HSC: Heredity Flashcards
SEXUAL REPRODUCTION
there is a mix of the parents’ genes. Each contributes their genetic material to the next generation.
ASEXUAL REPRODUCTION
offspring are genetically identical to each there and parent. Only one parent contributes their genetic material to the next generation.
EXTERNAL FERTILISATION
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.
INTERNAL FERTILISATION
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.
ADVANTAGES OF SEXUAL REPRODUCTION
Combination of chromosomes from two organisms increases variation, which assists with survival
DISADVANTAGES OF SEXUAL REPRODUCTION
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
Advantage of Sexual reproduction via internal
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
Advantage of Sexual reproduction via external
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
Disadvantage of Sexual reproduction via internal
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
Disadvantage of Sexual reproduction via external
Species must produce larger numbers of gametes, which requires extra energy. It also requires a watery environment (may be difficult for amphibians )
Pollination
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)
Male reproductive part of plants
the filament and the anther (together called stamens). Anthers produce pollen which contains sperm cells of a plant.
Female reproductive part of plants
the female part (carpel) consists of the stigma, style, ovary and ovule.
Vegetative propagation
type of asexual reproduction in plants, it results in the parent producing a plant genetically identical.
Cuttings
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
Runners
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
Bulbs
Bulbs are underground food stored organs that can grow and develop into new plants. E.G. onions
BUDDING
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.
SPORES
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)
BACTERIA: BINARY FISSION
- 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
PROTISTS: BINARY FISSION, BUDDING
- 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.
hormones involved in the first trimester of pregnancy
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.
hormones involved in the second trimester of pregnancy
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.
hormones involved in the third trimester of pregnancy
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.
Testosterone
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.
estrogen
Stimulates growth of sex organs at puberty, development of secondary sex characteristics, monthly preparation of endometrium, maintains pregnancy, develops uterine wall
Progestogen
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.
Luteinising hormone (LH)
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.
Follicle stimulating hormone
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
Oxytocin
Stimulates contraction of uterus, prostaglandin release, ejection of milk into ducts
prolactin
Stimulates milk production after breast has been prepared by estrogen and progesterone
Human Chorionic Gonadotropin
signals corpus luteum to continue to function if fertilization occurs
used to detect pregnancy
hypothalamus
produces gonadotropin releasing-hormone which stimulates the anterior pituitary, telling it when to secrete FSH and LH.
Describe the role and changes in levels of a hormone in pregnancy
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.
Nucleic acid
a biomolecule consisting of a chain of nucleotides (e.g: DNA and RNA)
Nucleotide
a biomolecule consisting of a nitrogenous base, a phosphate group, and a 5-carbon sugar molecule
Model of DNA structure (Watson and Crick)
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.
The process of DNA replication:
- Initiation (‘unzipping’) the enzyme helicase unwinds and separates complementary DNA strands by breaking the hydrogen bonds between nitrogenous bases.
- 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.
- 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.
DNA replication with enzymes
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.
Topoisomerase
relaxes DNA from its supercoiled sates, always working ahead of the replication fork
Helicase
follows topoisomerase and unwinds the double helix by breaking hydrogen bonds between bases causing the two strands to separate and creating a replication fork
Primase
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
DNA Polymerase
– adds nucleotides to make new DNA strands
Ligase
connects the two strands of the DNA molecule and also connects the Okazaki fragments
Faults within the basic model of DNA
- 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)
Nucleotide composition, hydrogen bonding and pairing
- 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
Difference between DNA and RNA
- 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
Stages in mitosis
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
Stages in meiosis
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
Law of segregation
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.
Law of independent assortment
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.
Transcription
The process of turning genetic information stored in the DNA into an intermediary molecule (mRNA)
- DNA polymerase binds to the ‘promotor’ which signals the DNA to unwind and allows enzymes to read the bases
- The mRNA molecule is built using the complementary bases
- The mRNA molecule detaches from the DNA strand
Translation
the process where genetic information encoded as mRNA turns into a polypeptide chain
- mRNA attaches to a ribosome
- the ribosome attaches the codons and anticodons together
- polypeptide chain forms and grows as amino acids are added
- once a stop codon is reached, the chain detaches
INCOMPLETE DOMIANANCE
Two dominant alleles result in a blended phenotype. E.G. a red flower x a white flower = heterozygous pink flower
CODOMINANCE
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
SEX LINKED
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.
MULTIPLE ALLELES
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)
Mendel’s Experiments
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.
X – linked dominant
If a father has the condition:
- 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.
