inheritance Flashcards
Define chromosomes
Chromosomes are made of DNA; which contains genetic information * in the form of genes.
Define gene
length of DNA
* that codes for a protein
Define allele
alternative form of gene!
what does sex determination depend on?
- All eggs have one X chromosome.
- However a sperm can have either X or Y chromosome.
- Therefore sex determination depends on whether the sperm that fertilizes the egg carries a Y or X chromosome.
what determines the sequence of amino acids used to make a specific protein?
- sequences of bases in a gene
- different sequences of amino acids give different shapes to protein molecules
How does DNA control cell function?
- controlling the production of proteins
including enzymes, membrane carriers & receptors for neurotransmitters
Explain how a protein is made
- the gene coding for the protein remains in the nucleus
- messenger RNA (mRNA) is a copy of a gene
- mRNA molecules are made in the nucleus and move to the cytoplasm
- the mRNA passes through ribosomes
- the ribosome assembles amino acids into protein molecules
- the specific sequence of amino acids is determined by the sequence of bases in the mRNA
Are all proteins made in all cells?
no.
most body cells in an organism contain the same genes, but many genes in a particular cell are not expressed
* because the cell only makes the specific proteins it needs
What’s a haploid nucleus?
nucleus containing a single set of chromosomes
What’s a diploid nucleus?
nucleus containing two sets of chromosomes
i.e. all body cells except gametes
- One pair of each type of chromosome
- 23 pairs in a human
define mitosis
nuclear division giving rise to
genetically identical cells
role of mitosis
growth, repair of damaged tissues, replacement of cells and
asexual reproduction
How does mitosis occur?
Chromosomes replicate before mitosis occurs
- Copies of chromosomes separate
- Chromosome number is maintained in each daughter cell
define stem cells
- unspecialised cells that divide by mitosis
- to produce daughter cells
- that can become specialised for specific functions
define meiosis
- reduction division in which the chromosome number is halved from diploid to haploid
- resulting in genetically different cells
Role of meiosis
- involved in production of gametes
- takes place in testes/ovaries
why is meiosis known as reductive division?
- Chromosome number is halved (from diploid to haploid)
- Results in genetically varied daughter cells
- New combinations of maternal and paternal genes made
define inheritance
- the transmission of genetic information
- from generation to generation
define genotype
- Genetic make-up of an organism
- i.e. which alleles are present in the organism’s genome
define phenotype
observable features of an organism
homozygous
- having 2 identical alleles of a particular gene
what happens when 2 homozygous individuals?
it’ll be pure-breeding
define heterozygous
having 2 different alleles of a particular gene
define dominant allele
- an allele that is expressed
- if it is present in the genotype
define recessive allele
- an allele that is only expressed
- when there’s no dominant allele
- of the gene present in the genotype
what’s codominance
- situation in which both alleles in heterozygous organisms
- contribute to the phenotype
Explain the inheritance of ABO blood groups
- phenotypes are A, B, AB and O blood groups
- alleles are IA, IB and Io
What’s a sex linked characteristic
- a feature in which the gene responsible is located on a sex chromosome
- and that this makes the characteristic more common in one sex than in the other
give an example of sex-linkage
- red-green colorblindness
what’s test cross used for
- To identify the genotype of an organism showing the dominant phenotype
hows test cross carried out
Cross the unknown individual with individual showing recessive phenotype
- Offspring either 50% dominant and 50% recessive OR all dominant
- If any offspring have recessive phenotype → unknown individual was heterozygous
- If no offspring have recessive phenotype → unknown individual was homozygous
Why are sex-linked diseases usually associated with the X chromosome?
- Y chromosome is much shorter than the X chromosome
- Comparatively few genes exist on the shorter Y chromosome
Why are X-linked dominant traits more common in females?
- Females have two X chromosomes = two alleles
- Either allele may be dominant and cause disease
- Can be either homozygous or heterozygous
Why are X-linked dominant traits more common in males?
Males have only one X chromosome = one allele
- Condition cannot be masked by a second allele
For sex-linked diseases:
- Only females can be carriers
- Males always inherit X-linked trait from mother
- Females cannot inherit X-linked recessive condition from unaffected father
