Variation and Sexual Reproduction Flashcards
Give three disadvantages of sexual reproduction
High metabolic cost, gametes are made by special type of cell division
Reproduction rate is much slower
Only half of the population can actually produce offspring
Give two disadvantages of needing males for sexual reproduction
- Males are unable to produce the offspring, so only half the population can reproduce
- Only half of each parent’s genome is passed on so disrupts successful parental genomes
Name a mechanism used by bacteria to allow the exchange of genetic material between generations
Horizontal Gene Transfer (HGT)
Give examples of vegetative cloning methods in plants
Bulbs - Daffodils
Tubers - Potato
Rhizomes - Ginger
Spores - Fungi
What is parthenogenesis?
Production of haploid offspring without needing males or fetilization
Give conditions that parthenogenesis is common
Cooler Climates
Lower level of Parasitism
In what conditions is asexual reproduction beneficial?
Very narrow and stable niche
Recolonising disrupted habitats
Give an example of an area where asexual reproduction is beneficial
Butter cups using stolons to spread into flower beds with clear soil, gaining a competitive advantage
What is the diploid number of chromosomes for humans?
46
Give characteristics that are the same in homologous chromosomes
Same size
Same centromere position
Same genes at the same loci
What is the first stage in meiosis?
Long uncoiled chromosomes replicate to form two identical chromatids
Chromosomes coil up and become visibile
What is the site called where homologous chromosomes cross called?
Chiasma (plr. Chiasmata)
What are seperated during Meiosis I?
Pairs of homologous chromosomes (Not actually any chromosomes, its the pairs)
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
How many different combinations of chromosomes is there in the resulting haploid cells where n is the number of homologous pairs?
2^n
What does Chiasmata allow?
The chromosomes to exchange DNA with their homologous partner
What happens during crossing over?
Chromosomes touch at chiasmata
Allows exchanging of DNA with homologous partner
Chromosomes in the gametes can have new combinations of alleles
What is the process that allows chromosomes in the gametes to have new combinations of alleles?
Recombination
The further apart genes are on a chromosome the more likely _____?
they are to have a chiasma form between them, leading to new allele combinations in the gametes
What are the two types of factors that can influence the sex of individual?
Genetic Factors
Enviromental Factors
What are hermaphordites?
Organisms which individually have both male and female reproductive structures
What is the heterogametic sex in humans?
Male (XY)
What causes embryos to develop as male?
SRY gene
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 is the default pathway for embryos?
To develop as a female
What leads to sex linked patterns of inheritance?
The fact that X and Y chromosomes do not have homologous alleles
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
What is X inactivation an example of?
Dosage Compensation
What does dosage compensation ensure?
The female has exactly the same level of gene products as a male and do not get a double dose of gene products
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?
Temperature
Size
Competition
Parasitic Infection
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
What type of cell undergoes meosis?
Gamete mother cell
