Unit 2 - section 3 Flashcards
What are the advantages and disadvantages of sexual reproduction?
Disadvantages
Half pop unable to reproduce - paradox existence makes
Mixing genetic info of parents means only half of the successful genome passed on to offspring
Advantages
Creates genetic diversity and variation allowing evolution to take place
Genetic variation it creates essential for running in red queen hypothesis
What are the advantages and disadvantages of asexual reproduction?
Disadvantages
Whole pop genetically identical so one disease could wipe out whole pop
Advantages
Successful for narrow stable niches
Faster so advantageous for recolonising disturbed habitats
What are two eukaryotic organisms that carry out asexual reproduction?
Common in plants - perennial weeds
Rarely in animals - kimono dragon absence males females give birth to only males
Stick insects absence males females give birth all females
What is asexual reproduction in plants called?
Vegetative propagation
What is parthenogenesis?
Asexual reproduction in animals
When does parthenogenesis occur?
When parasite diversity or density is low and in cooler climates
What is meiosis?
Process of cell division that results in the formation of new haploid cells
What are homologous chromosomes?
Chromosomes that are the same size and have their centromeres in the same place and carry the same genes at the same loci
What effect does meiosis have on variation?
Increases variation in organisms because for each pair of homologous chromosomes there is two possible arrangements
Process meiosis
?
What are the 2 divisions that occur in meiosis?
Meiosis I and meiosis ll
What happens to gamete mother cells during meiosis?
Divide into 4 haploid sex cells
What are the events of meiosis I?
Interphase - DNA replication occurs forming two sister chromatids
Homologous chromosomes pair up along the equator
Chromosomes can touch at chiasmata and crossing over can occur
Homologous chromosomes line up randomly (independent assortment) increasing variation
Spindle fibres separate homologous chromosomes forming two haploid daughter cells
What increases the chances of two genes crossing over?
The further they are apart
What are linked genes and what happens when you separate them?
All the genes on one chromosome are said to be linked
The separating of linked genes creates recombination
What are the events of meiosis II?
Pairs of chromatids are separated by spindle fibres creating haploid gametes
What forms gametes directly?
The cells that are produced by meiosis
What is an alternative way of forming gametes? (From algae)
Often the haploid cells from meiosis divide by mitosis to form haploid individuals rather than gametes fusing to form diploid zygotes. These haploid individuals produce their gametes through mitosis. These can fuse so the next generation is diploid
What is a hermaphroditic species?
A species where an individual contains both male and female reproductive systems and gametes
What are two factors that can determine sex and sex ratio?
Environmental temperature-controls sex in reptiles 31.7°C< temperature<34.5°C offspring will be male
Female deer produce more male offspring when conditions favourable but produce less males when conditions harsher
How can sex change in some species and what are theses species called?
Sequential hermaphrodites
Can be due to their size, a parasitic infection or competition
What are the sex bearing chromosomes in live-bearing mammals and some insects?
X and Y chromosomes
Which chromosome is responsible for characteristics related to maleness?
Y chromosome
Does the X or Y chromosome have more genes?
The X has more
Why do sex-linked patterns of inheritance occur?
Male lacks homologous alleles for genes on X chromosome which results in sex linked patterns of inheritance
How is a lethal double dose of the products of gene expression avoided in females?
In order to compensate for an extra double dose of genes the portions of the X chromosome that are lacking on the Y are randomly inactivated on 1 of the homologous X chromosomes in each cell
Why are carriers less likely to be affected by deleterious mutations?
Because X chromosome inactivation is random so half of the cells in any tissue sample will have a working copy of the gene
