Module 5 - Heredity

Question 1

Sexual Reproduction

Answer 1

The process of forming a new organism from the fusion of the offspring’s parent’s male and female gamete. The offspring that is formed are not genetically identical to either parent.

Question 2

Gamete

Answer 2

sex cells such as sperm and egg cells for humans

Question 3

Asexual Reproduction

Answer 3

The process of forming an offspring (usually a clone) from just one parent through cell division.

Question 4

difference between sexual and asexual reproduction

Answer 4

The most important distinguishing factor between sexual and asexual reproduction is whether pr not the fusion of gametes occurred. For sexual reproduction, there must be a fusion of gametes, whereas in asexual reproduction there is no fusion of gametes.

Question 5

External Fertilisation animals

Answer 5

involves the fusion of gametes outside of the body of a parent.
- It is most common with aquatic animals, where the water acts as a medium via which the gametes can travel. This method of fertilisation is susceptible to environmental influences, such as predators and pH changes.

Question 6

Internal Fertilisation animals

Answer 6

involves the fusion of gametes inside the body of a parent.

• Terrestrial animals typically use internal fertilisation so as to prevent exposure and desiccation (drying out) of gametes or embryos.
• Internal fertilisation offers more protection to the gametes and embryos, but at a potential survival cost to the parent.

Question 7

advantages of internal fertilisation

Answer 7

• Increased possibilities of union gametes because all conditions required for fusion of gametes is maintained inside the body
• More protection against the outside environments and predators, and therefore a higher chance of survival until birth
• More selective of their mates
• Less chance of desiccation of gametes

Question 8

advantages of external fertilisation

Answer 8

• Results in the production of a larger number of zygotes and thus more offspring cane be produced (but at a high energy cost)
• Easier to find mates as the gametes released can drift (wind, water etc)
• More genetic variation

Question 9

Sexual Reproduction plants

Answer 9

Flowers make up the reproductive organ in plants. The petals and nectar are often used to lure insects and other animals to assist the delivery or pollen.

The Male Parts: The filament and anther (together called stamens) are the male part. Pollen is produced in the anthers. Pollen grains are microscopic structures that contains the tube cell (which becomes the pollen tube) and the generative cell (which releases the sperm nuclei).

The Female Parts: The female part (carpel) consists of the stigma. The style, the ovary and the egg cell (called an ovule).

Pollination: describes the way in which the pollen grains reach the sticky style. The pollen grains may be transferred to other flowers by wind, insects and other animals

Fertilisation: after landing on the stigma, a pollen tube grows down through the style into the ovary/ it then moved down to try to fertilise the ovule.

Question 10

asexual reproduction plants

Answer 10

vegetative propagation is a type of asexual reproduction that occurs in plants. It results in the parent producing a plant that is genetically identical. Cuttings, runners and bulbs are some examples of vegetative propagation.

Cuttings: The stem from the plant is cut and is planted in the soil that will gradually grow and turn into another plant. This is used for plants like roses, hibiscus, sugarcane etc.

Runners: Strawberry plants can develop runners which are stolon extending from the plant and along the soil. At certain points along dunners, nodes can develop which extend into the soil, resulting in the formation of new plant roots at another area of the soil whereby a new strawberry plant can grow. The runner joins the new (and genetically identical) strawberry plant to the parent plant

Bulbs: Bulbs are underground food storage organs that can grow and develop into new plants. When anew plant forms, the underground bulb provide nutrients to the plant for its survival. E.g onions and garlic

Question 11

Asexual Reproduction fungi: budding

Answer 11

Budding in fungi such as yeast involves the parent cell developing a bud cell, a daughter nucleus. Over time, this bud undergoes cell division (mitosis) while still being attached to the parent which may result in a chain of bud cells. The bud separates from its parent fungus when it grows to a sufficient size to be to support itself independently. This now-separated bud undergoes further cell division to produce more bud cells. The result is yeast that is genetically identical to parent.

Question 12

Asexual Reproduction fungi: spores

Answer 12

Spores in moulds and mushrooms are microscopic reproductive units (cells) that can be formed as a result of mitosis or meiosis. Spores differ from gametes as they do not need to combine with another spore to form offspring. Hyphae are fine, thread like structures that branch out and have ends that are capable of producing spores called sporangia. These asexual spores are carried by the wind. Then germinate to form genetically identical new hyphae.

Question 13

Sexual Reproduction fungi

Answer 13

Sexual spores may be developed when opposite gender hyphae are coming together to develop a spore-producing structure known as zygospore. The zygospore is diploid as each of the hypha are haploid. The diploid zygospore undergoes meiosis to produce haploid sexual spores which are dispersed into the environment. These spores will then grow into haploid hyphae that are genetically different from their parents.

Question 14

Asexual Reproduction bacteria

Answer 14

The process of binary fission starts with copying the genetic material (in the form of bacterial chromosome) of the parent cell. As there is no nucleus in bacteria, no nuclear splitting occurs. The two daughter cells are genetically identical to each other as well as identical to the parent.

Question 15

Asexual and Sexual Reproduction protists

Answer 15

Protists (or protozoa) such as paramecium are single celled, eukaryotic organisms that may reproduce either asexually, sexually or both. They reproduce asexually by binary fission or budding. Protists such as paramaecium reproduce sexually by conjugation where the cells fuse together briefly to exchange nuclear material.

Question 16

Gametogenesis

Answer 16

the name of the gamete formation process and can be divided into spermatogenesis (producing sperm) and oogenesis (formation of matured egg cells). The hormone testosterone is produced in the testes and plays a role in producing sperm cells.

Question 17

Fertilisation

Answer 17

The fertilisation process occurs in one of the fallopian tubes of the female’s body. The sperm enters the vagina, travels up through the uterus and then along one of the fallopian tubes where it can combine with and fertilise the mature egg.
The gametes fuse to form a zygote, a single cell with 46 chromosomes (23 from each parent). During fusion, the head of the sperm cell detaches from its tail (flagellum) and activates the egg cell resulting in cell division. The resulting product is called a blastocyst.

Question 18

Implantation

Answer 18

the process whereby the blastocyst adheres (sticks) to the walls of the uterus. This establishes the blastocysts access to nutrients, allowing it to develop into an embryo (blood vessels surrounding the blastocyst carries blood which has dissolved nutrients). If the blastocyst implants successfully in the uterus, the cells continue to divide, moving to form two distinct structures. Three of four blastocysts cells develop into the inner cell mass, which over the next few weeks will form into the recognisable structures of a human embryo, with a head, beating heart and tiny limbs. Some of these cells also develop into the foetal membranes that form a fluid-filled protective ‘bag’ around the embryo. The remaining 100 or so blastocyst cells form a structure called the trophoblast, which will provide the baby’s contribution to the placenta.

Question 19

Hormonal Control of Pregnancy

Answer 19

HCG
Progesterone
Oestrogen
Oxytocin

Question 20

Human Chorionic Gonadotropin (HCG)

Answer 20

HCG is mainly responsible for the early pregnancy symptoms ranging from missed menstruation to nausea, vomiting and fatigue.

Question 21

Progesterone

Answer 21

This hormone maintains the functionality of placenta and prevents sudden movement and contraction of the uterus

Question 22

Oestrogen

Answer 22

It is an ovarian hormone that is controlled by luteinising hormone (LH) that triggers ovulation. An important role of oestrogen is to facilitate the maturity of lungs, kidneys adrenal gland, liver and bone density of the unborn baby. Besides this is also aids the flow of blood to foetus.

Question 23

Oxytocin

Answer 23

Facilitates the delivery process by helping the contraction of uterus and also stimulates the mammary glands to produce milk. The hypothalamus in the brain produces oxytocin and stores it in the pituitary gland (situated below the hypothalamus). Upon stimulation of hypothalamus’s neurone cells, the pituitary gland will secrete oxytocin into the blood.

Question 24

CELL REPLICATION

Answer 24

most cells grow, perform the activities needed to survive, and divide to create new cells. These basic processes, known collectively as the cell cycle, are repeated throughout the life cycle of a cell.
• Of the various parts of the cell cycle, the division portion is particularly important, because this is the point at which a cell passes its genetic information to its offspring cells. In many situations, division also ensures that new cells are able to replace the older cells within an organism whenever those cells die. Eukaryotic cells may divide via mitosis or meiosis.

Question 25

MITOSIS

Answer 25

Mitosis is a process during cell division in which the cell nucleus divides into two. Cells can only arise from pre-existing cells.
• Cell division is essential for the maintenance of organisms, both for continued growth of organisms and also for the replacement of damaged or worn-out cells within them.
• One cell replicates its genetic nuclear context exactly and then divides to become two cells, distributing one full set of genetic material to each cell. Living bodies have control mechanisms to ensure that only those cells required to divide do so. If the cells divide in an uncontrolled manner, tumours or cancer may result.

Question 26

Cell division occurs in a cycle and involves two main steps

Answer 26

mitosis

cytokinesis

Question 27

mitosis process

Answer 27

1. Interphase: DNA has replicated, but not formed the condense structure of chromosome. They remain as loosely coiled chromatin. The nuclear membrane is still intact to protect the DNA molecules from undergoing mutation.
2. Prophase: The DNA molecules progressively shorten and condense by coiling, to form chromosomes. The nuclear membrane and nucleolus are no longer visible. The spindle apparatus has migrated to opposite poles of the cell.
3. Metaphase: the spindle fibres attach themselves to the centromeres of the chromosomes and align the chromosomes at the equatorial plate.
4. Anaphase: thee spindle fibres shorten and centromere splits, separated sister chromatids are pulled along behind the centromere.
5. Telophase: the chromosomes reach the poles of their respective spindles. Nuclear envelope reform before the chromosomes uncoil. The spindle fibres disintegrate.

Question 28

cytokinesis

Answer 28

this is the last stage of mitosis. It is the process of splitting the daughter cells apart. A furrow forms and the cell is pinched in two. Each daughter cell contains the same number and same quality of chromosomes.
- Plant cells: cytokinesis involves the formation of a cell plate while the nucleus is still in telophase

Question 29

MEIOSIS

Answer 29

Meiosis is a form of cell division happening in sexually reproducing organisms by which two consecutive nuclear divisions (meiosis I and meiosis II) occur leading to the production of four haploid gametes (sex cells), with the maternal and paternal chromosomes being distributed randomly between the cells).

Question 30

Genetic Variation meiosis

Answer 30

During meiosis, genetic variation arises as a result of the behaviour of chromosomes at two stages:

1. during crossing over
2. when chromosomes randomly segregate and paternal and maternal chromosomes assort independent of each other.

Question 31

During meiosis I:

Answer 31

1. Chromosomes line up in homologous pairs (one maternal and one paternal chromosome in each pair) during prophase I
2. Crossing over occurs: arms of homologous chromosomes exchange genetic material during metaphase. Crossing over ensures that linked genes on a chromosome can be inherited independent of each other. The exchange of genetic material between homologous chromosomes during crossing over causes the mixing of paternal and maternal genes and the result is an increased number of combination of genes that may be transmitted by gametes to offspring, thereby increasing genetic variation.
3. The chromosomes in each pair of chromosomes separate during anaphase I, so that one entire chromosome of each pair moves into a daughter cell. This separation of chromosomes, also referred to as random segregation, ensures the chromosome number in the resulting gametes will be half that of the original cell.

Question 32

independent assortment

Answer 32

Independent assortment occurs whereby the paternal and maternal chromosomes sort themselves independent of each other.

Question 33

During meiosis II

Answer 33

The two daughter cells that result from meiosis I each undergo meiosis II, which is similar to mitosis, and the behaviour of chromosomes in the second meiotic division does not further affect genetic variation.

Question 34

Key features of meiosis

Answer 34

produces variation for survival and reproduction
• random assortment: 223 ways to line up, as there are 23 pairs of chromosomes
• Crossing over: swap genetic material
• Metaphase and telophase are the most important

Question 35

Genetic Consequences of Meiosis:

Answer 35

• one cell undergoes two meiotic divisions to generate four haploid cells
• the genes in each haploid cell are a new combination of the parent genes
• the new combination results from both crossing over and random segregation allowing the individual alleles of maternally and paternally derived chromosomes to assort independently

Question 36

DNA

Answer 36

deoxyribonucleic acid
• A gene is a discrete unit of hereditary information consisting of specific section of DNA. A DNA molecule is very large and usually consists of hundreds of thousands of genes. When a cell reproduces itself by dividing, its DNA is copied and passed along from one generation of cells to the next.
• Encoded in the structure of DNA is information that program all the cells activities.
• Chromosomes consist of 40% DNA and 60% protein (histone). Short lengths of DNA make up genes so genes have the same chemical compound as DNA

Question 37

Chromosomes

Answer 37

a compact coil of threadlike molecules called DNA, organised around proteins called histones.
• Chemically each gene is made up of a portion of DNA that stores information as a coded sequence, and each coded sequence/gene is located at a particular site or locus on the chromosome.
• The coded information within genes determines how living things look, behave and function or phenotypes.
• A chromosome can therefore be described as a linear sequence of genes
• When cells begin to divide, the chromatin material coils into short, thick, rod-shaped chromosomes for easy transfer.
• Maternal and paternal chromosomes that carry alleles of the same genes are known as homologous pairs of chromosomes.

Question 38

Watson and Crick

Answer 38

• As a result of their collaborative approach, Watson and crick revealed that DNA is a double helix. A DNA molecule is made up of two chains of small monomers called nucleotides

Question 39

Each nucleotide consists of three parts:

Answer 39

 A phosphate
 A sugar
 A nitrogenous base

Question 40

Nitrogenous bases:

Answer 40

 Adenine (A)
 Thymine (T)
 Guanine (G)
 Cytosine (C)

Question 41

Chemical structure of DNA

Answer 41

• Each of the two complimentary strands in a DNA molecule is made up of a sequence of many nucleotides and the strands are held together by weak hydrogen bonds in the centre.
• The vertical sides of the ladder are made up of alternating sugar and phosphate molecules (sugar-phosphate backbone) and the ‘rungs’ of the ladders are pairs of nitrogenous bases

Question 42

The Process of DNA Replication

Answer 42

Step 1: The DNA double helix is unwound by the enzyme helicase
Step 2: The DNA unzips forming two single strands
Step 3: Nucleotides are attached to the single strands resulting in two identical strands of DNA, by DNA polymerase. The two double stranded molecules are the chromatids.

Question 43

significance of dna replication

Answer 43

• The significance of this process is that the genetic information is passed from generation to generation.
• During sexual reproduction, the genetic code is copied and then half of the genetic information passes into each of the sex cells (ovum or sperm). When fertilisation occurs, the new organism has half the genetic material from each parent
• The DNA in a single cell contains the genetic information to make an entire organism. When a cell divides it takes with it an exact copy of the genetic code of that organism

Question 44

dna replication

Answer 44

• A unit made up of deoxyribose sugar, a phosphate molecule and one of four nitrogenous bases is called a nucleotide. Thus, DNA consists of nucleotide units.
• Along the DNA molecule, there are long sequences of genetic code made up of these bases. The replication of these long sequences’ accounts for the replication of the genetic code of an organism. During meiosis it is necessary for the DNA to make an exact copy of itself.

Question 45

The Role of Gamete Formation and Sexual Reproduction in Variability of Offspring

Answer 45

• Gamete formation results in the halving of the chromosome number (diploid to haploid and sexual reproduction results in combining gametes (haploid to diploid to produce a new diploid organism.
• The processes involved in forming this new organism result in variation of the offspring.
• In sexual reproduction each female or male cell produces 4 sex cells (gametes) from the process of meiosis. Each of these sex cells is haploid (has half the normal chromosome number) and has a random assortment of genes from the parent.
• The genes (Mendel’s factors) are separated and the sex cells have a random assortment of dominant and recessive genes.
• More variability is introduced depending on which sex cells are successful in fertilization. The resulting embryo has a completely different set of genes from either of the parent.