B13 - Reproduction Flashcards

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1
Q

What is a gene

A

A section of DNA on a chromosome that codes for the animo acid sequence of a specific protein

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2
Q

What are alleles

A

Different versions of the same gene

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3
Q

How many chromosomes are there in a normal human cell

A

23 pairs

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4
Q

What are gametes, how many chromosomes and how are they made

A
  • Sex cells - sperm in men and eggs in females or pollen and eggs in plants
  • They have 23 single chromosomes
  • They are made by meiosis
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5
Q

Features of sexual reproduction

A
  • Fusion of male and female gametes - the offspring has a mixture of genetic information from both parents
  • Every gamete is different - this causes variation in the offspring
  • Gametes are made by meiosis
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6
Q

Features of asexual reproduction

A
  • Only one parent involved - doesn’t involve gametes
  • Offspring are all genetically identical so they are clones
  • Only involves mitosis not meiosis
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7
Q

How are gametes produced by meiosis

A
  • Only takes place in reproductive organs - testes and ovaries
    1. All of the chromosomes are copied/DNa replicated and sub celluar structures are duplicated
    2. Cell divides into two
    3. The two cells then divide again to form 4 cells, halving the number of chromosomes in all cells so each cell only has a single set (divides twice)
    4. Each gamete is genetically different from each other
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8
Q

Stages in fertilisation and after

A
  • Gametes fuse in fertilisation restoring the number of chromosomes to 23 pairs
  • The cell then divides by mitosis producing an embryo - a clump of identical cells
  • The cells then differentiate into different cell types
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9
Q

Advantages and disadvantages of sexual reproduction

A

Advantages
* Produces variation in the offspring
* Allows more offspring to survive due to changes in the environment (GREATER CHANCE OF SURVIVAL)
* This can be used by humans in selective breeding

Disadvantages
* Slower than asexual
* Takes time and energy to find a mate, spread gametes

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10
Q

Advantages and disadvantages of asexual reproduction

A
  • only one parent needed
  • no need to find a mate so more efficient in boht time and energy
  • Faster than sexual reproduction
  • Useful to produce identical offspring when conditions are favourable

Disadvantages
* If conditions become unfavourable, all offpsring may die due to lack of variation

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11
Q

organisms that reproduce both sexually and asexually

A
  • malaria parasite - in humans uses asexual, in mosquitos uses sexual
  • Fungi - asexually by producing spores and they can reproduce sexually
  • Strawberry plant - asexually by strawberry runners, sexually by flowers
  • Daffodils - asexually by bulb divisions, sexually by flowers
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12
Q

Structure of DNA

A
  • Made of 2 polymer strands that wind around each other to make a double helix shape
  • The monomers that make up the polymer starnd are called nucleotides
  • A nucleotide has a phosphate group (circle) a sugar molecule (pentagon) and a base attached to the sugar molecule
  • The phosphate group joins to the sugar of another nucleotide forming a sugar-phosphate backbone
  • There are 4 different bases that a nucelotide can have - A,T,C or G
  • The DNA strands are complementary as A attaches to T and C attaches to G and vice versa
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13
Q

defenition of a genome

A

the entire genetic material that makes up an organism

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14
Q

Benefits of having studied the entire human genome

A
  • Enables scientists to search for genes linked to a disease e.g. that increase risk of cancer
  • Helps us understand and treat inherited disorders
  • Can trace human migration patterns - ancestry
  • Paternity determination
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15
Q

Stages of protein synthesis

A
  • Transcription - base sequence of the gene is copied into a complementary template molecule (mRNA)
  • mRNA passes into the cytoplasm as it is small
  • Translation - mRNA molecule attaches to a ribosome
  • Amino acids are brought to the ribosome on carrier molecules (tRNA) so each tRNA has 3 bases
  • The ribosome reads the triplet of bases and uses this to join the correct amino acids brought by the tRNA together
  • Once the protein chain is complete, it folds into its unique shape
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16
Q

What can proteins strands be used for in the body

A
  • Enzymes
  • Hormones
  • Forming structures e.g. collagen
17
Q

How many bases code for a specific amino acid

A

3

18
Q

How can non-coding parts of DNA affect gene expression

A

They can switch genes on or off

19
Q

What is a mutation

A

the change in the sequence of bases in DNA
They are spotaneuous and happen frequently

20
Q

How can mutations cause problems in the coding region of DNA

A
  • Most mutations have no effect of structure or function
  • Some mutations cause a change in the sequence of bases in mRNA leading to a drastic change in the amino acids sequence which means the folded shape of the protein will be different
  • This could have a dramatic effect e.g. the active site of an enzyme changing shape or it alters the strength of a structural protein
21
Q

How can mutations cause problems in the non-coding region of DNA

A
  • Affects how genes are switched on or off
  • Gene may be turned on when its meant to be turned off
  • This could cause an unwanted protein to be produced
  • This could lead to problems e.g. uncontrolled cell division and cancer
22
Q

What is cystic fibrosis

A
  • A disorder of cell membranes
  • It is controlled by a single gene
  • Is caused by a recessive allele and to have it, both parents have it
23
Q

What is polydactyly

A
  • Where people have extra fingers or toes
  • Caused by a dominant allele
24
Q

issues around embryo screening

A
  • Expensive - money should be spent elsewhere in the NHS
  • LArge number of embryos are created but only a few are used - means some healthy embryos are destroyed which is unethical
  • Designer babies - screen embryos to produce offspring with desriable features e.g. taller, smarter
  • Chance of miscarriage during fetal cell harvesting
  • Terminating a pregancy will have massive mental health affects and may go against people’s religions
25
Q

Sex chromosomes of males and females and what chromosomes do the gametes have

A
  • Females - XX
  • Males - XY
  • All egg cells have the X chromosome
  • Half of the sperm have X and the other half have Y
26
Q

How to tell the difference between the X and Y chromosomes

A

The Y chromosome is much shorter than the X