include prescription and non-prescription drugs, illegal drugs, alcohol, smoking, radiation, pollution, and maternal diseases

8. List down the maternal factors which influence prenatal development.

Maternal factors influencing prenatal development are: 

• Maternal nutrition, 
• Maternal age, and 
• Psychological stress.

9. Explain the biological foundations of human development in detail.

• Chromosomes and Genes: The biological foundation of human development is built upon chromosomes, which store and transmit genetic information from one generation to the next. Each chromosome contains thousands of segments of DNA called genes, which are the basic units of heredity.
• Cell Division: The process of cell division is crucial. Mitosis is the cell division and duplication process where the number of chromosomes remains the same. Meiosis is a type of cell division that reduces the number of chromosomes by half, resulting in the formation of sex cells called gametes (sperm and ovum).
• Sex Determination: The 23rd pair of chromosomes determines the sex of the child.
• Genetic Transmission: Genetic transmission occurs through the processes of mitosis and meiosis. At conception, the zygote receives 23 chromosomes from each parent, resulting in a total of 46 chromosomes.

10. Discuss the genetic and chromosomal abnormalities.

• Genetic Diseases: Some children are born with defects and disorders that follow the rules of dominant-recessive inheritance. The sources do not elaborate on what these diseases may be, other than mentioning Phenylketonuria (PKU) as an example.
• Chromosomal Abnormalities: Children can be born with congenital birth defects that are not hereditary, caused by the improper union of chromosomes or errors in development. Down syndrome (Trisomy 21) is one example of a chromosomal abnormality, where there are three copies of the 21st chromosome instead of two. Fragile X syndrome, where the X chromosome becomes constricted and often breaks, is another example. The sources also mention that sex chromosome abnormalities are caused by an incorrect division of sex chromosomes.
• It is important to note that these abnormalities can affect the physical and mental health of the child.

11. What is the importance of genetic counselling?

• Genetic counselling is a process of providing information about genetic disorders in the family and their preventive options.
• It helps couples make informed decisions about whether or not to have children, particularly when there is a family history of genetic disorders, repeated miscarriages, or stillbirths.
• Counsellors help couples understand the likelihood of having an abnormal child and consider options like conceiving, adoption, donor insemination, in-vitro fertilisation, or surrogate motherhood.

12. What are the various methods of prenatal diagnosis?

• Prenatal diagnostic methods help to detect problems before birth.
• These methods include:
  • Amniocentesis: A hollow needle is inserted through the abdominal wall to obtain a sample of fluid from the uterus to examine for genetic defects.
  • Ultrasound: Used to assess foetal age, detect multiple pregnancies, and identify physical defects.
  • Chorionic villus sampling: A thin tube is inserted through the vagina into the uterus to take a sample of cells from placental chorionic villi to examine genetic defects.
  • Foetoscopy: Used to inspect the foetus for defects of limbs and face.
  • Maternal blood analysis: Can help indicate foetal diseases.
• Foetal blood can also be obtained to diagnose disorders such as haemophilia, sickle cell anaemia, and other neural defects.

13. Briefly describe the alternative methods of conception.

Donor insemination: Injection of sperm from an anonymous man into a woman.

In-vitro fertilisation: Fertilisation of the ova by sperm outside the woman's womb.

Surrogate motherhood: A woman agrees to bear a child for another couple.

14. Discuss the prenatal development in detail.

Prenatal development is divided into three stages:

• Period of the Zygote (Conception to Two Weeks): The fertilised egg is called a zygote. The zygote travels down the fallopian tube, rapid cell division occurs (cleavage), and the zygote implants on the wall of the uterus. The outer layer of cells forms the placenta and the inner mass forms the embryo. The amnion and amniotic fluid develop.
• Period of the Embryo (Two to Eight Weeks): Inner cells of the blastocyst differentiate into three layers (ectoderm, mesoderm, and endoderm) that form different body parts. The amniotic fluid, placenta, and umbilical cord also develop in this period.
• Period of the Foetus (Third Month until Birth): The foetus grows and develops structures formed during the embryonic stage. Body size and muscular development increases, external genitals differentiate, and the central nervous system develops rapidly.

15. Describe the hazards of the prenatal period.

• Hazards during the prenatal period can be physical or psychological in nature.
• Physical hazards: The sources mention possibilities like the zygote dying of starvation, tubal pregnancies, miscarriages, developmental irregularities, premature or post-mature births, and complications during delivery.
• Psychological hazards: These can include traditional beliefs, preference for a particular sex of the child, and maternal stress. These factors can have long-term effects on the child's development.

16. How is prenatal development influenced by teratogens?

• Teratogens are environmental agents that cause damage during the prenatal period.
• The amount and length of exposure, the genetic makeup of the mother and child, and the age of the organism when exposed all influence the effects of teratogens.
• Teratogens can cause serious defects during the embryonic period when major body structures are developing.
• The sources mention that specific teratogens include drugs, alcohol, smoking, radiation, pollution, and maternal diseases.
• These factors can lead to physical defects, mental retardation, low birth weight, and other developmental problems.

17. Discuss the birth process and its complications.

• The birth process (labour) is divided into three stages:
  • Dilation and effacement of the cervix: The cervix opens up and flattens out.
  • Delivery of the baby: The baby is delivered.
  • Delivery of the placenta: The placenta is delivered.
• Complications during birth include:
  • Anoxia: Reduced oxygen supply that can lead to cerebral palsy or mental retardation.
  • Haemorrhaging: Caused by strong pressure on the foetus's head, affecting oxygen supply to the brain.
  • Low birth weight: Associated with high infant mortality, lower responsiveness, respiratory problems, and lower IQ.