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Biology F215

Meiosis and Genetics

Key Words

Autosomes - All the chromosomes expect X and Y

Bivalent - The structure formed when homologous chromosomes pair up

Centromere - The structure that holds two sister chromatids together

Chiasma(ta) - The structural point where non0sister chromosomes in a bivalent join during crossing…

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Zygote - A cell formed from the fertilization of an egg cell by a sperm cell

What are chromosomes?

In eukaryotes, chromosomes are linear DNA molecules, packaged with histone proteins to form chromatin
o Prior to nuclear division, the chromatin condenses to form discrete chromosomes

What are the male and…

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What are diploid and haploid cells?

Diploid cells have two copies of each chromosome so are annotated as (2n)
Haploid cells have only one copy of each chromosome so are annotated as (n)

What happens during interphase?

During interphase new proteins are synthesised and
alongside the production of organelles and…

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o The chiasmata separate and lengths of the chromatid which had been crossed
over remain with their newly attached to chromosome
o Telophase 1
In animal cells the chromosomes uncoil
Two nuclear envelope forms in most animal cells
o Cytokinesis occurs as the plasma membrane pinches inwards
o Prophase 2…

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o Resulting in genetic diseases such as Trisomy 21 - Down's Syndrome
o Leads to polyploidy if whole sets of chromosomes fail to separate

What other sources of variation arise from sexual reproduction?

The random mating within the population results in variation as different individuals have a different
combination of…

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If there are more than one allele for a gene, the gene represented by an upper case letter and the alleles are in
superscript e.g. IA, IB and Io

What is monohybrid inheritance?

This is the inheritance of one characteristic
o That is determined by one gene with two or…

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Why does the allele for sickle cell globin remain at high levels (up to 20%) in some populations?

In populations in areas of malaria sickle cell anaemia is an example of heterozygous advantage
o This is because sickle cell anaemia reduces the severity of malaria
As the Plasmodium is unable…

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When writing this out always choose symbols that show the gene is present on the X chromosome e.g. XH or Xh
o Also in your answer, remember to state phenotype AND sex of individuals

What problems in humans are sex linked?

Examples of recessive X-linked genes include
o Colour blindness…

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What is autosomal linkage?

If two genes are located on different chromosomes
o There are four different gametes
This can then lead to four possible phenotypes
o If two genes are located on the same chromosome (are linked)
They are usually inherited together so there are only two possible gametes…

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All the F1 generation have purple flowers if these are breed to produce the F2 generation they
have purple and white flowers in the ratio 9:7
This must be because at least one dominant allele for both gene loci C-R- has to be
present for the flowers to be purple…


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