Meoisis Flashcards
What number of chromosomes do normal body cells have
Haploid
2 of each chromosome
1 maternal and 1 paternal
What number of chromosomes do gametes have
Diploid
1 copy of each chromosome
How does random fertilisation help genetic diversity
Produces zygotes with different combinations of chromosomes from both parents
Where does meiosis happen
Reproductive organs
What happens before meiosis
DNA unravels and replicates and condenses
Forming 2 copies of each chromosome = chromatids
The sister chromatids join by a centromere
What happens in meiosis 1
Chromosomes arrange in homologous pairs
Homologous pairs are separated
Halving the number of number of chromosomes
What happens in meiosis 2
The pairs of sister chromatids are separated
As the centromere divides
What is the product if Meiosis
4 genetically different haploid cells
How is genetic diversity created In meiosis 1
Crossing over
And
Independent segregation
Explain crossing over
In meiosis 1 Homologous pairs pair up The chromatids twist around each other Exchanging alleles So the chromatids have different alleles
Explain independent segregation
In meiosis 1
Random as to what cells receive the maternal or paternal chromosome
So the 4 daughter cells have different combinations of maternal and paternal chromosomes
Difference between mitosis and meiosis
Mitosis = daughter cells have same number of chromosomes as parent cell. The daughter and parent cells are all genetically identical. Produces 2 daughter cells Meiosis = daughter cells have half the number of chromosomes as the parent cell. All daughter cells and parent cells are genetically different. Produces 4 daughter cells
What is chromosome mutations
Daughter cells have variations in the number of whole or parts of chromosomes
Why do chromosome mutations lead to inherited disorders
The errors are present in the gametes
What is non disjunction
The failure of chromosomes to separate
What causes Down’s syndrome
The non disjunction of chromosome 21
So 1 cell has an extra copy of c21 and 1 cell has no copy
When the gametes fuse the zygote has an extra chromosome
What is gene mutations
Change in the dna base sequence
What is substitution mutation
A base is substituted
What is a deletion mutation
A base is deleted
How do mutation affect cell function
The order of dna bases determines the order of amino acid they code for
If a mutation happens the sequence of amino acids changes
Changing the primary and tertiary structure of the protein
Hanging its shape and function
How is dna degenerate
1 amino acid is coded for by different dna triplets
Why does not all mutations result in a change in amino acid sequences
Dna is degenerate
So the mutation still coded for the same amino acid
It was a substitution mutation
Why do deletion mutations always result in a mutation
Change the number of bases present
Causing a frame shift in the bases after it
So more than 1 amino acid will change
How do mutations happen
Spontaneously by a mistake in dna replication
