HSC: Heredity

Question 1

SEXUAL REPRODUCTION

Answer 1

there is a mix of the parents’ genes. Each contributes their genetic material to the next generation.

Question 2

ASEXUAL REPRODUCTION

Answer 2

offspring are genetically identical to each there and parent. Only one parent contributes their genetic material to the next generation.

Question 3

EXTERNAL FERTILISATION

Answer 3

External fertilisation involves the fusion of gametes outside the body of a parent. It is most common in aquatic animals, where the water acts as a medium in which the gametes can travel. This method of fertilisation is susceptible to environmental influences, such as predators and pH changes. They usually release large quantities of gametes to compensate for losses.

Question 4

INTERNAL FERTILISATION

Answer 4

Internal fertilisation involves the fusion of gametes inside the body of a parent. Terrestrial animals typically use internal fertilisation to avoid desiccation (drying out) of gametes or embryos. Internal fertilisation offers more protection to the gametes and embryos, but as a potential survival cost to the parent.

Question 5

ADVANTAGES OF SEXUAL REPRODUCTION

Answer 5

Combination of chromosomes from two organisms increases variation, which assists with survival

Question 6

DISADVANTAGES OF SEXUAL REPRODUCTION

Answer 6

Requires mating of two organisms which is dependent on syncing fertility cycles, and the production of offspring is lower and less prolific than asexual reproduction

Question 7

Advantage of Sexual reproduction via internal

Answer 7

Increased likelihood of fertilisation as egg and sperm are in close proximity, with increased protection from the environment leading to higher survival rates of offspring. Less chance of desiccation of gametes

Question 8

Advantage of Sexual reproduction via external

Answer 8

Large number of gametes produced generally means more off spring. It is also a simpler behavioural process which does not require mating rituals. More genetic variation

Question 9

Disadvantage of Sexual reproduction via internal

Answer 9

Fewer offspring are produced, and it is more difficult to bring males and females into contact. There is higher risk of sexually transmitted infections passing between organisms

Question 10

Disadvantage of Sexual reproduction via external

Answer 10

Species must produce larger numbers of gametes, which requires extra energy. It also requires a watery environment (may be difficult for amphibians )

Question 11

Pollination

Answer 11

The transfer of male gametes (pollen) from the anthers (male) of one plant to the stigma (female) of the same or another flower so that fertilisation may occur (Stamen = male, Carpel = female)

Question 12

Male reproductive part of plants

Answer 12

the filament and the anther (together called stamens). Anthers produce pollen which contains sperm cells of a plant.

Question 13

Female reproductive part of plants

Answer 13

the female part (carpel) consists of the stigma, style, ovary and ovule.

Question 14

Vegetative propagation

Answer 14

type of asexual reproduction in plants, it results in the parent producing a plant genetically identical.

Question 15

Cuttings

Answer 15

the stem from the plant is cult and is planted in the soil that will gradually grows and turn into another plant. E.G., roses

Question 16

Runners

Answer 16

Stems extending from the plant and along the soil. Runners will develop nodes which extend into the soil resulting in the formation of a new plant root allowing another to grow. E.G. strawberry

Question 17

Bulbs

Answer 17

Bulbs are underground food stored organs that can grow and develop into new plants. E.G. onions

Question 18

BUDDING

Answer 18

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

Question 19

SPORES

Answer 19

Spores in moulds and mushrooms are micro reproductive units 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. (spores are carried by the wind)

Question 20

BACTERIA: BINARY FISSION

Answer 20

• A single cell divides into two identical daughter cells
• Begins with DNA replication where the genetic information of the bacteria is copied and divided in two.
• The cell elongates and splits into two (cytokinesis) producing daughter cells with identical genomic information (i.e. Clones of the parent).
• Very rapid
• Lack of genetic diversity in the resulting population lowers chance of organism survival

Question 21

PROTISTS: BINARY FISSION, BUDDING

Answer 21

• For haploid protists, two haploid cells fuse to form a new cell, a zygote. Genetic material is combined oin a new fused nucleus. The zygote undergoes meiosis to form a new haploid cells.
• For diploid protists, adult cells undergo, meiosis to produce 4 gametes. Gametes fuse during fertilisation to form a diploid zygote, which will grow into a diploid adult.

Question 22

hormones involved in the first trimester of pregnancy

Answer 22

high levels of progesterone also stimulate changes in the mother’s body. These changes include enlargement of the uterus, formation of a mucous plug to seal the cervix, growth of the maternal parts of the placenta, and breast growth.

Question 23

hormones involved in the second trimester of pregnancy

Answer 23

high levels of oestrogen and progesterone are vital to continue maintaining pregnancy. However, the production of embryonic hcg declines and the corpus luteum deteriorates, stopping it from producing these hormones. Instead, the placenta takes over the role of producing oestrogen and progesterone.

Question 24

hormones involved in the third trimester of pregnancy

Answer 24

increased oestrogen is released; this oestrogen induces receptors to form on the uterus wall that can bind the hormone oxytocin. Oxytocin is critical to triggering and maintaining labour. An increased production of oxytocin occurs during labour.

Question 25

Testosterone

Answer 25

this is produced in the interstitial cells between the seminiferous tubules. It targets the adjacent seminiferous tubules and promotes sperm development and secondary sex characteristics.

Question 26

estrogen

Answer 26

Stimulates growth of sex organs at puberty, development of secondary sex characteristics, monthly preparation of endometrium, maintains pregnancy, develops uterine wall

Question 27

Progestogen

Answer 27

this is produced in the ovary and targets the uterine lining. It maintains the thickness form the monthly cycle or a pregnancy. Progesterone also affects the development of secondary sex characteristics.

Question 28

Luteinising hormone (LH)

Answer 28

LH is produced in the anterior pituitary. It acts on the interstitial cells in the male to secrete testosterone. In the female, it acts on the ovary and causes ovulation of the egg from the follicle.

Question 29

Follicle stimulating hormone

Answer 29

produced in the anterior pituitary. The target organ in the males is the testes and stimulates the development of sperm. The target organ in the female is the ovaries and stimulates the follicle in the ovary

Question 30

Oxytocin

Answer 30

Stimulates contraction of uterus, prostaglandin release, ejection of milk into ducts

Question 31

prolactin

Answer 31

Stimulates milk production after breast has been prepared by estrogen and progesterone

Question 32

Human Chorionic Gonadotropin

Answer 32

signals corpus luteum to continue to function if fertilization occurs
used to detect pregnancy

Question 33

hypothalamus

Answer 33

produces gonadotropin releasing-hormone which stimulates the anterior pituitary, telling it when to secrete FSH and LH.

Question 34

Describe the role and changes in levels of a hormone in pregnancy

Answer 34

A hormone that is important in pregnancy is progesterone. Progesterone is initially produced by the corpus luteum in the ovary and causes the endometrium to thicken, which helps to support and maintain the pregnancy in the first weeks when the placenta is still developing. The developed placenta then produces progesterone at significantly higher levels to maintain the pregnancy. Prior to birth progesterone levels drop significantly to facilitate labour.

Question 35

Nucleic acid

Answer 35

a biomolecule consisting of a chain of nucleotides (e.g: DNA and RNA)

Question 36

Nucleotide

Answer 36

a biomolecule consisting of a nitrogenous base, a phosphate group, and a 5-carbon sugar molecule

Question 37

Model of DNA structure (Watson and Crick)

Answer 37

Deoxyribose nucleic acid or DNA is a double helical nucleic acid molecule which carries genetic information, encoded with sequences of nucleotide bases. DNA is double stranded, composed of stacked and complementarily bonded nucleotides.
A singular Nucleotide is a phosphate, bond to a deoxy rise sugar group, bound to a nitrogenous base (either Adenine, thiamine, guanine or cytosine)
Nucleotides are phosphate bonded to sugar, forming a sugar-phosphate. Backbone. Inwardly facing nitrogenous bases are bonded C-G or A-T, by hydrogen bonding.

Question 38

The process of DNA replication:

Answer 38

1. Initiation (‘unzipping’) the enzyme helicase unwinds and separates complementary DNA strands by breaking the hydrogen bonds between nitrogenous bases.
2. Elongation: small pieces of RNA called primers bind to the end of the strands, signalling the starting point of replication. DNA polymerase bind to separate DNA strands at primer sites, and begins ti add new base pairs which are complementary to the strand. For example, where the polymerase recognises A it will bind a T.
3. Termination: DNA polymerase reaches the end of the DNA molecule and two identical daughter strands now have been produced. Strands recoil into the double helix shape creating two new DNA molecules. Nuclease enzymes essentially proofread the double helix structures.

Question 39

DNA replication with enzymes

Answer 39

DNA replication is the process by which an existing DNA molecule is copied to produce 2 identical DNA molecules. The enzymes topoisomerase relaxes the DNA from its coiled structure. The enzyme helicase unwinds & unzips the DNA molecule at a particular point (an origin of replication) making two template strands of DNA available. The hydrogen bonds between the nitrogenous bases break. The enzyme primase synthesizes short RNA primers to start each new DNA strand or fragment. One of the strands is in the 3’ to 5’ direction, which is called the leading strand; the other is in the 5’ to 3’ direction and is called the lagging strand. The enzyme DNA polymerase catalyses’ the synthesis of the new DNA strands. DNA Polymerase helps the DNA nucleotides (which are readily available in the cell) match up with their complementary base on the template DNA (A&T, C&G). DNA polymerase continues to bond free nucleotides to the exposed bases according to the complementary base pairing rule until there are no more exposed bases. DNA ligase (enzyme) seals the two strands of DNA into double strands. The final result of DNA replication is two identical DNA molecules, made up of one old and one new strand which automatically coil back into a double helix.

Question 40

Topoisomerase

Answer 40

relaxes DNA from its supercoiled sates, always working ahead of the replication fork

Question 41

Helicase

Answer 41

follows topoisomerase and unwinds the double helix by breaking hydrogen bonds between bases causing the two strands to separate and creating a replication fork

Question 42

Primase

Answer 42

connects RNA primer to a strand to initiates DNA replication, synthesises a short complementary RNA molecule which binds to DNA, serving as the starting point for DNA synthesis by polymerase

Question 43

DNA Polymerase

Answer 43

– adds nucleotides to make new DNA strands

Question 44

Ligase

Answer 44

connects the two strands of the DNA molecule and also connects the Okazaki fragments

Question 45

Faults within the basic model of DNA

Answer 45

• Does not model major and minor groves (The major groove occurs where the backbones are far apart, the minor groove occurs where they are close together)

Question 46

Nucleotide composition, hydrogen bonding and pairing

Answer 46

• DNA is a polymer made up of nucleotide monomers
  A nucleotide contains a deoxyribose sugar joined to a phosphate group and a nitrogenous base
• The sugar-phosphate chain forms an external backbone for the DNA strand and the nitrogenous bases radiate towards the centre of the helical molecule, joined to the sugar in the backbone
• Two purine bases: Guanine (G) and adenine (A) and two pyrimidine bases - thymine (T) and cytosine (C) - are the nitrogenous bases.
• Hydrogen bonding results in the nitrogenous bases paring A-T and C-G

Question 47

Difference between DNA and RNA

Answer 47

• RNA has the sugar ribose present, whereas DNA has the sugar deoxyribose
• Uracil pairs with adenine in RNA, while thymine pairs with adenine in DNA
• RNA consists of a single strand, whereas DNA consists of a double strand

Question 48

Stages in mitosis

Answer 48

Interphase: Chromosome’s double

Prophase; Chromosomes condense; spindle fibres form; nuclear membrane disappears; centrosomes move to opposite poles

Metaphase: Kinetochores appear at centromeres; spindle fibres attach chromosomes align along equator of cell

Anaphase: Centromere divides into two; sister chromatids move to opposite poles

Telophase: Nuclear membranes reappear around two new sets of chromosomes; spindle fibres disappear; cytokinesis follows

Question 49

Stages in meiosis

Answer 49

Prophase I: Chromosomes condense and the nuclear membrane breaks down, crossing over

Metaphase I: Pairs of homologous chromosomes move to the equator of the cell; independent assortment

Anaphase I: Homologous chromosomes move to opposite poles of the cell

Telophase I and cytokinesis: Chromosomes gather at opposite poles and cytoplasm divides; 2 new daughter cells

Prophase II: New spindle fibres form

Metaphase II: Chromosomes line up at equator

Anaphase II: Centromeres divide; chromatids move to opposite ends of the cell

Telophase II and cytokinesis: Nuclear membrane forms around 2 new sets of chromosomes

Question 50

Law of segregation

Answer 50

The law of segregation states that the parental genes must separate randomly and equally into gametes during meiosis so there is an equal chance of the offspring inheriting either allele.

Question 51

Law of independent assortment

Answer 51

The law of independent assortment says inheriting an allele has nothing to do with inheriting an allele for any other trait. The alleles from parents are passed on independently to the offspring. After fertilization, the resulting zygote(s) can end up with any combination of chromosomes from the parents and all the possible combinations occur with equal frequency.

Question 52

Transcription

Answer 52

The process of turning genetic information stored in the DNA into an intermediary molecule (mRNA)

1. DNA polymerase binds to the ‘promotor’ which signals the DNA to unwind and allows enzymes to read the bases
2. The mRNA molecule is built using the complementary bases
3. The mRNA molecule detaches from the DNA strand

Question 53

Translation

Answer 53

the process where genetic information encoded as mRNA turns into a polypeptide chain

1. mRNA attaches to a ribosome
2. the ribosome attaches the codons and anticodons together
3. polypeptide chain forms and grows as amino acids are added
4. once a stop codon is reached, the chain detaches

Question 54

INCOMPLETE DOMIANANCE

Answer 54

Two dominant alleles result in a blended phenotype. E.G. a red flower x a white flower = heterozygous pink flower

Question 55

CODOMINANCE

Answer 55

two dominant alleles result in both phenotypes being expressed at the same time. E.G. black chicken X white chicken = heterozygous having both black and white feathers

Question 56

SEX LINKED

Answer 56

when an allele is located on the X chromosome E.G. haemophilia or colour blindless. In order to have haemophilia you have to have two copies of the recessive allele.

Question 57

MULTIPLE ALLELES

Answer 57

occur with genes that have more than two alleles. E.G. inheritance of human blood groups display multiple alleles (as well as co-dominance and complete dominance)

Question 58

Mendel’s Experiments

Answer 58

The gene height in pea plants has two alleles, these being tall and short.

Experiment:
Used pea plants and did many repeats to look at how characteristics are inherited through dominant and recessive inheritance. Classified as the ‘father’ of genetics.

Question 59

X – linked dominant

If a father has the condition:

Answer 59

• He cannot (0% chance) pass on the gene that does not work correctly to his sons, because it is on his X chromosome. Men pass only the Y chromosome to their sons.
• He will always (100% chance) pass on the gene that does not function properly to his daughters, because he only has one X chromosome, and he passes that X chromosome to all of his daughters.