Genetics - Inheritance and Mendel 164-171 Flashcards
what is an allele
a specific version of a gene
what is homozygous
when two alleles for a gene are the same
what is heterozygous
when two alleles for a gene are different
what happens when two alleles are heterozygous
2 points
1) only one can determine what characteristic is shown this is called a dominant allele
2) the other allele that isn’t expressed is called recessive
have can a recessive characteristic be expressed
both its alleles must be recessive
what is your genotype
the combination of alleles you have - e.g. Cc or cc
what is your phenotype
how the alleles express themselves in characteristics - e.g. having cystic fibrosis or not having it
what is cystic fibrosis
2 points
1) a genetic disorder of the cell membranes
2) which results in the body producing a lot of thick sticky mucus in the air passages and pancreas
what allele causes cystic fibrosis
a recessive allele ‘f’ carried by about 1/25 people
draw a genetic cross diagram and a Punnett square to show the possible alleles of the offspring of two people who are unaffected but carriers of CF
pg 168
what is polydactyly
a genetic disorder where a baby is born with extra fingers or toes
what allele causes polydactyly
a dominant allele ‘D’
draw a genetic cross diagram and a Punnett square to show the possible alleles of the offspring of someone who have polydactyly and someone who doesn’t
pg 168
what is embryonic screening
4 points
1) during IVF embryos are fertilised in a lab
2) before being implanted in the mother’s womb it’s possible to remove a cell from each embryo and analyse its genes
3) many genetic disorders can be detected this way
4) it’s also possible to get DNA from an embryo in the womb and test that for disorders
why are people for embryonic screening
3 points
1) will help to stop people suffering from genetic disorders
2) treatment of these disorders costs the government a lot of money
3) there are laws to stop it going too far, e.g. stop people from deciding the sex of their baby
why are people against embryonic screening#
4 points
1) embryos with ‘bad’ alleles would be destroyed, or could lead to a decision to terminate a pregnancy
2) implies people with genetic problems are ‘undesirable’
3) it’s expensive
4) may come to a point where people pick the most ‘desirable’ characteristics for their child - e.g. eye/ hair colour
what did Mendel do
4 points
1) in his garden Mendel noticed how characteristics in pea plants were passed on from one generation to the next
2) he had shown the height characteristic in peas was determined by separately inherited ‘hereditary units’
3) the ratios of tall and dwarf plants in the offspring showed the unit for tall plants was dominant and for dwarf plants it was recessive
4) the results of his research were published in 1866 and eventually became the foundation of genetics
what conclusions did Mendel reach
3 points
1) characteristics in plants were determined by ‘hereditary units
2) hereditary units are passed on to offspring unchanged from both parents, one units from each parent
3) hereditary units can be dominant or recessive, if someone has dominant and recessive units, the dominant characteristic will be expressed
why didn’t people understand Mendel’s work
they didn’t know about genes, DNA and chromosomes
how has Mendel’s work contributed to the understanding of genes today
5 points
1) Mendel’s work provided a starting point for many scientists observations
2) in the late 1800s scientists became familiar with chromosomes, able to observe how they behaved
3) in the early 1900s scientists realised there were similarities in the way chromosomes and Mendel’s ‘units’ acted
4) based on this it was proposed that the ‘units’ were found on chromosomes
5) in 1953 the structure of DNA was found, which allowed scientists to found out exactly how genes worked
