B2.7 - Cell divison & inheritance

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  • Created by: Leyha M
  • Created on: 09-12-15 17:25

Genes&Alleles

DNA is coiled up into chromosomes.

Humans have 46, 23 pairs.

Chromosomes--> sections genes --> alleles (diff versions of same gene)

Chromosomes are large DNA molecules (deoxyribonucleic acid) & have a double helix

You inherit 2 alleles, one from mum&dad

-These can be the same (HOMOZYGOUS) BB

-Or different (HETEROZYGOUS) Bb

Gametes are haploids. Only have 23 chromosomes. When fused, become diploids- have 46 chromosomes.

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Inheritance

Dominant: AN ALLELE THAT IS ALWAYS EXPRESSED, EVEN IF THERE IS ONE COPY

Recessive: AN ALLELE THAT IS ONLY EXPRESSED IF 2 VERSIONS ARE PRESENT IN ONE CELL

Genotype: the particular gene combination // BB Bb bb

Phenotype: characteristic that appears // blue eyes, brown eyes

Homozygous dominant: BB

Heterozygous: Bb

Homozygous recessive: bb

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All proteins are made from amino acids. sequence of bases code for same amino acids. 

substitution mutation // deletion mutation // addition mutation

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Inherited diseases

MENDEL// published his work in an obscure journal --> significance of work not realised // Austrain monk not scientist // he couldn't explain his findings

Inherited (genetic) diseases are caused by faulty genetic material that is passed onto future generations.

Carriers are individuals with a copy of the faulty allele that codes for an inherited disease, but do not have the disease themselves.

Cystic fibrosis (CF) is caused by a single recessive allele. Homozygous individuals--> CF.

Huntington's disease is caused by a single dominant allele. Heterozygous individuals-->Huntington's.

Polydactyle is caused by a single dominant allele. Heterozygous individuals--> Polydactyle.

 Hemophilia is a sex related disease.

When a woman is heterozygous for the allele she will be an unaffected 'carrier'.

 A man who has the 'h' allele on his single X chromosome will have the disease.

A woman who was homozygous for the 'h' allele would have the disease, but they never develop.

Embryos can be screened for the alleles that cause these. Cannot cure these --> Gene therapy.

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Mitosis

Cells divide to:

complete an organism // replace old + damaged cells // reproduction

Mitosis: cell division that forms two daughter cells, each witht the same number of chromosomes as the parent cell. ASEXUAL REPRODUCTION

Process:

1) Start w/ parent cells w/ two pairs of chromosomes

2) Chromosomes become shorter & thicker // chromosomes replicating themselves

3) Spindle fibres attatch to the chromosomes

4) Chromosomes align themselves to the centre of the cell

5) Spindle fibres contract, separating the chromosomes

6) Chromotids move to opposite side of cell

7) Cell divides into two daughter cells

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Meiosis

Meiosis: cell division that forms the daughter cells w/ half the number of chromosomes of the parent cell.  SEXUAL REPRODUCTIONish

Meiosis produces 4 unique daughter cells

Process:

1) Start w/ cell w/ two pairs of chromosomes

2) Chromosomes become shorter and thicker (replicating itself)

3) Homologous (same structural features and pattern of genes) chromosomes pair up in centre of cell

4) Spindle fibres separate 

5) Cell divides into two daughter cells

6) Chromosomes align in centre of each cell

7) Spindle fibres separate chromosomes into chromatids

8) Each cell divides into two daughter cells

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Stem cells

In decreasing potency (potential):

- Totipotent stem cell (zygote)

v. early embryo - ability turn into any type of cell

- Pluripotent stem cell (embryonic stem cell)

umbilical chord of embryo. ability to differentiate, turn to most type of cells

useful to freeze & could grow new cells to fix damaged ones

- Multipotent (adult) stem cell (adult stem cell)

found in bone marrow. can turn to limited types of cells.

- Stomatic cell (red blood cell)

Ethical issues: killing an embryo // expensive // not available for everyone

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