Unit 2 - KA2.3 Variation and Sexual Reproduction Flashcards
Give three disadvantages/costs of sexual reproduction
1 - Reproduction rate is much slower
2 - Males unable to produce offspring
3 - Successful parental genomes are disrupted as only half the genome is passed on
Give two disadvantages of needing males for sexual reproduction
1 - Males are unable to produce the offspring, so only half the population can reproduce
2 - Only half of each parent’s genome is passed on so disrupts successful parental genomes
List the three advantages of sexual reproduction
1 - Greater genetic variation
2 - Genetic variation allows sexually reproducing organisms a better chance of survival under changing selection pressures.
3 - Variation provides the raw material required to keep running in the Red Queen’s arms race between parasites and their hosts
List the three advantages of asexual reproduction
1 - Maintains the parent’s entire genome
2 - Advantage in re-colonising disturbed habitats
3 - Faster reproduction rates
Explain why maintaining the parental genome is an advantage in asexual reproduction.
In very narrow, stable niches it is advantageous as the offspring will be well adapted to this niche.
In what conditions is asexual reproduction beneficial?
1 - Very narrow and stable niche
2 - Recolonising disrupted habitats
Explain why the red queen hypothesis helps explain the persistence of sexual reproduction over time.
1 - Hosts better able to resist and tolerate parasitism have greater fitness.
2 - Parasites better able to feed, reproduce and find new hosts have greater fitness.
3 - If hosts reproduce sexually, the genetic variability in their offspring reduces the chances that all will be susceptible to infection by parasites
What are two examples of asexual reproduction in eukaryotes?
1 - Vegetative cloning in plants
2 - Parthenogenesis in some animals.
What is parthenogenesis?
Production of haploid offspring without needing males gametes to fertilise the female gamete.
Give conditions that parthenogenesis is common
1 - Cooler Climates
2 - Lower level of Parasitism
Name a mechanism used by bacteria to allow the exchange of genetic material between generations
Horizontal Gene Transfer (HGT)
What is the diploid number of chromosomes for humans?
46
Give characteristics that are the same in homologous chromosomes
1 - Same size
2 - Same centromere position
3 - Same genes at the same loci
What is a gametocyte?
Diploid cells located in the sex organs that produce the male and female sex cells.
What happens in the first stage in meiosis I?
The chromosomes, which have replicated prior to meiosis I, each consist of two genetically identical chromatids attached at the centromere. The chromosomes condense and the homologous chromosomes pair up.
What happens in the second stage in meiosis I?
Chiasmata form at points of contact between the non-sister chromatids of a homologous pair and sections of DNA are exchanged
What happens during crossing over?
Chromosomes touch at chiasmata which allows exchanging of DNA with homologous partner. Chromosomes in the gametes can have new combinations of alleles than the parent genome.
What is the process that allows chromosomes in the gametes to have new combinations of alleles?
Recombination due to crossing over.
What happens in the third stage in meiosis I?
Spindle fibres attach to the homologous pairs and line them up at the equator of the spindle
What happens in the fourth stage in meiosis I?
The chromosomes of each homologous pair are separated and move towards opposite poles
What happens in the fifth stage in meiosis I?
Cytokinesis occurs and two daughter cells form
What happens during the stages of meiosis I
1 - The chromosomes, which have replicated prior to meiosis I, each consist of two genetically identical chromatids attached at the centromere. The chromosomes condense and the homologous chromosomes pair up
2 - Chiasmata form at points of contact between the non-sister chromatids of a homologous pair and sections of DNA are exchanged.
3 - Spindle fibres attach to the homologous pairs and line them up at the equator of the spindle.
4 - The chromosomes of each homologous pair are separated and move towards opposite poles.
5 - Cytokinesis occurs and two daughter cells form
What happens during the stages of meiosis II
Each of the two cells produced in meiosis I undergoes a further division during which the sister chromatids of each chromosome are separated. A total of four haploid cells are produced
What is the site called where homologous chromosomes cross called?
Chiasma (plr. Chiasmata)
What is Independent Assortment?
A way of producing variation between daughter cells due to the fact there is no control over which chromosomes of each pair goes to which side of the cell
What are separated during Meiosis I?
Pairs of homologous chromosomes, e.g. X-X are separated NOT the chromatids that make up X
What are separated during Meiosis II?
Sister chromatids, e.g. the chromatids that make up X are pulled apart NOT the homologous chromosomes X-X
What are the two types of factors that can influence the sex of individual?
1 - Genetic Factors
2 - Environmental Factors
Describe the work of the SRY gene
Acts as a master switch which triggers a cascade to activate all male genes in the genome
What causes embryos to develop as male?
SRY gene
What is the heterogametic sex in humans?
Male (XY)
What is the homogametic sex in humans?
Female (XX)
What is different about the Y chromosome compared to the X chromosome?
The Y chromosome lacks most of the corresponding homologous alleles that are on the X chromosome, so many genes only have one allele as opposed to two.
What leads to sex linked patterns of inheritance?
The fact that X and Y chromosomes do not have homologous alleles
Which sex is affected most by sex-linked disorders?
Males as they only have one copy of each gene due to the shorter Y chromosome.
What is X inactivation?
Most of the genes on one X chromosome are inactivated so that cells have a single working copy of the X chromosome genes
Why does X inactivation happen?
To prevent a double dose of gene products, which could be harmful to cells.
What does X inactivation ensure?
The female has exactly the same level of gene products as a male and do not get a double dose of gene products
What are hermaphrodites?
Organisms which individually have both male and female reproductive structures
Describe the benefits of hermaphrodites?
If the chance of encountering a partner is an uncommon event it will increase reproductive success.
How many alleles are needed for a male to express the deleterious allele?
1
How many alleles are needed for a female to express the deleterious allele?
2
Who is less likely to express the effect of a deleterious allele carried on an X chromosome?
Female
What environmental factors have an effect on sex or sex ratio?
1 - Temperature
2 - Size
3 - Competition
4 - Parasitic Infection
5 - Resource Availability
Give an example of a species where temperature effects the sex ratio and explain how it does that
Hermann’s Tortoise If eggs are incubated at less than 31 degrees - all males produced. If eggs are incubated at above 31 degrees - all females produced
Give an example of a species where size effects the sex ratio and explain how it does that
Clown Fish live in groups, one large female and some smaller females. When the largest female is removed, the largest male becomes a female
Give an example of a species where competition effects the sex ratio and explain how it does that
Lesser Mouse Lemur - If a solitary female detects urine of another female, she produces more male offspring
Give an example of a species where parasite infection effects the sex ratio and explain how it does that
Insects infected by Wolbachia Bacteria. Bacterial infection of the eggs kills the males or feminises them
