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Flashcards in Gentetic variation (meiosis) Deck (16):

Species usually have different numbers of chromosome. Why are animals that are bred from two different species normally infertile?

1. (usually) an uneven number of chromosomes;
2. Chromosomes cannot pair
3. chromosomes are not homologous
4. meiosis cannot occur


Explain the role of independent segregation in meiosis.

1. To provide genetic variation;
2. Allows different combinations of
maternal and paternal chromosomes/
3. To produce haploid cells (half the
chromosome number);
4. Allows homologous pairs to arrange randomly
at equator of cell


What is the importance of meiosis?

Halves chromosome number and restores diploid number at fertilisation


Describe and explain how selection will have affected the genetic diversity of sugar

1. Diversity reduced
2. As alleles have been chosen


Explain the appearance of a chromosomes

Two chromatids;
Due to DNA replication;
Joined by a centromere;


Explain how the gametes with the combinations of alleles Ef and eF have been produced.

Crossing over;
Exchange of alleles between chromatids


Describe and
explain how the production of gametes by meiosis contributes to this variation

Independent assortment/random alignment of (homologous) chromosomes;
Different combinations of maternal and paternal chromosomes;
Crossing over;
Different combination of alleles/exchange of genetic material


Describe how crossing over occurs during meiosis I.

chromosomes in each homologous pair twist around each other;
chromatids break and rejoin to chromatid on sister chromosome


What is the biological importance of reducing the chromosome number when the cell
divides by meiosis?

Restoring diploid number
Later fertilisation


Describe 5 differences between meiosis and mitosis

1. Reduces the chromosome number
2. Homologous chromosomes associate in pairs
3. Crossing-over
4. Two divisions → 4 offspring cells
5. Genetically different product
1. Maintains the same chromosome
number as in the parent nucleus
2. Homologues do not pair
3. No crossing-over;
4. One division → 2 offspring cells;
5. Genetically identical product;


Explain why the chances of inheriting a genetic disorder increase with a smaller community who only reproduce with people in that comunity

1. Less genetic diversity
2. As individuals only breed within group
3. Therefore Higher chance of inheriting allele


Suggest how a mutation can lead to the production of a protein that has one amino
acid missing.

loss of 3 bases
3 bases code a for 1 amino acid


Suggest how the production of a protein with one amino acid missing may lead to a
genetic disorder

1.Change in sequence of bases
2. Therefore change in bonds formed in 1^0
3 . Therefore change in tertiary structure
4. Leading to a non-functional protein


Suggest four reasons why populations might show very low levels of genetic diversity.

1. genetic bottleneck
2. inbreeding
3. Population might have started with small
number of individuals
4. founder effect


How do changes to whole sets of chromosomes occur?

When organisms have more than the usual 2 sets of chromosomes. This is called polyploidy


Describe what non-disjunction is and what it results in

1. When individual homologous pairs of chromosomes fail to separate
2. during meiosis
3. resulting in gametes having 1 less or 1 more chromosomes