Diversity, Classification and Variation- Meiosis and Genetic Variation Flashcards
What are gametes?
The sperm cells in males and egg cells in females
When do the sperm and egg cells join together?
Fertilisation
What is formed at fertilisation?
A zygote which divides and develops into a new organism
How many chromosomes do normal body cells have?
The diploid number (2n)- each cell contains 2 of each chromosome, one from the mum, one from the dad
How many chromosomes do gametes have?
A haploid number (n)- only one copy of each chromosome
What happens at fertilisation?
A haploid sperm fuses with a haploid egg to make a cell with the normal diploid number of chromosomes- half of chromosomes are from the father and half are from the mother
What does random fertilisation produce?
Zygotes with different combinations of chromosomes to both parents
What is the advantage of random fertilisation?
Mixing of genetic material increases genetic diversity within a species
What is meiosis?
A type of cell division
Where does meiosis take place?
In the reproductive organs
What kind of cells are the cells that divide by meiosis?
Diploid
What kind of cells are the cells that are formed from meiosis?
Haploid
What would happen without meiosis?
You’d get double the number of chromosomes when the gametes fused
What happens before meiosis starts?
DNA unravels and replicates so that there are two copies of each chromosomes called chromatids
What happens after chromatids are formed?
DNA condenses to form double-armed chromosomes that are each made from two sister chromatids
What are the sister chromatids joined by?
A centromere
What happens in meiosis I?
The chromosomes arrange themselves into homologous pairs which are then separated, halving the chromosome number
What happens in meiosis II?
The pairs of sister chromatids that make up each chromosome are separated
What is produced in meiosis?
Four haploid cells that are genetically different from each other
What does the chromatids crossing over in meiosis I mean?
Chromatids still contain same genes but now have a different combination of alleles
How does crossing over of chromatids lead to genetic variation?
Means that each of the four daughter cells formed contains chromatids with different alleles
How does independent segregation of chromosomes lead to genetic variation?
- Each homologous pair of chromosomes is made up of one maternal chromosome and one paternal chromosome
- When homologous pairs are separated, it’s completely random which chromosome from each pair ends up in which daughter cell
- So four daughter cells produced have different combinations of maternal and paternal chromosomes
- Called independent segregation of chromosomes
- Shuffling of chromosomes leads to genetic variation in potential offspring
How is mitosis different from meiosis?
Mitosis- produces cells with same number of chromosomes as parent cell, daughter cells are genetically identical to each other and parent cell, two daughter cells produced
Meiosis- produces cells with half the number of chromosomes as parent cell, daughter cells are genetically different from one another and parent cell, four daughter cells produced
What happens if meiosis goes wrong?
Cells produced contain variations in the numbers of whole chromosomes or parts of chromosomes- chromosome mutation
What can chromosome mutations lead to?
Inherited conditions because error is in the gametes
