Flashcards
Human Reproduction Part 1
Cards in this deck (43)
- 1What is fission in terms of asexual reproduction?This is a form of mitosis in which the parent cell reproduces by separating into 2 or more daughter cells of equal size. An amoeba can reproduce this way.
- 2Can multicellular organisms undergo fission?Some can e.g. anenome or budding/sprouting plants.
- 3What is parthenogenesis? Provide 2 examples.Parthenogenesis is a form of reproduction in which the egg develops without fertilisation. Bees and wasps utilise this method of asexual reproduction --> fertilised eggs become females, unfertilised eggs become males.
- 4What are the 2 types of cells in the human body?1. Somatic cells
2. Gametes - 5What is a somatic cell? Include an explanation of diploid cells.These are growth and maintenance cells, produced via cell division through mitosis. Somatic cells are identical to their parent cells, and are diploid (2n), meaning they have 2 copies of each chromosome.
- 6What is a gamete? Include an explanation of haploid cells.A gamete is a sex cell, produced via cell division through meiosis. This means that gametes are haploid (1n), with only 1 copy of each chromosome. These are *not* identical to their parent cells.
- 7What process is represented? What is produced?This diagram displays meiosis. This produces up to 4 dissimilar daughter cells which are haploid (1n) meaning they only have 1 copy of each chromosome. This process creates gametes.
- 8What process is represented? What is produced?This diagram displays mitosis. This process produces 2 diploid (2n) cells, which are identical to their parent cell, and have 2 copies of each chromosome. Diploid cells can be somatic cells, which are used for growth and development in the body.
- 9Provide a definition of 'sexual reproduction'.Reproduction that brings the genes of 2 parent individuals together, generating a new individual (which grows out of the zygote).
- 10What 2 processes are vital to sexual reproduction?1. Meiotic event;
2. Fertilisation. - 11What is fertilisation?The fusion of 2 haploid gametes (n) which generates a diploid zygote (2n).
- 12What is the male gamete?Sperm
- 13What is the female gamete?Egg/oocyte/ovum.
- 14What is external fertilisation?The synchronised release of gametes (synchrony). The probability of fertilisation is low, so reproductive gametes are released in the thousands to increase the chances of survival. This can involve parental care e.g. frogs, fish, coral.
- 15What is internal fertilisation?The environment is important because the sperm are independently mobile i.e. not in water. The probability of fertilisation is higher than external fertilisation, because physical contact is required. Synchrony is required.
- 16Provide 5 advantages of sexual reproduction.1. Recombination of genes can purge deleterious mutations;
2. Facilitates adaptation to environmental changes over time
3. Allows natural selection to calibrate better = easier combination of traits;
4. Allows the genome of the species to be passed on, rather than that of the individual
5. Encourages fruitful collaborations. - 17What is meant by the 'two-fold cost of sex'?Females contribute half of the genes and all of the resources to the foetus. The male contributes half of the genes and *none* of the resources. Does this make evolutionary sense from the female perspective?
An asexual female would be able to twice as many genes for the same 'price' per offspring. - 18Provide 5 disadvantages (or 'costs') of sexual reproduction.1. Mating can be risky in terms of STIs, time, energy and parental care;
2. At low population densities, sexual reproduction can be difficult to coordinate, whereas asexual reproduction ensures it can happen at any time
3. Recombination scrambles genotypes, can disrupt favourably adapted gene combination, whereas asexual reproduction can preserve advantageous genotypes.
4. Due to recombination, male aspects of genetics become obsolete over time
5. Meiosis and fertilisation take longer than mitosis and slow the process of reproduction. - 19What 3 factors must be considered in the process of phenotype assignment (sex determination)?1. Chromosomal makeup = XX or XY
2. Internal organs = testes or ovaries
3. External genitalia = penis or vagina - 20What is a chromosome?The packaging of genes. There are 46 chromosomes = 23 pairs of chromosomes.
- 21Why are human males heterogametic?They have 2 different sex chromosomes = XY.
- 22Why are human females homogametic?They have 2 sets of the same types of chromosomes = XX.
- 23Which gamete determines the sex?It is the sperm which determines the sex, because these cam be X *or* Y, where an egg can only be X.
- 24What are the 4 arbitrary stages of reproductive development mentioned in the lecture?1. Formation of the urogenital ridge (tissue that will produce hormones and develop into either testes or ovaries);
2. Gonad formation: determined the presence and activity of the SRY gene (sex-determining region of the Y chromosome)
3. Sex determination: typically occurs as a consequence of gonads
4. Sex differentiation: recognising how the sexes are phenotypically different i.e. external features of biological sex. - 25At what stage of gestation does the urogenital ridge develop?Week 5
- 26At what stage of gestation do the sexes begin to diverge?Latter half of week 6. If a Y chromosome is present, the SRY is activated, and stimulates the production of male sex hormones. If the Y chromosome is missing, the zygote will be female.
- 27What are the 3 prerequisites for typical sex development?1. An intact chromosome complement of 46 chromosomes
2. Fully functioning sex determination genes
3. Intact steroid hormone pathway - 28What is the default development option for humans?Female --> no SRY gene, no production of testosterone or response to it causes the zygote to develop into a female. If the 3 pre-requisites are not working in tandem, a female will develop.
- 29What is nondisjunction?A pair of chromosomes or sister chromatids may adhere so tightly together that they don't separate during meiosis. Both go to one daughter cell, and the other daughter cell receives no chromosomal information.
- 30What happens if nondisjunction creates a gamete with an extra or missing chromosome which is fertilised?1. Trisomy: three representatives of a chromosome.
2. Monosomy: one representative of a chromosome. - 31What is Turner Syndrome?Occurs in individuals who have only one X chromosome (XO) - only affects females. This is an example of monosomy. This causes a short stature (because the SHOX gene is impaired) and largely causes infertility, due to ovary-irregularity.
- 32What is Klinefelter Syndrome?This is observed in males who are XXY - there are not always external signs of this. Signs tend to emerge during puberty - the testes do not grow, or do not produce enough testosterone which impairs muscle development. Testes may not produce sperm (infertile), and facial/body hair may fail to develop.
- 33What is Androgen Insensitivity Syndrome (AIS)?This is an X-linked inheritance, a mutation/error in the gene-encoding, which causes the body to become 'blind' to testosterone. Neither testosterone nor dihydrotestosterone (DHT - strong) can bind to the necessary receptor molecules.
- 34Why is androgen crucial to sex determination?Because human androgen receptor proteins are encoded by a gene located on the X chromosome - the body's inability to bind androgen results in phenotypical feminisation.
- 35What are the signs of Androgen Insensitivity Syndrome?External genitalia is female i.e. breast development, but internal genitalia is male
Because hormones act as modifying agents e.g. androgen, and the gonads develop based on XY genetics. Thus, AIS means that the person is chromosomally male, but phenotypically female. - 36What overarching conclusion can we draw from the AIS case study?Maleness is something that is imposed on the neutral female state by the secretion of androgens.
- 37What role do steroids like androgens and testosterone play in sex development?Steroids like androgen and testosterone promote sexual differentiation. These are important throughout puberty for:
a. Inducing sperm production;
b. Induction + maintenance of secondary sexual characteristics e.g. pubic hair
c. Influencing aggressive/sexual behaviour
d. Having anabolic effects on proteins e.g. muscle - 38Provide 1 key example of a hormone pathway and demonstrate how other hormones act as intermediary steps.1. Cholesterol is converted into progesterones
2. Progesterones are converted into corticosteroids *or* androgens which can be oestrogens or testosterones. - 39When androgen is converted into oestrogens, it causes 5 things. What are they?1. Stimulates secondary sexual characteristic development in females;
2. Prepares the uterus for sperm transport;
3. Stimulates the growth of mammary glands;
4. Slightly anabolic
5. Regulates hormone secretion. - 40What role do enzymes play in hormone synthesis?Many enzymes are responsible for converting cholesterol into active hormones. Genetic mutations that disrupt these enzymes can be detrimental.
- 41What is 5-Alpha Reductase Deficiency?Affects genetic males (XY), causing a lack of the enzyme which converts testosterone into DHT. Because DHT indices the development of the penis and the scrotum, the body's inability to produce DHT results in a biological male who is phenotypically female. As puberty begins, the body experiences a surge in testosterone levels, which generates a penis and fertility as a male.
- 42What does this diagram show?Hormonal pathway which demonstrates 5-Alpha Reductase deficiency. Demonstrates how hormones can act as intermediary steps in the development of other hormones.
- 43What is Congenital Adrenal Hyperplasia (CAH)?This syndrome consists of a mutation at the gene site of the enzyme which essentially blocks the hormone pathway that allows progesterone to be converted into corticosteroids or cortisol. As a result, the hormone overflow is redirected into the production of androgens = all progesterone becomes androgens. Thi causes female phenotypes with masculinised genitals.
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- Tertiary Biology Flashcards on Human Reproduction Part 1, created by Sophie Barnes on 11/04/2024.
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- Sophie Barnes
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