B5 INHERITANCE Flashcards
how are gametes made?
cell division called meiosis
what does meiosis produce?
non-identical cells
give an example on where meiosis takes place?
flowering plants
gametes = pollen and egg cells
what is sexual reproduction and the features of it?
fusion of male and female gametes. (fertilisation).
mixing of genetic material
what is an example of asexual reproduction?
aphid reproducing
what is asexual reproduction?
only one parent.
only 1 parent of the offspring.
does not involve gametes = no mixing of genetic material = genetically identical = clones
does meiosis take place in asexual reproduction?
no because it does not involve gametes
does mitosis take place in asexual reproduction?
yes
where does meiosis take place in the human body?
reproductive organs.
testes = male
ovaries = female
1st stage of meiosis?
all of the chromosomes are copied
2nd stage of meiosis?
cells divide into two
3rd stage of meiosis?
divide one more time forming gametes
what happens to the chromosomes in the gametes?
chromosomes are single , not paired .
(before they were in pairs)
meiosis has halved the number of chromosomes
how many gametes does meiosis produce?
4 gametes from one original cell,
genetically different from each other.
each gamete has different alleles
what happen to gametes after they are produced?
gamete from male and female join together (fertilisation).
after fertilisation the cell has normal number of chromosomes.
what happens after fertilisation?
The new cell is divided by mitosis , producing clumps of identical cells = embryo.
as the embryo develops the cells differentiate forming different cell types
(in animal = nerve and muscle cells)
what is DNA?
two polymer (lots of smaller molecules) strands that wrap around each other to form a double helix.
where is DNA found?
chromosomes
what is a gene?
small section of DNA on a chromosome , it encodes for a specific sequence for amino acids to make a specific protein
how are proteins made?
joining together amino acids.
how many genes does a human have?
thousands
what is a genome?
entire genetic material of an organism
what is the human genome?
entire genetic material that makes a human
why is understanding the human genome important?
help us to search for genes that are linked to disease. e.g genes that increase the risk of developing cancer or Alzheimer’s disease.
help us understand and treat inherited disorders e.g cystic fibrosis.
trace human migration patterns from the past (helps people to discover their ancestry)
where does each chromosome come from?
one from father
one from mother
how many copies of genes do we have?
2 because chromosome comes in pairs
what is an allele?
genes in different versions
what does genotype tell us?
alleles present
what does homozygous mean?
when a person has 2 copies of the same alleles
what does phenotype tell us?
the characteristics caused by the person alleles
what does heterozygous mean?
when a person has 2 different type of alleles
what does a dominant allele show?
the phenotype even if there is only one copy present.
what does a recessive allele show?
a recessive allele will only show in the phenotype if two copies are present (if no dominant allele is present)
how are some characteristics controlled?
by a single gene
but most characteristics are the result of many genes acting together e.g height
what is cystic fibrosis?
disorder of cell membranes
its controlled by a single gene
- has 2 alleles
- allele = normal cell membrane= dominant =
C
- allele = defective cell membrane = recessive = c
to have cystic fibrosis = person has to have two copies of defective allele (cc)
person with one defective allele and one normal allele does not have cf but thy are known as a carrier of cystic fibrosis allela
what is polydactyly caused by?
dominant allele
person with normal allele + polydactyly allele = polydactyly (cannot be a carrier)
what is polydactyly?
people have extra fingers or toes
solutions for inherited disorders?
gene therapy
embryo screening
what is embryo screening?
embryos are tested to see if they have the alleles for inherited disorders
embryos do not have defective alleles are implanted into the women = develop into healthy offspring
issues with embryo screening?
expensive (some people think the money should be spent elsewhere in the health service)
A large number of embryos are created = small numbers are implanted = some healthy embryos are destroyed = people think its unethical
in the future, we may be able to screen embryos to produce offspring with desirable features , many people find this unethical
gene therapy?
scientists may be able to correct faulty alleles and use this to treat inherited disorders
what does a family tree only show?
only shows phenotype not genotype
how many of the chromosome pairs determine the inherited characteristics only?
22
males have the … chromosome
….= xy
females have the…chromosome
….=xx
