Topic 6b- Genetics Flashcards
What are the male chromosomes?
XY
What are the female chromosomes?
XX
What are the chances that a baby is male / female?
50 / 50
How many alleles do normal cells in an organism have?
2
How many alleles do gametes have?
1
What does homozygous mean?
If an organism has two alleles for a particular gene that are the same
What is it called when an organism has two alleles for a particular gene that are the same
Homozygous
What does heterozygous mean?
When an organisms two alleles for a particular gene are different
What is the allele that is shown called?
The dominant allele
What is the allele that doesn’t show up?
recessive
What is a genotype?
The combination of alleles that an organism has
What is a person’s phenotype?
The physical characteristics that are displayed due to their genotype
What is single gene inheritence?
One gene is inherited from the father and one gene is inherited from the mother (it’s just a fance word for basically normal inheritence)
What are the two inherited disorders you need to know at GCSE?
cystic fibrosis and polydactyly
What is cystic fibrosis?
An inherited disorder of cell membranes resulting in the body producing lots of thick mucus in the air passages and in the pancreas
Is the allele that causes cystic fibrosis dominant or recessive?
recessive
What are carriers (in reference to genetic disorders e.g. cystic fibrosis)
people with only one copy of the allele (therefore they are heterozygous) meaning that they have no symptoms
What is polydactyly?
An inherited disorder where someone’s born with extra fingers or toes
Is the allele for polydactyly dominant or recessive?
dominant
What is a family tree in genetics?
A diagram that shows how a characteristic (or disorder) is inherited in a group of related people.
What is embyronic screening?
A way of detecting disorders such as cystic fibrosis in embryos
In what was can embryonic screening be done? How do they work?
- Pre-implantation genetic diagnosis (PGD) - During IVF the cells in an embryo can be removed and analysed, therefore embryos with ‘healthy’ alleles could then be implanted into the mother while the others destroyed.
- Chronic villus sampling (CVS) - Usually carried out between 10-13 weeks of pregnancy CVS involves taking a sample from part of the placenta and analysing their genes (since the placenta develops from the same original cell and therefore genes as the embryo) after analysis the parents can decide whether or not to terminate the pregnancy
What are arguments in support of screening?
- It helps stop people from suffering from suffering certain inherited disorders
- Treating disorders costs the government a lot of money so screening could reduce healthcare costs
- During IVF most of the embryos are destroyed anyway so PGD just ensures the one that’s selected is healthy
- If an inherited disorder is diagnosed through CVS, parents don’t have to have a termination- but it does give them a choice
What are arguments against screening?
- There could come a point where everyone screens embryos and pick the most ‘desired one’
- It implies that people with genetic disorders are undesirable- this could increase prejudice
- After PGD the rejected embryos are destroyed and some see this as unethical
- There’s a risk that CVS could cause a miscarriage
- Screening embryos is expensive
Who was Gregor Mendel?
- Austrian monk
- Trained in mathematics and natural history at the University of Vienna
- Used pea plants to look at how characteristics in plants were passed from one generation to the next
What was Mendel’s pea plant experiment?
- He crossed a tall pea plant and a dwarf pea plant
- All the offspring were tall pea plants
- He crossed two of the tall pea plants
- Resulting in 3 tall pea plants and 1 dwarf pea plant
- From this Mendel had shown that the height characteristic in pea plants was determined by seperately inherited “hereditary” units passed on from each parent
What conclusions did Mendel reach from his experiments on pea plants?
- Characteristics in plants are determined by “hereditary units”
- Hereditary units are passed on to offspring unchanged from both parents, one unit from each parent
- Hereditary units can be dominant or recessive
What is the timeline of events starting with Mendel publishing his research that we need to know for GCSE?
(note the dates aren’t that important- more the order)
1866- Mendel publishes work
1884- Mendel’s death
Late 19th century- Scientists became familiar with chromosomes. They were able to observe how they behaved during cell division.
Early 20th century- Scientists realised that there were striking similarities with how chromosomes and Mendel’s ‘units’ acted.
Mid 20th century- scientists discovered the structure of DNA
