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Flashcards in Variation Deck (15):
1

New combinations of genes (recombination)

Independent assortment
Crossing over
Fertilization

2

New variation (mutation)

Chromosome mutations
Gene mutations

3

Independent assortments

During metaphase 1 of meiosis- homozygous pairs of chromosomes line up and segregated into daughter cells
Chromosomes line up differently on the spindle
Results in gametes having different combinations of chromosomes
Number of combinations depends on number of pairs of chromosomes (2n)
2 pairs = 2 raises to the 2, 23 pairs 2 -||- 23
A human can produce c. 8 million unique gametes! (And more)

4

Crossing over

Crossing over results in the separations and recombination of alleles present on the same chromosome
During prophase 1 of meiosis - genetic material exchange between chromosomes
Results in alleles being inherited in new combinations

5

Fertilization

During fertilization, any of the c. 8 million possible variations of eggs can come together with any of the fathers c. 8 million genetically different sperm
Enormous amount of variation

6

New combination - sum up

Independent assortment, crossing over and fertilization each produce NEW COMBINATIONS of genetic material
They do not result in NEW ALLELES, GENES or CHROMOSOMES
For evolution to work we need more than new combination

7

What is a mutation?

Change in the nucleotide sequence of the DNA - can result in a completely new phenotype
Mutations arise spontaneously-not “directed” by the environment
Mutations are persistent - pass from generation to generation
Mutations are often harmful or of no benefit to the organism - but occasionally a helpful mutation turns up

8

Mutation rate

A particular gene mutates fairly slowly, in most organisms between c. 1 and 30 mutations per million gametes
HIV virus - mutates up to a million times faster than other viruses
Helps to overcome host immune system
Mutagens increase rate of mutation (eg. C-rays, UV light and various chemicals)

9

Chromosome mutation

During meiosis, things can go wrong

—>

10

Deletion

Deletion - a gene section of chromosome “drops out” missing genes

Usually fatal

11

Duplication

Sequence of genes is replaced

Usually harmful but can be helpful, new copies of genes can get new functions-haemaglobin

12

Inversion

Piece of chromosome is turned around

Some genes present, but regulation disrupted, mostly harmful

13

Translocation

“Switching” if genetic material between chromosomes

Some genes present, but regulation disrupted-mostly harmful

14

Non-disjunction errors

Homologous chromosomes do not separate - end up in same cell

15

Polyploidy

An organism with one or more complete extra sets of chromosomes

Occurs either:
before facilitation (cell division fails in meiosis resulting in diploid gametes)
After fertilization (DNA replicates but cells do not divide in mitosis)
Eg. Triploid (3N) Tetraploid (4n)